Development of respiratory gated myocardial SPECT system

The superposition of the diaphragm and abdominal structures on the inferior wall of the left ventricle has often distorted single photon emission computed tomography (SPECT). We developed a respiratory gated SPECT (RGS) system to diminish artifacts caused by overlap between the inferior wall and upper abdomen and have validated its feasibility for clinical use.

A 2-detector SPECT system equipped with a respiratory monitor based on impedance plethysmography and an original triggering apparatus was used for RGS in 7 healthy male volunteers. A pulse triggered 100 ms after every expiratory peak was processed in a SPECT system as well as an electrocardiogram (ECG) gating pulse. Inspiratory and expiratory frames were determined using the respiratory curve derived from fluctuation of the gall bladder uptake. Both sets of images were reoriented into short-axis and vertical long-axis slices. For quantification, data were reconstructed into polar plots and count density estimated in 9 myocardial segments. The mean percentage uptake of inferior segments at inspiration was significantly greater than that at expiration (81+/-8.3 versus 76+/-7.1; P < .0001). The inferior-lateral activity ratio improved from 0.78 at expiration to 0.81 at inspiration (P < .01). The coefficient of variance for each segment of inspiratory data was significantly smaller than that at expiration, indicating improved homogeneity of tracer distribution. The lowest cutoff threshold of the tomograms to separate the inferior uptake from that of the upper abdomen was significantly lower at inspiration than at expiration, suggesting smaller scatter from abdominal structures on inspiratory images.

RGS yielded improved tracer uptake of the inferior wall in healthy male subjects and may be suitable as an alternative method for attenuation and scatter correction. However, further clinical validation is needed.