THREE-DIMENSIONAL RECONSTRUCTION WITH DIVERGENT RAY GEOMETRY APPLIED TO NUCLEAR MEDICINE IMAGING (SPECT, PINHOLE COLLIMATOR, CONE BEAM)

Imaging in nuclear medicine using Single Photon Emission Computed Tomography (SPECT) techniques suffers from poor spatial resolution. In order to improve resolution, a convolution-backprojection three dimensional reconstruction algorithm with cone beam geometry has been developed. The cone beam apex moves on a circle in a transverse plane relative to the axis of rotation. As an approximation to the exact solution, a space-invariant one dimensional filter is applied to each projection line in each projection view independently. Subsequent backprojection is performed in a true three dimensional space with proper weighting. A linear two dimensional interpolation is used. The algorithm has been implemented on an ADAC 3300 nuclear medicine computer system interfaced to a Siemens ZLC 7500/SPECT rotating scintillation camera.;The pinhole SPECT imaging technique achieves ultra-high spatial resolution and therefore allows visualization of fine details of small organ structures. It should prove very useful in imaging situations where high spatial resolution is critical and sensitivity can be sacrificed. The SPECT imaging with a converging collimator offers significant improvement in sensitivity and in turn better utilization of radiation. Consequently, it will find wide applications in clinical work, such as brain imagings.;Three modes of SPECT imaging have been studied. The first, fan beam SPECT imaging, produces a 34 percent improvement in reconstructed system spatial resolution, and a 26 percent improvement in sensitivity. The second mode, pinhole SPECT imaging, offers a considerable improvement of 112.5 percent in spatial resolution at the expense of a reduction in sensitivity to 45 percent. The third mode, SPECT imaging with a converging collimator, obtains a 45 percent improvement in spatial resolution and a 62.5 percent improvement in sensitivity. All are compared to SPECT imaging with a Low Energy All Purpose parallel hole collimator. Results with phantom and patient studies indicate that the approximate three dimensional cone beam reconstruction algorithm developed is capable of generating satisfactory tomographic images.