Evaluation of a Spline Reconstruction Technique for SPECT: Comparison with FBP and OSEM

An efficient, two-dimensional, analytic, Spline Reconstruction Technique (SRT) for SPECT has been presented earlier in the literature. The SRT is a reconstruction algorithm based on an analytic formula of the inverse Attenuated Radon Transform which results from the approximation of the sinogram in terms of cubic splines. The algorithm incorporates the attenuation map obtained by a CT scan, to provide attenuation corrected images. The aim of this study is to evaluate the performance of the SRT algorithm, using phantoms and real SPECT/CT data, by comparing it with two commonly used reconstruction algorithms: FBP and OSEM. The uniformity and resolution limitations of the analytic SRT algorithm is assessed in simulation studies by using a Uniformity phantom, a slice of the Hoffman brain phantom, and two slices of the NCAT human torso phantom. Appropriate attenuation maps are used for each image. Reconstructed images are obtained for 60, 90, 120, and 180 projections over 360 degrees. Furthermore, real SPECT sinograms and their corresponding CT images are acquired from a clinical SPECT/CT system, and then reconstructed employing the SRT algorithm. The reconstructed images obtained via the SRT algorithm are compared to those produced by FBP and OSEM. Several profiles are presented which illustrate the ability of SRT algorithm to correct for attenuation. The SRT reconstructions from clinical data are also compared with the OSEM reconstructions provided by the commercial system. Comparisons between fused images are also presented. Our preliminary results suggest that SRT appears to provide better reconstructed images than FBP at least for the cases when no attenuation correction is applied to FBP. The reconstruction time for SRT was about 2 sec which is comparable to that of FBP and faster than OSEM. Regarding reconstructions for the data obtained from the clinical system, SRT appears to provide comparable quality images with the OSEM reconstructions processed by the comme- cial system. However, further evaluation of SRT is needed to substantiate this claim. It is also important to note that SRT suffers from striking artifacts, due to angular under-sampling, which become worse at low number of projection angles.