An Exocrine Pancreatic Stress Test with ¹¹C-Acetate PET and Secretin Stimulation

Abstract

The purpose of this study was to develop a noninvasive imaging test of pancreatic exocrine function. Methods: In this pilot study, 5 healthy volunteers underwent two 60-min dynamic 11 C-acetate PET studies, one before and one after intravenous secretin administration. Kinetic analysis of the pancreas was performed using a 1-compartment model and an image-derived input function. From summed images, standardized uptake values were measured from the pancreas and the liver, and the pancreas-to-liver ratio was computed. Results: The baseline k 1 and k 2 data for all 5 volunteers were consistent. After secretin stimulation, the k 1 and k 2 significantly increased (paired t test P 5 0.046 and P 5 0.023, respectively). In the summed PET images, the pancreas-to-liver ratio decreased (P 5 0.037). Increased 11 C-acetate activity was observed in the duodenum after secretin stimulation consistent with secretin-induced secretion. Conclusion: 11 C-acetate PET studies with secretin stimulation show potential as a noninvasive method for assessing pancreatic exocrine function. Chr onic pancreatitis has a high prevalence in developed countries, 25-30 cases per 100,000 people, and an even higher prevalence of approximately 5% in autopsy studies (1,2). The transition from acute pancreatitis, which is the second most common gastrointestinal discharge diagnosis in the United States, to chronic pancreatitis is challenging to identify. Accurate diagnosis of early chronic pancreatitis is difficult with imaging studies such as CT, MR imaging, endoscopic retrograde cholangiopancreatography, or endoscopic ultrasound. Pancreatic volume loss is evident only in the late stages, taking 5-10 y or longer to develop (3). Although imaging and function tests at the early stages of the disease are often negative, early recognition is important to help with accurate diagnosis, reduce disease progression, and prevent unnecessary interventions (4).A pancreas function test is the most sensitive test described but is not readily performed at most centers (5). The pancreas function test involves passing a tube into the duodenum, injecting a supraphysiologic dose of secretin, and then collecting the pancreatic secretions over an hour to measure the bicarbonate concentration. Secretin is a hormone that stimulates the pancreatic ductal cells to excrete fluid and bicarbonate, and normally, the bicarbonate concentration will double after secretin stimulation in 15 min (6). The pancreas function test is uncomfortable for the patient, expensive, and time-consuming. A shorter-duration endoscopic collection of the pancreatic secretions is an alternative but is less sensitive (7). These current pancreatic function tests are so cumbersome and insensitive that they are essentially obsolete and not being used by most practitioners.11 C-acetate PET was developed first to study oxygen metabolism in the myocardium and is currently applied in oncology for prostate cancer, hepatocellular carcinoma, and brain tumors (8). Intense 11 C-acetate uptake is consistently noted in t...

Normal Uptake of 11C-Acetate in Pancreas, Liver, Spleen, and Suprarenal Gland in PET

“…Few theories exist regarding distribution of 11 C-acetate, for example, its high concentration in pancreas which may correspond with increased lipid synthesis in acinar cells [ 7 ], incorporating into zymogens or generating hydrogen carbonate ions [ 8 ]. A recent study showed also potential of evaluating pancreatic exocrine function as 11 C-acetate activity increased in duodenum after secretin administration [ 9 ].…”

“…No statistically significant differences were found in radiotracer uptake in body and uncinate process of pancreas in this study. Inclusion criteria in our study required no previous history of pancreas pathology and normal lab test results, but as other studies show [ 9 , 10 ] it is possible to use 11 C-acetate in evaluating pancreas exocrine function.…”

Radiosynthesis, Preclinical, and Clinical Positron Emission Tomography Studies of Carbon-11 Labeled Endogenous and Natural Exogenous Compounds

“…Further clinical PET studies in abdominal parenchymal organs confirmed the pancreas as the organ with high uptake, with no statistically significant differences found between the head and body of the organ. , Other studies highlighted a prolonged clearance of [ 1 - 11 C]­acetic acid from the pancreas (roughly 64% of activity retained 30 min post-injection) with a pancreas-to-liver ratio 10–20 min post-injection ranging from 2.1 to 4.5, among the normal subjects studied, also suggesting its potential to evaluate exocrine pancreas function and disease-related. , …”

Evaluation of Prostate Cancer with 11C-Acetate PET/CT

“…Pancreas, kidneys, spleen, heart, and liver received the highest organ doses. The consistently high tracer uptake in the pancreas was recently exploited for secretin testing of the pancreatic exocrine function (25). The effective whole-body dose was low, at 0.0049 mSv/MBq.…”