ABSOLUTE RADIONUCLIDE CONCENTRATION MEASUREMENT USING MAXIMUM-LIKELIHOOD EXPECTATION-MAXIMIZATION ITERATIVE RECONSTRUCTION, ATTENUATION, AND SCATTER CORRECTION

The aim of this study was to evaluate the accuracy with which radionuc lide concentration could be measured after implementation of the chann el ratio (CR) scatter correction method and incorporation of transmiss ion attenuation coefficients into a maximum-likelihood expectation-max imization iterative reconstruction algorithm regularize using a multin omial prior, A water-filled thorax phantom containing a liver insert a nd a variable spleen volume was used to simulate different clinical si tuations. An uncollimated Co-57 sheet source was used to obtain attenu ation matrices, All emission data were acquired in two 10% energy wind ows straddling the photopeak, Planar and SPECT sensitivities were dete rmined, After scatter correction was performed data were first reconst ructed using the measured attenuation matrices, and, second, using the good geometry attenuation coefficient for water, Radionuclide concent ration with the attenuation matrix using 64 projections varied between 48.9 +/- 3.1% (49.6 +/- 3.1%) and 76.5 +/- 3.0% (76.5 +/- 3.2%) when 25 and (50) iterations were used, Similar results were obtained using 128 projections, and no statistical difference could be found (p < 0.0 5), The inaccuracy of the results obtained with the implementation of the attenuation matrix from the transmission tomogram is due to the ef fective attenuation coefficients used in conjunction with the scatter compensation method, Results obtained with the attenuation coefficient of water varied between 70.1 +/- 3.1% (70.8 +/- 3.0%) and 103.2 +/- 3 .5% (103.3 +/- 3.4%), The influence of volume and concentration is cle arly demonstrated, Edge detection plays an important role in the accur acy of concentration calculations.