A Skew-Slit Collimator for Small-Animal SPECT

The main objective of this work was the development of a skew-slit collimator for small-animal SPECT to replace the state-of-the-art multipinhole collimator. Methods: A pinhole forms a cone-beam imaging geometry. If the collimator rotates around the object in a circular orbit, the projection measurements acquired by the cone-beam imaging geometry are incomplete and not enough for artifact-free image reconstruction. The severity of the artifact is proportional to the cone angle of the pinhole in the direction of the axis of rotation. Multipinhole geometry can greatly reduce the data-insufficiency artifacts; however, image magnification is sacrificed. By transforming a pinhole into a pair of skewed slits, we are able to use a large cone angle in the transaxial direction to increase image magnification and a small cone angle in the direction of the axis of rotation to reduce data-insufficiency artifacts. This transformation is achieved by placing a vertical slit (i.e., the slit is parallel to the axis of rotation) close to the object and placing a horizontal slit farther out. Similar to the multipinhole collimator, we also propose a multiple-skew-slit collimator that has a single vertical slit and several horizontal slits. Results: Computer simulations were performed to verify the working principle of the skew-slit collimator. A prototype multiple-skew-slit collimator was fabricated, and phantom experiments were performed on a SPECT system. The smallest channels (of 0.75-mm diameter) in the phantom were clearly separated in the reconstructed image. Conclusion: This study suggests a novel technology in small-animal SPECT to replace the multipinhole collimator, resulting in significantly reduced image artifacts and increased transaxial resolution. A physical multiple-skew-slit system was built and tested. Compared with the multipinhole system, the multiple-skew-slit system has a larger image magnification in the transaxial direction and thus has better image resolution.