Characterization of Spillover and Recovery Coefficients in the Gated Mouse Heart for Non-Invasive Extraction of Input Function in microPET Studies: Feasibility and Sensitivity Analysis

We characterize spillover (SP) and recovery coefficients (RC) in the gated mouse heart to address the feasibility of extracting the plasma time activity curve (pTAC) from the left-ventricle (LV) blood pool during the diastolic phase of the cardiac cycle. The pTAC can be formulated as pTAC(t) = alphaCLV(t) - betaCMYO(t) where alpha and beta are functions of the LV RC, r_LV; myocardial RC, r_m; myocardium to LV SP, s_mb; and LV to myocardium SP, s_bm. We use anatomical images of the digital mouse phantom undergoing both cardiac and respiratory motion at 0.005sec increments to simulate continuous microPET mouse data. The microPET images were smoothed with FWHM = 1.7mm and summed to produce 8-gate cardiac images. Diastolic images were used to characterize temporal and average SP and RC values in the presence and absence of both cardiac and respiratory gating. To test the sensitivity of RC and SP to mouse heart dimension, we scaled the 3D volume of the heart by -20% to 20% of its original size and repeated the above analysis. Assuming a 1-sec frame duration, average SP and RC values were not significantly different across frames. Of the four coefficients, smb is most sensitive to heart dimension followed by rm, rb, and sbm. For example, at -10% scaling of the heart the bias attributed to alpha and beta is 4% and 12%, respectively. These results suggest that appropriate characterization of SP and RC would enable to extract the pTAC from the LV.