Use of conventional gamma cameras for small animal imaging

Compared with human imaging, the small volume of the mouse or rat allows certain geometrical advantages to be exploited in nuclear imaging. This paper investigates the options available for small animal imaging given the constraint of using a modern NaI gamma camera. There are two groups of collimation schemes: (1) those employing magnification, namely pinhole, multiple pinhole, and coded aperture; and (2) the collimator methods including parallel hole, "sparse hole", and converging designs such as fan beam and cone beam collimation. A comparison of sensitivity between a 3 mm tungsten pinhole and a high resolution, parallel hole collimator found that a factor of 2 improvement in sensitivity can be achieved by using the parallel hole collimator with little loss in spatial resolution. The results of this comparison can be used to compute the expected performance of a sparse hole collimator. For large, relatively inexpensive and moderate spatial resolution detectors such as NaI, high resolution can be achieved most readily by using magnification. For next generation solid state detectors with improved intrinsic spatial resolution and (initially) high cost, the sparse hole design achieves good system resolution and keeps the overall size and cost of the device to a minimum.