Optimized Multipinhole Design for Mouse Imaging

The aim of this study was to enhance high-sensitivity imaging of a limited field of view in mice using multipinhole collimators on a dual head clinical gamma camera. A fast analytical method was used to predict the contrast-to-noise ratio (CNR) in many points of a homogeneous cylinder for a large number of pinhole collimator designs with modest overlap. The design providing the best overall CNR, a configuration with 7 pinholes, was selected. Next, the pinhole pattern was made slightly irregular to reduce multiplexing artifacts. Two identical, but mirrored 7-pinhole plates were manufactured. In addition, the calibration procedure was refined to cope with small deviations of the camera from circular motion. First, the new plates were tested by reconstructing a simulated homogeneous cylinder measurement. Second, a Jaszczak phantom filled with 37 MBq ^99mTc was imaged on a dual head gamma camera, equipped with the new pinhole collimators. The image quality before and after refined calibration was compared for both heads, reconstructed separately and together. Next, 20 short scans of the same phantom were performed with single and multipinhole collimation to investigate the noise improvement of the new design. Finally, two normal mice were scanned using the new multipinhole designs to illustrate the reachable image quality of abdomen and thyroid imaging. The simulation study indicated that the irregular patterns suppress most multiplexing artifacts. Using body support information strongly reduces the remaining multiplexing artifacts. Refined calibration improved the spatial resolution. Depending on the location in the phantom, the CNR increased with a factor of 1 to 2.5 using the new instead of a single pinhole design. The first proof of principle scans and reconstructions were successful, allowing the release of the new plates and software for preclinical studies in mice.