SUV assessment of lung lesions without and with respiratory gating

Objectives Respiratory gating following PET-CT whole body can improve lesion registration and accuracy in calculation of SUV values but the contribute of elapsed time between the two scan usually is not considered.Aim of the study was to compare the SUVmax measured on images of lung lesions obtained with WB scan and with respiratory gating by considering also the effect of temporal changes due to different uptake time of 18F-FDG.

Methods Fourteen pts. with lung lesions were enrolled(9 m,5 f,mean age 68.6±6.6 y).One hour after i.v. of 18F-FDG a whole body PET/CT(WBPETCT)scan was acquired for 10-15 min followed by a respiratory gated thoracic(RGPETCT) acquisition of 10-15 min.Acquisitions were performed on a Siemens Biograph True V PET-CT system.Always CT preceded PET and was acquired under free shallow breathing.Respiratory gated data were acquired in list mode and then reframed by dividing the respiratory cycle into 6 phases by using the AZ7333V System (Anzai Medical) for synchronism.By summing all frames from the list mode acquisition a single non-gated frame (SF) was also derived. SUVmax values were compared between WBPETCT and RGPETCT (WB free vs gated breathing at different times),RGPETCT and SF (free vs gated breathing at same time),WBPETCT and SF (free breathing at different times).The SUVmax on RGPETCT study was assessed by selecting the one out of the 6 frames which better matched the correspondent CT lesion position.

Results In 14 pts. 28 nodules were detected.SUVmax mean values(+ s.d.)derived from WBPETCT,RGPETCT and SF were respectively 5.3 ± 4.0,7.8 ± 6.2 and 6.1 ± 5.1.The Δ%SUVmax resulted for:WBPETCT vs RGPETCT = 44%(p< 0.001),RGPETCT vs SF = 31%(p<0.001)and SF vs WBPETCT = 11%(p<0.005).

Conclusions These findings suggest that the increase(44%)of SUV values between WBPETCT and RGPETCT is mainly (31%)due to reduction of the smearing effect of lesions with gated acquisition and the delay(10-15 min)between the two scans can contribute to its further increasing (11 %)due to different time FDG uptake