Non-invasive MRI to Quantify the Effect of Secretin on Pancreatic Blood Flow and Perfusion in Healthy Volunteers

Background An alteration in pancreatic blood flow may be important in a number of clinical conditions. Reduction of blood flow is seen in patients with acute and chronic pancreatitis and the quantification of perfusion may be useful in the management of pancreatic malignancy and assessment of pancreatic transplants. Unfortunately, the measurement of pancreatic blood flow is technically difficult due to the anatomical location of the organ and complex blood supply. The pancreas receives its blood supply from a rich plexus of arteries but the foremost arterial supply arises from the splenic and pancreaticoduodenal arteries, both superior and inferior. Various methods have been used in an attempt to quantify the blood flow but all have potential drawbacks. The use of endoscopic and laparoscopic methods are invasive as is the use of intravenous contrast media. Furthermore, the use of computed tomography exposes patients to ionising radiation. As the arterial supply to the pancreas is complex, measuring single artery flow does not provide an accurate measure of perfusion. Furthermore, as some of the named branches supplying the arteries are secondary or tertiary branches of more major vessels, narrow arterial diameter precludes accurate radiological measurement. Arterial Spin Labelling (ASL) magnetic resonance imaging (MRI), on the other hand is a validated technique allowing accurate measurement of visceral perfusion. Transient physiological changes occur in pancreatic blood flow secondary to increased demands such as eating. Changes can also be induced pharmacologically using pancreatic stimulating agents, such as secretin. This naturally occuring peptide is produced within the S cells of the proximal small bowel mucosa. It causes an increase in bicarbonate secretion by the duct cells of the pancreas and biliary tract via an oxygen dependant cyclic AMP mediated pathway. Secretin has been used previously to assess alterations in blood flow and is used clinically in the assessment of sphincter of Oddi dysfunction in conjunction with magnetic resonance cholangiopancreatography. Aims and Hypothesis This pilot study aims to evaluate the MRI techniques of measuring pancreatic perfusion and blood flow at rest and during secretin stimulation in healthy volunteers, prior to an evaluation in the chronic pancreatitis patient group. Experimental protocol and methods Volunteers will be recruited from advertisements placed on designated University of Nottingham notice boards. All volunteers will complete a questionnaire of abdominal symptoms, Hospital anxiety and depression scale (HAD) and the patient health questionnaire 15 (PhQ15). Each volunteers will attend the 1.5T Brain and Body Imaging centre on the University of Nottingham Campus for all study evaluations. Following an overnight fast a baseline MRI scan will be undertaken. Volunteers will then receive 1 IU/kg of secretin (Sanochemia Pharmazeutika AG, Wien, Germany) via the intravenous route over 3 minutes. The volunteers will then be scanned again at 5, 10, 20, 30 and 40 min following the stimulus. MRI scanning will be carried out on the Philips 1.5T Achieva MRI scanner located in the Brain and Body Imaging Centre University of Nottingham. The volunteers will be placed supine in the scanner with a receiver body coil wrapped around the abdomen. All image analysis will be carried out using commercial and/or in house packages. Outcome measures at baseline and following secretin stimulation: 1. Pancreatic perfusion 2. Superior mesenteric artery blood flow 3. Gastroduodenal artery blood flow 4. Hepatic artery blood flow 5. Splenic artery blood flow