Accuracy and Precision of Compartmental Model Parameters Obtained From Directly Estimated Dynamic SPECT Time-Activity Curves

Abstract

Quantitative kinetic analysis of dynamic cardiac single photon emission computed tomography (SPECT) data has the potential to provide better contrast between healthy and diseased tissue, compared to static images. However, imaging a rapidly changing radiopharmaceutical distribution with the use of a moving gantry yields inconsistent projection data that can generate artifacts in a time sequence of conventional reconstructed images. The artifacts can lead to biases in kinetic parameters estimated from the image sequence. This source of bias can be eliminated by estimating B-spline models for time-activity curves directly from the projections. In this study, we perform Monte Carlo simulations to determine how the polynomial order and initial time sampling of the splines affect the accuracy and precision of compartmental model parameters obtained from directly estimated time-activity curves. The Mathematical Cardiac Torso (MCAT) phantom is used to simulate a realistic 15 min dynamic /sup 99m/Tc-teboroxime patient study in which 10 million total events are detected. For a large volume of normal myocardium (250 cc), the relative bias of the uptake and washout parameter sample means does not exceed 0.3% when using cubic or quadratic splines that provide rapid initial sampling. The coefficient of variation is about 1%. For small (8.4 cc) myocardial defects that exhibit reduced uptake and accelerated washout, the relative bias and coefficient of variation increase to maximum values of about 16% and 50%, respectively. These levels of accuracy and precision provide good contrast between the compartmental model time-activity curves for the defects and normal myocardium. There is also good contrast for compartmental model time-activity curves obtained from noisy data containing 5 million events.