This paper considers the single‐photon emission CT (SPECT) for the object containing a large spatial variation of g‐ray absorption distribution, and proposes a new correction method for the effect of attenuation. In the past correction of the image degradation by attenuation in the SPECT source distribution image, it is necessary to have an a priori knowledge about the attenuation distribution within the object. However, it should be noted that the emission data measured on the opposite side are not the same when the object has attenuation. By utilizing this property, it seems possible to acquire both the source distribution and the attenuation distribution from the measured emission data. The proposed method is based on this idea, and while estimating in parallel the source distribution and the attenuation distribution from the emission data, makes a correction of the source distribution using the attenuation distribution. A practical and clinical application of the method is expected. As a result of numerical simulation, it was verified that the proposed method is effective even when the emission data contain a noise of the level usually observed in a clinical situation.
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