Note: This copy is for your personal, non-commercial use only To order presentation-ready copies for distribution to your colleagues or clients, use the RadioGraphics Reprints form at the end of this article EDUCATION EXHIBIT 1951 Pediatric MR Cholangiopancreatography: Principles, Technique, and Clinical Applications1 Online-Only CME See www.rsna org/education /rg_cme.html LEARNING OBJECTIVES After reading this article and taking the test, the reader will be able to: ■■Discuss the principles, imaging sequences, and clinical applications of MR cholangiopancreatography in children ■■List various factors affecting the quality of MR cholangiopancreatographic images ■■Describe potential challenges to obtaining good-quality MR cholangiopancreatographic images in children and ways to overcome them TEACHING POINTS See last page Govind B Chavhan, MD, DNB • Paul S Babyn, MD • David Manson, MD • Logi V idarsson, PhD High-quality magnetic resonance (MR) cholangiopancreatographic images are difficult to obtain in children due to the small caliber of the pediatric bile ducts and to motion artifacts However, there has been ongoing improvement in image quality, thanks to better coil technology, increased speed of acquisition, refinement in respiratory compensation techniques, and newer sequences Heavily T2-weighted fast spin-echo (FSE) and single-shot FSE MR imaging sequences with long echo times are used to image the biliary and pancreatic ducts Secretin has been shown to improve the visualization of the pancreatic duct and pancreaticobiliary junction Factors that affect image quality in pediatric MR cholangiopancreatography include sedation, negative oral contrast material, radiofrequency coil selection, respiratory compensation techniques, echo time, echo train length, section-slab thickness, planes of scanning, field of view, and number of signals acquired However, giving proper attention to these factors and tailoring the study to the body size of the patient (which varies considerably) can lead to high-quality diagnostic MR cholangiopancreatographic images Use of MR cholangiopancreatography in children is limited by the need for sedation or anesthesia, high cost, limited availability, and long scanning times Nonetheless, this modality can be a viable alternative to endoscopic retrograde cholangiopancreatography (ERCP) in the evaluation of various entities such as choledochal cyst, recurrent pancreatitis, primary sclerosing cholangitis, and a transplanted liver, and may obviate ERCP © RSNA, 2008 • radiographics.rsnajnls.org Abbreviations: CBD = common bile duct, ERCP = endoscopic retrograde cholangiopancreatography, ETL = echo train length, FSE = fast spinecho, MIP = maximum-intensity-projection, PBJ = pancreaticobiliary junction, PSC = primary sclerosing cholangitis, RF = radiofrequency, SNR = signal-to-noise ratio, TSE = turbo spin-echo, 2D = two-dimensional, 3D = three-dimensional RadioGraphics 2008; 28:1951–1962 • Published online 10.1148/rg.287085031 • Content Codes: From the Department of Diagnostic Imaging, The Hospital For Sick Children and University of Toronto, 555 University Ave, Toronto, ON, Canada M5G 1X8 Presented as an education exhibit at the 2007 RSNA Annual Meeting Received February 19, 2008; revision requested March 18 and received March 31; accepted April All authors have no financial relationships to disclose Address correspondence to G.B.C (e-mail: drgovindchavhan@yahoo.com) © RSNA, 2008 1952 November-December 2008 Introduction Magnetic resonance (MR) cholangiopancreatography can be an effective, noninvasive imaging tool for the evaluation of pancreaticobiliary disease in children (1–5) Its diagnostic accuracy is reported to exceed 90% compared with direct cholangiopancreatography in conditions such as choledocholithiasis, absent gallbladder, and pancreas divisum (2) and to approach 100% in conditions such as choledochal cyst (4,6) However, it is challenging to perform a good-quality MR cholangiopancreatographic examination in children, especially very young children Pediatric MR cholangiopancreatography is limited by small-caliber ducts, poor signal, and patient motion, which creates artifacts Nonetheless, it is possible to visualize ducts as small as mm in diameter, thanks to improvements in coil technology, increased speed of acquisition, refinements in respiratory compensation techniques that reduce motion artifacts, and newer sequences (7,8) In a large series of 85 pediatric MR cholangiographic studies performed in 78 patients (mean age, 10.3 years), excellent image quality was seen in 85% of cases (1) With the continuous improvement in image quality, more and more studies on MR cholangiopancreatography in children are appearing in the literature (1–6) In this article, we review the basic principles of MR cholangiopancreatography and the types of imaging sequences used In addition, we discuss and illustrate various factors affecting MR cholangiopancreatographic image quality, with emphasis on potential challenges and ways to overcome them We also discuss the current clinical applications of pediatric MR cholangiopancreatography Principles of MR Cholangiopancreatography Teaching Point At MR cholangiopancreatography, the bile within the biliary tree is imaged with heavily T2weighted sequences The sequences are heavily T2 weighted with use of long echo times in the range of 300–1000 msec, such that only tissues or fluid with prolonged transverse relaxation time (T2) retain signal These tissues and fluid are seen as hyperintense structures The background soft tissues with shorter T2 not retain significant signal long enough in a sequence with prolonged echo time and are, therefore, suppressed Blood vessels are not seen, since flowing blood does not produce any signal on these images RG ■ Volume 28 • Number Types of Sequences Used Fast Spin-Echo (Turbo Spin-Echo) Sequence With the fast spin-echo (FSE) (turbo spin-echo [TSE]) sequence, a 90° radiofrequency (RF) pulse is followed by a train of 180° RF pulses The number of 180° pulses is called the echo train length (ETL) or turbo factor The speed of acquisition increases with an increase in ETL For the purposes of MR cholangiopancreatography, FSE imaging is performed with a long ETL, repetition time, and echo time (>250 msec) (7) A long ETL is well suited for the type of longecho-time acquisition required for MR cholangiopancreatography FSE imaging can be performed with a breath hold or with free breathing with use of respiratory gating or a navigator technique It can be performed as a two-dimensional (2D) sequence with a slab thickness of 2–7 cm or as a three-dimensional (3D) sequence with thinner sections The resultant data can then be reconstructed into cholangiographic images with a maximum-intensity-projection (MIP) technique Fast recovery FSE (FRFSE; GE Medical Systems, Waukesha, Wis), RESTORE (Siemens Medical Solutions, Forchheim, Germany), and driven equilibrium FSE (DRIVE; Philips Medical Systems, Best, the Netherlands) sequences are modified FSE sequences in which a 90° RF pulse is used at the end of the ETL to get the magnetization immediately in longitudinal plane, thereby reducing repetition time Single-Shot FSE (TSE) Sequence Single-shot FSE (SSFSE, GE Medical Systems), half-Fourier single-shot TSE (HASTE, Siemens), and single-shot TSE (SSTSE, Philips) sequences are FSE sequences in which just more than onehalf of k-space is filled, thus reducing scanning time significantly All of the required k-space lines (phase-encoding steps) are filled in a single repetition time; hence the name “single-shot.” Acquisition times are in seconds, with reasonably good spatial resolution (9) SSFSE imaging has a higher signal-to-noise ratio (SNR) than does FSE imaging as a result of less motion artifact producing noise (7) Limitations of SSFSE imaging Teaching Point RG ■ Volume 28 • Number include image blur induced by long ETLs, flow artifacts, and problems with saturation of adjacent sections (9) Echo times typically range between 300 and 1000 msec These sequences can be performed with a breath hold or with respiratory triggering, and good-quality images can be obtained, even with quiet breathing Other Sequences Fast gradient-echo sequences such as balanced fully refocused steady-state sequences (true fast imaging with steady-state precession, fast imaging employing steady-state acquisition, balanced fast field echo) show the biliary tree well, with excellent SNR and good spatial resolution These sequences can be performed with a breath hold or with quiet breathing and may show ducts reasonably well when other sequences fail to so because of motion artifacts One limitation, however, is the fact that blood vessels are seen as bright structures, which may make it difficult to differentiate them from bile ducts Contrast Material–enhanced Functional Evaluation.—Three-dimensional fast gradient-echo T1-weighted sequences such as fast low-angle shot (FLASH, Siemens) and spoiled gradient-echo (SPGR, GE Medical Systems) sequences can be performed after the intravenous injection of a contrast agent such as mangafodipir trisodium (Teslascan; Nycomed Amersham, Princeton, NJ) that is excreted via the biliary system This technique offers a few additional advantages, including assessment of biliary function, less problematic background suppression of ascites and bowel fluid, and identification of potential biliary leaks (9) Mangafodipir trisodium has been used in neonates to study biliary atresia (10) Secretin MR Cholangiopancreatography.— Secretin is a polypeptide hormone secreted by duodenal mucosa in response to acid stimulation It increases the pancreatic secretion of water and bicarbonate, improves the tone of the sphincter of Oddi, and increases the amount of fluid in the duodenum (1) Thus, the normal response to secretin administration is increased fluid signal in the pancreatic duct and subsequent fluid excretion into the duodenum Secretin is administered intravenously in a dose of unit per kilogram Chavhan et al 1953 of body weight slowly over minute (11,12) It has been used in children in doses of 0.2 µg per kilogram of body weight (maximum dose, 16 µg) injected intravenously slowly over minute (1) Images obtained with fast T2-weighted sequences, usually constituting a coronal slab along the pancreatic duct, are acquired every 30 seconds for 10 minutes Normal response includes increased signal and an increase in the diameter of the pancreatic duct to as much as mm that peaks 3–5 minutes after secretin injection, followed by a progressive return to the baseline diameter within 10 minutes (11,12) Persistent dilatation of the pancreatic duct after 10 minutes is considered an abnormal response and can be seen in stricture, sphincter of Oddi dysfunction, or papillary stenosis (13) Secretin has been shown to improve visualization of the pancreatic duct and its junction with the common bile duct (CBD) (1,2,12) It also improves the sensitivity of MR cholangiopancreatography in diagnosing early-onset idiopathic chronic pancreatitis (11) A major disadvantage of secretin MR cholangiopancreatography is the high cost of secretin Problems in Obtaining MR Cholangiopancreatograms The smaller duct caliber in children makes it difficult to visualize nondilated ducts at MR cholangiopancreatography, especially when evaluating intrahepatic duct caliber Lack of signal, along with reduced spatial resolution, can make the visualization of ducts more difficult Image quality is often poor because of motion and breathing artifacts Even with respiratory triggering, image quality can be poor, since it is difficult to achieve respiratory cycles with a regular rhythm and adequate amplitude in infants and small children The need for sedation or general anesthesia is another major drawback of pediatric MR cholangiopancreatography Factors Affecting MR Cholangiopancreatographic Image Quality Sedation We sedate most neonates, infants, and young children Children under months of age are sedated with oral chloral hydrate (50–100 mg 1954 November-December 2008 RG ■ Volume 28 • Number per kilogram of body weight) Children between months and years of age are usually sedated with the intravenous injection of midazolam (Versed; Hoffman–La Roche, Basel, Switzerland) (0.05 mg per kilogram of body weight) or pentobarbital (Nembutal; Ovation Pharmaceuticals, Deerfield, Ill) (5 mg per kilogram of body weight) Most children over 6–8 years of age can cooperate sufficiently without sedation Negative Oral Contrast Material Negative oral contrast material can be used in nonsedated children to reduce the high signal of gastric secretion and intestinal fluid Its use has been shown to improve image quality without causing any significant adverse reactions (1,6,11) Ferumoxsil and ferric ammonium citrate are two commonly used negative oral contrast agents Ferumoxsil consists of superparamagnetic iron oxide particles and is administered as 150–300 mL of oral suspension (1,11) Ferric ammonium citrate, a T2-negative contrast agent, is mixed with water (1 g/10 mL) and administered orally (1 mL per kilogram of body weight) (6) Oral negative contrast agent is given just before the examination, when the patient is placed on the table RF Coil Selection The smallest coil that fits the pediatric patient being imaged should be selected as the receiver coil Smaller coils permit use of smaller fields of view and offer better resolution The noise detected with the coil increases with coil size Infants and neonates can be imaged in a quadrature knee coil, a head coil, or even flexible surface coils Older children are usually imaged with torso phased-array coils The body coil is used only for transmission; its use as a receiver coil should be avoided if possible because signal quality is poor Respiratory Compensation Techniques MR cholangiopancreatographic sequences performed with a breath hold provide the bestquality images However, not all patients can hold their breath, especially younger children, infants, and neonates Moreover, breath-hold technique limits the number of signals that can be acquired Figure 1. Respiratory triggering methods (a) Drawing illustrates how a respiratory tracing is obtained by tying a bellows over the chest Images are acquired in a designated phase of respiration with each respiratory cycle (b) Image illustrates the navigator technique, in which the position of the diaphragm is detected with a navigator pulse, and signal acquisition is prospectively or retrospectively gated to the most stable portion of the respiratory cycle Box and arrow indicate the position of the navigator where the navigator pulse will hit and the phase-encoding steps that can be used Both of these factors improve image quality but at the cost of increased scanning time Respiratory triggering can be performed in two ways In the first method, respiratory tracings are obtained by tying a bellows around the chest, and images are acquired in a designated phase of respiration with each respiratory cycle (Fig 1) The second method of respiratory triggering is the navigator technique With this technique, the position of the diaphragm is detected with a navigator pulse, and signal acquisition is prospectively or retrospectively gated to the most stable portion of the respiratory cycle, typically end expiration (Fig 1b) (9) Acquisition time with respiratory gating is typically 3–7 minutes but may last for more than 10 minutes if breathing is not regular Section misregistration due to irregular breathing can also occur with some respiratory gating techniques RG ■ Volume 28 • Number Chavhan et al 1955 Figure 2. Effect of changes in echo time Coronal FSE T2-weighted MR images of the biliary tree obtained with echo times of 180 (a), 400 (b), 600 (c), and 1100 (d) msec (a, b, and d obtained in the same patient) show how background tissue suppression increases as echo time increases Arrow indicates the CBD Echo Time Echo time is an important parameter in MR cholangiopancreatographic sequences As echo time increases, background tissue suppression increases, improving visualization of the bile ducts Higher echo times above 1000 msec reduce overall signal and may complicate the visualization of small ducts containing only small amounts of bile in the pediatric population (Fig 2) Hence, the echo time used in these patients should be moderate The use of a wide range of echo times (180–1000 msec) for pediatric MR cholangiopancreatography has been reported in the literature (1,6,11,14–19) In our experience, an echo time of 300–600 msec provides a good balance between signal in the ducts and tissue suppression Echo Train Length ETL is the number of 180° RF pulses sent after a 90° pulse in a single repetition time in FSE sequences As ETL increases, scanning time is reduced; however, image blurring also increases Moderate ETL in the range of 16–20 should be used, especially with respiratory-gated FSE T2weighted sequences that are not constrained by 1956 November-December 2008 RG ■ Volume 28 • Number Figure 3. Effect of changes in section-slab thickness Coronal SSFSE (GE Medical Systems) images obtained with an echo time of 400 msec and section-slab thicknesses of (a), 20 (b), and 50 (c) mm show how tissue overlap increases as section thickness increases Arrow indicates the CBD GB = gallbladder breath-hold time With single-shot sequences, ETL usually equals the number of k-space lines to be filled Section-Slab Thickness Sections obtained with 3D FSE sequences should be as thin as possible without any gap In fact, an overlap of sections is preferable With 2D FSE and single-shot sequences, thin sections in the range of 3–5 mm as well as slabs ranging from to cm in thickness are acquired Slab thickness should be tailored to the size of the child such that a maximum volume of the biliary tree is obtained without significant overlap by other structures (Fig 3) For infants and neonates, a slab thickness less than cm is usually sufficient Thin sections are used for smaller filling defects in ducts and provide better spatial resolution However, thinner sections also have a lower SNR Planes of Scanning Three-dimensional FSE sequences are usually performed in the coronal plane MIP reformatted images can then be obtained in any plane Two-dimensional FSE and SSFSE thin-section images are typically acquired in the axial and coronal planes For evaluation of tiny calculi or ductal filling defects, the axial plane is preferred Slabs with a 2–7-cm thickness can be acquired in straight coronal or axial planes or in a radiating fashion in coronal oblique planes Coronal oblique sections are acquired at the porta hepatis and radiating from a point anterior to the portal vein bifurcation (Fig 4a) (7) Straight coronal and initial left posterior oblique images more clearly depict the anteriorly located common hepatic duct, left hepatic duct, and proximal pancreatic duct, whereas the more posteriorly located CBD, right hepatic ducts, and distal pancreatic duct including the ampulla are seen on left posterior oblique images obtained at a steeper angle (7) Most of the pancreatic duct may be visualized in an axial oblique plane (Fig 4b) Segmental liver transplants are better evaluated in sagittal oblique planes, since the “neo” porta hepatis is oriented in a more anteroposterior direction (19) Other Parameters The field of view should be adjusted to the size of the child A field of view that is too small, together with a large matrix, may make images grainy and reduces SNR A 256 × 256 matrix is RG ■ Volume 28 • Number Chavhan et al 1957 Figure 4. Planes of scanning (a) Axial FRFSE (GE Medical Systems) image shows coronal oblique planes radiating from a point anterior to the portal vein bifurcation (b) Axial oblique SSFSE image shows nearly the entire normal pancreatic duct (small arrows) and a prominent CBD (large arrow) Optimization of Pediatric MR Cholangiopancreatography Figure 5. MIP image from 3D FSE imaging data shows a normal CBD (long arrow) and part of the pancreatic duct (short arrow) Note the improved spatial resolution and SNR of the image typically used, with a pixel size ranging between and 1.5 mm2 An increased number of signals averaged (about four to six) can be used in pediatric MR imaging to improve the signal Pediatric MR cholangiopancreatography needs to be tailored to the different body sizes intrinsic to children of various ages For visualization of smaller-caliber ducts, spatial resolution and SNR need to be improved The first step toward such improvement is proper coil selection Either a phased-array or a surface coil that fits the child well should be used for signal reception Poor signal in children can be compensated for to some extent by increasing the number of signals averaged to between four and eight However, this needs to be balanced with the ETL, since increasing the number of signals averaged increases scanning time Proper slab thickness in 2D FSE and SSFSE imaging is the next step toward obtaining optimal-quality images Smaller children such as neonates and infants not need a slab thickness of more than cm Thin-section (3–5mm) images in the axial and coronal planes, as well as thick slabs in radiating coronal planes, should be acquired A 3D FSE sequence should be performed whenever breathing is regular It provides better SNR and spatial resolution than does 2D FSE imaging (Fig 5) Moreover, anomalies can be better understood by rotating 3D images Because neonates and infants usually have irregular breathing with varying respiratory amplitude, 3D FSE imaging with respiratory triggering may not be possible in many of these patients (16) SSFSE imaging with varying section thickness can be useful in this situation, providing adequate image quality even with free shallow breathing Alternatively, balanced steady-state free precession, with its excellent SNR, insensitivity to motion, and speed of acquisition, can be Teaching Point Teaching Point 1958 November-December 2008 used as a problem-solving sequence A 3-T imager provides superior-quality MR cholangiopancreatographic images because it has double the SNR of a 1.5-T imager Clinical Applications In spite of its capacity to provide anatomic and pathologic details of the biliary tree, MR cholangiopancreatography is not widely used because of the ready availability of other modalities such as ultrasonography (US) and scintigraphy, as well as the frequent need for sedation, high cost, limited availability, and time required for scanning With recent improvements in image quality and resolution, however, MR cholangiopancreatography is increasingly being used and has become a viable alternative to endoscopic retrograde cholangiopancreatography (ERCP) and percutaneous transhepatic cholangiography for diagnostic purposes As mentioned earlier, in a series of 85 pediatric MR cholangiographic studies performed in 78 patients, excellent image quality was seen in 85% of cases (1) Concordance with ERCP findings was seen in 81% of cases, with additional findings that could not have been visualized with ERCP alone seen in 35 of 85 studies (1) These findings included hepatosplenomegaly, hepatic tumors, pancreatic masses, varices, adrenal hemorrhage, multicystic dysplastic kidney, and omental and mesenteric metastases MR cholangiopancreatography should be considered before ERCP and percutaneous transhepatic cholangiography In the following sections, we discuss a variety of applications of MR cholangiopancreatography in children Biliary Atresia The extrahepatic bile ducts are almost always visualized at MR cholangiopancreatography Biliary atresia can be ruled out if the entire extrahepatic bile duct is seen (16) In a study of 26 infants (mean age, months), MR cholangiography was shown to be 82% accurate, 90% sensitive, and 77% specific for depicting extrahepatic biliary atresia (20) However, MR cholangiopancreatography faces strong competition from (a) scintigraphy, which has excellent sensitivity (96%–97%) in differentiating biliary atresia from neonatal hepatitis (21), and (b) US, in which constant improvements are being made A constellation of various signs at US have been found to be highly accurate (98%) in the detection of biliary atresia (22) MR cholangiopancre- RG ■ Volume 28 • Number atography is not routinely used in biliary atresia due to its high cost and the need for sedation Choledochal Cyst Choledochal cysts represent common congenital abnormalities that may be associated with complications such as infection, obstruction, and development of malignancy Therefore, complete cyst excision without compromising the pancreatic duct and common pancreaticobiliary channel should be performed as soon as the diagnosis is made to reduce the risk of malignancy later in life (4,23) The diagnosis of choledochal cyst is usually made with US However, information about the type of cyst, the length of the involved duct, the presence and location of protein plugs or calculi, the pancreaticobiliary junction (PBJ), and the length of the common channel is required for preoperative planning ERCP has traditionally been used to obtain this information However, MR cholangiopancreatography has been shown to be 100% accurate in the evaluation of choledochal cyst (Fig 6) (2,4,6) Evaluation of the PBJ Abnormal union of the PBJ with a long common channel has been implicated as the cause of choledochal cyst formation and as one of the causes of pancreatitis in children (5,6) It has been hypothesized that abnormal union of the PBJ outside the duodenal wall and the sphincter of Oddi allows the reflux of pancreatic exocrine enzymes into the biliary duct, causing cholangitis and increased pressure leading to dilatation of the bile ducts Conversely, reflux of bile into the pancreatic duct can cause pancreatitis (6,24) Reports vary with respect to the detection rate of abnormal union of the PBJ at MR cholangiopancreatography, which ranges from 40% to 83% (6) It is difficult to visualize abnormal union of the PBJ in children under years of age and in those with a large choledochal cyst, especially with cystic dilatation overlapping the PBJ (6,25) Secretin MR cholangiopancreatography has been shown to improve the visualization of abnormal union of the PBJ (1,2,4) A common pancreaticobiliary channel more than 15 mm in length is considered abnormal in adults (24) To our knowledge, however, there are no data on the normal length of the common channel in children (Fig 7a) The mean length of the common channel increases with age (6) A length of mm was used as the upper limit of “normal” for the common channel in pediatric studies by Fitoz et al (4) and Kim et al (25) (Fig 7b) Teaching Point RG ■ Volume 28 • Number Chavhan et al 1959 Figure 6. Type IV choledochal cyst in a 13-year-old girl MIP image from 3D FSE imaging data (a) and coronal fast imaging employing steady-state acquisition image (b) show a large cystic structure representing a grossly dilated CBD Moderate dilatation of the intrahepatic ducts is also seen, along with downward displacement of the pancreatic duct (arrowheads in a) Figure 7. (a) Normal union of the PBJ in a 9-year-old child Coronal thick-slab SSFSE image shows normal union of the PBJ (arrowhead) The common hepatic duct is mildly dilated dd = duodenum, PD = pancreatic duct (b) Abnormal union of the PBJ in an 11-year-old boy with a choledochal cyst Coronal short inversion time inversion-recovery image shows a dilated CBD (curved arrow) containing multiple calculi A long common pancreaticobiliary channel (arrowhead) inferior to the junction of the CBD and the pancreatic duct (straight arrow) is also seen Recurrent Pancreatitis Common causes of pancreatitis in children include trauma, structural pancreaticobiliary anomalies, systemic diseases, infection, and drugs; however, recurrent pancreatitis may be idiopathic (26) Common structural anomalies causing pancreatitis include choledochal cyst, abnormal union of the PBJ, and pancreas divisum MR cholangiopancreatography is useful for noninvasively identifying these structural anomalies and ruling them out as a cause of pancreatitis (5,24,27) It can be performed in 1960 November-December 2008 RG ■ Volume 28 • Number Figure 8. Pancreas divisum in a 9-year-old girl Coronal SSFSE images show that the CBD is opening at the major papilla (arrow in a) and the pancreatic duct draining the body is opening at the minor papilla (arrowhead in b) The pancreatic duct normally joins the CBD and opens at the major papilla dd = duodenum the acute stage of pancreatitis—unlike ERCP, which is contraindicated in the acute stage MR cholangiopancreatography is highly sensitive and specific for pancreas divisum (Fig 8) (24) It is difficult to visualize pancreatic ducts and anomalies such as pancreas divisum and (as mentioned earlier) anomalous union of the PBJ in children less than years of age (6) It has been reported that the pancreatic duct is visible at MR cholangiopancreatography in 45%–60% of cases (4) Again, secretin has been shown to improve visualization of the pancreatic duct and its junction with the CBD (1,2,12) Secretin also improves the sensitivity of MR cholangiopancreatography in diagnosing early-onset idiopathic chronic pancreatitis (11) and pancreas divisum (12) Primary Sclerosing Cholangitis Primary sclerosing cholangitis (PSC) is an idiopathic condition characterized by obliterative fibrosis and inflammation of the bile ducts It is most commonly seen in patients with inflammatory bowel disease such as ulcerative colitis PSC is being recognized with increasing frequency in children ERCP is the standard of reference for establishing the diagnosis, since pathologic changes are nonspecific In a study by Ferrara et al (28), MR cholangiopancreatography was found to have a specificity and positive predictive value of 100% and an accuracy of 85% The authors of that study concluded that positive MR cholangiopancreatographic findings in a child with clinical suspicion for PSC are very likely to be correct; hence, ERCP should not be performed Figure 9. PSC in a 14-year-old boy Coronal MIP image from 3D FSE T2-weighted imaging data shows dilated extra- and intrahepatic ducts with multiple strictures, outpouchings, and peripheral cystic dilatations The cystic duct (long arrow) is also dilated and irregular and joins the bile duct (short arrows) at a point inferior to the normal point of juncture The pancreatic duct (arrowheads) is normal in such cases Cholangiographic findings of PSC include irregularity of the bile duct wall; areas of mild dilatation, with intermittent strictures giving the bile ducts a “beaded” appearance; formation of sacculations and pseudodiverticuli; and nonvisualization of the intrahepatic ducts (Fig 9) (29) Other Conditions Affecting the Liver and Pancreas MR cholangiopancreatography can be useful in the evaluation of pathologic conditions such as RG ■ Volume 28 • Number Chavhan et al 1961 Figure 10. Biliary system involvement in an 8-year-old child with Langerhans cell histiocytosis (a, b) Axial FSE T2-weighted images of the liver show dilated and irregular bile ducts in the left lobe (arrows) The round filling defects (arrowheads in b) represent calculi (c) Axial contrast-enhanced T1-weighted image shows irregular wall thickening and enhancement of the bile ducts (arrows) (d) Percutaneous transhepatic cholangiogram shows sclerosing cholangitis–like changes reflecting involvement of the biliary tree by Langerhans cell histiocytosis, findings that correlate well with those in a–c Langerhans cell histiocytosis is one of the causes of secondary sclerosing cholangitis Caroli disease that demonstrate cystic dilatation of the intrahepatic bile ducts In autosomal recessive polycystic kidney disease, MR cholangiopancreatography can help confirm nonobstructive dilatation of the intrahepatic bile ducts Biliary tree involvement in Langerhans cell histiocytosis can also be evaluated with MR cholangiopancreatography (Fig 10) In addition, MR cholangiopancreatography may show or help rule out communication of any cystic lesion with bile ducts or the pancreatic duct Evaluation of a Transplanted Liver MR cholangiopancreatography has been found useful in delineating the anatomic and morpho- logic features of bile ducts in a transplanted liver (15) It is also useful in diagnosing strictures of the biliary-enteric anastomosis or of central ducts (19) A normal MR cholangiopancreatographic image may obviate percutaneous transhepatic cholangiography (19) Summary There has been constant improvement in the quality of pediatric MR cholangiopancreatographic images This improvement is reflected in the increasing use of MR cholangiopancreatography in children Diagnostic-quality MR 1962 November-December 2008 cholangiopancreatographic images can be obtained in children of any age if proper attention is paid to imaging technique The factors affecting image quality include sedation, RF coil selection, respiratory compensation techniques, echo time, ETL, planes of scanning, sectionslab thickness, and number of signals acquired Current clinical applications of MR cholangiopancreatography in children include evaluation of choledochal cyst, recurrent pancreatitis, abnormal junction of the PBJ, PSC, and biliary disease in a transplanted liver References Delaney L, Applegate KE, Karmazyn B, Akisik MF, Jennings SG MR cholangiopancreatography in children: feasibility, safety, and initial experience Pediatr Radiol 2008;38:64–75 Tipnis NA, Dua KS, Werlin SL A retrospective assessment of magnetic resonance cholangiopancreatography in children J Pediatr Gastroenterol Nutr 2008;46:59–64 Tipnis NA, Werlin SL The use of magnetic resonance cholangiopancreatography in children Curr Gastroenterol Rep 2007;9:225–229 Fitoz S, Erden A, Boruban S Magnetic resonance cholangiopancreatography of biliary system abnormalities in children Clin Imaging 2007;31:93–101 Shimizu T, Suzuki R, Yamashiro Y, Segawa O, Yamataka A, Kuwatsuru R Magnetic resonance cholangiopancreatography in assessing the cause of acute pancreatitis in children Pancreas 2001;22:196–199 Suzuki M, Shimizu T, Kudo T, et al Usefulness of non-breath-hold single-shot magnetic resonance cholangiopancreatography for the evaluation of choledochal cyst in children J Pediatr Gastroenterol Nutr 2006;42:539–544 Vitellas KM, Keogan MT, Spritzer CE, Nelson RC MR cholangiography of bile and pancreatic duct abnormalities with emphasis on single-shot FSE technique RadioGraphics 2000;20: 939–957 Fulcher AS, Turner MA, Capps GW MR cholangiography: technical advances and clinical applications RadioGraphics 1999;19:25–41 Glockner JF Hepatobiliary MRI: current concepts and controversies J Magn Reson Imaging 2007;25:681–695 10 Ryeom HK, Choe BH, Kim JY, et al Biliary atresia: feasibility of mangafodipir trisodium–enhanced MR cholangiography for evaluation Radiology 2005;235:250–258 11 Manfredi R, Lucidi V, Gui B, et al Idiopathic chronic pancreatitis in children: MR cholangiopancreatography after secretin administration Radiology 2002; 224:675–682 12 Matos C, Metens T, Deviere J, Delhaye M, Le Moine O, Cremer M Pancreas divisum: evaluation RG ■ Volume 28 • Number with secretin-enhanced magnetic resonance cholangiopancreatography Gastrointest Endosc 2001;53:728–733 13 Matos C, Metens T, Deviere J, et al Pancreatic duct: morphologic and functional evaluation with dynamic MR pancreatography after secretin stimulation Radiology 1997;203:435–441 14 Norton KI, Glass RB, Kogan D, Emre S, Schwartz M, Shneider BL MR cholangiography in children and young adults with biliary disease AJR Am J Roentgenol 1999;172:1239–1244 15 Laor T, Hoffer FA, Vacanti JP, Jonas MM MR cholangiography in children after liver transplantation from living related donors AJR Am J Roentgenol 1998;170:683–687 16 Guibaud L, Lachaud A, Touraine R, et al MR cholangiography in neonates and infants: feasibility and preliminary applications AJR Am J Roentgenol 1998;170:27–31 17 Chan YL, Yeung CK, Lam WW, Fok T, Metreweli C MR cholangiography: feasibility and application in the pediatric population Pediatr Radiol 1998; 28:307–311 18 Schaefer JF, Kirschner H, Lichy M, et al Highly resolved free-breathing MRCP in the diagnostic workup of pancreaticobiliary diseases in infants and young children: initial experiences J Pediatr Surg 2006;41:1645–1651 19 Arcement CM, Meza MP, Arumanla S, Towbin RB MRCP in the evaluation of pancreaticobiliary diseases in children Pediatr Radiol 2001;31:92–97 20 Norton KI, Glass RB, Kogan D, Lee JS, Emre S, Shneider BL MR cholangiography in the evaluation of neonatal cholestasis: initial results Radiology 2002;222:687–691 21 Nadel HR Hepatobiliary scintigraphy in children Semin Nucl Med 1996;26:25–42 22 Humphrey TM, Stringer MD Biliary atresia: US diagnosis Radiology 2007;244:845–851 23 Watanabe Y, Toki A, Todani T Bile duct cancer development after cyst excision for choledochal cyst J Hepatobiliary Pancreat Surg 1999;6:207–212 24 Mortele KJ, Rocha TC, Streeter JL, Taylor AJ Multimodality imaging of pancreatic and biliary congenital anomalies RadioGraphics 2006;26: 715–731 25 Kim MJ, Han SJ, Yoon CS, et al Using MRCP to reveal anomalous pancreaticobiliary ductal union in infants and children with choledochal cyst AJR Am J Roentgenol 2002;179:209–214 26 Benifla M, Weizman Z Acute pancreatitis in childhood: analysis of literature data J Clin Gastroenterol 2003;37:169–172 27 Hirohashi S, Hirohashi R, Uchida H, et al Pancreatitis: evaluation with MR cholangiopancreatography in children Radiology 1997;203:411–415 28 Ferrara C, Valeri G, Salvolini L, Giovagnoni A Magnetic resonance cholangiopancreatography in primary sclerosing cholangitis in children Pediatr Radiol 2002;32:413–417 29 Majoie CB, Reeders SW, Sanders JB, Huibregtse K, Jansen PL Primary sclerosing cholangitis: a modified classification of cholangiographic findings AJR Am J Roentgenol 1991;157:495–497 This article meets the criteria for 1.0 AMA PRA Category Credit TM To obtain credit, see www.rsna.org/education /rg_cme.html RG Volume 28 • Volume • November-December 2008 Chavhan et al Pediatric MR Cholangiopancreatography: Principles, Technique, and Clinical Applications Govind B Chavhan, MD, DNB, et al RadioGraphics 2008; 28:1951–1962 • Published online 10.1148/rg.287085031 • Content Codes: Page 1952 At MR cholangiopancreatography, the bile within the biliary tree is imaged with heavily T2-weighted sequences The sequences are heavily T2 weighted with use of long echo times in the range of 300-1000 msec, such that only tissues or fluid with prolonged transverse relaxation time (T2) retain signal These tissues and fluid are seen as hyperintense structures The background soft tissues with shorter T2 not retain significant signal long enough in a sequence with prolonged echo time and are, therefore, suppressed Blood vessels are not seen, since flowing blood does not produce any signal on these images Page 1952 Single-shot FSE (SSFSE, GE Medical Systems), half-Fourier single-shot TSE (HASTE, Siemens), and single-shot TSE (SSTSE, Philips) sequences are FSE sequences in which just more than one-half of k-space is filled, thus reducing scanning time significantly All of the required k-space lines (phaseencoding steps) are filled in a single repetition time; hence the name "single-shot." Acquisition times are in seconds, with reasonably good spatial resolution (9) Page 1957 Pediatric MR cholangiopancreatography needs to be tailored to the different body sizes intrinsic to children of various ages For visualization of smaller-caliber ducts, spatial resolution and SNR need to be improved The first step toward such improvement is proper coil selection Either a phased-array or a surface coil that fits the child well should be used for signal reception Poor signal in children can be compensated for to some extent by increasing the number of signals averaged to between four and eight However, this needs to be balanced with the ETL, since increasing the number of signals averaged increases scanning time Page 1957 A 3D FSE sequence should be performed whenever breathing is regular It provides better SNR and spatial resolution than does 2D FSE imaging (Fig 5) Moreover, anomalies can be better understood by rotating 3D images Because neonates and infants usually have irregular breathing with varying respiratory amplitude, 3D FSE imaging with respiratory triggering may not be possible in many of these patients (16) Page 1958 Abnormal union of the PBJ with a long common channel has been implicated as the cause of choledochal cyst formation and as one of the causes of pancreatitis in children (5,6) It has been hypothesized that abnormal union of the PBJ outside the duodenal wall and the sphincter of Oddi allows the reflux of pancreatic exocrine enzymes into the biliary duct, causing cholangitis and increased pressure leading to dilatation of the bile ducts Conversely, reflux of bile into the pancreatic duct can cause pancreatitis (6,24) RadioGraphics 2008 This is your reprint order form or pro forma invoice (Please keep a copy of this document for your records.) 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