Role of MRCP in the measurement of the CBD diameter

Several diagnostic methods such as ultrasonography, endoscopic retrograde cholangiopancreatography, and multidetector computed tomography have been used to measure the diameter of the common bile duct (CBD). Magnetic resonance cholangiopancreatography (MRCP) is a noninvasive procedure and a novel method for delineating biliary and pancreatic disorders. It requires no contrast material injection, generates both cross-sectional and projectional images, and provides an overview of the entire biliary and pancreatic ductal system. Furthermore, MRCP spatial and contrast resolutions are crucial in the effort to obtain the highest quality imaging results, which determine the detection rate of small pathologies and anatomic variants. Recent technical developments have also improved the image quality provided by magnetic resonance imaging of the abdomen, such as receiver coils, use of parallel-imaging and respiratory-monitoring techniques, and a more powerful gradient system, such as 3.0T MRI. Although different kinds of MRCP imaging techniques have been used, most current protocols often use a twodimensional (2D) single-shot fast spineecho technique to obtain a combination of coronal thin-section images and rotating oblique-coronal thick-slab images. Thick-slab MR images are necessary to capture the entire biliary tree or pancreatic duct on one image by rotating oblique-coronal planes, and provide an overview of biliary and pancreatic ductal anatomic characteristics. However, the technique is operator-dependent, and necessitates identification of complex anatomic characteristics by a skilled MR technologist or a radiologist monitoring the examination. Even when MRCP examinations are well performed, inherent in-place volume averaging effects may obscure small stones or anatomic variants. It is true that thick-slab imaging provides an expanded anatomic overview, and thin-section imaging provides fine details. However, patient respiratory motion during examination may result in areas of missed anatomic features, and can limit the suitability of these thin-section data from maximum intensity projections or other multiplanar reformations. Twodimensional techniques have anisotropic resolution with increased slice thickness compared with in-place resolution, which results in a marked degradation of maximum-intensity projections in areas oblique to the acquisition plane. Threedimensional acquisition is also appealing for MRCP because it provides intrinsically contiguous sections that may be used