A FILTERING TECHNIQUE TO COMPENSATE FOR DETECTOR RESPONSE IN CONVERGING-BEAM SPECT RECONSTRUCTION

In this study a non-stationary filtering technique was developed to co mpensate for spatially variant detector response in fan- and cone-beam SPECT. First the frequency-distance relation for fan- and cone-beam g eometries was derived from their parallel-beam counterpart, and then u sed to compute the Fourier transform of the detector response that was used as the MTF of a Metz filter. The filter was applied to the blurr ed data before reconstruction. The unique feature of the derived MTF i s that it depends on source location, so the filtering is spatially va riant. Results of evaluation studies demonstrate that the ratio betwee n the tangential and radial FWHMS of the reconstructed point response function obtained from our filtering technique is closer to one and va ries less with source location as compared to the ratio obtained witho ut compensation or using Metz filtering with a stationary detector res ponse. This improvement is mainly because the tangential FWHM is incre ased to match the radial FwHm better. With a higher order of Metz filt er, both tangential and radial FWHMS are slightly smaller but their ra tio deviates more from one compared to those of lower orders. In concl usion, our filtering technique provides an effective means to compensa te for detector response mainly in terms of reducing anisotropy of the point response function.