Effect of Low-Dose 18F-FDG on Image Quality in Digital PET/CT

Patients in Japan undergoing PET/CT are injected with 3.7 MBq of 18 F-FDG which is a standard based on outdated instrumentation. We investigated whether informative 18 F-FDG-PET/CT images of tumor glucose metabolism could be acquired with lower 18 F doses. MethodsThe background activity of a NEMA body phantom with 10–37-mm hot spheres containing 18 F-FDG was set at 2.53 kBq/mL (= 3.7 MBq/kg dose; Hot/BG = 4; standard ), and 1.73 and 1.34 kBq/mL (= 2.5 and 2.0 MBq/kg doses, respectively). Images were reconstructed using TOF-3D-OSEM and a Gaussian filter (GF) (FWHM 4 mm) and Clear adaptive Low-noise Method (CaLM Mild). Image quality was evaluated as % background variability (N B,10mm ), % contrast of 10-mm hot sphere (Q H,10 mm ), background coefficients of variation (CV background ), ratios of Q H,10mm to N B,10 mm (Q H,10 mm /N B,10 mm ), and recovery coefficients (RC). The detectability of 10 mm hot spheres was evaluated at each dose.ResultsThe N B,10 mm on images of 3.7 MBq/kg doses acquired for 270 sec was 5.5% (GF and CaLM Mild), which met the guideline standard (< 5.6%), and 6.9% and 7.6% (GF) at 2.5 and 2.0 MBq/kg respectively, on images acquired for 300 sec, and 7.1% and 7.4% (CaLM Mild), which exceeded the standard.The Q H,10 mm indicated better contrast on images acquired for 120 sec (clinical standard), with CaLM Mild, than the GF. The CV background values for 3.7 MBq/kg dose equivalents were 9.9% (GF) and 10% (CaLM Mild) respectively, for images acquired for 270 and 300 sec, which met the guideline criterion (≤ 10%), and 11% and 12% (GF), and 13% (CaLM Mild) for 2.5 and 2.0 MBq/kg doses for images acquired for 300 sec. The Q H,10 mm /N B,10 mm values at 2.0 MBq/kg for images acquired for 120 sec were 3.8 (GF) and 3.5 (CaLM Mild), which met the criterion (> 2.8), and the RCs of 0.73 (GF) and 0.98 (CaLM Mild) for the 10-mm hot sphere, also satisfied the criterion (> 0.38). Visual detectability at all doses met the criterion at 120 sec. ConclusionsThe quality of semiconductor digital PET/CT images was good at doses below the current standard.