Volume calculation by means of SPECT: analysis of imaging acquisition and processing factors

To assess the effect of image acquisition and processing factors on the volume calculated from single photon emission computed tomography (SPECT) images, the authors evaluated technical factors including image matrix size, size of the region of interest (ROI), activity concentration in the region, amount of background subtraction, type of reconstruction filter, section thickness, and number of projections. They found that the percentage of background subtraction was the single most important factor affecting volume calculation. The smaller the volume, the greater the amount of background subtraction needed before the ROI is drawn. As an acceptable means to circumvent the varying percentage of background subtraction for different volumes, a calibration curve was constructed relating the true volume with the calculated volume for a fixed percentage of background subtraction. The use of a 128 X 128 acquisition matrix and zooming of the reconstructed images were necessary for accurate calculation of volumes smaller than 300 mL.