Utility of serum blood ketone levels and other risk factors for inadequate myocardial glucose suppression ketogenic FDG-PET/CT: a prospective and retrospective cohort study

Utility of serum blood ketone levels and other risk factors for inadequate myocardial glucose suppression ketogenic FDG-PET/CT: a prospective and retrospective cohort study | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Utility of serum blood ketone levels and other risk factors for inadequate myocardial glucose suppression ketogenic FDG-PET/CT: a prospective and retrospective cohort study Ya Ruth Huo, Sandeep Gupta, Natalie Rutherford, Megan Saul, Michael Vinchill Chan This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7776884/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 15 Dec, 2025 Read the published version in Annals of Nuclear Medicine → Version 1 posted 4 You are reading this latest preprint version Abstract OBJECTIVES Incomplete myocardial glucose suppression (MGS) in ketogenic 18F-FDG-PET/CT is a common problem that reduces the diagnostic accuracy in detecting myocardial inflammation. This study assesses the usefulness of a dietary logbook, blood ketone testing and risk factors for inadequate MGS. METHODS Retrospective (2022–2024) and prospective (2024–2025) analysis was performed on all patients who underwent a ketogenic 18F-FDG-PET/CT. In April 2024, blood ketone testing, a dietary logbook, and improved dietary guidelines were introduced. All patients were instructed to follow > 24-hour ketogenic diet and > 12-hour fast before imaging. RESULTS After introducing the dietary logbook and guidelines, inadequate MGS rates decreased from 26% to 17% (95 patients 2022–2024 vs 92 patients 2024–2025)(p-value 0.14). Mean blood ketones were significantly lower in patients with incomplete MGS (0.34mmol/L vs 0.76mmol/L, p-value 0.04). On univariate analysis, significant risk factors for inadequate MGS included prednisolone use (75% vs 14.9%, OR: 17.1 [95%CI 1.65-177.04], p = 0.009), low blood ketones (≤ 0.3mmol/L)(OR: 5.77 [95%CI 1.69–19.68], p = 0.003) and female sex (7.5% vs 9.6% in males, OR: 3.57 [95%CI 1.12–11.3], p = 0.025). Multivariate analysis confirmed prednisolone use, low ketones (≤ 0.3mmol/L) and < 24-hour ketogenic diet as independent risk factors. Rates of inadequate MGS were 50%, 26% and 7% for patients with blood ketone levels of 0.1, 0.2–0.3 and ≥ 0.4mmol/L, respectively. All patients on prednisolone with ketones ≤ 0.3mmol/L had inadequate MGS. CONCLUSIONS Dietary logbook and clear instructions improve adherence. Low ketones, prednisolone use and short ketogenic preparation are risk factors for inadequate MGS. Ketogenic PET/CT cardiac sarcoidosis ketone β-hydroxybutyrate myocardial glucose suppression Figures Figure 1 INTRODUCTION The ketogenic diet (KD) is an effective preparatory strategy for suppressing physiological myocardial glucose uptake prior to 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT), particularly in the evaluation of inflammatory cardiac conditions such as cardiac sarcoidosis [ 1 ]. Under normal metabolic conditions, myocardium primarily utilizes glucose and free fatty acids for energy. This leads to significant physiological 18F-FDG uptake in healthy myocardial tissue, which can obscure pathological uptake and reduce diagnostic accuracy [ 1 ]. A high-fat, low-carbohydrate KD induces a metabolic shift from glucose metabolism to fatty acid oxidation and ketone body utilization. This shift suppresses myocardial glucose uptake, effectively reducing background FDG signal and enhancing the contrast between normal and inflamed myocardium. As a result, pathological foci—such as those seen in cardiac sarcoidosis—can be more clearly visualized [ 1 , 2 ]. The efficacy of KD preparation has been supported by several studies. For example, Özütemiz and colleagues demonstrated a 72-hour KD with overnight fasting achieved complete myocardial suppression in 96.9% of cases, compared to 68.1% with a 24-hour KD and 52.3% with an 18-hour fasting protocol [ 1 ]. These findings highlight the importance of both the duration and adherence to ketogenic protocols for optimal image quality. However, the duration of the ketogenic diet varies considerably between hospitals, with many adopting a shorter 24-hour protocol due to patient compliance, time constraints, and logistical challenges. Serum ketone β-hydroxybutyrate levels have emerged as a useful biomarker for assessing the adequacy of myocardial glucose suppression. Elevated serum ketone β-hydroxybutyrate concentrations are associated with successful suppression, whereas lower levels may reflect suboptimal dietary adherence or insufficient metabolic transition to ketosis [ 2 , 3 ] Although heparin administration has been proposed to improve suppression, there are limitations for patients with inadequate ketone levels [ 4 ]. Despite these advances, inadequate myocardial suppression remains a challenge in a subset of patients, with reported rates of non-diagnostic scans as high as 7.1% even after ketogenic preparation [ 5 ]. Contributing risk factors include poor compliance with dietary protocols, inadequate preparation time and individual metabolic variability. These limitations underscore the need for standardized preparation protocols and objective biomarkers to guide and assess readiness for PET/CT imaging. This study aims to investigate clinical and metabolic risk factors for inadequate suppression by comparing cohorts before and after the implementation of enhanced dietary protocols—including a standardized ketogenic diet guide, dietary logbook, patient questionnaire, and point-of-care blood ketone testing to further improve patient selection and preparation strategies for cardiac PET imaging. The study will also evaluate an optimal blood ketone level threshold that best predicts adequate myocardial glucose suppression (MGS) in patients undergoing a 24-hour KD preparation for 18F-FDG PET/CT. MATERIALS AND METHODS This was a combined retrospective and prospective observational study conducted at two tertiary hospitals to assess the utility of blood ketone levels and other clinical factors in predicting adequate MGS in patients undergoing 24-hour ketogenic preparation for 18F-FDG PET/CT scans. The retrospective component included all patients who underwent ketogenic PET/CT imaging between August 2022 and April 2024. No patients were excluded. The prospective arm of the study included all patients scanned from April 2024 to January 2025, during which time new preparation protocols were introduced in April 2024. For the retrospective cohort, data was extracted from patient records, including demographic data such as age, gender, inpatient or outpatient status, scan indication, and the adequacy of myocardial suppression as determined on PET/CT review. Adequate suppression was defined as myocardial 18F-FDG uptake lower than blood pool activity. Cases with higher or heterogeneous myocardial uptake without known pathology were classified as having inadequate suppression. For the prospective cohort, a new departmental protocol was implemented to improve myocardial suppression in April 2024. Patients in the prospective arm received revised dietary instructions that emphasized strict adherence to a high-fat, low-carbohydrate ketogenic diet for a minimum of 24 hours prior to the scan and fasting 12 hours prior to the study. These instructions, along with a newly introduced patient questionnaire and a dietary logbook, were emailed to all patients at least 72 hours in advance of their scheduled scan. Upon arrival on the day of imaging, patients underwent point-of-care testing of capillary blood β-hydroxybutyrate (ketone) and glucose levels using handheld meters (Abbott Freestyle Optium Neo). These biochemical parameters were recorded in addition to the patient’s age, gender, BMI, inpatient or outpatient status, exercise level, diabetic status, dietary adherence (as per the logbook), and any recent use of immunosuppressive medications, including corticosteroids. Myocardial glucose suppression was assessed visually by experienced nuclear medicine physicians. Myocardial glucose suppression was considered adequate when normal myocardial FDG uptake was lower than the blood pool—defined as a negative study if all LV wall segments showed uptake equal to or less than the blood pool, and a positive study if focal or multifocal uptake was present or if corresponding regions demonstrated late gadolinium enhancement on cardiac MRI (when available). Scans not meeting these criteria—such as those showing diffuse LV uptake, basal LV ring uptake, lateral LV wall uptake, or patchy uptake exceeding blood pool activity—in the absence of known myocardial inflammation, were classified as inadequate myocardial glucose suppression (Fig. 1 ). Scans were correlated with clinical notes as well as cardiac MRI findings where available. Blood ketone levels were analyzed to determine if they correlated with suppression outcomes, with the aim of identifying a minimum threshold predictive of successful suppression. Statistical analysis was performed using SPSS 27 (IBM Corp., Armonk, NY). For univariate analysis, the chi-squared test was used for categorical variables and the independent t-test for continuous variables. Variables with a p-value < 0.20 in univariate analysis were entered into a multivariate logistic regression model to identify independent predictors of inadequate myocardial suppression. A p-value < 0.05 was considered statistically significant. Ethics approval was obtained from the institutional Human Research Ethics Committee. As this study evaluated routine clinical practice, informed consent was waived for the retrospective data and deemed not required for the prospective observational data collection. RESULTS There was a total of 95 patients from Aug 2022 - April 2024 in the retrospective cohort and 92 patients from April 2024 - January 2025 in the prospective cohort. The demographic data for the cohort are summarized in Table 1 . There were no significant differences between the demographic data between the retrospective and prospective cohort. Table 1 Demographic and Clinical Characteristics of participants Retrospective Cohort Prospective Cohort p-value* Number of patients (n) 95 92 Age (mean) 62.3 years 60.2 years 0.95 Gender (n) Male 52 52 Female 43 40 0.81 Patient Location Outpatients 45 57 Inpatients 40 35 0.57 PET Indication Sarcoid assessment 57 49 Non-sarcoid 38 46 0.35 *P-value for difference between subgroups with dichotomous factors (Chi-squared) or means (Independent T-test) Following the introduction of improved dietary guidelines and logbook in April 2024, the rate of inadequate MGS reduced from 26% down to 17% (9% decrease, p = 0.14). The overall rate of inadequate MGS was 22% (retrospective and prospective cohort study combined). On univariate analysis of dichotomous variables, significant risk factors for inadequate MGS included prednisolone use (75% vs 14.9% for no prednisolone use, OR: 17.1 [95%CI 1.65-177.04], p = 0.009), low blood ketone level (≤ 0.3 mmol/L)(OR: 5.77 [95%CI 1.69–19.68], p = 0.003) and female sex (27.5% vs males 9.6%, OR: 3.57 [95%CI 1.12–11.3], p = 0.025) (Table 2 ). Table 2 Univariate analysis of dichotomous factors associated with incomplete MGS in the Prospective cohort Inadequate myocardial glucose suppression OR (95% CI) p-value Female vs Male 3.57 (1.12–11.3) 0.025 Current Prednisolone use vs No prednisolone use 17.1 (1.65-177.04) 0.009 Blood ketone level ≤ 0.3 vs > 0.4 mmol/L 5.77 (1.69–19.68) 0.003 ≤ 0.4 vs > 0.5 mmol/L 4.11 (1.08–15.6) 0.028 Ketogenic diet duration < 24hrs vs ≥ 24hrs 4.72 (1.08–20.6) 0.049 Inpatient vs Outpatient 1.33 (0.45–3.97) 0.61 Sarcoid vs non-sarcoid assessment 1.58 (0.52–4.79) 0.42 Poor Keto diet adherence vs Good keto diet adherence 2.09 (0.64–6.83) 0.22 Diabetic vs non-diabetic 0.39 (0.05–3.37) 0.35 Univariate analysis of the continuous variables associated with inadequate MGS are outlined in Table 3 . Mean blood ketone levels were significantly lower in patients with incomplete MGS (0.34 mmol/L vs 0.76 mmol/L, p-value 0.04). The ketogenic diet duration was lower in patients with incomplete MGS (20.9 hrs vs 29.6 hrs, p = 0.07). Table 3 Univariate analysis of continuous factors associated with incomplete MGS in prospective cohort Characteristic Inadequate Cardiac Suppression Adequate Cardiac Suppression P-value Age 55.9 years 61.1 years 0.22 Weight 88.9 kg 88.0 kg 0.87 BMI 30.3 29.6 0.78 Blood Glucose Level 5.3 mmol/L 5.4 mmol/L 0.89 Blood Ketone Level 0.34 mmol/L 0.76 mmol/L 0.04 Ketogenic Diet Duration 20.9 hrs 29.6 hrs 0.07 Fasting Duration 16.7 hrs 17.2 hrs 0.88 Multivariate analysis demonstrated prednisolone use, low blood ketone levels (≤ 0.3 mmol/L), female gender and < 24hr ketogenic diet remained significant risk factors for inadequate MGS (Model 2, Table 4 ). Model 1 multivariate analysis demonstrated female was a risk factor for inadequate MGS however became non-significant after the addition of a ketogenic diet duration < 24hrs as a variable (Table 4 ). Table 4 Multivariate analysis of factors associated with incomplete MGS Odds Ratio for Incomplete MGS (95% CI) P-value Model 1 Low Blood Ketone level (≤ 0.3mmol/L) 4.04 (1.09–14.98) 0.037 Female Gender 4.50 (1.11–18.26) 0.036 Prednisolone use 26.97 (91.84-396.25) 0.016 Model 2 Low Blood Ketone level (≤ 0.3 mmol/L) 7.1 (1.2–41.4) 0.029 Female Gender 4.49 (0.79–25.64) 0.09 Prednisolone use 51.03 (2.55-1023.3) 0.01 Ketogenic diet duration < 24hrs 20.08 (2.28-176.47) 0.007 The rates of inadequate MGS were 50%, 26% and 7% for patients with blood ketone level of 0.1 mmol/L, 0.2–0.3 mmol/L and ≥ 0.4 mmol/L, respectively (Table 5 ). If patients were on prednisolone, 100% had inadequate MGS if the blood ketone level was 0.3 mmol/L or lower. There were two patients who were on prednisolone (10mg daily and 25mg daily) had a low blood ketone level of 0.1 mmol/L and had inadequate MGS, despite adherence to the ketogenic diet for 24hrs. There was one patient on prednisolone (10mg daily) who had a borderline blood ketone level of 0.3 mmol/L and had inadequate MGS. There was one patient on prednisolone (10mg) who had a blood ketone level of 0.4 mmol/L and had adequate MGS. Table 5 Ketone level and association with incomplete MGS Blood Ketone Level (mmol/L) 0.1 0.2–0.3 ≥ 0.4 Risk of inadequate MGS 50% 26% 7% + Poor Ketogenic diet adherence 100% 50% 18.8% + On Prednisolone 100% 100% 0% + Female 100% 28% 16% + Male 29% 22% 3% There were four patients who had high blood ketone levels (> 0.3 mmol/L) but had inadequate cardiac suppression. One patient had a high ketone level of 1.4 mmol/L however they reported that they consumed mashed pumpkin and crackers the day prior to the scan. Another patient had a ketone level of 0.6 mmol/L but reported they ate potato soup and bread the day before. Another patient had a ketone level of 0.4 mmol/L but had crackers at 10pm the night before. One patient had a ketone level of 0.7mmol/L but denied having carbohydrates the day before. DISCUSSION This present study reinforces the clinical utility of ketogenic preparation for cardiac FDG PET/CT to suppress physiological myocardial glucose uptake, thereby enhancing diagnostic accuracy in evaluating inflammatory cardiac pathologies such as sarcoidosis. Our findings suggest that emailing patients clear ketogenic dietary instructions along with a dietary logbook significantly improves adherence to the ketogenic protocol. It clarifies adherence to the ketogenic diet prior to the scan. This simple intervention may optimize myocardial suppression and improve scan interpretability. This study also demonstrated that measuring serum ketone levels remains a valuable adjunct, providing objective insight into the patient's metabolic state. In our cohort, the rates of inadequate MGS were 50%, 26% and 7% for patients with blood ketone levels of 0.1, 0.2–0.3 and ≥ 0.4 mmol/L, respectively. This is consistent with a previous study which demonstrated a ketone level cut-off value of 0.35 mmol/L to predict adequate myocardial suppression, with a specificity of 90% and sensitivity of 56% in patients with 24–48 hrs of a ketogenic diet [ 6 ]. In comparison, another study including patients on a 24-hour or 72-hour ketogenic diet, or given a ketogenic drink, found that a ketone threshold of ≥ 0.58 mmol/L correctly classified 92% of scans [ 7 ]. The differences in ketone levels across studies is attributable to the variable duration of the ketogenic diet, with studies showing significantly higher ketone levels after a 72-hour regimen compared to a 24-hour ketogenic diet protocol (0.3 ± 0.4 versus 1.0 ± 0.7 mmol/L; p < 0.001)6. However, optimal myocardial suppression appears to require both biochemical ketosis and strict dietary compliance. This study demonstrated that relying solely on serum blood ketone levels can be insufficient without assessment of actual dietary adherence, as some patients demonstrated poor suppression despite adequate ketone levels. The specific example which highlights this was a patient with inadequate MGS with a blood ketone level of 1.4mmol/L but had mashed pumpkin and crackers 24hrs prior to the scan. This highlights the importance of a combined approach involving both metabolic (serum ketone) and behavioral (dietary log) assessment to determine true ketogenic adherence [ 9 , 10 ] These findings maybe particularly valuable in indeterminate cases wherein the combination of high serum ketone levels and good dietary adherence favors a highly likelihood of adequate myocardial glucose suppression and any uptake is likely pathological myocardial uptake, whereas low ketones and poor adherence favors a higher likelihood of inadequate myocardial glucose suppression. This distinction may help clinicians avoid misdiagnosis or unnecessary further testing [ 11 ]. This present study also highlights the increased difficulty for patients on prednisolone to achieve a ketogenic metabolic state and adequate MGS, even with adherence to a standard 24-hour ketogenic diet and fasting protocol. This contrasts with a previous study which demonstrated patients treated with systemic corticosteroids had adequate suppression (88%) compared to 57% without systemic corticosteroids (p = 0.096) [ 12 ]. Corticosteroids such as prednisolone are well-known to induce hyperglycemia and insulin resistance, which can impair the metabolic shift required for effective suppression of myocardial glucose uptake. Glucocorticoids upregulate hepatic gluconeogenesis and reduce peripheral glucose uptake, thereby sustaining elevated serum glucose levels and blunting ketogenesis [ 13 , 14 ]. These metabolic effects directly oppose the physiologic conditions necessary for myocardial fatty acid utilization during FDG PET imaging. In this present study, all patients on prednisolone demonstrated a markedly reduced ability to achieve adequate myocardial suppression when prepared with a 24-hour ketogenic protocol. Specifically, 100% of patients on prednisolone with a blood ketone level of ≤ 0.3 mmol/L failed to achieve adequate MGS. Two patients on prednisolone (10 mg and 25 mg daily) had low ketone levels of 0.1 mmol/L and demonstrated inadequate suppression, despite reportedly adhering to the prescribed ketogenic diet. Another patient, also on 10 mg daily of prednisolone, had a borderline ketone level of 0.3 mmol/L and similarly showed inadequate suppression. Notably, the only patient on prednisolone to achieve adequate MGS had a ketone level of 0.4 mmol/L, suggesting that higher ketone thresholds may be necessary in corticosteroid-treated individuals to compensate for glucocorticoid-induced metabolic derangements. These findings suggest that shorter 24-hour ketogenic preparation protocols may be insufficient for patients receiving systemic corticosteroids. It is plausible that these patients require an extended ketogenic diet duration of 48 to 72 hours, with more stringent fasting, to overcome the counterregulatory effects of corticosteroids on glucose metabolism and to promote sufficient ketone production. Additionally, a higher minimum ketone threshold (e.g. >0.4 mmol/L) may be a more appropriate indicator of readiness for imaging in this subgroup. These results are consistent with previous literature indicating that individual metabolic and pharmacologic factors can significantly influence FDG biodistribution and suppression protocols [ 15 , 16 ]. Given the prevalence of corticosteroid use in patients undergoing inflammatory cardiac imaging, particularly for suspected sarcoidosis, our findings underscore the need for tailored preparation protocols for this high-risk group. Larger studies are warranted to define optimal ketogenic duration and ketone cutoffs in corticosteroid-treated populations, and to evaluate whether adjunctive strategies such as prolonged fasting or exogenous ketone supplementation could improve MGS outcomes. Previous study by Hartikainen and colleagues [ 6 ] also identified diabetes and obesity predicted adequate myocardial suppression. Our study did not identify diabetes or obesity (based on BMI) associated with myocardial suppression in our prospective cohort. Cost Analysis Implementing a streamlined ketogenic preparation protocol that includes blood ketone testing and emailed dietary instructions with a logbook presents a highly cost-effective strategy for ensuring adequate myocardial glucose suppression in cardiac FDG PET/CT imaging. A single ketone strip costs approximately $ 0.85 AUD and point-of-care testing typically requires only one minute of staff time to perform, often using the same glucose monitor and single skin prick. Emailing the dietary guidelines and logbook to patients takes about one minute, and patients typically spend around 10 minutes completing the logbook and adhering to the ketogenic diet. In contrast, inadequate myocardial suppression can necessitate repeated PET/CT scans, leading to significant additional costs and resource utilization. The Medicare Benefits Schedule (MBS) fee for a whole-body FDG PET scan is $ 953.00 AUD, with Medicare covering 85% ( $ 810.05 AUD) and patients potentially facing out-of-pocket expenses depending on the provider's billing practices. Repeat scans also impose further burdens, including extended dietary restrictions [up to 72 hours], increased patient inconvenience, and additional strain on departmental resources and scheduling. Therefore, pre-test qualitative and quantitative assessment of diet and ketones may be a practical method to improve resource utilization. Limitations This study has several limitations that may affect the generalizability of its findings. The external validity is constrained by the specific protocol used: a 24-hour ketogenic diet with a 12-hour fast prior to FDG injection. Other institutions employ longer preparation protocols — including 48- to 72-hour ketogenic diets — which have been shown to more consistently suppress physiological myocardial uptake [ 16 , 17 ]. However, there are also many hospital departments which utlise a 24-hour ketogenic diet with a 12-hour fast to reduce patient scan delays. Moreover, the findings from this study may assist in identifying which patients may be suitable for earlier imaging at 24-hours rather than wait 72-hours. Another limitation of our study was the low number of patients on corticosteroids, however despite the small numbers, it had an overt quantitative and qualitive impact on MGS. The metabolic impact of glucocorticoids may necessitate higher ketone thresholds (ie. >0.4mmol/L) or prolonged dietary preparation to achieve adequate myocardial suppression. Further research is warranted to determine the appropriate preparation strategy for this subgroup. Another limitation was not utilising intravenous unfractionated heparin (50 IU/kg) approximately 15 minutes prior to FDG injection. While theoretically beneficial by inducing lipolysis and increase serum free fatty acids [ 18 ], clinical studies have shown mixed results regarding MGS and may have added confounding variables in this present study [ 15 , 19 , 20 , 21 ]. A previous study demonstrated heparin did not significantly affect suppression in patients with a low ketone level [ 21 ]. This study also did not utilise exogenous ketone supplements, such as ketone esters or ketogenic formulas, to induce rapid ketosis in patients unable to adhere to dietary restrictions. Early data suggest these strategies may enhance myocardial suppression, but evidence remains limited and variable [ 23 , 23 ]. Previous studies have also identified fatty liver predicted adequate myocardial suppression [ 6 ]. Our study did not assess the presence of fatty liver. Conclusion In conclusion, this study demonstrates providing patients clear ketogenic dietary instructions along with a dietary logbook improves dietary adherence prior to 18F-FDG PET/CT. Moreover, incorporating point-of-care ketone level testing can further refine patient preparation, ensuring higher rates of diagnostic-quality imaging. Future research should focus on exploring additional strategies to mitigate the identified risk factors for preparation of failure. Declarations Sources of Funding: None Disclosure of Potential Conflicts of Interest: None References Özütemiz C, Koksel Y, Froelich JW, Rubin N, Bhargava M, Roukoz H, Cogswell R, Markowitz J, Perlman DM, Steinberger D. Comparison of the effect of three different dietary modifications on myocardial suppression in 18F-FDG PET/CT evaluation of patients for suspected cardiac sarcoidosis. J Nucl Med. 2021;62(12):1759–67. Madamanchi C, Weinberg RL, Murthy VL. Utility of serum ketone levels for assessment of myocardial glucose suppression for 18F-fluorodeoxyglucose PET in patients referred for evaluation of endocarditis. J Nuclear Cardiol. 2023;30(3):928–37. Osborne MT, Qamar I, Selvaraj S. A level of confidence: beta-hydroxybutyrate and myocardial glucose uptake suppression on 18F-FDG PET imaging. J Nuclear Cardiol. 2023;30(3):938–40. Hartikainen S, Vepsäläinen V, Laitinen T, Hedman M, Laitinen T, Tompuri T. Heparin does not improve myocardial glucose metabolism suppression in [18 F] FDG PET/CT in patients with low β-hydroxybutyrate level. EJNMMI Res. 2024;14(1):92. Özütemiz C, Koksel Y, Froelich JW, Rubin N, Bhargava M, Roukoz H, Cogswell R, Markowitz J, Perlman DM, Steinberger D. The active papillary muscle sign in 18F-FDG PET/CT cardiac sarcoidosis exams and its relationship with myocardial suppression. Ann Nucl Med. 2024;38(5):391–9. Hartikainen S, Tompuri T, Laitinen T, Laitinen T. Point-of‐care β‐hydroxybutyrate measurement predicts adequate glucose metabolism suppression in cardiac FDG‐PET/CT. Clin Physiol Funct Imaging. 2024;44(5):349–58. Selvaraj S, Margulies KB, Dugyala S, Schubert E, Tierney A, Arany Z, Pryma DA, Shah SH, Rame JE, Kelly DP, Bravo PE. Comparison of exogenous ketone administration versus dietary carbohydrate restriction on myocardial glucose suppression: a crossover clinical trial. J Nucl Med. 2022;63(5):770–6. Vidula MK, Selvaraj S, Rojulpote C, Bhattaru A, Kc W, Hansbury M, Schubert E, Clancy CB, Rossman M, Goldberg LR, Farwell M. Relationship of ketosis with myocardial glucose uptake among patients undergoing FDG PET/CT for evaluation of cardiac sarcoidosis. Circ Cardiovasc Imaging. 2024;17(8):e016774. Abikhzer G et al. [2021]. Impact of dietary noncompliance on myocardial FDG uptake in PET imaging. Clin Nucl Med, 46[2], e75–80. Osborne MT et al. [2019]. Ketogenic preparation for cardiac sarcoidosis imaging: effects on FDG suppression and patient compliance. JACC: Cardiovasc Imaging, 12[4], 765–7. Dilsizian V, Bacharach SL. [2017]. FDG PET imaging in cardiac sarcoidosis: need for standardization of protocols and interpretation criteria. J Nucl Med, 58[2], 199–200. Hartikainen S, Vepsäläinen V, Tompuri T, Laitinen TM, Hedman M, Laitinen T. Cardiometabolic disorders affect myocardial [18F] fluorodeoxyglucose uptake–impact on diagnostic PET/CT imaging. EJNMMI Res. 2025;15[1]:80. van Raalte DH, Ouwens DM, Diamant M. [2009]. Novel insights into glucocorticoid-mediated diabetogenic effects: towards expansion of therapeutic options? Eur J Clin Invest, 39[2], 81–93. https://doi.org/10.1111/j.1365-2362.2008.02068.x Schacke H, Docke WD, Asadullah K. [2002]. Mechanisms involved in the side effects of glucocorticoids. Pharmacol Ther, 96[1], 23–43. https://doi.org/10.1016/s0163-7258[02]00297-8 Vita T, Okada DR, Veillet-Chowdhury M et al. [2021]. A standardized patient preparation protocol for FDG PET imaging in cardiac sarcoidosis: the stepwise use of low-carbohydrate diet, fasting, and heparin. J Nucl Med, 62[12], 1759–65. https://doi.org/10.2967/jnumed.121.261997 Osborne MT, Hulten EA, Murthy VL et al. [2019]. Patient preparation for cardiac fluorodeoxyglucose positron emission tomography imaging of inflammation. J Nuclear Cardiol, 26[2], 389–99. https://doi.org/10.1007/s12350-017-0966-7 Dweck MR, Abgral R, Trivieri MG et al. [2022]. The current and future role of cardiac PET imaging. Eur Heart J, 43[14], 1206–17. https://doi.org/10.1093/eurheartj/ehab864 Masuda A, Naya M, Manabe O, Magota K, Yoshinaga K, Tsutsui H, Tamaki N. Administration of unfractionated heparin with prolonged fasting could reduce physiological 18F-fluorodeoxyglucose uptake in the heart. Acta Radiol. 2016;57:661–8. Piriou N, Vuilleumier H, Liechti ME et al. [2017]. The effect of heparin on myocardial glucose uptake: A randomized trial. J Nuclear Cardiol, 24[6], 1972–1977. https://doi.org/10.1007/s12350-016-0508-1 Chareonthaitawee P, Beanlands RS, Chen W, Dorbala S, Miller EJ, Murthy VL, Birnie DH, Chen ES, Cooper LT, Tung RH, White ES, Borges-Neto S, Di Carli MF, Gropler RJ, Ruddy TD, Schindler TH, Blankstein R. Joint SNMMI-ASNC expert consensus document on the role of [18]F-FDG PET/CT in cardiac sarcoid detection and therapy monitoring. J Nucl Med. 2017;58:1341–53. Hartikainen S, Vepsäläinen V, Laitinen T, Hedman M, Laitinen T, Tompuri T. Heparin does not improve myocardial glucose metabolism suppression in [18 F]FDG PET/CT in patients with low β-hydroxybutyrate level. EJNMMI Res. 2024;14:92. Hossain ME, Bhandari S, Mueller C. [2023]. Exogenous ketone esters to achieve myocardial suppression in FDG PET imaging. Eur J Nucl Med Mol Imaging, 50[2], 413–21. https://doi.org/10.1007/s00259-022-05964-1 de Vos B, Slart RHJA, Glaudemans AWJM. [2022]. Dietary and pharmacological approaches to optimize FDG-PET myocardial suppression: an emerging role for ketone supplements? Eur Heart J – Cardiovasc Imaging, 23[6], 810–8. https://doi.org/10.1093/ehjci/jeac016 Supplementary Files APPENDIX1.docx Cite Share Download PDF Status: Published Journal Publication published 15 Dec, 2025 Read the published version in Annals of Nuclear Medicine → Version 1 posted Reviewers agreed at journal 09 Oct, 2025 Reviewers invited by journal 09 Oct, 2025 Editor assigned by journal 05 Oct, 2025 First submitted to journal 03 Oct, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7776884","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":527330454,"identity":"a0a445c9-5a4c-47d3-b812-400ccea13f1b","order_by":0,"name":"Ya Ruth Huo","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwUlEQVRIiWNgGAWjYHACNgbGBgYGfhAzoYAoHcwQLZINIC0GpGgxOADiEKPFfEb+sQeMOw7LGZ9fnfjhgQGDPL/YAfxaZG4ksxswnjlsbHbj7WYJoMMMZ85OwK9FQiKZTYKx7XDithtnN4C0JBjcJlbL5hlnN/8gTcsG/t5tRNrC89hMIrEt3VjiBu82iwQDCSL8wp74TOJjm7Ucf//ZzTd/VNjI80sT0AIGYDUSEJII5XDAf4AU1aNgFIyCUTCSAAAgST9sZRSIhAAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0001-6282-7677","institution":"Nepean Hospital, NSW, Australia","correspondingAuthor":true,"prefix":"","firstName":"Ya","middleName":"Ruth","lastName":"Huo","suffix":""},{"id":527330455,"identity":"e59c5b5c-17d4-4ea2-8020-1ca1436402b6","order_by":1,"name":"Sandeep Gupta","email":"","orcid":"","institution":"Department of Nuclear Medicine, John Hunter Hospital, NSW, Australia","correspondingAuthor":false,"prefix":"","firstName":"Sandeep","middleName":"","lastName":"Gupta","suffix":""},{"id":527330456,"identity":"b6cdb8f9-bf55-410c-a1cf-0368c2a1ca47","order_by":2,"name":"Natalie Rutherford","email":"","orcid":"","institution":"Department of Nuclear Medicine, John Hunter Hospital, NSW, Australia","correspondingAuthor":false,"prefix":"","firstName":"Natalie","middleName":"","lastName":"Rutherford","suffix":""},{"id":527330457,"identity":"a32508f8-fc3b-4496-99aa-3bac27d83e97","order_by":3,"name":"Megan Saul","email":"","orcid":"","institution":"Department of Nuclear Medicine, John Hunter Hospital, NSW, Australia","correspondingAuthor":false,"prefix":"","firstName":"Megan","middleName":"","lastName":"Saul","suffix":""},{"id":527330458,"identity":"c728dd14-04d9-4c19-9c2f-d267e713e311","order_by":4,"name":"Michael Vinchill Chan","email":"","orcid":"","institution":"Department of Radiology, Concord General Repatriation Hospital, NSW, Australia","correspondingAuthor":false,"prefix":"","firstName":"Michael","middleName":"Vinchill","lastName":"Chan","suffix":""}],"badges":[],"createdAt":"2025-10-04 02:31:43","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7776884/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7776884/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s12149-025-02141-5","type":"published","date":"2025-12-15T15:58:25+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":94224281,"identity":"cec7c175-7f2a-490d-a6b8-9ab6e3f591c7","added_by":"auto","created_at":"2025-10-23 19:17:31","extension":"xml","order_by":1,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":7280,"visible":true,"origin":"","legend":"","description":"","filename":"anmeANMED2500413.xml","url":"https://assets-eu.researchsquare.com/files/rs-7776884/v1/9dc1f2cdd89a695a3498012f.xml"},{"id":94223655,"identity":"b040984c-e62f-461c-b293-e1c9f00e8fd1","added_by":"auto","created_at":"2025-10-23 19:09:31","extension":"xml","order_by":2,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":966,"visible":true,"origin":"","legend":"","description":"","filename":"ANMED25004135866.go.xml","url":"https://assets-eu.researchsquare.com/files/rs-7776884/v1/4532c99d1822a281f4a74a8f.xml"},{"id":94224999,"identity":"6af58fa1-5f87-4d75-9a38-edb9f297db66","added_by":"auto","created_at":"2025-10-23 19:25:31","extension":"xml","order_by":3,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":875,"visible":true,"origin":"","legend":"","description":"","filename":"ANMED2500413Import.xml","url":"https://assets-eu.researchsquare.com/files/rs-7776884/v1/8df1aa8959af71f1de3ee5be.xml"},{"id":94223658,"identity":"c9522ced-a9a6-4eec-a23f-3c66ae7a3c6f","added_by":"auto","created_at":"2025-10-23 19:09:31","extension":"xml","order_by":4,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":97077,"visible":true,"origin":"","legend":"","description":"","filename":"ANMED25004130enriched.xml","url":"https://assets-eu.researchsquare.com/files/rs-7776884/v1/a19e5a4c1e9faf48d335a0d9.xml"},{"id":94224285,"identity":"4b400e64-7cf6-48e1-a48c-024ee3e0f587","added_by":"auto","created_at":"2025-10-23 19:17:31","extension":"png","order_by":6,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":54904,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7776884/v1/84a5302f1df2501dbac2ef9c.png"},{"id":94224998,"identity":"0917730c-5fb4-4502-a1f9-3c9c07c0bc25","added_by":"auto","created_at":"2025-10-23 19:25:31","extension":"png","order_by":7,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":91706,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7776884/v1/e2fe1c6431b9155deb3fd5e9.png"},{"id":94223659,"identity":"a4ee952f-a9d6-4b1d-ad6b-9a36942334df","added_by":"auto","created_at":"2025-10-23 19:09:31","extension":"png","order_by":8,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":24924,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7776884/v1/4a4890d79d0da9fcfee32286.png"},{"id":94223665,"identity":"8c9772c1-f0d4-4b96-89ef-6f9ad57872d9","added_by":"auto","created_at":"2025-10-23 19:09:31","extension":"xml","order_by":9,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":94359,"visible":true,"origin":"","legend":"","description":"","filename":"ANMED25004130structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-7776884/v1/ddd46df02f090775db14e47d.xml"},{"id":94223664,"identity":"6b5735a7-166e-45a1-8e78-542dd31c2485","added_by":"auto","created_at":"2025-10-23 19:09:31","extension":"html","order_by":10,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":105756,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7776884/v1/d9c4fd06741b9afac2dfa498.html"},{"id":94224283,"identity":"99b85b83-a1ca-4722-9809-f3539e098e7d","added_by":"auto","created_at":"2025-10-23 19:17:31","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":789174,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eExample of Adequate vs Inadequate myocardial glucose suppression on fused PET/CT\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7776884/v1/d01103b6f2e9eede314b305c.png"},{"id":98814255,"identity":"be62219e-152d-4dd4-9817-80cb70197206","added_by":"auto","created_at":"2025-12-22 16:12:08","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1819102,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7776884/v1/3c0d9678-7d50-4561-8268-b2343e1b4a14.pdf"},{"id":94223663,"identity":"49db59cd-09f2-470b-b057-e13447d00656","added_by":"auto","created_at":"2025-10-23 19:09:31","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":79678,"visible":true,"origin":"","legend":"","description":"","filename":"APPENDIX1.docx","url":"https://assets-eu.researchsquare.com/files/rs-7776884/v1/4efa8d0e5f9ff036a75099ed.docx"}],"financialInterests":"","formattedTitle":"Utility of serum blood ketone levels and other risk factors for inadequate myocardial glucose suppression ketogenic FDG-PET/CT: a prospective and retrospective cohort study","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eThe ketogenic diet (KD) is an effective preparatory strategy for suppressing physiological myocardial glucose uptake prior to 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT), particularly in the evaluation of inflammatory cardiac conditions such as cardiac sarcoidosis [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Under normal metabolic conditions, myocardium primarily utilizes glucose and free fatty acids for energy. This leads to significant physiological 18F-FDG uptake in healthy myocardial tissue, which can obscure pathological uptake and reduce diagnostic accuracy [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eA high-fat, low-carbohydrate KD induces a metabolic shift from glucose metabolism to fatty acid oxidation and ketone body utilization. This shift suppresses myocardial glucose uptake, effectively reducing background FDG signal and enhancing the contrast between normal and inflamed myocardium. As a result, pathological foci\u0026mdash;such as those seen in cardiac sarcoidosis\u0026mdash;can be more clearly visualized [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe efficacy of KD preparation has been supported by several studies. For example, \u0026Ouml;z\u0026uuml;temiz and colleagues demonstrated a 72-hour KD with overnight fasting achieved complete myocardial suppression in 96.9% of cases, compared to 68.1% with a 24-hour KD and 52.3% with an 18-hour fasting protocol [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. These findings highlight the importance of both the duration and adherence to ketogenic protocols for optimal image quality. However, the duration of the ketogenic diet varies considerably between hospitals, with many adopting a shorter 24-hour protocol due to patient compliance, time constraints, and logistical challenges.\u003c/p\u003e\u003cp\u003eSerum ketone β-hydroxybutyrate levels have emerged as a useful biomarker for assessing the adequacy of myocardial glucose suppression. Elevated serum ketone β-hydroxybutyrate concentrations are associated with successful suppression, whereas lower levels may reflect suboptimal dietary adherence or insufficient metabolic transition to ketosis [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] Although heparin administration has been proposed to improve suppression, there are limitations for patients with inadequate ketone levels [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eDespite these advances, inadequate myocardial suppression remains a challenge in a subset of patients, with reported rates of non-diagnostic scans as high as 7.1% even after ketogenic preparation [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Contributing risk factors include poor compliance with dietary protocols, inadequate preparation time and individual metabolic variability. These limitations underscore the need for standardized preparation protocols and objective biomarkers to guide and assess readiness for PET/CT imaging.\u003c/p\u003e\u003cp\u003eThis study aims to investigate clinical and metabolic risk factors for inadequate suppression by comparing cohorts before and after the implementation of enhanced dietary protocols\u0026mdash;including a standardized ketogenic diet guide, dietary logbook, patient questionnaire, and point-of-care blood ketone testing to further improve patient selection and preparation strategies for cardiac PET imaging. The study will also evaluate an optimal blood ketone level threshold that best predicts adequate myocardial glucose suppression (MGS) in patients undergoing a 24-hour KD preparation for 18F-FDG PET/CT.\u003c/p\u003e"},{"header":"MATERIALS AND METHODS","content":"\u003cp\u003eThis was a combined retrospective and prospective observational study conducted at two tertiary hospitals to assess the utility of blood ketone levels and other clinical factors in predicting adequate MGS in patients undergoing 24-hour ketogenic preparation for 18F-FDG PET/CT scans. The retrospective component included all patients who underwent ketogenic PET/CT imaging between August 2022 and April 2024. No patients were excluded. The prospective arm of the study included all patients scanned from April 2024 to January 2025, during which time new preparation protocols were introduced in April 2024.\u003c/p\u003e\u003cp\u003eFor the retrospective cohort, data was extracted from patient records, including demographic data such as age, gender, inpatient or outpatient status, scan indication, and the adequacy of myocardial suppression as determined on PET/CT review. Adequate suppression was defined as myocardial 18F-FDG uptake lower than blood pool activity. Cases with higher or heterogeneous myocardial uptake without known pathology were classified as having inadequate suppression.\u003c/p\u003e\u003cp\u003eFor the prospective cohort, a new departmental protocol was implemented to improve myocardial suppression in April 2024. Patients in the prospective arm received revised dietary instructions that emphasized strict adherence to a high-fat, low-carbohydrate ketogenic diet for a minimum of 24 hours prior to the scan and fasting 12 hours prior to the study. These instructions, along with a newly introduced patient questionnaire and a dietary logbook, were emailed to all patients at least 72 hours in advance of their scheduled scan. Upon arrival on the day of imaging, patients underwent point-of-care testing of capillary blood β-hydroxybutyrate (ketone) and glucose levels using handheld meters (Abbott Freestyle Optium Neo). These biochemical parameters were recorded in addition to the patient\u0026rsquo;s age, gender, BMI, inpatient or outpatient status, exercise level, diabetic status, dietary adherence (as per the logbook), and any recent use of immunosuppressive medications, including corticosteroids.\u003c/p\u003e\u003cp\u003eMyocardial glucose suppression was assessed visually by experienced nuclear medicine physicians. Myocardial glucose suppression was considered adequate when normal myocardial FDG uptake was lower than the blood pool\u0026mdash;defined as a negative study if all LV wall segments showed uptake equal to or less than the blood pool, and a positive study if focal or multifocal uptake was present or if corresponding regions demonstrated late gadolinium enhancement on cardiac MRI (when available). Scans not meeting these criteria\u0026mdash;such as those showing diffuse LV uptake, basal LV ring uptake, lateral LV wall uptake, or patchy uptake exceeding blood pool activity\u0026mdash;in the absence of known myocardial inflammation, were classified as inadequate myocardial glucose suppression (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Scans were correlated with clinical notes as well as cardiac MRI findings where available. Blood ketone levels were analyzed to determine if they correlated with suppression outcomes, with the aim of identifying a minimum threshold predictive of successful suppression.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eStatistical analysis was performed using SPSS 27 (IBM Corp., Armonk, NY). For univariate analysis, the chi-squared test was used for categorical variables and the independent t-test for continuous variables. Variables with a p-value\u0026thinsp;\u0026lt;\u0026thinsp;0.20 in univariate analysis were entered into a multivariate logistic regression model to identify independent predictors of inadequate myocardial suppression. A p-value\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e\u003cp\u003eEthics approval was obtained from the institutional Human Research Ethics Committee. As this study evaluated routine clinical practice, informed consent was waived for the retrospective data and deemed not required for the prospective observational data collection.\u003c/p\u003e\u003c/p\u003e"},{"header":"RESULTS","content":"\u003cp\u003eThere was a total of 95 patients from Aug 2022 - April 2024 in the retrospective cohort and 92 patients from April 2024 - January 2025 in the prospective cohort. The demographic data for the cohort are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. There were no significant differences between the demographic data between the retrospective and prospective cohort.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eDemographic and Clinical Characteristics of participants\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRetrospective\u003c/p\u003e\u003cp\u003eCohort\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eProspective\u003c/p\u003e\u003cp\u003eCohort\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003ep-value*\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNumber of patients (n)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e95\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e92\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAge (mean)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e62.3 years\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e60.2 years\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.95\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGender (n)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMale\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e52\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e52\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFemale\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e43\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.81\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePatient Location\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOutpatients\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e57\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eInpatients\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.57\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePET Indication\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSarcoid assessment\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e57\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e49\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNon-sarcoid\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e38\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e46\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.35\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"4\"\u003e*P-value for difference between subgroups with dichotomous factors (Chi-squared) or means (Independent T-test)\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e Following the introduction of improved dietary guidelines and logbook in April 2024, the rate of inadequate MGS reduced from 26% down to 17% (9% decrease, p\u0026thinsp;=\u0026thinsp;0.14). The overall rate of inadequate MGS was 22% (retrospective and prospective cohort study combined).\u003c/p\u003e\u003cp\u003eOn univariate analysis of dichotomous variables, significant risk factors for inadequate MGS included prednisolone use (75% vs 14.9% for no prednisolone use, OR: 17.1 [95%CI 1.65-177.04], p\u0026thinsp;=\u0026thinsp;0.009), low blood ketone level (\u0026le;\u0026thinsp;0.3 mmol/L)(OR: 5.77 [95%CI 1.69\u0026ndash;19.68], p\u0026thinsp;=\u0026thinsp;0.003) and female sex (27.5% vs males 9.6%, OR: 3.57 [95%CI 1.12\u0026ndash;11.3], p\u0026thinsp;=\u0026thinsp;0.025) (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eUnivariate analysis of dichotomous factors associated with incomplete MGS in the Prospective cohort\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eInadequate myocardial glucose suppression\u003c/p\u003e\u003cp\u003eOR (95% CI)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003ep-value\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFemale vs Male\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e3.57 (1.12\u0026ndash;11.3)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e0.025\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCurrent Prednisolone use vs No prednisolone use\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e17.1 (1.65-177.04)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e0.009\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBlood ketone level\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u0026le;\u0026thinsp;0.3 vs\u0026thinsp;\u0026gt;\u0026thinsp;0.4 mmol/L\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e5.77 (1.69\u0026ndash;19.68)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e0.003\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u0026le;\u0026thinsp;0.4 vs\u0026thinsp;\u0026gt;\u0026thinsp;0.5 mmol/L\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e4.11 (1.08\u0026ndash;15.6)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e0.028\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eKetogenic diet duration\u0026thinsp;\u0026lt;\u0026thinsp;24hrs vs\u0026thinsp;\u0026ge;\u0026thinsp;24hrs\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003e4.72 (1.08\u0026ndash;20.6)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e0.049\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eInpatient vs Outpatient\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.33 (0.45\u0026ndash;3.97)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.61\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSarcoid vs non-sarcoid assessment\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.58 (0.52\u0026ndash;4.79)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.42\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePoor Keto diet adherence vs Good keto diet adherence\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2.09 (0.64\u0026ndash;6.83)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.22\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDiabetic vs non-diabetic\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.39 (0.05\u0026ndash;3.37)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.35\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eUnivariate analysis of the continuous variables associated with inadequate MGS are outlined in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. Mean blood ketone levels were significantly lower in patients with incomplete MGS (0.34 mmol/L vs 0.76 mmol/L, p-value 0.04). The ketogenic diet duration was lower in patients with incomplete MGS (20.9 hrs vs 29.6 hrs, p\u0026thinsp;=\u0026thinsp;0.07).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eUnivariate analysis of continuous factors associated with incomplete MGS in prospective cohort\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCharacteristic\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eInadequate Cardiac Suppression\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eAdequate Cardiac Suppression\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eP-value\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eAge\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e55.9 years\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e61.1 years\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.22\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eWeight\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e88.9 kg\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e88.0 kg\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.87\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eBMI\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e30.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e29.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.78\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eBlood Glucose Level\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e5.3 mmol/L\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5.4 mmol/L\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.89\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eBlood Ketone Level\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.34 mmol/L\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.76 mmol/L\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.04\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eKetogenic Diet Duration\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e20.9 hrs\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e29.6 hrs\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.07\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eFasting Duration\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e16.7 hrs\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e17.2 hrs\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.88\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eMultivariate analysis demonstrated prednisolone use, low blood ketone levels (\u0026le;\u0026thinsp;0.3 mmol/L), female gender and \u0026lt;\u0026thinsp;24hr ketogenic diet remained significant risk factors for inadequate MGS (Model 2, Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Model 1 multivariate analysis demonstrated female was a risk factor for inadequate MGS however became non-significant after the addition of a ketogenic diet duration\u0026thinsp;\u0026lt;\u0026thinsp;24hrs as a variable (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eMultivariate analysis of factors associated with incomplete MGS\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eOdds Ratio for Incomplete MGS (95% CI)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eP-value\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eModel 1\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLow Blood Ketone level (\u0026le;\u0026thinsp;0.3mmol/L)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e4.04 (1.09\u0026ndash;14.98)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.037\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFemale Gender\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e4.50 (1.11\u0026ndash;18.26)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.036\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePrednisolone use\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e26.97 (91.84-396.25)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.016\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eModel 2\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLow Blood Ketone level (\u0026le;\u0026thinsp;0.3 mmol/L)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e7.1 (1.2\u0026ndash;41.4)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.029\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFemale Gender\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e4.49 (0.79\u0026ndash;25.64)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.09\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePrednisolone use\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e51.03 (2.55-1023.3)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.01\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eKetogenic diet duration\u0026thinsp;\u0026lt;\u0026thinsp;24hrs\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e20.08 (2.28-176.47)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.007\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe rates of inadequate MGS were 50%, 26% and 7% for patients with blood ketone level of 0.1 mmol/L, 0.2\u0026ndash;0.3 mmol/L and \u0026ge;\u0026thinsp;0.4 mmol/L, respectively (Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). If patients were on prednisolone, 100% had inadequate MGS if the blood ketone level was 0.3 mmol/L or lower. There were two patients who were on prednisolone (10mg daily and 25mg daily) had a low blood ketone level of 0.1 mmol/L and had inadequate MGS, despite adherence to the ketogenic diet for 24hrs. There was one patient on prednisolone (10mg daily) who had a borderline blood ketone level of 0.3 mmol/L and had inadequate MGS. There was one patient on prednisolone (10mg) who had a blood ketone level of 0.4 mmol/L and had adequate MGS.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eKetone level and association with incomplete MGS\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e\u003cp\u003eBlood Ketone Level (mmol/L)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.1\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.2\u0026ndash;0.3\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u0026ge;\u0026thinsp;0.4\u003c/p\u003e \u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eRisk of inadequate MGS\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e50%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e26%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e7%\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e+ Poor Ketogenic diet adherence\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e100%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e50%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e18.8%\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e+ On Prednisolone\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e100%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e100%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0%\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e+ Female\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e100%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e28%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e16%\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e+ Male\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e29%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e22%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3%\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThere were four patients who had high blood ketone levels (\u0026gt;\u0026thinsp;0.3 mmol/L) but had inadequate cardiac suppression. One patient had a high ketone level of 1.4 mmol/L however they reported that they consumed mashed pumpkin and crackers the day prior to the scan. Another patient had a ketone level of 0.6 mmol/L but reported they ate potato soup and bread the day before. Another patient had a ketone level of 0.4 mmol/L but had crackers at 10pm the night before. One patient had a ketone level of 0.7mmol/L but denied having carbohydrates the day before.\u003c/p\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eThis present study reinforces the clinical utility of ketogenic preparation for cardiac FDG PET/CT to suppress physiological myocardial glucose uptake, thereby enhancing diagnostic accuracy in evaluating inflammatory cardiac pathologies such as sarcoidosis. Our findings suggest that emailing patients clear ketogenic dietary instructions along with a dietary logbook significantly improves adherence to the ketogenic protocol. It clarifies adherence to the ketogenic diet prior to the scan. This simple intervention may optimize myocardial suppression and improve scan interpretability.\u003c/p\u003e\u003cp\u003eThis study also demonstrated that measuring serum ketone levels remains a valuable adjunct, providing objective insight into the patient's metabolic state. In our cohort, the rates of inadequate MGS were 50%, 26% and 7% for patients with blood ketone levels of 0.1, 0.2\u0026ndash;0.3 and \u0026ge;\u0026thinsp;0.4 mmol/L, respectively. This is consistent with a previous study which demonstrated a ketone level cut-off value of 0.35 mmol/L to predict adequate myocardial suppression, with a specificity of 90% and sensitivity of 56% in patients with 24\u0026ndash;48 hrs of a ketogenic diet [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. In comparison, another study including patients on a 24-hour or 72-hour ketogenic diet, or given a ketogenic drink, found that a ketone threshold of \u0026ge;\u0026thinsp;0.58 mmol/L correctly classified 92% of scans [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. The differences in ketone levels across studies is attributable to the variable duration of the ketogenic diet, with studies showing significantly higher ketone levels after a 72-hour regimen compared to a 24-hour ketogenic diet protocol (0.3 \u0026plusmn; 0.4 versus 1.0 \u0026plusmn; 0.7 mmol/L; p\u0026thinsp;\u0026lt;\u0026thinsp;0.001)6.\u003c/p\u003e\u003cp\u003eHowever, optimal myocardial suppression appears to require both biochemical ketosis and strict dietary compliance. This study demonstrated that relying solely on serum blood ketone levels can be insufficient without assessment of actual dietary adherence, as some patients demonstrated poor suppression despite adequate ketone levels. The specific example which highlights this was a patient with inadequate MGS with a blood ketone level of 1.4mmol/L but had mashed pumpkin and crackers 24hrs prior to the scan. This highlights the importance of a combined approach involving both metabolic (serum ketone) and behavioral (dietary log) assessment to determine true ketogenic adherence [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/p\u003e\u003cp\u003eThese findings maybe particularly valuable in indeterminate cases wherein the combination of high serum ketone levels and good dietary adherence favors a highly likelihood of adequate myocardial glucose suppression and any uptake is likely pathological myocardial uptake, whereas low ketones and poor adherence favors a higher likelihood of inadequate myocardial glucose suppression. This distinction may help clinicians avoid misdiagnosis or unnecessary further testing [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThis present study also highlights the increased difficulty for patients on prednisolone to achieve a ketogenic metabolic state and adequate MGS, even with adherence to a standard 24-hour ketogenic diet and fasting protocol. This contrasts with a previous study which demonstrated patients treated with systemic corticosteroids had adequate suppression (88%) compared to 57% without systemic corticosteroids (p\u0026thinsp;=\u0026thinsp;0.096) [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eCorticosteroids such as prednisolone are well-known to induce hyperglycemia and insulin resistance, which can impair the metabolic shift required for effective suppression of myocardial glucose uptake. Glucocorticoids upregulate hepatic gluconeogenesis and reduce peripheral glucose uptake, thereby sustaining elevated serum glucose levels and blunting ketogenesis [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. These metabolic effects directly oppose the physiologic conditions necessary for myocardial fatty acid utilization during FDG PET imaging.\u003c/p\u003e\u003cp\u003eIn this present study, all patients on prednisolone demonstrated a markedly reduced ability to achieve adequate myocardial suppression when prepared with a 24-hour ketogenic protocol. Specifically, 100% of patients on prednisolone with a blood ketone level of \u0026le;\u0026thinsp;0.3 mmol/L failed to achieve adequate MGS. Two patients on prednisolone (10 mg and 25 mg daily) had low ketone levels of 0.1 mmol/L and demonstrated inadequate suppression, despite reportedly adhering to the prescribed ketogenic diet. Another patient, also on 10 mg daily of prednisolone, had a borderline ketone level of 0.3 mmol/L and similarly showed inadequate suppression. Notably, the only patient on prednisolone to achieve adequate MGS had a ketone level of 0.4 mmol/L, suggesting that higher ketone thresholds may be necessary in corticosteroid-treated individuals to compensate for glucocorticoid-induced metabolic derangements.\u003c/p\u003e\u003cp\u003eThese findings suggest that shorter 24-hour ketogenic preparation protocols may be insufficient for patients receiving systemic corticosteroids. It is plausible that these patients require an extended ketogenic diet duration of 48 to 72 hours, with more stringent fasting, to overcome the counterregulatory effects of corticosteroids on glucose metabolism and to promote sufficient ketone production. Additionally, a higher minimum ketone threshold (e.g. \u0026gt;0.4 mmol/L) may be a more appropriate indicator of readiness for imaging in this subgroup.\u003c/p\u003e\u003cp\u003eThese results are consistent with previous literature indicating that individual metabolic and pharmacologic factors can significantly influence FDG biodistribution and suppression protocols [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Given the prevalence of corticosteroid use in patients undergoing inflammatory cardiac imaging, particularly for suspected sarcoidosis, our findings underscore the need for tailored preparation protocols for this high-risk group. Larger studies are warranted to define optimal ketogenic duration and ketone cutoffs in corticosteroid-treated populations, and to evaluate whether adjunctive strategies such as prolonged fasting or exogenous ketone supplementation could improve MGS outcomes.\u003c/p\u003e\u003cp\u003ePrevious study by Hartikainen and colleagues [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] also identified diabetes and obesity predicted adequate myocardial suppression. Our study did not identify diabetes or obesity (based on BMI) associated with myocardial suppression in our prospective cohort.\u003c/p\u003e\n\u003ch3\u003eCost Analysis\u003c/h3\u003e\n\u003cp\u003eImplementing a streamlined ketogenic preparation protocol that includes blood ketone testing and emailed dietary instructions with a logbook presents a highly cost-effective strategy for ensuring adequate myocardial glucose suppression in cardiac FDG PET/CT imaging. A single ketone strip costs approximately \u003cspan\u003e$\u003c/span\u003e0.85 AUD and point-of-care testing typically requires only one minute of staff time to perform, often using the same glucose monitor and single skin prick. Emailing the dietary guidelines and logbook to patients takes about one minute, and patients typically spend around 10 minutes completing the logbook and adhering to the ketogenic diet.\u003c/p\u003e\u003cp\u003eIn contrast, inadequate myocardial suppression can necessitate repeated PET/CT scans, leading to significant additional costs and resource utilization. The Medicare Benefits Schedule (MBS) fee for a whole-body FDG PET scan is \u003cspan\u003e$\u003c/span\u003e953.00 AUD, with Medicare covering 85% (\u003cspan\u003e$\u003c/span\u003e810.05 AUD) and patients potentially facing out-of-pocket expenses depending on the provider's billing practices. Repeat scans also impose further burdens, including extended dietary restrictions [up to 72 hours], increased patient inconvenience, and additional strain on departmental resources and scheduling. Therefore, pre-test qualitative and quantitative assessment of diet and ketones may be a practical method to improve resource utilization.\u003c/p\u003e\n\u003ch3\u003eLimitations\u003c/h3\u003e\n\u003cp\u003eThis study has several limitations that may affect the generalizability of its findings. The external validity is constrained by the specific protocol used: a 24-hour ketogenic diet with a 12-hour fast prior to FDG injection. Other institutions employ longer preparation protocols \u0026mdash; including 48- to 72-hour ketogenic diets \u0026mdash; which have been shown to more consistently suppress physiological myocardial uptake [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. However, there are also many hospital departments which utlise a 24-hour ketogenic diet with a 12-hour fast to reduce patient scan delays. Moreover, the findings from this study may assist in identifying which patients may be suitable for earlier imaging at 24-hours rather than wait 72-hours.\u003c/p\u003e\u003cp\u003eAnother limitation of our study was the low number of patients on corticosteroids, however despite the small numbers, it had an overt quantitative and qualitive impact on MGS. The metabolic impact of glucocorticoids may necessitate higher ketone thresholds (ie. \u0026gt;0.4mmol/L) or prolonged dietary preparation to achieve adequate myocardial suppression. Further research is warranted to determine the appropriate preparation strategy for this subgroup.\u003c/p\u003e\u003cp\u003eAnother limitation was not utilising intravenous unfractionated heparin (50 IU/kg) approximately 15 minutes prior to FDG injection. While theoretically beneficial by inducing lipolysis and increase serum free fatty acids [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], clinical studies have shown mixed results regarding MGS and may have added confounding variables in this present study [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. A previous study demonstrated heparin did not significantly affect suppression in patients with a low ketone level [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThis study also did not utilise exogenous ketone supplements, such as ketone esters or ketogenic formulas, to induce rapid ketosis in patients unable to adhere to dietary restrictions. Early data suggest these strategies may enhance myocardial suppression, but evidence remains limited and variable [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Previous studies have also identified fatty liver predicted adequate myocardial suppression [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Our study did not assess the presence of fatty liver.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn conclusion, this study demonstrates providing patients clear ketogenic dietary instructions along with a dietary logbook improves dietary adherence prior to 18F-FDG PET/CT. Moreover, incorporating point-of-care ketone level testing can further refine patient preparation, ensuring higher rates of diagnostic-quality imaging. Future research should focus on exploring additional strategies to mitigate the identified risk factors for preparation of failure.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eSources of Funding:\u003c/strong\u003e None\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDisclosure of Potential Conflicts of Interest:\u0026nbsp;\u003c/strong\u003eNone\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003e\u0026Ouml;z\u0026uuml;temiz C, Koksel Y, Froelich JW, Rubin N, Bhargava M, Roukoz H, Cogswell R, Markowitz J, Perlman DM, Steinberger D. Comparison of the effect of three different dietary modifications on myocardial suppression in 18F-FDG PET/CT evaluation of patients for suspected cardiac sarcoidosis. J Nucl Med. 2021;62(12):1759\u0026ndash;67.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMadamanchi C, Weinberg RL, Murthy VL. Utility of serum ketone levels for assessment of myocardial glucose suppression for 18F-fluorodeoxyglucose PET in patients referred for evaluation of endocarditis. J Nuclear Cardiol. 2023;30(3):928\u0026ndash;37.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOsborne MT, Qamar I, Selvaraj S. A level of confidence: beta-hydroxybutyrate and myocardial glucose uptake suppression on 18F-FDG PET imaging. J Nuclear Cardiol. 2023;30(3):938\u0026ndash;40.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHartikainen S, Veps\u0026auml;l\u0026auml;inen V, Laitinen T, Hedman M, Laitinen T, Tompuri T. Heparin does not improve myocardial glucose metabolism suppression in [18 F] FDG PET/CT in patients with low β-hydroxybutyrate level. EJNMMI Res. 2024;14(1):92.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003e\u0026Ouml;z\u0026uuml;temiz C, Koksel Y, Froelich JW, Rubin N, Bhargava M, Roukoz H, Cogswell R, Markowitz J, Perlman DM, Steinberger D. The active papillary muscle sign in 18F-FDG PET/CT cardiac sarcoidosis exams and its relationship with myocardial suppression. Ann Nucl Med. 2024;38(5):391\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHartikainen S, Tompuri T, Laitinen T, Laitinen T. Point-of‐care β‐hydroxybutyrate measurement predicts adequate glucose metabolism suppression in cardiac FDG‐PET/CT. Clin Physiol Funct Imaging. 2024;44(5):349\u0026ndash;58.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSelvaraj S, Margulies KB, Dugyala S, Schubert E, Tierney A, Arany Z, Pryma DA, Shah SH, Rame JE, Kelly DP, Bravo PE. Comparison of exogenous ketone administration versus dietary carbohydrate restriction on myocardial glucose suppression: a crossover clinical trial. J Nucl Med. 2022;63(5):770\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eVidula MK, Selvaraj S, Rojulpote C, Bhattaru A, Kc W, Hansbury M, Schubert E, Clancy CB, Rossman M, Goldberg LR, Farwell M. Relationship of ketosis with myocardial glucose uptake among patients undergoing FDG PET/CT for evaluation of cardiac sarcoidosis. Circ Cardiovasc Imaging. 2024;17(8):e016774.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAbikhzer G et al. [2021]. Impact of dietary noncompliance on myocardial FDG uptake in PET imaging. Clin Nucl Med, 46[2], e75\u0026ndash;80.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOsborne MT et al. [2019]. Ketogenic preparation for cardiac sarcoidosis imaging: effects on FDG suppression and patient compliance. JACC: Cardiovasc Imaging, 12[4], 765\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDilsizian V, Bacharach SL. [2017]. FDG PET imaging in cardiac sarcoidosis: need for standardization of protocols and interpretation criteria. J Nucl Med, 58[2], 199\u0026ndash;200.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHartikainen S, Veps\u0026auml;l\u0026auml;inen V, Tompuri T, Laitinen TM, Hedman M, Laitinen T. Cardiometabolic disorders affect myocardial [18F] fluorodeoxyglucose uptake\u0026ndash;impact on diagnostic PET/CT imaging. EJNMMI Res. 2025;15[1]:80.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003evan Raalte DH, Ouwens DM, Diamant M. [2009]. Novel insights into glucocorticoid-mediated diabetogenic effects: towards expansion of therapeutic options? Eur J Clin Invest, 39[2], 81\u0026ndash;93. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/j.1365-2362.2008.02068.x\u003c/span\u003e\u003cspan address=\"10.1111/j.1365-2362.2008.02068.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSchacke H, Docke WD, Asadullah K. [2002]. Mechanisms involved in the side effects of glucocorticoids. Pharmacol Ther, 96[1], 23\u0026ndash;43. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/s0163-7258[02]00297-8\u003c/span\u003e\u003cspan address=\"10.1016/s0163-7258[02]00297-8\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eVita T, Okada DR, Veillet-Chowdhury M et al. [2021]. A standardized patient preparation protocol for FDG PET imaging in cardiac sarcoidosis: the stepwise use of low-carbohydrate diet, fasting, and heparin. J Nucl Med, 62[12], 1759\u0026ndash;65. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.2967/jnumed.121.261997\u003c/span\u003e\u003cspan address=\"10.2967/jnumed.121.261997\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOsborne MT, Hulten EA, Murthy VL et al. [2019]. Patient preparation for cardiac fluorodeoxyglucose positron emission tomography imaging of inflammation. J Nuclear Cardiol, 26[2], 389\u0026ndash;99. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s12350-017-0966-7\u003c/span\u003e\u003cspan address=\"10.1007/s12350-017-0966-7\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDweck MR, Abgral R, Trivieri MG et al. [2022]. The current and future role of cardiac PET imaging. Eur Heart J, 43[14], 1206\u0026ndash;17. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1093/eurheartj/ehab864\u003c/span\u003e\u003cspan address=\"10.1093/eurheartj/ehab864\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMasuda A, Naya M, Manabe O, Magota K, Yoshinaga K, Tsutsui H, Tamaki N. Administration of unfractionated heparin with prolonged fasting could reduce physiological 18F-fluorodeoxyglucose uptake in the heart. Acta Radiol. 2016;57:661\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePiriou N, Vuilleumier H, Liechti ME et al. [2017]. The effect of heparin on myocardial glucose uptake: A randomized trial. J Nuclear Cardiol, 24[6], 1972\u0026ndash;1977. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s12350-016-0508-1\u003c/span\u003e\u003cspan address=\"10.1007/s12350-016-0508-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChareonthaitawee P, Beanlands RS, Chen W, Dorbala S, Miller EJ, Murthy VL, Birnie DH, Chen ES, Cooper LT, Tung RH, White ES, Borges-Neto S, Di Carli MF, Gropler RJ, Ruddy TD, Schindler TH, Blankstein R. Joint SNMMI-ASNC expert consensus document on the role of [18]F-FDG PET/CT in cardiac sarcoid detection and therapy monitoring. J Nucl Med. 2017;58:1341\u0026ndash;53.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHartikainen S, Veps\u0026auml;l\u0026auml;inen V, Laitinen T, Hedman M, Laitinen T, Tompuri T. Heparin does not improve myocardial glucose metabolism suppression in [18 F]FDG PET/CT in patients with low β-hydroxybutyrate level. EJNMMI Res. 2024;14:92.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHossain ME, Bhandari S, Mueller C. [2023]. Exogenous ketone esters to achieve myocardial suppression in FDG PET imaging. Eur J Nucl Med Mol Imaging, 50[2], 413\u0026ndash;21. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00259-022-05964-1\u003c/span\u003e\u003cspan address=\"10.1007/s00259-022-05964-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ede Vos B, Slart RHJA, Glaudemans AWJM. [2022]. Dietary and pharmacological approaches to optimize FDG-PET myocardial suppression: an emerging role for ketone supplements? Eur Heart J \u0026ndash; Cardiovasc Imaging, 23[6], 810\u0026ndash;8. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1093/ehjci/jeac016\u003c/span\u003e\u003cspan address=\"10.1093/ehjci/jeac016\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"annals-of-nuclear-medicine","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"anme","sideBox":"Learn more about [Annals of Nuclear Medicine](http://link.springer.com/journal/12149)","snPcode":"12149","submissionUrl":"https://www.editorialmanager.com/anme/default2.aspx","title":"Annals of Nuclear Medicine","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Ketogenic, PET/CT, cardiac sarcoidosis, ketone, β-hydroxybutyrate, myocardial glucose suppression","lastPublishedDoi":"10.21203/rs.3.rs-7776884/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7776884/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eOBJECTIVES\u003c/h2\u003e\u003cp\u003eIncomplete myocardial glucose suppression (MGS) in ketogenic 18F-FDG-PET/CT is a common problem that reduces the diagnostic accuracy in detecting myocardial inflammation. This study assesses the usefulness of a dietary logbook, blood ketone testing and risk factors for inadequate MGS.\u003c/p\u003e\u003ch2\u003eMETHODS\u003c/h2\u003e\u003cp\u003eRetrospective (2022\u0026ndash;2024) and prospective (2024\u0026ndash;2025) analysis was performed on all patients who underwent a ketogenic 18F-FDG-PET/CT. In April 2024, blood ketone testing, a dietary logbook, and improved dietary guidelines were introduced. All patients were instructed to follow\u0026thinsp;\u0026gt;\u0026thinsp;24-hour ketogenic diet and \u0026gt;\u0026thinsp;12-hour fast before imaging.\u003c/p\u003e\u003ch2\u003eRESULTS\u003c/h2\u003e\u003cp\u003e After introducing the dietary logbook and guidelines, inadequate MGS rates decreased from 26% to 17% (95 patients 2022\u0026ndash;2024 vs 92 patients 2024\u0026ndash;2025)(p-value 0.14). Mean blood ketones were significantly lower in patients with incomplete MGS (0.34mmol/L vs 0.76mmol/L, p-value 0.04). On univariate analysis, significant risk factors for inadequate MGS included prednisolone use (75% vs 14.9%, OR: 17.1 [95%CI 1.65-177.04], p\u0026thinsp;=\u0026thinsp;0.009), low blood ketones (\u0026le;\u0026thinsp;0.3mmol/L)(OR: 5.77 [95%CI 1.69\u0026ndash;19.68], p\u0026thinsp;=\u0026thinsp;0.003) and female sex (7.5% vs 9.6% in males, OR: 3.57 [95%CI 1.12\u0026ndash;11.3], p\u0026thinsp;=\u0026thinsp;0.025). Multivariate analysis confirmed prednisolone use, low ketones (\u0026le;\u0026thinsp;0.3mmol/L) and \u0026lt;\u0026thinsp;24-hour ketogenic diet as independent risk factors. Rates of inadequate MGS were 50%, 26% and 7% for patients with blood ketone levels of 0.1, 0.2\u0026ndash;0.3 and \u0026ge;\u0026thinsp;0.4mmol/L, respectively. All patients on prednisolone with ketones\u0026thinsp;\u0026le;\u0026thinsp;0.3mmol/L had inadequate MGS.\u003c/p\u003e\u003ch2\u003eCONCLUSIONS\u003c/h2\u003e\u003cp\u003eDietary logbook and clear instructions improve adherence. Low ketones, prednisolone use and short ketogenic preparation are risk factors for inadequate MGS.\u003c/p\u003e","manuscriptTitle":"Utility of serum blood ketone levels and other risk factors for inadequate myocardial glucose suppression ketogenic FDG-PET/CT: a prospective and retrospective cohort study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-23 19:09:26","doi":"10.21203/rs.3.rs-7776884/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2025-10-09T23:47:38+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-10-09T22:59:27+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-10-06T02:20:51+00:00","index":"","fulltext":""},{"type":"submitted","content":"Annals of Nuclear Medicine","date":"2025-10-03T22:31:23+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"annals-of-nuclear-medicine","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"anme","sideBox":"Learn more about [Annals of Nuclear Medicine](http://link.springer.com/journal/12149)","snPcode":"12149","submissionUrl":"https://www.editorialmanager.com/anme/default2.aspx","title":"Annals of Nuclear Medicine","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"e599c21e-3477-490b-871f-95c48eff73b1","owner":[],"postedDate":"October 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-12-22T16:06:12+00:00","versionOfRecord":{"articleIdentity":"rs-7776884","link":"https://doi.org/10.1007/s12149-025-02141-5","journal":{"identity":"annals-of-nuclear-medicine","isVorOnly":false,"title":"Annals of Nuclear Medicine"},"publishedOn":"2025-12-15 15:58:25","publishedOnDateReadable":"December 15th, 2025"},"versionCreatedAt":"2025-10-23 19:09:26","video":"","vorDoi":"10.1007/s12149-025-02141-5","vorDoiUrl":"https://doi.org/10.1007/s12149-025-02141-5","workflowStages":[]},"version":"v1","identity":"rs-7776884","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7776884","identity":"rs-7776884","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}