Since its introduction, MRCP has been improved over the years due to the introduction of several technical advances and innovations. It consists of a noninvasive method for biliary tree representation, based on heavily T2-weighted images. Conventionally, its protocol includes two-dimensional single-shot fast spin-echo images, acquired with thin sections or with multiple thick slabs. In recent years, three-dimensional T2-weighted fast-recovery fast spin-echo images have been added to the conventional protocol, increasing the possibility of biliary anatomy demonstration and leading to a significant benefit over conventional 2D imaging. A significant innovation has been reached with the introduction of hepatobiliary contrasts, represented by gadoxetic acid and gadobenate dimeglumine: they are excreted into the bile canaliculi, allowing the opacification of the biliary tree. Recently, 3D interpolated T1-weighted spoiled gradient echo images have been proposed for the evaluation of the biliary tree, obtaining images after hepatobiliary contrast agent administration. Thus, the acquisition of these excretory phases improves the diagnostic capability of conventional MRCP—based on T2 acquisitions. In this paper, technical features of contrast-enhanced magnetic resonance cholangiography are briefly discussed; main diagnostic tips of hepatobiliary phase are showed, emphasizing the benefit of enhanced cholangiography in comparison with conventional MRCP.
Magnetic Resonance Cholangiopancreatography (MRCP) provides high diagnostic accuracy in the assessment of biliary disease. It consists of a noninvasive method for biliary tree representation—based on heavily T2-weighted images in which stationary and slow-moving fluids in the bile ducts appear hyperintense in contrast to the hypointensity of the surrounding tissue [
Conventional MRCP includes two-dimensional (2D) sequences acquired with a radial thick-slab imaging or with coronal thin acquisitions oriented toward the hepatic hilum. In recent years, three-dimensional (3D) sequences have been added to the conventional protocol, increasing the possibility of biliary anatomy demonstration and leading to a significant benefit over conventional 2D imaging [
Thanks to 2D and/or 3D sequences, conventional MRCP plays an important role in the diagnosis and characterization of several diseases. In the assessment of biliary lithiasis, it offers high diagnostic capability in comparison with other methods [
Gadolinium liver-specific contrasts are cleared by glomerular excretion and biliary excretion; using gadoxetic acid, the percentage of elimination is about 50% for each route [
Thus, the role of hepatobiliary contrast-enhanced Magnetic Resonance Cholangiography (MRC) is discussed in this article, exploring technical adjustments of imaging protocol; an overview of the most important clinical applications and tips is briefly reported, in order to help radiologists and nonradiologists in the management of biliary diseases.
3D interpolated T1-weighted spoiled gradient echo images have been proposed for the evaluation of the biliary tree after hepatobiliary contrast agent administration [
Biliary opacification (Figure
Gadolinium-enhanced MRC. MIP images of 3D T1-weighted spoiled gradient echo. (a) shows opacification of biliary tract after Gd-EOB-DTPA administration; hepatobiliary phase could be obtained 20 minutes after intravenous contrast. In a different patient, (b) demonstrates excretory phase obtained after gadobenate dimeglumine intravenous administration. In this case, the elimination of contrast media is provided by the kidney (95–97%) and the biliary system (2–5%): a satisfactory opacification of the biliary tree—in patients with preserved biliary function—is observed at least 60 minutes after contrast administration.
Gadobenate dimeglumine has both an extracellular phase and a hepatobiliary phase; it has high relaxivity, with a weak transient albumin binding [
Gadoxetic acid has different pharmacokinetic properties: it is generally excreted in a percentage of 50% and 50%, respectively, by the liver and by the kidneys; in the liver, mechanisms of excretion involve multidrug resistance-associated proteins (MRPs) [
Thus, the choice of contrast agent influences the time for the acquisition of “excretory phase.”
Increased flip angle is recommended in the evaluation of the biliary tree using liver-specific gadolinium-enhanced MRC. Indeed, this flip angle variation influences the quality of hepatobiliary acquisitions (Figure
Influence of flip angles. 3D T1-weighted spoiled gradient echo sequences, with different flip angles (10° in (a), 30° in (b)). Delineation of the biliary ducts is better increasing the flip angle, depicted in (b) as well. The increase of flip angle improves the SNR and the CNR; a flip angle >20° is generally recommended.
In a recent paper by Stelter et al. [
In another study, Stelter et al. [
The importance of flip angle variation has been reported also in a paper by Frydrychowicz et al. [
Anatomical variations of the biliary tree are common (about 30% of patients) [
The biliary tree can be well depicted in the hepatobiliary phase MRI after administration of hepatobiliary contrast. Fat-suppressed 3D T1-weighted axial images are acquired with thin thickness, allowing MIP reformations [
Gd-EOB-DTPA-enhanced hepatobiliary phase MRI is a useful tool to evaluate biliary tree variations—also providing additional information as regards biliary flow, as referred by Hyodo et al. [
Anatomical variations of the biliary tree. 2D thick-slab cholangiography and 3D MIP FRFSE ((a) and (b), resp.), show a caudal confluence between right and left biliary ducts; in addition, an aberrant right duct is suspected on (a) and (b) (white arrow). Gadoxetic acid-enhanced MRC clearly demonstrates the right aberrant duct and the cystic duct (black arrow), with a separate insertion along left biliary duct.
Anatomical variations of the biliary tree. MIP image of 3D FRFSE cholangiography shows multiple stones in the gallbladder (a). Axial 3D fast spoiled gradient echo images ((b) and (c)), obtained in an excretory phase, show right aberrant duct (white arrow in (b) and (c)) and the insertion of cystic duct (white dashed arrow).
Gd-EOB-DTPA-enhanced MR imaging is characterized by a higher SNR in the bile duct than conventional T2-weighted MRCP, with a better visualization of bile duct anatomy, especially in the intrahepatic bile ducts, even if there are no dilatations [
However, contrast-enhanced MRC reported an accurate visualization of bile duct anomalies also using Gd-BOPTA; 3D T1-weighted images acquired 90 minutes after Gd-BOPTA administration demonstrated a better visualization of bile duct anomalies in a population of potential liver donor, in comparison with 2D SSFSE cholangiography [
Biliary cysts account for about 1% of all benign biliary diseases [
Generally, they are diagnosed in infants or children, even if occasionally they are detected in adults (up to 20%) [
The cystic dilatation of the biliary tree has been classified by several authors; mainly, there are 2 classifications, edited, respectively, by Alonso-Lej in 1959 and by Todani in 1977 [
The latest distinguishes 5 types of congenital biliary cysts [ Type I, represented by choledochal cyst Type II, usually represented by a diverticulum of common bile duct Type III, also known as choledochocele Type IV, which includes multiple communicating intra- and extrahepatic duct cysts Type V, which is called Caroli’s disease
The diagnosis of intrahepatic forms should be differentiated by other conditions, such as adult polycystic liver disease or the von Meyenburg complex [
Hepatobiliary contrast agent excretion could be useful in differentiating choledochal cyst (Figure
Biliary cystic disease, type II. MRCP image (a) shows a small paracholedochal cyst, with homogeneous hyperintense signal (white arrow). 3D T1-weighted spoiled gradient echo image (b)—obtained in an excretory phase—shows opacification of the cystic lesion (white arrow); a diagnosis of type II biliary cystic disease was achieved.
Lee et al. [
Surgical injuries—which can cause irregular excretion of bile—are mainly represented by leakage, stricture, or complete transection and excision of a ductal segment, with or without obstruction of the proximal biliary tree by surgical clips [
Biliary leak after hepatic resection. (a) shows a large fluid collection—hyperintense on MR cholangiography—located in the cranial part of the liver. (b) and (c)—obtained in excretory phase—show opacification of the fluid collection, suggesting a biliary injury.
The possibility to detect the bile leak using MRCP has many advantages: there is no ionizing exposure, in contrast to conventional cholangiography; in addition, it is less invasive, without any risk of cholangitis. However, conventional 2D and/or 3D unenhanced MRCP is limited in the evaluation of biliary leak, because it provides only a morphologic information about damage. Moreover, a biliary leak could be suspected in case of a fluid collection—hyperintense on unenhanced cholangiography sequences—contiguous to the site of surgical anastomosis or cystic duct ligation. However, a clear explanation is reached only with contrast opacification of the biliary system (Figure
Biliary leak after cholecystectomy. Coronal T2-weighted single-shot fast spin-echo image (a) and 3D FRFSE cholangiography (b) show a small fluid collection (white arrows in (a) and (b)). Images obtained in excretory phase ((c) and (d)) show progressive opacification (white arrows): a diagnosis of biliary leak was performed.
To increase the diagnostic accuracy of bile leak detection, conventional MRCP, based on T2-weighted acquisition, has been compared to gadoxetic acid-enhanced T1-weighted gradient echo sequences.
In the assessment of bile leak, Gd-BOPTA-enhanced MRC has been compared to “conventional bile duct opacification obtained by endoscopy or t-tube cholangiogram,” as reported by Fontarensky et al. [
In the paper published by Kantarcı et al. [
The accuracy of the combination of conventional MRCP (based on morphological T2 sequences) and contrast-enhanced MRC was superior to T2 sequences alone: mean sensitivities were, respectively, 79% and 59%, and diagnostic accuracy was 84% and 58% [
Gadoxetic acid-enhanced MRC reported high sensitivity and specificity in the diagnosis of bile leak after biliary surgery [
However, gadoxetic acid-enhanced MRC is “a highly reliable technique” for the detection of bile leak after hepatobiliary surgery, even if three-dimensional T1-weighted gradient-echo sequences were acquired 20 minutes after contrast administration [
Biliary-enteric anastomoses may develop some complications, represented by anastomotic leak, stricture, hemorrhage, inflammation, and stones [
Biliary-enteric anastomosis. Excretory phase provides a clear visualization of the anastomoses.
A 60-year-old patient with a biliary-enteric anastomoses. Coronal T2-weighted image (a) and 3D MRCP (b) clearly provide morphological representation of biliary-enteric anastomoses (white arrows). Contrast-enhanced MRC images show opacification of anastomoses (white arrows in (c) and (d)), adding functional information to morphology.
Patient with a biliary-enteric anastomosis, performed after duodenopancreatectomy. 2D T2-weighted cholangiography (a) shows normal appearance of a biliojejunal anastomosis. Excretory phase—obtained after contrast administration of Gd-BOPTA—confirms regular opacification at the surgical connection (b).
Biliary anastomosis after OLT. 3D MIP FRFSE image (a) and excretory phase (b) show a functioning choledochal anastomosis after OLT.
In the past, MRC has been used as a reliable method for the assessment of stricture or other complications in patients with biliary-enteric anastomoses [
The diagnostic capability of MRCP using a hepatobiliary contrast agent seems to be dependent on the type of contrast medium. Kandasamy et al. [
After liver transplantation, biliary complications occur commonly, ranging from 5% up to 30% of patients [
As previously reported, assessment of biliary leakages using heavily T2-weighted MR cholangiography is limited, due to the fact that it is based only on morphologic demonstration of fluid collections.
MRCP allows the visualization of anastomotic or nonanastomotic strictures (Figure
However, contrast-enhanced MRC should be routinely performed in patients with high clinical suspicion of biliary complications after liver transplantation, in order to increase diagnostic accuracy in the detection of biliary leakage or biliary strictures [
Normal MRC findings include narrowing of the common bile duct and mild thickening of the wall, without bile duct dilatation involving the cranial segments of the biliary tree [
Typical imaging findings of cholecystitis are represented by wall thickening, oedema, and fluid collection around the gallbladder. These findings are very often observed on ultrasonography, CT, and MR examinations. However, sometimes clinical and morphological appearances remain doubtful.
Gadoxetic acid-enhanced scans could be adopted as “functional markers” of gallbladder contraction. Several studies evaluated the kinesis of the cholecyst: generally, the wall contraction has been induced using a fatty meal or a stimulant agent [
Akpinar et al. [
Choi et al. [
Diagnosis of gallbladder dyskinesia was analyzed by Lee et al. [
In the last years, contrast-enhanced MRC has increased diagnostic accuracy for biliary disease, allowing the addition of “functional information” or “excretory function” to conventional imaging.
Clinical indications of contrast-enhanced MRC—that have been introduced in daily routine—include the following: (a) evaluation of congenital biliary cysts; (b) detection of biliary leaks; (c) assessment of biliary-enteric anastomoses; and (d) demonstration of biliary complications after OLT. In these clinical scenarios, the diagnostic capabilities of contrast-enhanced MRC may reach high values; namely, in detection of biliary leaks and assessment of biliary-enteric anastomoses, sensitivities and diagnostic accuracy are superior to those reported by conventional MRCP based on T2 sequences alone [
Contrast-enhanced MRC may be useful to better demonstrate the presence of biliary variants—when preoperative assessment of biliary anatomy remains doubtful after conventional MRCP; finally, it represents a valid alternative to hepatobiliary scintigraphy—for patients having clinical suspicion of gallbladder dyskinesia.
The authors declare that there is no conflict of interest regarding the publication of this paper.