On reconstruction and segmentation of piecewise continuous images

We evaluate an image model for simultaneous reconstruction and segmentation of piecewise continuous images. The model assumes that the intensities of the piecewise continuous image are relatively constant within contiguous regions and that the intensity levels of these regions can be determined either empirically or theoretically before reconstruction. The assumptions might be valid, for example, in cardiac blood-pool imaging or in transmission tomography of the thorax for non-uniform attenuation correction of emission tomography. In the former imaging situation, the intensities or radionuclide activities within the regions of myocardium, blood-pool and background may be relatively constant and the three activity levels can be distinct. For the latter case, the attenuation coefficients of bone, lungs and soft tissues can be determined prior to reconstructing the attenuation map. The contiguous image regions are expected to be simultaneously segmented during image reconstruction. We tested the image model with experimental phantom studies. The phantom consisted of a plastic cylinder having an elliptical cross section and containing five contiguous regions. There were three distinct activity levels within the phantom. Projection data were acquired using a SPECT system. Reconstructions were performed using an iterative maximum a posteriori probability procedure. As expected, the reconstructed image consisted of contiguous regions and the acitivities within the regions were relatively constant. Compared with maximum likelihood and a Bayesian approach using a Gibbs prior, the results obtained using the image model demonstrated the improvement in identifying the contiguous regions and the associated activities.