Magnetic Resonance Cholangiopancreatography - An Overview

Introduction:

The pancreas and hepatobiliary organs, such as the liver, gallbladder, and bile duct, are vital organs of the digestive system. Diseases of the hepatobiliary system are common, and prompt diagnosis and treatment are crucial. A spectrum of diagnostic tests is available to assess and evaluate pancreatic and biliary diseases. They include laboratory blood assays, imaging tests such as computed tomography (CT), magnetic resonance imaging (MRI), nuclear imaging, and ultrasound. However, the most promising diagnostic test for evaluating hepatobiliary disorders is endoscopic retrograde cholangiopancreatography (ERCP).

ERCP is an invasive endoscopic diagnostic test. It employs a long flexible tube-like device with a camera on one end. The tube is inserted through the mouth or nose into the stomach and the small intestine. ERCP also enables concomitantly to perform minor surgical procedures such as biopsy or other corrective surgeries. However, this invasive procedure is associated with complications such as infection, bleeding, or damage to the mucosal lining. Also, ERCP may not be feasible if there is ductal blockage or other anatomical limitations, such as esophageal diverticula (esophageal pouches). Hence the need for an ancillary and less invasive procedure was in demand. This was fulfilled by magnetic resonance cholangiopancreatography.

What Is Magnetic Resonance Cholangiopancreatography?

Magnetic resonance cholangiopancreatography (MRCP) is a novel diagnostic test that utilizes the principle of magnetic resonance imaging to image the hepatobiliary organs and pancreas. It is safe, non-invasive, and diagnostically as efficient as ERCP. It is significantly valuable in high-risk patients with anatomical challenges in whom ERCP cannot be done. It uses a magnetic field and radio waves to image the internal organs.

Where Is MRCP Indicated?

MRCP has proved to be an essential imaging tool in the diagnosis of the following conditions:

• Inflammatory or infectious conditions of the liver, pancreas, gallbladder, pancreatic, or bile duct.

• Tumors in the pancreas or the hepatobiliary organs.

• Gallstones.

• Unexplained abdominal pain.

• In conditions where ERCP cannot be performed.

• To diagnose congenital anomalies.

• Biliary obstruction or strictures.

• Trauma.

• Cystic lesions.

What Is the Working Principle of MRCP?

The MRI unit comprises a large tunnel-shaped device with a sliding table. It uses radio waves and a magnetic field to capture images of the internal body structures. The duct's pancreatic and biliary fluids act as the contrast medium. There is no radiation used; hence this procedure is relatively safe. The hydrogen atoms in the body fluid are realigned when the radio waves pass through the body. Once these atoms return to their original position, they emit certain energy based on their tissue type. The magnetic field is produced by individual wire coils placed around the body part to be imaged. The radio waves are emitted and received by these coils. The returned energy is then captured by the scanner in the form of signals and processed in a computer as images.

What Are the Pre-procedural Instructions?

• Patients would be advised to fast for four hours before the procedure. Routine medicines can be taken with a few sips of water. Fasting helps reduce abdominal secretions and peristalsis, thereby reducing motion-related artifacts.

• Patients are advised to wear loose, comfortable clothes.

• Any allergy to medications, contrast material, or latex should be informed to the doctor before the procedure.

• Patients with renal diseases should also inform about their condition as the contrast material used for MRI examination is gadolinium-based, potent nephrotoxins.

• Pregnant women and lactating mothers should also inform the doctor, as MRI is not usually indicated in the first trimester. Also, lactating mothers may have to stop breastfeeding for 24 hours or till the dye is eliminated from the body.

• Claustrophobic patients may inform the doctor so that they can receive a mild sedative before the procedure.

• Any jewelry and metallic accessories, including wallets, buckles, belts, clips, debit cards, or credit cards, should be removed before the procedure. Patients with removable dentures and hearing aids should also remove them before the procedure.

• Patients with cochlear implants, pacemakers, defibrillators, and insulin pumps should inform the doctor. These patients should be thoroughly evaluated before being subjected to an MRI scan.

• Patients must carry their recent medical test reports and prescription medicines to the diagnostic center.

How Is MRCP Performed?

• MRCP is performed as an outpatient procedure. The patient will be asked to change into a hospital gown and be assisted to the scanning room.

• The patient will be asked to lie on the examination table, and a sedative, if required, will be administered.

• Straps may be used to help patients remain still.

• An intravenous line (I.V) would be accessed for contrast MRI, and the contrast agent would be administered through the I.V.

• The magnetic coil would be in the form of a blanket placed over the body covering the area to be imaged.

• The table then slides into the MRI unit. Some thumping and other noises are common. Patients can request earplugs.

• The technicians would be present in an adjacent room and could see patients and communicate with them through an intercom.

• The entire procedure takes around 45 minutes.

What Are the Instructions After the Procedure?

MRCP is a relatively simple and painless procedure. No specific instructions are required after the procedure, and the patients may resume their normal activities and diet unless instructed by their physician. Patients in whom contrast material was injected may be advised to drink plenty of fluid so that the contrast material can be expelled from the body via urine or feces. Allergic reactions, though rare, must be watched out for.

What Are the Benefits and Risks Associated with the Procedure?

Benefits:

• Non-invasive, painless, and relatively safe as it does not involve radiation.

• Efficient imaging of the soft tissues.

• Well tolerated and readily accepted by the patients.

• It can help evaluate the functioning of the internal organs along with morphologic imaging.

Risks:

• Allergic reactions to the contrast material.

• Since gadolinium-based contrast materials are nephrotoxic, their use in compromised renal patients could result in renal failure.

• It is not indicated in pregnant women, particularly in their first trimester.

• Lactating mothers may need to stop breastfeeding for 24 to 48 hours after the procedure. Hence they will be required to pump and store the milk.

What Are the Limitations of This Procedure?

• Patients who may find it difficult to remain still, such as those with neurologic conditions, are unsuitable for MRI scanning or may need sedatives before the procedure.

• Since MRI scanners have weight limits, obese patients are not ideal candidates for MRI scanning.

• Patients with metallic implants do not have absolute contraindications but will require thorough evaluation before the procedure.

• Patients with irregular heartbeat may affect the image quality as certain MRI techniques are based on cardiac electrical activity.

Conclusion:

Though MRCP is a novel hepatobiliary system imaging modality, it has evolved considerably and proved to be the most efficient diagnostic tool. It has become the diagnostic test of choice for pancreatic and hepatobiliary disorders. Though ERCP should be considered, alternative imaging suggests the need for biopsy or other concomitant corrective surgeries.