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Commentary |
1 Department of Radiology, Boston University Medical Center, 88 E Newton St., H-2, Boston, MA 02118.
Received December 21, 2006; accepted after revision December 29, 2006.
Each month the American Journal of Roentgenology will republish
online one of the 100 most-cited articles from its first century. A
corresponding commentary in the print journal by a contemporary radiologist
will provide a current perspective. For a full list of these articles, see
page 3 of the January
2006 issue of the AJR or go to
www.ajronline.org.
Centennial article series Guest Editor: Liem T. Bui-Mansfield, ARRS Figley
Fellow 2004.
Keywords: biliary system • cholangiopancreatography • HASTE • MRCP • MR technique • pancreaticobiliary imaging
Imaging of the biliary tract and the pancreatic duct system has traditionally been a topic of considerable interest for radiologists, who have always been at the forefront of multidisciplinary groups that concentrate on the diagnosis and therapy of pancreaticobiliary diseases. It is therefore not surprising that MR cholangiopancreatography (MRCP) is the subject of one of the articles that has made it to the elite group of most often cited articles published in the American Journal of Roentgenology (AJR) during its first century.
The historical importance of the development of MRCP in the early 1990s and its later establishment as the definitive noninvasive imaging test for the biliary and pancreatic ducts cannot be overemphasized. By the mid to late 1980s, sonography had essentially replaced oral cholecystography for detecting gallstones and other gallbladder diseases and gastroenterology endoscopists had gained ownership of direct imaging of the biliary and pancreatic ducts. IV cholangiography had, for the most part, been abandoned as a diagnostic technique. Despite the invasiveness and known risks associated with ERCP [1], this procedure was favored over the percutaneous transhepatic approach in most practices. MRCP arrived at the right time to fill this gap and soon thereafter reestablished the critical role of radiologists in guiding the evaluation and therapy of patients with biliary disorders.
The article by Miyazaki et al. [2], published in 1996, was not the first description of MRCP. Several groups reported on the value of imaging the biliary and pancreatic ducts using T2-weighted, fluid-sensitive sequences (in which relatively static fluids with high water content appear bright), between 1991 and 1993 [3–8]. Other groups followed soon thereafter, capitalizing on the rapid and continuous improvements in MR equipment and software applications. Studies providing evidence about the clinical applications of MRCP for imaging the bile ducts [9–12] and pancreatic ducts [13, 14] flourished. Although these studies varied considerably in the specific pulse sequences and receiver coils used, the images included in the publications and presented at national and international meetings by various groups of researchers left little doubt that MRCP would eventually compete with ERCP for supremacy in biliary tract imaging. The advantages of MRCP were obvious from the beginning: the test is noninvasive and virtually risk-free provided that contraindications to MR scanning are avoided, the procedure can be concluded successfully in most patients, complex biliary and pancreatic ductal anatomy is depicted with exquisite detail, and the images are relatively easy to interpret by radiologists and nonradiologists alike.
What was unique about the work by Miyazaki et al. [2] published in 1996 that led it to be cited more often than others that preceded it, also published in the AJR [9, 10]? The answer is simple, but not trivial. Miyazaki et al. introduced HASTE (half-Fourier acquisition single-shot turbo spin-echo) sequences for acquiring MRCP images. With HASTE acquisitions, Miyazaki et al. were able to generate projection MRCP images using very short scanning times: 2 seconds for the single-slice technique and 18 seconds for the multislice technique [2]. This virtually guaranteed that MRCP images could be acquired in a single breath-hold. Other groups around that time also published impressive results using similar breath-hold techniques [15, 16]. Studies published previously had used either non-breath-hold techniques with unavoidable motion artifact that caused image quality degradation, multiple segmented breath-holds causing misregistration artifacts, or excessively long breath-hold periods of 45 seconds or more that could not be realistically implemented in clinical practice.
Breath-hold techniques, especially using the HASTE sequence as introduced by Miyazaki et al. [2], were rapidly disseminated throughout the world and became the preferred method used for MRCP. The diagnostic performance of MRCP for evaluating multiple congenital and acquired abnormalities that affect the biliary and pancreatic ducts in adults and children has since been investigated by innumerable researchers. MRCP has been repeatedly shown to be precise for revealing benign (inflammatory, postsurgical, ischemic, and traumatic) and malignant strictures, stones, cystic diseases, and anatomic variants. Use of MRCP in clinical practice has increased steadily since the introduction of the technique more than a decade ago. Currently, MRCP is one of the most commonly performed abdominal MRI examinations in many academic and community practice settings.
Today, single-slice and multislice HASTE sequences acquired in oblique coronal and axial planes are included in MRCP protocols at most institutions. Image quality has improved substantially with the introduction of stronger gradients, multichannel receiver coils, and parallel imaging. Other trends include the widespread use of negative (iron-based) oral contrast agents to eliminate the high background signal arising from fluid in the gastric fundus and duodenum and an increase in the use of secretin to stimulate production of pancreatic fluid and evaluate pancreatic exocrine function [17], anatomic variants [18], and pancreatic duct integrity [19].
In summary, MRCP is an excellent example of how radiologists can transform engineering developments in imaging equipment into clinically relevant tools. Gastroenterologists evolved from being antagonistic and skeptical to embracing the technique that has repeatedly proven to be beneficial for patient care in many circumstances. Work like that of Miyazaki et al. [2] undoubtedly served to move our field and medicine forward.
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