Determining the effect of cardiac blood volume on accuracy of uptake rate constants by simulation

Abstract

Objective. There is great interest in better understanding coronary microvascular disease using mouse models. Typical quantification requires dynamic imaging to estimate the rate constant K 1 of the tracer moving from the blood into the myocardium. In addition to K 1, it is also desirable to determine blood volume fraction V, which if known allows for more accurate fitting of K 1. Our previously published kinetic modeling software did not consider the effect of V. To ensure a better fit of experimental data to the model for myocardial SPECT imaging, in this work we updated our kinetic modeling software to include a blood volume fraction V, which adds a fraction of the arterial activity concentration into the tissue concentration. Approach. The tissue and blood time-activity curves (TACs) used for fit input were generated using ideal equations with known values in MATLAB. This allowed post-fit results to be compared to known values to determine fit errors. Parameters that were varied in generating the TACs included blood volume fraction (0, 0.05, 0.1, 0.2 and 0.3), K 1 (0.5, 1.5, 2.5 ml min−1 g−1), frame length (1, 2, 5, 10, 15, 20 s), FWHM of the input Gaussian (10, 20, 40 s), and time of the injection peak relative to frame duration. Blood volume-fraction results have low error when blood volume is lowest, but results worsen as frame length and K 1 increase. Main results. We demonstrated that blood volume can be accurately determined, and also show how fit accuracy varies across TACs with different input properties. Significance. This information allows for robust use of the fitting algorithm and aids in understanding fit performance when used in animal studies.