Detached Multipinhole Small Animal SPECT Device With Real-Time Calibration

High-resolution small animal single photon emission computed tomography (SPECT) with pinhole collimation has become well-established in preclinical research. Conventional scanner designs use custom fixtures that precisely attach and align pinholes to dedicated detectors. As a lower-cost alternative, we have developed a compact small animal SPECT device with integrated pinholes that is physically detached from gamma camera detectors and uses real-time calibration. The device consists of a shielded lead box with multiple integrated tungsten pinholes on the sides and with a rotating platform at the bottom. The animal or phantom to be imaged is positioned within a hollow cylinder mounted to the platform, with point source markers attached to the cylinder's outer surface. The entire device is placed on the patient table of a standard dual-head gamma camera system with collimators removed. Projection data are acquired with multiple energy windows to separate the point source data from the emission data. The complete geometric calibration is derived through analysis of the point source data. The system matrix is computed based on the calibration parameters and then applied to reconstruction of the emission data. Real-time calibration was found to be robust and accurate, even in the presence of downscatter from
$^99 m$
Tc emission data or dual-isotope
$^99 m$
Tc/
$^111$
In emission data. Successful calibration was consistently achieved in all pinhole configurations tried (up to seven pinholes per detector). Accuracy of real-time calibration was demonstrated in phantom studies and animal studies, where structures as small as 0.8 mm could be resolved in reconstructed images. Images appeared to be free of artifacts, and no cross-contamination from the calibration point sources was observed. Real-time calibration is feasible for pinhole SPECT, thus enabling standalone pinhole devices to be used without special alignment fixtures. The calibration accuracy is sufficient for high-resolution small animal studies. The hardware is compatible with nearly all gamma camera models and represents a lower-cost entry-level solution to the field of small animal SPECT.