Coronal T2-weighted fast, thick-section section, spin-echo MR sequences with no post-processing are used allowing for repeated breath-holds for a dynamic series. These images allow for direct visualization of the pancreatic duct in a few seconds. A negative oral contrast agent, such as superparamagnetic nanoparticles suspensions (ferumoxil oral suspension, e.g Lumirem, GastroMARK) is given 10 minutes before dynamic imaging. The negative oral contrast suppresses gastrointestinal overlap and prevents confusion between pancreatic fluid outflow and possible gastric emptying, i.e. nulls the fluid signal in the stomach and duodenum. Our institution has been using pineapple juice as a negative oral contrast agent, given at a dose of 3 cups (approximately 500-600 cc) 5-10 minutes before the imaging study. Pineapple juice is very inexpensive, easily available, and well accepted by most patients. Compared to certain commercially available superparamagnetic oral contrast agents, pineapple juice offers a more subtle shortening of T2 by our observation, therefore avoiding the susceptibility artifacts associated with these standard superparamagnetic contrast agents. The mechanism of pineapple juice to shorten T2 is due to its relatively high manganese concentration. There have been reports to administer blueberry juice as oral contrast in the past for the same mechanism, however, we use pineapple juice because of its easy availability. Our institution does not give an antiperistaltic drug to eliminate motion artifact, since each image acquistion takes only 3 seconds and motion artifact is not a big issue.
Next, the patient is placed in supine position for imaging. A set of images is acquired before secretin stimulation to allow for optimal positioning of the imaged section. After administration of IV secretin (dose of 1 clinical unit per kilogram body weight or dose stated on the specific secretin brand insert), image acquisition of the optimal section is repeated every 30 seconds. This dynamic procedure is conducted for 10 minutes. The delay between ingestion of the oral contrast and the acquisition of the secretin dynamic images is less than 5 minutes. The overall study time is approximately 15 minutes. It is assumed that once the pancreatic fluid reaches the duodenum its signal is not dramatically suppressed by the negative oral contrast agent. In fact, the density of the negative oral contrast agents is different from the density of the pancreatic fluid, thus, the two liquid phases may coexist without mixing. The pancreatic outflow after secretin stimulation in healthy subjects is in the range of 2-5 mL per minute, presumably low enough to allow the two liquid phases to coexist without mixing. The extent of pancreatic fluid secretion is then classified using the above duodenal filling scoring system.
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