Longitudinal Assessment of 11C-5-Hydroxytryptophan Uptake in Pancreas After Debut of Type 1 Diabetes.

The longitudinal alterations of the pancreatic beta cell and islet mass in the progression of type 1 diabetes (T1D) are still poorly understood. The objective of this study was to repeatedly assess the endocrine volume and the morphology of the pancreas for up to 24 months after T1D diagnosis (n=16), by 11C-5-Hydroxytryptophan (11C-5-HTP) Positron Emission Tomography (PET) and Magnetic Resonance Imaging (MRI). Study participants were examined four times by PET/MRI; at recruitment and then after 6, 12 and 24 months. Clinical examinations and assessment of beta cell function by a Mixed Meal Tolerance Test and fasting blood samples was performed in connection to the imaging examination. Pancreas volume has a tendency to decrease from 50.2±10.3 mL at T1D debut to 42.2±14.6 mL after 24 months (p<0.098). Pancreas uptake of 11C-5-HTP (e.g. the volume of the endocrine pancreas) did not decrease from T1D diagnosis (0.23±0.10 ID%) to 24 months follow-up 0.21±0.14 %ID and exhibited low interindividual changes. Pancreas perfusion was unchanged from diagnosis to 24 months follow up. The pancreas uptake of 11C-5-HTP correlated to the long-term metabolic control as estimated by HbA1c (p<0.05). Our findings argue against a major destruction of beta cell or islet mass in the 2-year period after diagnosis of T1D.