Evaluation of 111In-Pentetreotide SPECT imaging correction for GEP-NET.

Purpose: The number of patients with the extremely rare disease GEP-NET (gastroenteropancreatic neuroendocrine tumor) has increased rapidly in recent years. In-111-pentetreotide single photon emission computed tomography (111In-pentetreotide SPECT) in somatostatin receptor scintigraphy (SRS) has been used for the assessment of GEP-NET patients. To diagnose GEP-NET, appropriate selection of the image correction parameters is of critical importance. Correction methods may improve the 111In-pentetreotide SPECT image quality, but there is currently no standard technique. The purpose of this study was to determine the optimal correction parameter settings for 111In-pentetreotide SPECT imaging. Materials and Methods: A phantom study produced scan images with a tumor-to-background ratio as high as 16:1. Triple energy window was used for scatter correction (SC), and computed tomography-based attenuation correction was used for attenuation correction (AC). Correlation analysis was performed in four groups: no correction (NC), SC, AC, and combined SC with AC corrections (CC). 111In-pentetreotide SPECT results of twenty patients (13 men and 7 women; age range, 37-81 years) randomly selected patients with confirmed GEP-NET were analyzed, using data collected four hours after injection of 111 MBq 111In-pentetreotide. Emission data were reconstructed using ordered subset expectation maximization (OSEM) reconstruction, with different settings. Different combinations of the correction parameters were used to analyze the contrast to noise ratios (CNR) obtained with the phantom. In the clinical study, 20 GEP-NET patients evaluated the GEP-NET lesion CNR by four different image correction methods obtained from 111In-pentetreotide SPECT images: 1) NC, 2) SC, 3) AC, and 4) CC. NC was employed as a reference method. Results: The phantom study revealed that the optimal energy window in the photopeak for SRS was 171 keV ± 10% and 245 keV ± 7.5%, and the optimal OSEM reconstruction conditions were 8 subsets and 6 iterations. Among the OSEM collection conditions, CC produced a significantly higher CNR than NC or SC (p<0.05). In the clinical study, CC was found to increase the CNR (p<0.05).　 Conclusion: CC improves the correction in 111In-pentetreotide SPECT studies, compared with NC, providing better contrast and sharper outlines of lesions and organs.