Improvement of image resolution and quantitative accuracy in clinical Single Photon Emission Computed Tomography

Clinical Single Photon Emission Computed Tomography (SPECT) is a scanning t echnique which acquires gamma-camera images ('projections') over a range of angles around a patient. These projections allow the reconstruction of cro ss sectional ('tomographic') images of the gamma-radiating pharmaceutical d istribution in the patient, thus providing interesting information about th e functioning of organs and tissues. SPECT images are seriously affected by a variety of image degrading process es. Restrictions on the amount of radio-pharmaceutical that can be administ ered to a patient cause noise in the projections and the limited spatial re solution of the gamma-camera results in blurring of the projections. In add ition to these image degradations, the reconstruction of cross-sections is complicated by Compton scattering of gamma -photons in tissue, which causes attenuation of the photon flux received by the gamma-camera and causes imp roper detection of photons which have been scattered in tissue. This result s in some additional blurring and loss of accuracy of the SPECT images in p redicting activity concentrations. Tremendous efforts have been made to improve the quantitative accuracy and the spatial resolution of SPECT, and to reduce the noise in the reconstruct ed images. These efforts have resulted in corrective reconstruction algorit hms, which are generally based on incorporation of accurate models of the m ain image degrading factors. Improvements of the data acquisition hardware can further increase image quality. In this paper, the image formation proc ess of SPECT, including image-degrading factors, is explained. In addition, reconstruction algorithms and hardware modifications are reviewed, and the ir effects on image quality are illustrated with physical phantom and simul ation experiments. (C) 2001 Elsevier Science Ltd. All rights reserved.