USE OF THE GEOMETRIC MEAN OF OPPOSING PLANAR PROJECTIONS IN PRERECONSTRUCTION RESTORATION OF SPECT IMAGES

This paper presents a restoration scheme for single photon emission computed tomography (SPECT) images that performs restoration before reconstruction (pre-reconstruction restoration) from planar (projection) images. In this scheme, the pixel-by-pixel geometric mean of each pair of opposing (conjugate) planar projections is computed prior to the reconstruction process. The averaging process is shown to help in making the degradation phenomenon less dependent on the distance of each point of the object from the camera. The restoration filters investigated are the Wiener and power spectrum equalization filters. These filters are used to obtain SPECT images of a hollow cylinder phantom, a resolution phantom, and a truncated conic phantom containing two types of cold spots-a sphere, and a triangular object. A comparison of results obtained by pre-reconstruction restoration with and without averaging is performed through measurement of root mean squared errors and contrast ratios. The SPECT images obtained from the averaged images show a significant increase in contrast, and a decrease in the root mean squared error over non-averaged pre-reconstruction restored images.