Ultra high resolution pinhole SPECT for small animal study.

The aim of the study is to develop an ultra high-resolution pinhole SPECT system and analyze the performance by simulations. The pinhole SPECT was conducted with a Toshiba GCA-7200A gamma camera. The diameter of the pinhole was 1 mm. Data were acquired with a 128 x 128 matrix, and the distance from the center of rotation (COR) to the pinhole was 20 mm [case 1] of 28 mm [case 2]. The data were collected at 4 degree increments over 360 degrees. The Feldkamp method was used for image reconstruction. Before the image reconstruction, we corrected the COIL of the pinhole collimator. The imaging voxel was 0.27 x 0.27 x 0.27 mm(3) [case 1] or 0.4 x 0.4 x 0.4 mm(3) [case 2]. From the experiments with a resolution phantom the spatial resolution (FWHM) was 1.1 mm [case 1] or 1.3 mm [case 2]. The pinhole SPECT was also examined for in vivo imaging for studies of the heart in mice which were injected with Tc-99m-Tetrofosmin intravenously. In the reconstructed image the heart muscle of the mouse was clearly visualized. We also investigated the spatial resolution of the reconstructed image by means of simulations.