Positron Emission Tomography and Magnetic Resonance Techniques in Diabetes
Abstract: In order to further advance the field of diabetes research there is a great need for establishing validated non-invasive quantitative techniques to study the pancreas and other tissues of importance for blood glucose regulation. The general aim of this thesis was to explore magnetic resonance techniques and positron emission tomography as such tools.In paper I pancreatic perfusion under basal conditions and in response to glucose in nondiabetic and type 1 diabetic individuals was studied with [15O]H2O PET/CT. Individuals with type 1 diabetes were found to have reduced basal pancreatic perfusion and a severely impaired pancreatic and splanchnic perfusion response to intravenous glucose stimulation.In paper II four groups of subjects at different stages of type 2 diabetes development and a control group of individuals without diabetes were examined with PET/CT and MRI. The [11C]5-HTP uptake in pancreas was hypothesized to correlate with remaining functional capacity of the β-cells. The progressive loss of β-cell function indicated by metabolic testing was not mirrored by a decrease in [11C]5-HTP tracer accumulation in the pancreas. This provides evidence of retained islet mass despite decreased β-cell function, indicating that β-cell dysfunction or dedifferentiation, and not necessarily endocrine cell loss, constitutes a major cause of β-cell failure in type 2 diabetes.In paper III the feasibility of using ex-vivo MR spectroscopy for assessment of viability of human pancreas grafts prior to transplantation was studied. It was found that 31P-MRS may provide quantitative parameters for evaluating graft viability ex vivo, and is a promising tool for objective non-invasive assessment of the quality of human pancreas grafts.In paper IV the Imiomics method for automatic image analysis was validated in whole-body [18F]-FDG PET/MR images in subjects with varying degree of insulin resistance. Imiomics was found to provide association screening and timesaving analysis of whole-body data and detected differences in glucose uptake and tissue composition between subjects on voxel-level. However, it did not show complete correlation with traditional volume of interest based tissue analysis in a small cohort.
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