CT Data Driven Gating for Respiratory Motion Compensation in PET/CT

摘要

The possibility of using CT raw data as the basis for estimating a respiratory waveform during the CT portion of a PET/CT scan is considered. Because this is analogous to PET data drive gating (PET DDG) we use the name CT DDG for this approach. Data from eight whole-body PET/CT scans, covering the head and the entire torso, were analyzed, including CT raw data and waveform measurements based on a pressure sensor in a belt around the patient’s chest. In a semi-automated approach, CT raw data were converted to lateral projections in which the anterior surface y(z,t), moving with respiration, could be detected as an edge in the space of the CT measurement. Since some z positions were seen two or more times during the spiral scan (e.g. X rays directed right to left, then left to right) the velocity v = dy/dt could be calculated. The time of full inspiration, tIN-CTDDG was determined by determining when v(t) changed from positive to negative, and these times were compared with inspiration peak times tIN-belt based on the pressure sensor. In all patients, at least one of the inspiration peaks was correctly detected, tIN-CTDDG matching tIN-belt with a mean absolute difference of 0.18 s. In seven of these peaks, the two times agreed within 0.05 s. As expected, motion was undetectable in areas not moving with respiration. Of 21 detected peaks, four were spurious. Additionally, a CT-DDG-based respiratory waveform was estimated. A clear correspondence between this and the belt- based waveform could be demonstrated in one patient study. In conclusion, the prototype CT-DDG method was effective at detecting at least one inspiration peak in all patients in the study. Although this is less information than in the belt-based measurement, the method’s partial success is notable because no operator setup was required.