The impact of TOF PET/CT respiratory gating on pulmonary tumor: Quantitative assessment for both position gap and FDG uptake

Objectives Respiratory movement causes blurring of PET images and inaccurate attenuation correction in PET/CT. The aim is to evaluate prospectively the impact of TOF PET/CT respiratory gating on position gap (between PET and CT) and FDG uptake in routine study for pulmonary tumor.

Methods 55 patients (M: 33, F: 22, age range: 19 - 84y) with pulmonary tumor were studied by PET/CT (GE 690). After breath hold (BH) CT, FDG PET was acquired with respiratory gating (5min) on 1 bed containing tumor and with free breathing (FB) on the other beds (2min/bed) from head to pelvic floor. Finally, CT covering the tumor was obtained with cine mode using respiratory gating during one breathing cycle. For conventional method, FB PET was attenuation-corrected by BH CT. For respiratory gating, gated PET was attenuation-corrected by gated CT. Both position gap and SUVmax by conventional method and gating were analyzed.

Results Success rate of respiratory gating study was 96.4% (53/55, mean total scan time: 21.0 ± 1.9min) and 7 tumors were ruled out (SUVmax <1, n=6; blood glucose level >150mg/dl, n=1). The 46 tumors (mean size: 2.6 ± 1.8cm) were analyzed and located at lower lobe (LL) (n=21) and upper or middle lobe (UML) (n=25). Position gap (mm) was 5.2 ± 3.3 vs. 3.0 ± 1.4 (26.5% decrease, P=0.0078) in LL, and was 4.6 ± 2.6 vs. 3.5 ± 1.0 (11.7% decrease, P=0.035) in UML by conventional method and gating, respectively. SUVmax was 7.5 ± 5.9 vs. 9.0 ± 6.5 (26.0 % increase, P=0.00040) in LL, and was 6.5 ± 4.3 vs. 6.8 ± 4.5 (5.3 % increase, P=0.12) in UML by conventional method and gating, respectively. Percentage change in both position gap and SUVmax didn’t depend on the size.

Conclusions TOF PET/CT with respiratory gating in routine study for pulmonary tumor can reduce position gap in any lung field and may obtain more accurate FDG uptake especially in lower lobe.