Comparison of an alternative and existing binning methods to reduce the acquisition duration of 4D PET/CT

International audience; Purpose: Respiratory motion is a source of artifacts that reduces image quality in PET. Four dimensional (4D) PET/CT is one approach to overcome this problem. Ex- isting techniques to limiting the eects of respiratory motions are based on prospec- tive phase binning which requires a long acquisition duration (15-25 min). This time is uncomfortable for the patients and limits the clinical exploitation of 4D PET/CT. In this work, we evaluated an existing and an alternative retrospective binning meth- ods to reduce the acquisition duration of 4D PET/CT. Methods: We studied an existing mixed-amplitude binning (MAB) and an alterna- tive binning method by mixed-phases binning (MPhB). Before implementing MPhB, we analyzed the regularity of the breathing patterns in patients. We studied the breathing signal drift and missing CT slices that could be challenging for implement- ing MAB. We compared the performance of MAB and MPhB with current binning methods to measure the maximum uptake, internal volume and maximal range of tumour motion. Results: MPhB can be implemented depending on an optimal phase (in average the exhalation peak phase - 4:1% of the entire breathing cycle duration). Signal drift of patients was in average 35% relatively to the breathing amplitude. Even after correcting this drift, MAB was feasible in 4D CT for only 64% of patients. No sig- nicant dierences appeared between the dierent binning methods to measure the maximum uptake, internal volume and maximal range of tumour motion. We also determined the inaccuracies of MAB and MPhB to measure the maximum amplitude of tumour motion with 3 bins (less than 3 mm for movement inferior to 12 mm, up to 6:4 mm for a 21 mm movement). Conclusions: We proposed an alternative binning method by mixed-phase binning that halves the acquisition duration of 4D PET/CT. Mixed-amplitude binning was challenging because of signal drift and missing CT slices. We showed that more than 3 bins were necessary for a more accurate measurement of the maximum amplitude of the tumour motion. However, the current 4D-CT technology limits the increase of the number of bins in 4D PET/CT because of missing CT slices. One can reconstruct 4D PET images with more bins but without attenuation/scatter correction.