Thyroid volume determination by single photon tomography and 3D processing for activity dose estimation

This study demonstrates a method of determination of thyroid glandpsilas volume by use of SPECT gamma camera data, in order to calculate thyroidpsilas mass useful in Nuclear medicine therapy. The method consists of the determination of the borders of the gland from a set of transaxial tomographic images by use of a specific for each case threshold value. We have measured the thyroid volume of 48 hyperthyroid patients by adding transaxial slices We analysed the slicespsila data producing interfile format images by Procyon Starlab program and transferring these images in a PC and saved in an uncompressed bitmap format in order to be processed by Interactive Data Language (IDL) tools and Matlab program. Ellipse ROIs are created around each thyroid lobe while rectangular ROIs include both lobes uptake data. Matrices of the maps of the counted voxels of the slices of the organ were created. Their total is multiplied by the elementary voxel size in mm to obtain the final organ volume. Data were extracted and Area, Eccentricity, major & minor axis length, Orientation, equivalent Diameter and Integral Intensity of both left & right lobes were calculated. The delineation procedure adopted in this study was validated by 10 cylindrical phantoms 10 to 100 ml which were imaged under conditions similar to those of the patientspsila studies and by measuring the actual volume of the gland of 3 patients who subsequently underwent thyroidectomy by submersion. The method is simple and fast with a relative error of up to 3% for length, 11% for area and 8% for volume determinations.