SPECT simulation and reconstruction using a combination of ray collimation geometries

John C. Engdahl, David A. Reimann, Jian-Qiao Luo, and Tsur Bernstein

Society of Nuclear Medicine, 37th Annual Meeting, Washington D.C., June 19-22, 1990. Journal of Nuclear Medicine, 31(5):719, May 1990.

Tomographic reconstructions have been performed utilizing simulated projection images from a combination of differing collimator geometries. The combination of geometries devotes more detector area to viewing the organ of interest within the center field-of-view (CFOV) while still sampling the balance of the FOV to permit artifact free reconstruction. The combination of ras acquired from the two geometries completely spans the Radon (or sinogram) space but the sampling density and collimation are not uniform. The rays from the two different collimation geometries were combined into a single set of evenly spaces orthogonal points, as if they were acquired from a parallel hole collimator. The resultant rays were formed from a linear combination of the input rays where the weights were computed as the fraction of area in the input space surrounding a ray point that overlapped a resultant ray area in the orthogonal grid sinogram. The mapping scheme utilized does not significantly degrade reconstructed resolution, as did the linear or higher order interpolation schemes tested, and has the further attributes that the weights are computed only once and the resultant ray calculations are not dependent on the uncertainty of the input ray values. Since the ray density is not uniform and the sensitivity of each ray is variable, the input ray values are normalized before mapping. Areas in the sinogram of low sensitivity, corresponding to areas of the FOV which could contain activity but not the organ of interest, can be preferentially smoothed to reduce noise at the expense of resolution where it is not of interest anyway. Reconstructions of simulated projections of different source geometries have been performed to validate the method with regards to preserving resolution and not generating additional artifacts.

Copyright © 1990, David A. Reimann. All rights reserved.