Simultaneous 3D correction for attenuation, scatter, and detector response in SPECT

Among all the factors that contribute to the degradation of image quality, 3 physical phenomena have a major impact: photonic attenuation, Compton scatter, and detector point response. The correction of each of these factors have been intensively studied. It is generally considered that using algebraic methods is the best way to correct for physical effects. The drawback of these methods is the intensive computational time and the large amount of memory they require. That is the reason why only few methods have been proposed to correct simultaneously for attenuation, scatter, and detector response. This paper presents a new algebraic method to correct for the three physical effects previously mentioned. The method is based on a simultaneous acquisition of transmission and emission projection data. The reconstructed attenuation map is then used to estimate the 3D distribution of scattered photons, but the map is also incorporated in the projector/backprojector used to correct for 3D detector response. The key point of the algorithm is the use of a 3D set of line integrals, calculated as a part of the attenuation technique, as the basis of a model of the 3D distribution of scattered events, but also for the estimation of the 3D geometric response of the detector. The triple correction method has been tested on phantom data, acquired with a two detector camera equipped with parallel collimators. The results show that best results are obtained using the three corrections simultaneously, compared to results obtained with only 1, or 2, of the 3 corrections.