Abstract
BackgroundQuantitative single photon emission computed tomography (SPECT) is challenging, especially for pancreatic beta cell imaging with 111In-exendin due to high uptake in the kidneys versus much lower uptake in the nearby pancreas. Therefore, we designed a three-dimensionally (3D) printed phantom representing the pancreas and kidneys to mimic the human situation in beta cell imaging. The phantom was used to assess the effect of different reconstruction settings on the quantification of the pancreas uptake for two different, commercially available software packages.Methods3D-printed, hollow pancreas and kidney compartments were inserted into the National Electrical Manufacturers Association (NEMA) NU2 image quality phantom casing. These organs and the background compartment were filled with activities simulating relatively high and low pancreatic 111In-exendin uptake for, respectively, healthy humans and type 1 diabetes patients. Images were reconstructed using Siemens Flash 3D and Hermes Hybrid Recon, with varying numbers of iterations and subsets and corrections. Images were visually assessed on homogeneity and artefacts, and quantitatively by the pancreas-to-kidney activity concentration ratio.ResultsPhantom images were similar to clinical images and showed comparable artefacts. All corrections were required to clearly visualize the pancreas. Increased numbers of subsets and iterations improved the quantitative performance but decreased homogeneity both in the pancreas and the background. Based on the phantom analyses, the Hybrid Recon reconstruction with 6 iterations and 16 subsets was found to be most suitable for clinical use.ConclusionsThis work strongly contributed to quantification of pancreatic 111In-exendin uptake. It showed how clinical images of 111In-exendin can be interpreted and enabled selection of the most appropriate protocol for clinical use.
Highlights
Quantitative single photon emission computed tomography (SPECT) is challenging, especially for pancreatic beta cell imaging with 111In-exendin due to high uptake in the kidneys versus much lower uptake in the nearby pancreas
We have studied the use of Woliner-van der Weg et al EJNMMI Physics (2016) 3:29 pancreatic uptake of 111In-exendin as an imaging biomarker for the beta cell mass preclinically, and recently in type 1 diabetes (T1D) patients and healthy humans [1]
Homogeneity and intensity within the 3D-printed organs Increasing the number of iterations or subsets led to noisier images, which resulted in more spots in the pancreas (Fig. 3 for Hybrid Recon, Flash 3D gives similar results). These spots in the pancreas could be misinterpreted as inhomogeneous uptake of 111In-exendin, which could be related with the patient having an insulinoma
Summary
Quantitative single photon emission computed tomography (SPECT) is challenging, especially for pancreatic beta cell imaging with 111In-exendin due to high uptake in the kidneys versus much lower uptake in the nearby pancreas. We have studied the use of Woliner-van der Weg et al EJNMMI Physics (2016) 3:29 pancreatic uptake of 111In-exendin as an imaging biomarker for the beta cell mass preclinically, and recently in type 1 diabetes (T1D) patients and healthy humans [1]. Pancreatic uptake of 111In-exendin is low compared to the uptake in the nearby kidneys and strongly varies amongst healthy humans, in which at least a factor seven of difference in pancreatic uptake was observed [2]. This is in line with the expected variation in beta cell mass. In order to use this tracer as a biomarker for beta cell mass, reliable quantification of the uptake is required
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