Evaluation of a Correction Method for ¹¹¹In-Pentetreotide SPECT Imaging of Gastroenteropancreatic Neuroendocrine Tumors

Abstract

The number of patients with the extremely rare disease gastroenteropancreatic (GEP) neuroendocrine tumor (NET) has increased rapidly in recent years. ¹¹¹In-pentetreotide SPECT in somatostatin receptor scintigraphy has been used for the assessment of GEP NET patients. To diagnose GEP NET, appropriate selection of image correction parameters is critical. 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. Methods: A phantom study produced images with a tumor-to-background ratio of as high as 16:1. A triple energy window was used for scatter correction (SC), and attenuation correction (AC) was CT-based. Correlation analysis was performed in 4 groups: no correction (NC), SC, AC, and combined SC with AC (CC). The ¹¹¹In-pentetreotide SPECT results for 20 randomly selected patients (13 men and 7 women; age range, 37–81 y) with confirmed GEP NET were analyzed using data collected 4 h after injection of 111 MBq of ¹¹¹In-pentetreotide. Emission data were reconstructed using ordered-subset expectation maximization (OSEM) with different settings. Different combinations of the correction parameters were used to analyze the contrast-to-noise ratios (CNRs) obtained with the phantom. In the clinical study, 20 GEP NET patients were used to evaluate the GEP NET lesion CNR by 4 different image correction methods obtained from ¹¹¹In-pentetreotide SPECT images: NC, SC, AC, and CC. NC was used as a reference method. Results: The phantom study revealed that the optimal energy window in the photopeak for somatostatin receptor scintigraphy 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.