**-Postprandial pancreatic [11C]methionine uptake after pancreaticoduodenectomy mirrors basal beta cell function and insulin release

Abstract

Purpose: [S-methyl-11C]-L-methionine ([11C]MET) uptake in the pancreas might be a central indicator of beta cell function. Since gastric emptying was recently shown to influence glycemic control in subjects after pancreaticoduodenectomy (PD, the surgical treatment of neoplasms of the pancreas head), we looked for imaginable relationships between gastric emptying, pre- and postprandial insulin concentrations, and [11C]MET uptake. Methods: Nineteen tumor-free survivors after PD (age mean ± SD: 61 ± 8.7 yrs.; 10 male, 9 female) and 10 healthy controls (age: 27 ± 8.7 yrs.; 7 male, 3 female) were given a mixed test meal. One gram of paracetamol was ingested with the meal to evaluate the speed of gastric emptying. Insulin, glucose, and paracetamol plasma concentrations were measured before and over 180 minutes after ingestion. Beta cell function was calculated from fasting glucose and insulin plasma concentrations. Simultaneously, 800 MBq of [11C]MET were administered and the activity (maximum tissue standardized uptake values [SUVmax]) over the pancreas was measured at 15, 30, and 60 minutes after injection. Total integrated SUVmax (area under the curve [AUC]) and incremental SUVmax were calculated. Results: The uptake of [11C]MET in the pancreas was significantly higher (p < 0.0001) in controls compared to the PD group. Gastric emptying was significantly slower in controls compared to pancreatectomy subjects (p < 0.0001). Paracetamol AUC30 correlated with the SUVmax increment between 15 and 30 minutes (R2 = 0.27, p = 0.0263), suggesting a relationship between gastric emptying and the uptake of [11C]MET. Total integrated SUVmax correlated with insulin AUC60 (R2 = 0.66,p < 0.0001) in patients after PD. Multivariate regression analysis revealed insulin AUC60 and beta cell function, calculated from the fasting insulin to glucose ratio, as independent predictors of 11C-methionine uptake, i.e. total integrated SUVmax, in patients after PD (R2 = 0.78, p < 0.0001). Conclusion: Postprandial [11C]MET uptake may represent basal and postprandial beta cell function. The findings suggest a possible usefulness of this imaging procedure for further studying beta cell function.