Patients in Japan undergoing PET/CT are injected with 3.7 MBq of 18F-FDG which is a standard based on outdated instrumentation. We investigated whether informative 18F-FDG-PET/CT images of tumor glucose metabolism could be acquired with lower 18F doses.
Methods
The background activity of a NEMA body phantom with 10–37-mm hot spheres containing 18F-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 (NB,10mm), % contrast of 10-mm hot sphere (QH,10 mm), background coefficients of variation (CVbackground), ratios of QH,10mm to NB,10 mm (QH,10 mm/NB,10 mm), and recovery coefficients (RC). The detectability of 10 mm hot spheres was evaluated at each dose.
Results
The NB,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 QH,10 mm indicated better contrast on images acquired for 120 sec (clinical standard), with CaLM Mild, than the GF. The CVbackground 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 QH,10 mm/NB,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.
Conclusions
The quality of semiconductor digital PET/CT images was good at doses below the current standard.