Effect of detector energy response on image quality of myocardial perfusion SPECT

The goal of this study was to evaluate the effect of the detector energy response on the quality of Tc-99m myocardial perfusion SPECT images. A Data Spectrum torso phantom was prepared to model the low-dose rest portion of a standard one-day myocardial perfusion protocol. Projection data were acquired with a recently developed Ultra-Fast Cardiac SPECT System (UFC, GE Healthcare). UFC utilizes an array of CZT detector modules and pinhole collimators. A point source in air was used to measure the Tc-99m spectrum in CZT. In addition to acquiring emission data, the phantom was scanned with high resolution CT and converted into a 3D model for the SimSET Monte Carlo simulation package, which was then used to generate photon history files. We developed a collimator-detector response module that operates on the SimSET photon history riles. This module performs multi-pinhole collimation followed by a stochastic energy blurring operation and generates projection data. The simulated CZT detector response was derived from a measured spectrum, and ideal energy response served as reference. Simulation results were compared to actual torso phantom acquisitions. Components of the resulting projection data (amount of primary and scattered photons) and reconstructed slices were compared. For fixed energy acceptance windows, the asymmetric CZT energy response shape leads to a 30% reduction of the scatter component in measured data and contributes to superior reconstructed image quality.