An evaluation of the effect of scatter and attenuation correction of gamma photons on the reconstructed radionuclide distribution in the myocardial wall during spect imaging
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The purpose of this study was firstly to evaluate the selection of reconstruction parameters (i.e. the number of subsets and the number of iterations) based on phantom studies. The second aim was to evaluate the effect of the non-uniform attenuation and scatter correction on myocardial perfusion studies performed on healthy volunteers as well as patients with proven inferior wall perfusion defects. The quality of the images from the phantom studies showed that 16 subsets with 2 iterations gave the best results if considering image noise and image resolution. These number of subsets and iterations were therefore used as reconstruction parameters in the patient studies The application of an attenuation correction to the emission data required that attenuation coefficient maps of the subjects were obtained from transmission images. I39Ce was chosen as the transmission source and used in conjunction with 99mTcas the emission source. The emission data were corrected for scatter according to the triple energy window method. In the healthy male and female volunteers, the attenuation and scatter corrected myocardial SPECT images showed an improvement in the homogeneity of the counts distribution compared to the uncorrected images. The counts distribution in the inferior region improved after the attenuation correction was applied, however it exceeded the counts in the anterior region. After applying a scatter as well as an attenuation correction to the emission data, the counts in the inferior region of the myocardium were slightly reduced. This was a result of the scatter correction eliminating scattered counts in the inferior region originating mainly from the liver. The apparent lower counts in the anterior region could be a result of too little compensation for scatter in the inferior wall, and needs to be investigated further. The defects in the three unhealthy patients, were not obscured after applying the scatter and attenuation correction to the emission data. The correction technique did not introduce false negative results in these patients. The application of scatter and attenuation correction techniques shows promising results for the interpretation of myocardial perfusion studies. These correction algorithms however need to be investigated thoroughly before being used in the routine clinical practice to avoid the introduction of artefacts.