3-D Single photon emission computed tomography in the KEMA source-term research

A description is presented of the development and testing of two three-dimensional tomographic reconstruction techniques for use in the tomography-part of the source-term investigation as is performed presently at the N.V. KEMA in Arnhem. The first technique: Multiplicative Algebraic Reconstruction Technique (MulART) tries by means of iterations to bring the discretized reconstruction space into conformity with the gamma intensities obtained with a narrow-slit collimator. The second technique is a direct discretization of the analytic solution of the reconstruction problem, the three-dimensional Radon transformation. From simulation studies it has become clear that with the technique of inverse Radon transformations good results can be obtained. It is a flexible and fast technique while MulART yields finally less proper reconstructions after very intensive computations. For the computation of the inverse Radon transformation the scan orientations have to be partitioned homogeneously over a (half) sphere and the measured data have to be differentiated. During the investigation three methods have been used for differentiation, by means of the difference equation, Fast Fourier Transformations (FFT) and smoothed cubic splines. Besides also a method is presented for the determination of homogeneously partitioned scan orientations. The best results were obtained with differentiation by means of FFT. The final implementation in standard FORTRAN 77 has achieved the level at which direct examination in practice by means of well defined fantoms is desired. (author). 8 refs.; 53 figs.; 2 tabs