Secretin-Enhanced MRCP: Review of Technique and Application ...

Secretin-Enhanced MRCPables a more thorough evaluation of chronicpancreatitis and expands the horizon of thistest to other pancreatic abnormalities. Thisimproves on ERCP and EUS, which evaluateonly the morphologic changes. In this article,we will discuss the technique and indicationsof secretin-enhanced MRCP and present theresults of a study performed for the quantificationof pancreatic exocrine function withsecretin-enhanced MRCP in patients withsuspected chronic pancreatitis.Secretin-Enhanced MRCP: Technique,Applications, and QuantificationSecretinSecretin is a gastrointestinal peptide thatstimulates pancreatic duct epithelial cellsto produce a bicarbonate-rich fluid. Physiologicgastrointestinal actions of secretin includeinhibition of gastric acid secretion anddecreasing intestinal motility [5]. Productionof biologically derived porcine secretin,which was used for pancreatic stimulationtests, ceased in 1999. Synthetic forms ofboth porcine and human secretin (ChiRho-Stim, ChiRhoClin and SecreFlo, Repligen)are now available. All three forms—that is,biologic, synthetic porcine, and synthetic humansecretin—have been shown to be equivalentand can be used interchangeably [6].The adverse effects of secretin are mainlynausea, flushing, abdominal pain, and vomitingand can be seen in up to 5% of patients.Acute pancreatitis is listed as a contraindicationto secretin administration (package insert,ChiRhoClin). However, some institutions injectsecretin before resolution of acute episodeswithout reported major adverse effects [7, 8].Secretin-Enhanced MRCP TechniqueThe MRI protocol used for secretinenhancedMRCP, which is the functionalevaluation of the pancreas, can be performedalone or in combination with a standard pancreasprotocol. At our institution, patients referredfor their first secretin-enhanced MRCPwho have never had a pancreatic MR evaluationusually undergo an examination in whichthe standard pancreas protocol is combinedwith the secretin-enhanced MRCP protocolto evaluate both pancreatic morphology andfunction. In this article, we describe the sequencesused only for the secretin-enhancedMRCP portion of the protocol.Patient PreparationA superparamagnetic iron oxide–containingoral MR contrast agent (such as ferumox-Fig. 1—32-year-old woman imaged withoutadministration of oral ferumoxsil. MR image showspreexisting T2 bright natural duodenal secretions(arrows).sil, [Gastromark, Covidien]) is administeredorally before the examination. Two bottles,300 mL each, are administered 30 minutes andjust before the examination. This T2-shorteningnegative enteric contrast agent mixes withthe preexisting T2 bright gastric and duodenalfluid, essentially eliminating its T2 signal. T2bright pancreatic fluid subsequently secreted inresponse to secretin can be easily identified onthis T2 dark background (Figs. 1 and 2). Naturallyoccurring negative oral contrast can beobtained from blueberry and pineapple juicesand may be used as a lower cost alternative toferumoxsil for qualitative evaluation [9]. Thesejuices have a natural high manganese contentthat makes them paramagnetic and thereforedark on T2 imaging.SequencesSecretin-enhanced MRCP were performedusing 1.5-T systems at our institute. After obtainingscout images, axial and coronal T2-weighted HASTE images through the abdo-TABLE 1: Typical Sequence ParametersFig. 2—50-year-old woman imaged with oralferumoxsil administration. MR image shows T2 darkfluid (ferumoxsil) in stomach and duodenum (arrows).men are obtained. Table 1 contains typicalsecretin-enhanced MRCP parameters.An initial breath-hold thick oblique coronalfat-suppressed heavily T2-weighted long-TE HASTE image encompassing the pancreasand duodenum is acquired and assessedfor position. After an IV test dose of 0.2 μg ofhuman secretin (ChiRhoStim), 0.2 μg/kg ofthe same is administered over 1 minute withthe patient in the gantry and the breath-holdoblique coronal heavily T2-weighted fatsuppressedlong-TE HASTE sequence (thickslab MRCP sequence) is repeated every 30seconds for 10 minutes. A slice thickness of60 mm is used so that the entire pancreas andduodenum are included. When these 20 imagesare viewed sequentially, they provide adynamic assessment of pancreatic exocrinefunction in response to secretin (Fig. 3).At the end of the 10-minute dynamic assessment,another set of axial and coronal HASTEimages is obtained through the abdomen. Thisset of images allows estimation of the totalSequence HASTE Long TE HASTETR (ms) Infinite 3000Time between slice acquisition (ms) 1050 3000TE (ms) 72 972Matrix256 x 176 (axial)256 x 256256 x 256 (coronal)Slice thickness (mm) 4 60Acquisition 2D 2DFlip angle 180° 150°Slices Multislice Thick slabFOV (mm)350 x 240 (axial)200 x 200350 x 350 (coronal)Pixel bandwidth (Hz) 780 130AJR:198, January 2012 125