Single photon emission computed tomography (SPECT) has become an important diagnostic tool in cardiovascular nuclear medicine. While most cardiac SPECT procedures are accomplished using a large field-of-view rotating gamma camera with a general purpose parallel collimator, for a small organ like the heart, a converging geometry can be utilized to improve the sensitivity and resolution of projection images. In the two and half years of this grant, we have designed and built fan and cone beam collimators, developed reconstruction algorithms, performed computer simulations and phantom studies, and from patient studies obtained the first fan and cone beam tomographic images of the human heart. While these results have shown that the technical difficulties of converging collimation - algorithm complexity, insufficient angular sampling, truncation of projection data, and additional attenuation due to angular sampling requirements of greater than 180 degrees - can be solved to obtained improved diagnostic images, a more extensive study is needed to evaluate the sensitivity and specificity of the technique. In addition, preliminary experiments have shown that converging collimation combined with a multi-head SPECT system offers significant potential for simultaneous emission-transmission tomography that can improve quantification of radiopharmaceutical uptake with no increase in patient imaging time. Imaging with convergent hole collimators using present large field view rotating gamma cameras has significant potential for improved quanitification and spatial and contrast resolution of cardiac imaging. This is important for better diagnosis of coronary artery disease including better detection of myocardial infarction and diagnosis of ischemic heart disease and for performing physiologic imaging as is only possible with PET at the present. The goal of this proposal is to provide a systematic quantitative evaluation of emission and transmission tomography for four types of detection geometries on a single head and a three head SPECT system in terms of image quality, measurement accuracy, and specificity and sensitivity of lesion detection. The importance of the proposed research is to provide the scientific basis for establishing guidelines for the selection and specification of collimators, transmission sources and algorithms. The intent is to improve patient care without any cost increase using present cardiac SPECT procedures.
The aim of this proposal is to apply converging collimation to cardiac imaging using both single head and multi-head SPECT systems, to design and build an astigmatic collimator, to design and build transmission sources for these collimators, and to develop new algorithms that reconstruct three-dimensional images of the heart without artifacts from projections obtained using these collimators and transmission sources. In particular, comparisons will be made between parallel geometry, fan beam geometry, cone beam, and astigmatic geometries for advantages and disadvantages in terms of image quality, specificity and sensitivity of lesion detection, sizing of lesions, and quantification of radiopharmaceutical uptake.
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