Optimized acquisition protocols for dynamic cardiac SPECT imaging of rats with 123I-MIBG

Our previous work in dynamic cardiac SPECT imaging of rats with 123I-MIBG showed that with a slow rotation camera (dual head acquisition with 90s per rotation and a 1s acquisition interval at each angle) we could accurately obtain the time activity curves (TACs) and estimate compartmental model parameters. However, the long acquisition time (usually exceeding 60 rotations) limits the throughput and the animal survival rate. The short acquisition interval (1s) can result in the poor photon statistics which increases the variance of the TACs even though it reduce the bias of the TACs. In this study, we tried to shorten the whole acquisition time, optimize the acquisition time interval at each projection view adaptively, while maintaining the estimation accuracy of the kinetic parameters through computer simulations studies. First, the original blood pool TAC (bTAC) was obtained by averaging the bTACs of 5 WKY rats acquired previously. The tissue TAC (tTAC) was the two-tissue compartmental model output with pre-defined kinetic parameters and the original bTAC as the input. Then we cut off the first n segments of 2s, 5s, 10s, 20s and 30s in the bTAC to mimic the acquisition intervals during the acquisition. The cut-off portions were extrapolated to form new bTACs. The relative entropy of the new bTAC and the original bTAC was calculated to decide the max segment number n that could be tolerable. The same segments were also cut off in the tTAC. Finally, the resultant bTACs and tTACs were truncated with acquisition lengths of 1.5, 3, 4.5, 9, 18, 36, and 72 mins and fit to the two-tissue compartment model to estimate the kinetic parameters (K1,k2,k3,k4). The Distribution Volume (DV) was calculated from the kinetic parameters. The percentage error (PE) between the estimated parameters and pre-defined parameters were calculated. The results showed that, to match the PE with the original protocol, the kinetic parameter K1 could be estimated with an acquisition time of 90s with non-uniform acquisition protocols of 2s. The DV could be estimated with an acquisition time of 180s with non-uniform acquisition protocols of 5s.