Effects of breathing motion on PET acquisitions: Step and shoot versus continuous bed motion

Objectives Continuous bed motion (CBM) acquisition recently became available in whole-body PET/CT scanners in addition to the conventional step and shoot (S&S) acquisition. In this work, we compared the image quality between these acquisition methods using a phantom simulating periodic motion to mimic motion from patient breathing in a controlled manner. Methods PET image quality was assessed using the National Electrical Manufacturers Association IQ torso phantom filled with an ¹⁸F-FDG solution using a 4 : 1 targetto- background ratio. The phantom was scanned in two states: no motion (stationary) and with periodic motion in the axial direction with a displacement ± 10mm from the initial position. Both S&S and CBM scans were repeated 10 times in an alternating order, whereby the acquisition duration of each scan was adjusted to make the true counts approximately comparable to compensate for the decaying ¹⁸F-FDG. Results The recovery coefficient analysis showed that in the stationary state, the 10mm sphere recovery did not show any difference between S&S and CBM. With motion, the recovery coefficient was lower by ∼40% for both modes of acquisition. In addition, the image-based volume analysis of the 10mm sphere showed 1.67 (1.57-1.69) cm3 for S&S and 1.73 (1.66-1.83) cm3 for CBM (P=0.13), and there was no difference between two modes. Our study indicated that when the acquisition conditions for S&S and CBM (equivalent net trues, identical phantom motion, and identical CT image used for PET corrections) were controlled carefully, these acquisition modes resulted in equivalent image quality.