Continuous bed motion acquisition on a whole body combined PET/CT system

The continuous motion of the patient bed during the acquisition of PET data represents an alternative to the standard step and shoot protocol where a sequence of discrete, overlapping steps are performed. This PET acquisition mode, similar to the whole body CT scan in which the patient bed moves continuously through the scanner has significant advantages, including uniform axial signal-to-noise ratio (SNR), elimination of resolution artifacts by sampling continuously in the axial direction and a reduction in noise from detector normalization. We have implemented and evaluated continuous bed motion acquisition on the combined PET/CT scanner (CPS Innovations, Knoxville, TN). Methods: Emission data were acquired in list mode format with the bed moving at a constant velocity. The position of the bed was recorded in a separate file together with the current event count. The list mode data were then rebinned into sinograms and reconstructed using the same routines applied to reconstruct the standard images. Each sinogram corresponded to an axial plane thickness of 2.4 mm. Phantom data were acquired with both the standard discrete, overlapping steps and with continuous movement of the bed. Data were collected for a whole body phantom containing lesions carefully positioned in the overlap region between two bed positions to specifically emphasize the effect of the improved SNR. Results: The continuous movement of the patient bed resulted in a uniform axial SNR, improving lesion detectability in the bed overlap region. The continuous axial sampling allowed the 10mm lesion in the whole body phantom to have 45% improvement in contrast compared to the step and shoot acquisition. Patient studies demonstrated improved detectability due to finer axial sampling and uniform SNR.