Impact of continuous bed motion (CBM) PET/CT scanners on clinical operation

Objectives CBM PET/CT imaging has been suggested as an approach to improve image uniformity, decrease patient radiation dose, and increase patient comfort. Our objective was to determine the validity of the first two of these claims using phantom and patient studies and evaluate their overall impact on clinical operation.

Methods A uniform Ge-68 phantom (20 by 32 cm long) was imaged on a SIEMENS mCT TrueV scanner using traditional step and shoot (SS) with 11, 15, 23, and 43% slice overlap as well as CBM. The same acquisition time was set for both imaging modes (3 min/bed). Uniformity was determined by measuring the standard deviation (STD) in a 10cm region across 30 central slices. In addition, 32 PET/CT patient studies acquired using CBM (1 mm/s) were also simulated using SS imaging protocol (scan range - 80 to190 cm). The scan coverage of both modes was analyzed and the difference was calculated and reported in terms of CT radiation dose as well as scan time.

Results Uniformity decreased with decreasing slice overlap. CBM uniformity was equal or better than 43% (default on mCT SS mode) slice overlap in SS mode. Scan coverage of CBM was on average 3.5% smaller than SS and resulted in 0.5 mSv savings in CT radiation dose. Scan time on the other hand was 0.5% (0.1 min) longer in CBM compared to SS (including bed transition times of 5 sec) owing to the need to start and end the scan at mid axial FOV.

Conclusions CBM has advantages compared to SS with regards to uniformity and CT radiation dose. The extent of these advantages; however, depends on the patient imaging range. Patient comfort is expected to be the major advantage of CBM compared to SS.