Attenuation Correction and Incomplete Projection in Single Photon Emission Computed Tomography

Correction for internal γ-ray absorption is an important aspect in single photon emission computed tomography. An algorithm has been developed to compensate for the effect of attenuation of γ-rays within the body. This algorithm consists of two correction steps and assumes a constant attenuation coefficient and a known body contour. The correction steps are applicable for both parallel beam and fan beam geometries. Computer simulations and experimental results have shown that this method provides a simple and effective correction for attenuation. The incomplete projection problem arises in whole body emission CT imaging, especially when fan beam collimators are used. It has been shown that fan beam geometry provides better spatial resolution than parallel beam geometry. For small organs inside the thoracic and abdominal cavities, however, fan beam geometry often produces incomplete projections which are caused by a decreased field of view of gamma cameras equipped with fan beam collimators. Two methods are described to reduce the artifacts generated from reconstruction of incomplete (truncated) projections.