Positron emission computed tomography apparatus and image reconstruction method

A positron emission computed tomography apparatus comprising:

• a detector ring comprised of a plurality of photon detectors arranged in ring shape around a predetermined center axis to surround a measurement space, each said photon detector detecting a photon incident thereto from said measurement space to output a photon detection signal corresponding to energy of said photon;
• a rotating mechanism for relatively rotating a calibration radiation source for emitting a positron to generate a photon pair with annihilation of electron-positron pair, relative to said detector ring about the center axis of said detector ring in said measurement space;
• a position-direction measuring section for measuring position and direction of an object set in said measurement space, relative to said detector ring, and outputting position-direction data corresponding to the position and direction of said object;
• a coincidence counting circuit for performing energy discrimination to determine if photons detected by said detector ring are a photon pair generated with annihilation of electron-positron pair in said measurement space, based on said photon detection signals received from said detector ring, and outputting a detector pair identification signal corresponding to a photon detector pair of said detector ring each having detected the two photons constituting said photon pair;
• a sensitivity data producing section for counting events of detection of photon pair for every photon detector pair of said detector ring each having detected the two photons constituting said photon pair, based on said detector pair identification signal received from said coincidence counting circuit, while without setting said object in said measurement space said rotating mechanism rotates said calibration radiation source relative to said detector ring, and producing and storing sensitivity data corresponding to photon pair detection frequencies for all photon detector pairs of said detector ring;
• a cumulative data producing section for producing cumulative data having values inversely proportional to values of said sensitivity data taken out from said sensitivity data producing section and, with setting said object in said measurement space, outputting said cumulative data corresponding to the photon detector pair of said detector ring each having detected the two photons constituting said photon pair, based on said detector pair identification signal received from said coincidence counting circuit;
• coordinate converting means for converting, based on said detector pair identification signal received from said coincidence counting circuit, distance and direction of a detector line being a straight line connecting the photon detector pair of said detector ring each having detected the two photons constituting said photon pair into coordinate values expressed by predetermined polar coordinates set in said measurement space, compensating the coordinate values of said detector line in correspondence to the position and direction of said object, based on said position-direction data received from said position-direction measuring section, and outputting coordinate data corresponding to the coordinate values of said detector line;
• a projection data accumulating section for cumulating said cumulative data received from said cumulative data producing section at an address of a memory space corresponding to the coordinate values of said detector line, based on said coordinate data received from said coordinate converting means, and accumulating said cumulative data distributed in said memory space, as projection data;
• and
• an image reconstructing section for calculating a spatial distribution of photon pair occurrence frequencies with annihilation of electron-positron pair in said object, based on said projection data taken out of said projection data accumulating section, and producing reconstructed image data corresponding to said spatial distribution of photon pair occurrence frequencies.