Measured accuracy and precision in quantitative SPECT imaging with iodine-123

This study evaluated ¹²³I SPECT volume and activity quantitation in terms of accuracy and precision using experimental phantom data. Two reconstruction methods were considered. The filtered backprojection (FB) method with 2D Metz pre-filtering and single iteration Chang attenuation compensation was compared with an iterative ML-EM method that used Gaussian post-filtering and incorporated the 3D divergent detector response and attenuation in the detection kernel. Both methods were examined over a range of resolution and noise characteristics. An ensemble of 21 SPECT data sets were acquired of a cylindrical phantom that contained spheres of size 21.4, 12.0, and 5.7 ml, filled with high purity ¹²³I in a uniform background (5:1 uptake ratio). Each data set was reconstructed by both methods, and sphere volume and activity measurements were obtained from the reconstructions using a semi-automatic method that defines the region-of-interest based on the intensity gradient in the area of increased ¹²³I concentration. The mean and standard deviation of the 21 measurements provided accuracy and precision indices, respectively. For the 21.4 ml sphere, the measured volume with either reconstruction method was accurate to within 5% of the true volume with a standard deviation of approximately 8% of the true volume. For the 12.0 ml sphere the measured volume with the iterative method exhibited substantially smaller standard deviation for equal accuracy compared with the FB method. Sphere activity was underestimated with both methods due to spatial resolution effects. The 5.7 ml sphere was generally below the size limit for volume and activity quantitation by these methods