High spatial resolution reconstruction technique for SPECT using a fan-beam collimator

The physical characteristics of the collimator cause degradation of resolution with increasing distance from the collimator surface. A convolutional backprojection algorithm is derived for fan beam single-photon-emission computed tomography (SPECT) data without rebinding into parallel beam geometry. The projections are filtered and then backprojected into the area within an isosceles triangle whose vertex is the focal point of the fan-beam and whose base is the fan-beam collimator face, and outside of the circle whose center is located midway between the focal point and the center of rotation and whose diameter is the distance between the focal point and the center of rotation. Consequently, the backprojected area is close to the collimator surface. This algorithm, implemented on a GCA-9300A SPECT system, shows good results with phantom and patient studies. The SPECT transaxial resolution is 4.6 mm FWHM (reconstructed image matrix size of 256×256) at the center of SPECT field of view using ultra-high-resolution fan beam collimators for brain study. Clinically, Tc-99m HMPAO and Tc-99m ECD brain data are reconstructed using this algorithm. The reconstruction results are compared with MRI images of the same slice position and show significant improvement over results obtained with standard reconstruction algorithms