Respiratory motion gated PET with end-expiratory, amplitude based gating

Objectives Established approaches to reducing influence of respiratory motion in PET are predominantly time based, dividing the respiratory cycle into multiple bins based on an inspiratory gate signal, analogous to the approach in cardiac gating. We have investigated an alternative gating method based on the amplitude of the respiratory signal.

Methods Forty patients underwent whole-body (WB) F18-FDG in a Biograph-6 True V PET/CT scanner with 3 min/bed position, followed by a 9 min respiratory gated study of the chest. Respiration amplitudes from the Anzai AZ-733V strain gauge system were analyzed to determine a narrow range of amplitudes with 35% of the sensitivity of the static scan, and this was used to gate the PET data. The optimally gated data set (OG) was processed, giving a study with sensitivity matching the WB scan. True-X reconstructions were used for both data sets. Resolution metrics were evaluated based on reconstructions of the left ventricle (LV) and of tumors in the field of view.

Results OG reduced the standard deviation of amplitude signals by 84% to 92% and in every case corresponded to a narrow range of breathing amplitudes near end-tidal respiration. OG sharpened the image of the LV. Tumors in the central 75% of the field of view were visualized more clearly when OG was employed. In most cases, OG increased SUV values in tumors when respiratory motion was significant.

Conclusions These initial results suggest the utility of this novel gating approach, that improves statistics compared to the multi-frame time-based gating approach, while retaining benefits of reducing impact of organ motion during the respiratory cycle.