A Novel Phantom for Dynamic Myocardial Perfusion SPECT

Introduction: In recent years, significant effort has been devoted to the validation of noninvasive myocardial blood flow (MBF) measurement in dynamic SPECT/PET systems in both phantom and clinical studies. Since MBF is calculated from time-activity curves (TACs) reflecting radiotracer concentration in the left ventricular (LV) cavity and the myocardium, the phantom must mimic the physiologic radionuclide temporal behavior in both of these regions during the injection phase (first-pass and perfusion), which is not possible with existing phantoms.

Objectives: To develop a novel cardiac phantom which allows controllable radiotracer variation in the LV cavity and in the myocardium and which generates TACs similar to those obtained in patients, while generating a beating-like motion.

Methods: The novel phantom consists of: (1) Two nested flexible silicon membranes – the internal volume representing the LV and the myocardium surrounding it, with dimensions resembling human endocardium and epicardium. (2) Ports for injection and flushing of radiotracer in each region, connected to programmable syringe injectors. (3) A large port connected to the base of the LV region and a pulsatile pump to generate "cardiac beating". A mathematical model describing radiotracer concentrations in the phantom as a function of time was developed from mass conservation principles and served to plan and validate experimental measurements.

Results: A comparison between a typical dynamic SPECT measurement of the phantom and its mathematical model simulation is shown in the attached figure. These curves closely resemble TACs observed in human patients, achieved for the first time in a phantom model. Also, the measurements and the experiment simulation agree to within ±5%.

Conclusions: The newly developed cardiac phantom for dynamic SPECT/PET measurements is able to generate reproducible and reliable results to investigate key parameters of dynamic SPECT/PET systems, namely, the accuracy and reproducibility of TACs and their propagated effect on the computed MBF.