Advances in Biliary Imaging

Introduction

Over the past two decades, significant advances in crosssectional imaging techniques have led to increased usage in the diagnostic evaluation of suspected biliary tract pathology. Traditionally, endoscopic retrograde cholangiopancreatography (ERCP) has been regarded as the gold standard for diagnostic evaluation of the pancreaticobiliary tree. In addition to its diagnostic role, ERCP offers the benefit of potential therapeutic intervention, including brush biopsy, sphincterotomy, stone retrieval, or stent placement. The advent of endoscopic ultrasound has extended the role of ERCP to include exquisite local tissue imaging and improved image guidance for tissue sampling. Unfortunately, ERCP has a technical failure rate that varies between 12% and 20% depending on endoscopist experience. Reported complication rates for ERCP range from 9.8% to 15.9%, with a procedure-related mortality of 0.2–1.0% in various studies. In contrast, modern magnetic resonance imaging (MRI) techniques and state-of-the-art multidetector computed tomography (CT) technology can depict the biliary tree with high technical success and negligible complications. Cross-sectional imaging techniques are increasingly advocated as the primary diagnostic tool for biliary investigations in patients whose presenting history makes biliary intervention unlikely, patients with suspected highgrade biliary obstruction, or patients with complex postsurgical anatomy that would render ERCP technically challenging. In fact, a recent consensus statement from the National Institutes of Health concludes that advances in modern cross-sectional imaging techniques have transformed ERCP into a predominantly therapeutic procedure. As multidisciplinary approaches to biliary disease are more frequently being used to pool the cooperative talents of radiologists, gastroenterologists, and pancreaticobiliary surgeons, understanding the principles of cross-sectional biliary imaging modalities has become imperative. This article will discuss modern CT and MRI techniques used for evaluation of the biliary tree.

Abstract

Noninvasive imaging of the biliary tree has undergone substantial technological innovation over the past two decades and has led to increased usage in the diagnostic evaluation of suspected biliary tract pathology. While endoscopic retrograde cholangiopancreatography has been regarded as the gold standard for diagnostic evaluation of the pancreaticobiliary tree and offers the benefit of therapeutic intervention, technical failure and complications rates are not insignificant. Multidetector computed tomography (CT) and magnetic resonance imaging (MRI) can depict the biliary tree with high technical success and minimal procedural risk. The development of helical scanning technique and multidetector technology has revolutionized CT, allowing volumetric data acquisition with sub-millimeter voxels. Evaluation of the biliary tree by MRI relies on one of several available magnetic resonance cholangiopancreatography (MRCP) protocols, which offer superior contrast resolution versus CT. Thick slab single-section and thin slice multi-section techniques provide satisfactory complementary techniques that can obtained very quickly, including in uncooperative patients. Recent innovations in MRI sequence design and scanner technology have resulted in improved MRCP techniques, including newer 3D T2-weighted techniques and high field strength imaging at 3.0 Tesla. Newer contrast agents excreted into the hepatobiliary tree may provide a valuable adjunct to patients undergoing liver MRI for other reasons, including preoperative transplant evaluation or suspected postoperative complication. The diagnostic performance of both CT and MRI has been proven for many biliary clinical applications, including calculi, strictures, and tumor staging.

Keywords

Biliary imaging, MRI, MRCP, CT