Virtual contouring for transmission scanning in spect and pet studies

Abstract

A nuclear gamma camera employs a virtual contouring technique in order to maximize the portion of transmission radiation fan beams ( ) which pass through a subject ( ). A plurality of radiation detector heads ( ) having radiation receiving faces and a plurality of radiation sources ( ) are mounted to a gantry ( ). An orbit memory ( ) stores clearance offset orbit ( ) around the subject and a subject support ( ). A tangent calculator ( ) calculates virtual lines ( ) between the radiation sources ( ) and the corresponding radiation detector heads ( ). The virtual lines ( ) correspond to edge rays of the transmission radiation fans ( ). A shift calculator ( ) calculates and sends shift commands to a motor orbit controller ( ) which controls rotational and translational drives attached to the detector heads ( ). The detector heads are translated such that the virtual lines ( ) remain tangent to a predefined contour of the subject throughout rotation of the detector heads about the subject receiving aperture ( ). The detected transmission radiation ( ) is reconstructed ( ) into an attenuation volumetric image representation and used to correct ( ) detected emission radiation data. The corrected emission data is then reconstructed ( ) into a volumetric image representation. The virtual contouring minimizes lost rays ( ) of transmission radiation and facilitates an artifact-free attenuation volumetric image representation.