2-DIMENSIONAL RESTORATION OF SINGLE-PHOTON EMISSION COMPUTED-TOMOGRAPHY IMAGES USING THE KALMAN FILTER

The discrete filtered backprojection (DFBP) algorithm used for the rec onstruction of single photon emission computed tomography (SPECT) imag es affects image quality because of the operations of filtering and di scretization. The discretization of the filtered backprojection proces s can cause the modulation transfer function (MTF) of the SPECT imagin g system to be anisotropic and nonstationary, especially near the edge s of the camera's field of view. The use of shift-invariant restoratio n techniques fails to restore large images because these techniques do not account for such variations in the MTF. This study presents the a pplication of a two-dimensional (2-D) shift-variant Kalman filter for post-reconstruction restoration of SPECT slices. This filter was appli ed to SPECT images of a hollow cylinder phantom; a resolution phantom; and a large, truncated cone phantom containing two types of cold spot s, a sphere, and a triangular prism. The images were acquired on an AD AC GENESYS camera. A comparison was performed between results obtained by the Kalman filter and those obtained by shift-invariant filters. Q uantitative analysis of the restored images performed through measurem ent of root mean squared errors shows a considerable reduction in erro r of Kalman-filtered images over images restored using shift-invariant methods.