Beyond list mode: On-line rebinning and histogramming for continuous bed motion in clinical whole-body TOF PET/CT

In this article, methods are described which help move the concept of continuous bed motion (CBM) for TOF PET (i.e. for PET/CT applications) out of the realm of list-mode-only research and into everyday clinical usage. Long proposed for PET, CBM moves the patient horizontally (at a more or less steady rate) through the PET FOV during the acquisition and offers several points of advantage over the more common patient-held-stationary-to-PET-FOV approach. One primary obstacle to frequent clinical application of CBM in PET has been the inability to provide on-line, real-time detector-pair-to-projection-space-bin-address rebinning calculations along with the associated on-line histogramming. Here are presented details for one approach to overcome just such obstacles - significantly allowing the on-line generation of single TOF projection data sets which may each represent an entire whole-body scan. A set of 5 real list-mode data files were collected from a TOF PET/CT - a system which has been outfitted with a patient handling system (PHS or “bed”) which is shown to be largely sufficient for CBM in PET. For an F-18 point source - placed for first a 1cm and then a 10cm transaxial offset, list-mode data was collected for both stationary and horizontal bed motion cases. In addition, a CBM list-mode data set was collected for a custom, F-18, 100cm-long, cylindrical phantom. These data sets were processed in a manner computationally equivalent to that proposed for the realtime, on-line processing case. By comparing stationary to CBM image quality, the resulting analysis strongly suggests these proposed methods will provide real-time CBM processing which is compatible with the needs of clinical-grade TOF PET. As perhaps expected from CBM, the Z-axis FWHM is shown to generally improve over the stationary case via finer axial sampling in the rebinning step. As may be atypical, one specific data point showed a Z-axis improvement of 6.5%. Other examples - which may be more typical - showed little or no Z-axis FWHM improvement when applying CBM.