Reconstruction parameters for 111In-pentetreotide SPECT: variability with respect to body weight and body region

This study, which was based on a large series of consecutive patients imaged by (111)In-pentetreotide SPECT for a neuroendocrine tumor, evaluated variability in reconstruction parameters in relation to patient body weight and the body region imaged, looking for the possibility of standardizing such parameters.

One hundred twenty-four patients underwent (111)In-pentetreotide scintigraphy: 4- and 24-h whole-body and planar scans and a 24-h SPECT examination. All patients were injected with 140-150 MBq of (111)In-pentetreotide at least 1 wk after somatostatin analogs had been discontinued. SPECT images were systematically acquired at the levels of the head, chest, and abdomen. SPECT was performed using a dual-head gamma-camera with medium-energy collimators, step-and-shoot method, no circular orbit, a 64 x 64 matrix, and 30 s per view for a total of 64 views. Two reconstruction procedures were compared: the iterative method using 10 iterations and the filtered backprojection method using a Butterworth filter with different cutoffs and orders.

Optimal SPECT images were obtained by applying the Butterworth filter. The reconstruction parameters could be standardized for the head and chest but were more variable for the abdomen, mainly because (111)In-pentetreotide is physiologically trapped in different intestinal areas and varies over time, especially in the liver, spleen, bowel, and urinary tract.

Filtered backprojection using a Butterworth filter appears adequate for standardizing the reconstruction parameters for (111)In-pentetreotide SPECT of the head and chest. Processing of abdominal images is more operator-dependent. A 150-MBq dose of (111)In-pentetreotide is recommended when planning multiple SPECT acquisitions in the same patient.