A new approach of dynamic pinhole SPECT imaging for evaluation of sympathetic nervous system function in animal models of cardiac hypertrophy

Typically ¹²³I-MIBG is used for the study of innervation and function of the sympathetic nervous system in heart failure. The protocol involves two studies: first a planar or SPECT scan is performed to measure initial uptake of the tracer, followed some 3-4 hours later by another study measuring the wash-out of the tracer from the heart. A fast wash-out is indicative of a compromised heart. In this work, a dual head pinhole SPECT system was used for imaging the distribution and kinetics of ¹²³I-MIBG in the myocardium of spontaneous hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats. The system geometry was calibrated based on a nonlinear point projection fitting method using a three-point source phantom. The angle variation effect of the parameters was modeled with a sinusoidal function. A dynamic acquisition was performed by injecting ¹²³I-MIBG into rats immediately after starting the data acquisition. The detectors rotated continuously traversing 360deg every 90 seconds. We applied the FADS method to obtain time activity curves in the blood pool and myocardium. Since the initial injection bolus is too fast to obtain a consistent tomographic data set in the first minute of the study, we applied the FADS method directly to projections during the first rotation. In the future, the method will be applied to determine if there are differences in the kinetics between SHR and WKY rats. This approach requires less time by replacing the delayed scan at 3-4 hours after injection with a dynamic acquisition of 90 to 120 minutes