MRI - Looking inside the body

In a doctor’s bag of magic ‘tricks’, one essential tool to help him make us better is an imaging technique known as magnetic resonance imaging. And it really does give an intimate picture of the innards of the human body. Here’s a summary of what to expect when you undergo an MRI.

MAGNETIC Resonance Imaging, commonly referred to as MRI, provides an extraordinary look inside the human body. It is a non-invasive medical test that helps physicians diagnose and treat medical conditions.

Unlike other techniques, MRI uses no x-rays or radiation, but rather combines the naturally occurring force of a magnetic field with radio waves to produce signals that are reconstructed on a digital computer.

Detailed MR images allow physicians to better evaluate parts of the body and certain diseases that may not be assessed adequately with other imaging methods such as X-ray, ultrasound or computed tomography (also known as CT scan).

In addition to your safety and comfort, MRI offers an exceptional view of internal organs. The high sensitivity of MRI, combined with three dimensional viewing, produces diagnostic images of outstanding clarity.

Purposes of MRI

MRI yields exceptionally detailed pictures of soft-tissue structures near and around bones, blood vessels, organs and the brain. It is widely used to examine such diverse things as:

·Spinal and joint problems

·Small tears to tendons and ligaments

·Sports injuries

·Work-related disorders from repeated strain

·Arthritis

·Stroke

·Reproductive organs

·Organs of the chest and abdomen

Physicians use the MR examination to help diagnose or monitor treatment for conditions such as:

·Tumors of the chest, abdomen or pelvis.

·Coronary artery disease and heart problems including the aorta, coronary arteries and blood vessels, by examining the size and thickness of the chambers of the heart and the extent of damage caused by a heart attack or progressive heart disease.

·Tumors and other abnormalities of the reproductive organs (eg uterus, ovaries, testicles, prostate).

·Causes of pelvic pain in women, such as endometriosis.

·Functional and anatomical abnormalities of the heart.

·Diseases of the liver, such as cirrhosis, and that of other abdominal organs (when a complete diagnostic assessment can not be done with other techniques).

·Congenital arterial and venous vascular anomalies and diseases (eg atherosclerosis) of the chest, abdomen and pelvis (MR Angiography).

·Conditions involving the bile duct, gallbladder and pancreatic ducts (MRCP).

·Breast cancer and implants.

General patient preparation

A patient sent for an MRI scan typically requires no preparation, dietary restrictions, shielding, or injections. A simple explanation of the procedure and thorough check for contraindications are all that is required prior to the exam.

Electro mechanical implants – such as cardiac pacemakers, cochlear implants, and neurotransmitters – may be “frozen” or switched off in the presence of the magnetic field. Ferromagnetic clips are highly dangerous because the torque induced by the magnetic field could potentially dislodge a recently implanted clip.

Similar concern should be expressed for any patient with a history of steel working, because tiny metal fragments may be imbedded in their eyes. To prevent any possibility of optic damage, these patients should be screened with plain films prior to their MRI exam.

Some MRI examinations may require the patient to swallow contrast material or receive an injection of contrast into the bloodstream. The radiologist or technologist may ask if you have allergies of any kind, such as allergy to iodine or x-ray contrast material, drugs, food, the environment, or asthma.

The radiologist should also know if you have any serious health problems and what surgeries you have undergone. Some conditions, such as severe kidney disease, may prevent you from having an MRI with contrast material.

It is also very important that you inform your referring physician and the MRI staff if you have any of the following:

·Shrapnel

·Pregnancy

·Pacemaker

·Hearing aid

·Metal implants

·Dental bridges

·Aneurysm clips

·Surgical staples

·Cochlear implant

·Dorsal column stimulator

·Inferior vena cava umbrella

·Electronic objects

All jewellery and other accessories should be removed prior to the MRI scan. This is because they can interfere with the magnetic field of the MRI unit.


The MRI machine

MRI system can be generally categorised under Open MRI and short bore MRI. The traditional Open MRI unit is a large cylinder-shaped tube surrounded by a circular magnet. The patient will lie on a moveable examination table that slides into the centre of the magnet. Certain types of exams cannot be performed using the Open MRI.

Short Bore MRI systems provide the best of both worlds with a high magnetic field for outstanding image resolution and an open architecture that significantly enhances patient comfort. The bore is very short, posing little difficulty for all but the extremely claustrophobic. It allows a patient’s head to be outside the scanner, except for head scans. This makes the exam experience far more comfortable. The 1.5 field strength allows for shorter scan times and enhanced imaging capabilities.

Advantages of MRI

·MRI is a non-invasive imaging technique that does not involve exposure to radiation.

·MR images of the soft-tissue structures of the body – such as the heart, liver and many other organs – is more likely to identify and characterise abnormalities and focal lesions than other imaging methods. This detail makes MRI an invaluable tool in early diagnosis and evaluation of many focal lesions and tumours.

·MRI has proven valuable in diagnosing a broad range of conditions, including cancer, heart and vascular disease, and muscular and bone abnormalities.

·MRI enables the detection of abnormalities that might be obscured by bone with other imaging methods.

·MRI allows physicians to assess the biliary system non-invasively and without contrast injection.

·The contrast material used in MRI exams is less likely to produce an allergic reaction than the iodine-based materials used for conventional x-rays and CT scanning.

·MRI can eliminate the need for biopsy or exploratory surgery in some cases, and can detect problems that have been hidden on prior tests. This can result in earlier diagnosis of many diseases.

·MRI provides a fast, non-invasive alternative to x-ray angiography for diagnosing problems of the heart and blood vessels.

Unlike conventional x-ray examinations and computed tomography (CT) scans, MRI does not depend on radiation. Instead, while in the magnet, radio waves redirect the axes of spinning protons, which are the nuclei of hydrogen atoms, in a strong magnetic field.

The magnetic field is produced by passing an electric current through wire coils in most MRI units. Other coils, located in the machine and in some cases, placed around the part of the body being imaged, send and receive radio waves, producing signals that are detected by the coils.

A computer then processes the signals and generates a series of images each of which shows a thin slice of the body. The images can then be studied from different angles by the interpreting physician.

Overall, the differentiation of abnormal (diseased) tissue from normal tissues is often easier with MRI than with other imaging modalities such as x-ray, CT and ultrasound.

What will patients experience pre- and post-MRI?

Most MRI exams are painless. Some patients, however, find it uncomfortable to remain still during MR imaging. Others experience a sense of being closed-in (claustrophobia). Therefore, sedation can be arranged for those patients who anticipate anxiety, but fewer than one in 20 require it.

It is normal for the area of your body being imaged to feel slightly warm, but if it bothers you, notify the radiologist or technologist.

It is important that you remain perfectly still while the images are being recorded, which is typically only a few seconds to a few minutes at a time.

For some types of exams, you may be asked to hold your breath. You will know when images are being recorded because you will hear tapping or thumping sounds when the coils that generate the radiofrequency pulses are activated. You will be able to relax between imaging sequences, but will be asked to maintain your position as much as possible.

You will be alone in the exam room during the MR imaging. However, the technologist will be able to see, hear and speak with you at all times using a two-way intercom.

Many MRI centres allow a friend or parent to stay in the room.

You may be offered or you may request earplugs to reduce the noise of the MRI scanner, which produces loud thumping and humming noises during imaging. MRI scanners are air-conditioned and well-lit. Some scanners have music to help you pass the time.

When the contrast material is injected, it is normal to feel coolness and a flushing for a minute or two. The intravenous needle may cause you some discomfort when it is inserted and once it is removed, you may experience some bruising. There is also a very small chance of irritation of your skin at the site of the IV tube insertion.

If you have not been sedated, no recovery period is necessary. You may resume your usual activities and normal diet immediately after the exam.

A few patients experience side effects from the contrast material, including nausea and local pain. Very rarely, patients are allergic to the contrast material and experience hives, itchy eyes or other reactions.

It is recommended that nursing mothers not breastfeed for 36 to 48 hours after an MRI with a contrast material.

- THE STAR
www.thestar.com.my