Ultra-low dose FDG PET imaging for nutrition and metabolism studies

Objectives In vivo visualization and objective quantification of specific tissues such as brown adipose tissue (BAT) is highly desirable for nutrition and metabolism studies. However, current clinical FDG doses (avg. 13 mCi) lead to undesirable radiation exposure levels for such uses. We therefore embarked upon a methodology development to perform ultra-low dose FDG PET imaging for such applications.

Methods As part of a clinical study, we performed low dose (avg. 2.5 mCi) FDG PET/CT studies on 18 subjects using a Gemini 64 time of flight PET/CT system (Philips, Cleveland). In order to activate BAT, the subjects were exposed to cold temperatures for 2 hours. All acquisitions were performed with 360 s per bed / volume position 60 to 70 min p.i. and in list mode which enables the subsampling to simulate lower count densities or dosing levels. Data sets were additionally reconstructed using only 240s, 120s, 90s, 60s and 15s list mode events representing dose reductions by 33%, 66%, 75%, 83% and 96%. The images were visually and quantitatively analyzed by ROI by three blinded, independent readers. A receiver operator curve (ROC) was determined for each case, reader and cumulative.

Results The blinded assessment resulted that a 66% dose reduction from the avg. 2.5 mCi could be implemented without impact on visual or quantitative assessment facilitating an effective dose requirement of only 0.8 mCi FDG on current generation systems. Based on other work using the upcoming solid state detector PET system, we were able to further simulate that a dose of 0.4 mCi appears achievable for ultra-low dose PET.

Conclusions Ultra-low dose FDG PET imaging to assess metabolism of tissue such as brown adipose tissue has been demonstrated to be possible at 0.8 mCi FDG on current generation systems and are predicted to be possible at 0.4 mCi on new solid state digital detector system such facilitating the innovative and safe use of FDG PET for nutrition and metabolism evaluations.

Research Support This research was supported by the Wright Center of Innovation in Biomedical Imaging Pilot project program.