The Potential Role of the Regional Skull Conditions in Predicting the Efficacy of Transcranial Magnetic Resonance-guided Focused Ultrasound in Patient with Low Skull Density Ratio

2025 · doi:10.1101/2025.03.12.25323386
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This retrospective study analyzed 171 consecutive low-SDR candidates for transcranial magnetic resonance-guided focused ultrasound, measuring whole-skull and region-specific skull density ratio (SDR), skull thickness, and ultrasound incident angle (IA) across 10 predefined transducer regions, and evaluating symptom change at 6 months using established tremor scales. Among 26 patients with SDR < 0.40, 15 achieved success (< half the preoperative symptom score), and in this subgroup IA of the parietal region on the sonication side and bilateral temporal SDR were lower in the success group, though the parietal/temporal subgroup differences were not statistically significant. For prediction of maximum temperature rise across all 171 cases, multiple regression models performed better when IA of the parietal region on the sonication side was included, and replacing overall SDR with SDR excluding the bilateral temporal region improved model performance, as assessed by Akaike information criterion. The paper does not explicitly discuss endometriosis or adenomyosis; it was included in the corpus via a keyword match in the upstream search index.

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Abstract

Structured Abstract Objective The therapeutic effect of magnetic resonance-guided focused ultrasound is limited to patients with a low skull density ratio (SDR). We explored the skull conditions associated with successful treatment among low-SDR patients, and, to compensate for the small sample size, performed analyses using all cases irrespective of SDR. This is the first report to examine the significance of regional skull conditions. Methods We retrospectively analyzed 171 consecutive cases. Descriptive statistics for the entire skull, and averages for 10 regions, were obtained for variables including the SDR, skull thickness, and ultrasound incident angle (IA; smaller = more vertical). The 1,024 ultrasonic transducer elements were divided into 10 regions predefined by ExAblate4000. Symptoms were evaluated by Clinical Rating Scale for Tremor for essential tremor and Unified Parkinson’s Disease Rating Scale tremor score for Parkinson’s tremor. Successful treatment was defined as <half preoperative symptom score at 6 months postoperatively. First, univariate analysis of cases with SDR < 0.40 was conducted to explore candidates for skull conditions associated with successful treatment. Subsequently, for all cases regardless of SDR, several multiple regression models were built to predict the maximum temperature rise, and their performance was compared. Results Of the cases, 26 had SDR < 0.40, and 15 were successful. Among the cases with SDR < 0.40, IA of the parietal region on the sonication side and SDR of the bilateral temporal region tended to be smaller in the success group (not statistically significant). The maximum temperature was more accurately predicted when IA of the parietal region on the sonication side was included in the model (Akaike information criterion, 777 [from 757]). Furthermore, replacing SDR with SDR excluding the bilateral temporal region enhanced predictions (Akaike information criterion, 777 [from 767]). Conclusions Even if SDR is low, treatment success may be more attainable if the IA in the parietal region on the sonication side is smaller, or if the SDR excluding the bilateral temporal regions is large.
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Objective

The therapeutic effect of magnetic resonance-guided focused ultrasound is limited to patients with a low skull density ratio (SDR). We explored the skull conditions associated with successful treatment among low-SDR patients, and, to compensate for the small sample size, performed analyses using all cases irrespective of SDR. This is the first report to examine the significance of regional skull conditions.

Methods

We retrospectively analyzed 171 consecutive cases. Descriptive statistics for the entire skull, and averages for 10 regions, were obtained for variables including the SDR, skull thickness, and ultrasound incident angle (IA; smaller = more vertical). The 1,024 ultrasonic transducer elements were divided into 10 regions predefined by ExAblate4000. Symptoms were evaluated by Clinical Rating Scale for Tremor for essential tremor and Unified Parkinson’s Disease Rating Scale tremor score for Parkinson’s tremor. Successful treatment was defined as <half preoperative symptom score at 6 months postoperatively. First, univariate analysis of cases with SDR < 0.40 was conducted to explore candidates for skull conditions associated with successful treatment. Subsequently, for all cases regardless of SDR, several multiple regression models were built to predict the maximum temperature rise, and their performance was compared.

Results

Of the cases, 26 had SDR < 0.40, and 15 were successful. Among the cases with SDR < 0.40, IA of the parietal region on the sonication side and SDR of the bilateral temporal region tended to be smaller in the success group (not statistically significant). The maximum temperature was more accurately predicted when IA of the parietal region on the sonication side was included in the model (Akaike information criterion, 777 [from 757]). Furthermore, replacing SDR with SDR excluding the bilateral temporal region enhanced predictions (Akaike information criterion, 777 [from 767]).

Conclusions

Even if SDR is low, treatment success may be more attainable if the IA in the parietal region on the sonication side is smaller, or if the SDR excluding the bilateral temporal regions is large. Competing Interest Statement The authors have declared no competing interest. Funding Statement This study did not receive any funding Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethics Comittee of Hamamatsu University School of Medicine I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Footnotes Previous Presentations: The 20th Biennial Meeting of the World Society for Stereotactic & Functional Neurosurgery, 2024/09/04, Chicago, USA, e-Poster Presentation. No significant differences between this version and previous versions of the manuscript Data Availability All data produced in the present study are available upon reasonable request to the authors

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