MRI of the spine

Alternative names
Magnetic resonance imaging - spine; Nuclear magnetic resonance - spine; Spine MRI; NMR - spine

Definition

Magnetic resonance imaging (MRI) of the spine is a noninvasive procedure that uses powerful magnets and radio waves to construct pictures of the vertebral bodies that make up the spine, the spinal cord, and the spaces between the vertebrae through which the nerves travel.

Unlike conventional radiography and CT imaging, which make use of ionizing radiation (X-rays) passing through a patient to generate images, MRI is based on the magnetic properties of atoms. A very small percentage of hydrogen atoms within the body will align with this field. When short radio wave pulses are broadcast toward the aligned hydrogen atoms in tissues of interest, they will return a signal of their own.

MRI scans differentiate between various organs, and potentially, provide contrast between benign and malignant tissue. Any imaging plane, or “slice,” can be projected and then stored in a computer or printed on film. MRI can easily be performed through clothing and bones. However, certain types of metal in or around the area of interest can cause significant errors in the reconstructed images (artifact).

How the test is performed

Since MRI makes use of radio waves very close in frequency to those of ordinary FM radio stations, the scanner must be located within a specially shielded room to avoid outside interference. The patient will be asked to lie on a narrow table which slides into a large tunnel-like tube within the scanner. If contrast is to be administered, intravenous access will be placed, usually in a small vein of the hand or forearm. A technologist will operate the machine and observe you during the entire study from an adjacent room.

Several sets of images are usually required, each taking from 2 to 15 minutes. A complete scan may take up to one hour. Newer scanners with more powerful magnets utilizing updated software and advanced sequences may complete the process in less time.

How to prepare for the test

Because the strong magnetic fields can displace or disrupt the action of implanted metallic objects, people with the following should not be scanned:

     
  • Cardiac pacemakers. People with implanted pacemakers should not enter the MRI area.  
  • Inner ear (cochlear) implants  
  • Brain aneurysm clips  
  • Certain artificial heart valves  
  • Older vascular stents  
  • Recently placed artificial joints

Sheet metal workers, or persons with similar potential exposure to small metal fragments, will first be screened for metal shards within the eyes with X-rays of the skull.

The patient will be asked to sign a consent form confirming that none of the above issues apply before the study will be performed.

A hospital gown may be recommended, or the patient may be allowed to wear clothing without metal fasteners.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child’s age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child’s age:

How the test will feel

Generally there is no pain associated with MRI. Some people are uncomfortable with being inside the scanner and may feel claustrophobic. The table may be hard or cold, but you can request a blanket or pillow. The machine produces loud thumping and humming noises during normal operation. Ear plugs are usually given to the patient to reduce the noise.

A technologist observes the patient during the entire procedure and may be spoken to through an intercom in the scanner. Some MRI scanners are equipped with televisions and special headphones to help time pass during the scan.

Excessive movement can blur MRI images and cause certain image errors. If the patient has difficulty lying still or is very anxious, an oral or intravenous sedative may be given. There is no usually no need for a recovery period, unless sedation was necessary.

After an MRI scan, you can resume normal diet, activity, and medications.

Why the test is performed

Spine MRI may show the exact location of tumors or other lesions of the spine, spinal cord, or intervertebral disks. It provides detailed pictures of hard-to-view areas of the spine, including the spinal canal, bony segments, and soft tissue. MRI is sometimes used to avoid the dangers of exposure to contrast dye or radiation.

Spine MRI may be performed in a trauma setting to rule out acute compression of the spinal cord in the setting of weakness or paralysis. MRI is also superior to CT in the evaluation of abscesses, tumors, or other masses near the spinal cord. While CT is better at detecting fractures of the vertebrae, MRI can detect subtle changes in the bone which may be due to infection or tumor.

What abnormal results mean


Spine MRI may reveal disorders such as:

     
  • Spinal cord compression  
  • Syringomyelia  
  • Cervical disk disorders  
  • Lumbar disk disorders  
  • Tumors of the spine  
  • Enlarged Lymph nodes near the spine  
  • Degenerative lesions of the spinal cord  
  • Herniated disk

Additional conditions under which the test may be performed:

The sensitivity of MRI depends, in part, on the experience of the radiologist.

What the risks are

There is no ionizing radiation involved in MRI, and there have been no documented significant side effects of the magnetic fields and radio waves used on the human body to date. The most commonly used MRI intravenous contrast agent, gadolinium, is very safe. There have been documented allergic reactions to it, but that has been an extremely rare occurrence.

If sedation is used, there are associated risks of over-sedation. The technologist monitors the patient’s vital signs, including heart rate and respiration as needed.

Bbecause the effects of strong magnetic fields on a fetus are not well documented at this time, pregnant women are usually advised to avoid MRI scans.

Johns Hopkins patient information

Last revised: December 4, 2012
by Harutyun Medina, M.D.

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