Continuous bed motion Vs. step-and-shoot acquisition on clinical whole-body dynamic and parametric PET imaging

Continuous bed motion (CBM) has been recently introduced in the clinic as an alternative PET acquisition mode with respect to the traditional time-discretized step-and-shoot (SS) multi-bed acquisitions. In CBM mode, each slice can be considered as a different bed, since it is scanned over a different acquisition window. By reducing scan time discretization from a whole bed down to a single slice, the CBM acquisition offers additional degrees of freedom when designing acquisition protocols and thus larger margins for their optimization. Therefore, CBM mode could be particularly important for protocols of higher complexity, such as whole-body (WB) dynamic PET acquisitions. However, only a few studies have quantitatively validated the 2 modes on clinical data. In this work, we evaluate CBM vs. SS quantitative performance on a set of clinical data acquired over a 0-60min period using a WB dynamic PET acquisition protocol with a Biograph mCT TOF scanner. The TOF resolution (580ps) of the scanner allowed selecting faster CBM speeds (4.2mm/sec) and equivalent SS frames (30sec/bed), eventually permitting acquisition of 12 WB total passes of which half were performed in CBM mode and half in SS mode. The two modes were alternated between successive passes to allow a balanced interleaving of post-injection time between them to ensure an objective comparison. The evaluation of the 2 modes in terms of target-to-background (TBR) contrast and contrast-to-noise ratio (CNR) has been conducted for various noise levels by gradually adding all respective passes from each mode as well as in the parametric images after applying post-reconstruction WB Patlak analysis. Our results indicate a bias of ∼10% between the 2 modes for the low count frames, reducing to <3% as we gradually add all respective frames. In addition, a small bias of <10% was observed in Patlak images at overlapped slices between beds, which is attributed to the non-uniformity of the axial sensitivity profile of SS mode.