Techniques and applications for preclinical SPECT

Two developments of the past decade have spurred the development of SPECT as a useful tool for preclinical research. Development of the pinhole collimator, and the growing library of imaging probes for use with SPECT beyond the traditional markers for perfusion or tumor metabolism have both increased the potential uses of SPECT for small animal research. The oblique geometry of pinhole rays originating toward the edges of the FOV results in incomplete sampling and poor image quality away from the pinhole orbit plane. Correction requires an orbit that includes an axial component of motion. A simple solution was developed by placing circular orbits at multiple axial locations along the length of the object. When reconstructed with an OSEM algorithm, the multiple projection sets improved data completeness and reconstructed image quality for simulated and experimental data. Pinhole collimators provide the greatest resolution and highest sensitivity when the object distance is minimized. In actuality, objects are placed some distance from the aperture to ensure that the camera field-of-view is large enough to avoid truncation. A method for improvement was tested by decreasing object distance and obtaining multiple offset projection sets. The two truncated projection sets were then be reconstructed with OSEM to create an image at with improved resolution. In addition to advancements in acquisition strategies, the work in this dissertation details two preclinical projects using the microSPECT camera. The microSPECT camera was used to examine the biodistribution of labeled monoclonal and polyclonal antibodies against the neutrophil protein myeloperoxidase. Mice injected with Staph-A were imaged at 24hr post infection with increased uptake of the tracer probe witnessed in the infected region. A second application required the measurement of hematocrit values using SPECT and labeled erythrocytes and plasma with 99mTc in ischemic rats. SPECT imaging of the labeled plasma and RBCs showed increases in hematocrit values within the ischemic lesion as defined from an HMPAO perfusion image. Moreover, the hematocrit value varied inversely with the perfusion deficit. For regions of poor blood flow, hematocrit was higher. During reperfusion, when flow was restored, or increased above normal levels, hematocrit levels dropped