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Lumbosacral spine MRI

Definition

A lumbosacral spine MRI uses powerful magnets and radio waves to create pictures of the structures that make up the spine, the spinal cord, and the spaces between the vertebrae, through which the nerves travel.

Alternative Names

NMR - lumbosacral spine; Magnetic resonance imaging - lumbosacral spine; Nuclear magnetic resonance - lumbosacral spine; MRI of lumbosacral spine

How the Test is Performed

A powerful magnet in the MRI generates a strong magnetic field, which causes hydrogen atoms in your tissues to line up in a certain way.

When radio waves are sent toward the lined-up hydrogen atoms, they bounce back, and a computer records the signal. Different types of tissues send back different signals.

The computer uses these signals to create a 3-dimensional image of your body. Single MRI images are called slices. The images can be stored on a computer or printed on film.

MRI can easily be performed through clothing and bones. However, certain types of metal can cause errors in the images.

During the test, you will be asked to lie on a narrow table that slides into a large, tunnel-like tube within the scanner. If contrast dye is used, it will be injected into a small vein in your hand or forearm. A technician will operate the machine and observe you during the entire study from an adjacent room.

Several sets of images are usually needed, each taking 2 - 15 minutes. A complete scan may take up to 1 hour or more. Newer scanners with more powerful magnets and updated software may reduce the time.

How to Prepare for the Test

Because of the strong magnets, certain metallic objects are not allowed into the room.

  • Items such as jewelry, watches, credit cards, and hearing aids can be damaged.
  • Pens, pocketknives, and eyeglasses can become dangerous projectiles when the magnet is activated and should not be taken into the scanner area.
  • Pins, hairpins, metal zippers, and similar metallic items can distort the images.
  • Removable dental work should be taken out just before the scan.

Because the strong magnetic fields can displace or disrupt the action of implanted metallic objects, people with cardiac pacemakers cannot be scanned and should not enter the MRI area. MRI also should not be used on people with metallic objects in their bodies, such as:

  • Brain aneurysm clips
  • Inner ear (cochlear) implants
  • Older vascular stents
  • Recently placed artificial joints
  • Some artificial heart valves

The technician will usually give you a questionnaire that lists the potentially dangerous items.

Sheet metal workers, or people who may have been exposed to small metal fragments, will first have an x-ray of the skull to check for metal shards in the eyes. You will be asked to sign a consent form confirming that none of the above issues apply before the study is done.

You may need to wear a hospital gown, or you may be allowed to wear clothing that does not have metal fasteners.

In infants and children, the preparation you can provide for this or any test or procedure depends on your child's age, previous experiences, and level of trust. For specific information regarding how to prepare your child, see the following topics by your child's age:

How the Test Will Feel

There is no pain. You cannot feel the magnetic field and radio waves. Some people experience a claustrophobic feeling from being inside the scanner. The table may be hard or cold, but you can request a blanket or pillow.

The machine produces loud thumping and humming noises while it is on. You should get ear plugs to reduce the noise. You can speak to the technician through an intercom in the scanner during the entire procedure. Some MRI scanners have televisions and special headphones to help you pass the time.

Too much movement can blur MRI images and cause errors in the image. If you have trouble lying still or are very anxious, you may get medicine to relax you (a sedative). There is no recovery time, unless you need sedation. After an MRI scan, you can continue your normal diet, activity, and medications.

Why the Test is Performed

MRI is an imaging test used to look into back pain and spreading leg pain. MRI is excellent at showing changes, such as from arthritis, which may be narrowing the spaces through which the spinal nerves travel.

In addition, MRI can show disease of the lumbar disks that may be bulging and compressing the spinal cord.

An MRI may be done after traumatic injury if you have weakness or paralysis. MRI is better than CT scans at evaluating abscesses, tumors, or other masses near the spinal cord. While CT is better at detecting fractures of the vertebrae, MRI can detect slight changes in the bone which may be due to an infection or tumor.

Risks

There is no ionizing radiation involved in MRI. To date, there have been no significant side effects reported from the magnetic fields and radio waves used on the human body during an MRI scan.

The most common MRI contrast dye, gadolinium, is very safe. However, you should not receive gadolinium if you are pregnant because of potential harm to the unborn baby. In very rare cases, patients have had allergic reactions to this contrast dye.

There have been recent reports of fibrotic skin diseases in patients with severe kidney failure who received MRI dye. If you have severe kidney failure, tell your doctor before the study.

If sedation is used, there are risks of too much sedation. The technician will monitor your vital signs, including heart rate and breathing, as needed.

People have been harmed in MRI machines when they did not remove metal objects from their clothes or when metal objects were left in the room by others.

Considerations

MRI is more accurate than a CT scan or other tests for certain conditions, but less accurate for others. The disadvantages include:

  • High cost
  • Sensitivity to movement
  • Time involved with the scan

People with a fear of enclosed spaces (claustrophobia), or who are confused or anxious, may have difficulty lying still during the scan.

MRI is not portable and does not work with:

  • Life-support devices
  • Some metallic implants
  • Traction equipment

MRI is a preferred technique in most cases where telling differences in soft tissues is necessary. It can show organs without being blocked by bones and foreign bodies. It can show the tissues from many viewpoints and is a noninvasive way to evaluate blood flow.


Review Date: 4/10/2008
Reviewed By: Benjamin Taragin, MD, Department of Radiology, Montefiore Medical Center, Bronx, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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