Recent progress on SPECT imaging with near-field coded aperture collimation: A small animal study

A small animal study of three-dimensional (3-D) single photon emission computerized tomography (SPECT) imaging with near-field coded aperture collimation is reported. In our early effort to develop high-sensitivity and high-resolution SPECT technology, we introduced an imaging protocol and a reconstruction method for 3-D near-field coded aperture SPECT, and obtained good SPECT reconstructions of 3-D objects, including a micro hot-rod phantom with complex structures. In this study, we aim to reconstruct low contrast and slow-varying radioactivity distribution in an ex vivo rat heart, in contrast to point-like distributions such as that in the micro hot-rod phantom that we previously reported. In our new experiment, the rat underwent an open-chest surgery and its left anterior descending coronary artery was ligated to induce permanent myocardial infarction in the left ventricular (LV) myocardium. After the surgical procedures the rat was injected with 6.29 mCi of ^99mTc-Tetrofosmin via the jugular vein. One hour post the radiotracer injection, the rat was sacrificed and the LV was dissected from the heart. Dental alginate paste was subsequently injected into the LV to sustain its shape for imaging. Coded aperture projections with a magnification factor of 2.6 were acquired from 64 evenly distributed angles over a 360 degree camera rotation on a micro-SPECT system equipped with NaI detectors. Images of cross-sectional slices were successfully reconstructed using our four-step reconstruction algorithm, and special care was taken to account for the wide projection angle in the small animal imaging system. In the reconstructed images, the donut-shape of the LV was well visualized, and the surgically induced infarct, resulting in myocardial perfusion defect in the apical anterior regions of the LV, could be clearly identified, further demonstrating the feasibility of the near-field coded aperture SPECT imaging methods we proposed.