Activity in pulmonary nodules on standard iterative compared to time of flight reconstructed 18F-FDG PET/CT.

Objectives To determine the extent of activity in pulmonary nodules on standard iterative compared to time of flight reconstructed 18F-FDG PET/CT.

Methods The 18F-FDG PET/CT scans completed between January 2011 and June 2012 at the local Veteran’s Administration Hospital for pulmonary nodule evaluation (116) were reviewed. Ninety of these exams were reconstructed using both time of flight and standard iterative techniques. From these exams, 95 pulmonary nodules were identified. The percent increase in maximum activity on time of flight compared to standard iterative reconstruction was determined for each of these nodules. Also, a qualitative analysis for activity greater than that of background lung parenchyma was completed for each nodule on time of flight and standard iterative reconstructions.

Results The mean percent increase in maximum activity on time of flight compared to iterative reconstruction was 63% with standard deviation of 42% and range from -40% to 196%. It was noted that the nodules showing decreased activity on time of flight compared to standard iterative reconstruction also had corresponding decreased activity in the blood pool and liver. On qualitative analysis of the nodules, 57 (60%) showed activity above lung parenchyma on both time of flight and standard iterative reconstructions, 26 (27%) did not show obvious activity above lung parenchyma and 12 (13%) nodules showed activity greater than lung parenchyma on time of flight but not on standard iterative reconstruction.

Conclusions A majority of the pulmonary nodules show increased maximum activity on time of flight compared to iterative reconstruction techniques with average increased maximum activity of 63%. Also, 13% of the nodules studied showed qualitative activity on 18F-FDGPET/CT with time of flight but not on standard iterative reconstruction.