Diagnostic Tests

MRI Scan

What is it?

Magnetic resonance imaging (MRI) is a fairly new test that does not use radiation. Rather, magnetic and radio waves are used to create computer-generated images. MRI pictures can scan multiple layers of the spine and show abnormalities of bones and soft tissues, such as nerves and ligaments. The MRI is probably the most commonly used to evaluate the spine.

Why is it done?

The MRI shows the spine in very clear detail, including information about the bones, ligaments, muscles, nerves and discs. It can show if there is a loss of water in the nucleus pulposus, which occurs in the earliest stage of disc degeneration. An MRI can be used to show facet joint arthritis, spinal stenosis (narrowing of the spinal canal), or a herniated disc (protrusion or rupture of the intervertebral disc). The test is useful for diagnosing any condition in which the anatomy of the spine and its soft tissues need to be seen clearly.

How is it done?

You will be asked to lie on a table that slides into a machine with a large, round tunnel. The machine’s scanner takes many pictures that are watched and monitored by a technician. The MRI scanner is noisy. You might be offered headphones to listen to music while the scan is taking place. The tunnel that you lie in is narrow and may cause some patients to feel claustrophobic. You might be given a mild sedative to make the experience more tolerable. Newer MRI machines, called open MRI scanners, are sometimes more comfortable for patients who experience claustrophobia. The procedure takes 30-60 minutes.

What are the limitations?

There is little the MRI does not show. However, X-rays and CT scans have a role in adding helpful information in spine conditions that require them.

What are the risks?

There appear to be no known risks associated with exposure to the magnetic waves used during an MRI. These waves can cause problems however, if you have any metal objects in your body that could be attracted to the strong magnetic field. For example if you had any type of metal clips or implants used in a previous surgery, including a pacemaker, make sure to inform the technician. X-rays may be taken of your head before the test to verify there are no metal fragments in your eyes or brain that could move when the magnet is turned on.

CT Scan

What is it?

The CT or “CAT” scan is an X-ray test that shows bones and soft tissues. The abbreviation “CAT” stands for Computer Assisted Tomography. X-rays are taken and then interpreted by a powerful computer that makes them appear as “slices” through the body. Special software can combine these images into a three-dimensional view of the bones.

Why is it done?

The “slices” produced by a CT scan allow each section of the spine to be examined separately. The images show details of spine bones in great detail. A CT scan can show if bone spurs are pushing against spinal nerve roots. It is often used when looking at fractures or damaged bones due to infection or cancer. Some doctors have recently begun using CT scan technology on a limited basis to test for osteoporosis in the spine.

How is it done?

You will be asked to lie on a table that slides into a scanner. This is similar to having an MRI test. The scanner used for CT scans is essentially an X-ray tube that rotates in a circle. You will need to lie very still for short periods while the scanner takes many pictures. The procedure takes 30-60 minutes.

What are the limitations?

The CT scan does not show muscles or ligaments clearly. To make the nerves and soft tissues easier to see, this test is often combined with a myelogram. With the myelogram, dye is injected into the spinal sac to outline the nerves and spinal sac so they show up clearly on the CT scan. A CT scan without dye is not as good at showing the discs and the nerves of the spine. The CT scan was developed before magnetic resonance imaging (MRI). The pictures of soft tissues are not as clear as they are with an MRI. The MRI is a better test to show problems within the disc, particularly a recurring disc herniation. It is also helpful for showing the health of a disc following surgery.

What are the risks?

The CT scan uses X-rays. In large doses, radiation from the X-rays can increase the risk of cancer. The vast majority of patients who have a CT scan will never get enough radiation to worry about cancer. Only patients who must have large numbers of X-rays or CT scans-hundreds-over many years need to be concerned. Children, and young adults who plan to have children, should be protected from radiation exposure to the testicles and ovaries. Otherwise the radiation may damage the sperm and eggs. It is simple to protect these areas by shielding them with a lead apron or lead blanket.

Bone Scan

What is it?

A bone scan is a test used to show trouble spots on the spine. A radioactive chemical, sometimes called a “tracer”, is injected into the bloodstream. The chemical quickly attaches itself to areas of the skeleton that are busy making new bone. Several hours after the injection, pictures are taken of the skeleton.

Why is it done?

A bone scan is very useful when it is unclear exactly where the problem is in the skeleton. It offers the ability to take a picture of the entire skeleton and pinpoint any problem areas. Concentrations of the chemical appear as dark spots on the film. In an adult, this usually indicates that there is a problem. The increased bone-making activity is a response to the problem. For example, if there is a fracture of the bone, bone cells will very quickly begin to make new bone to try to repair it. Once these areas are located on the bone scan, the doctor may order additional tests for specific information about your condition.

A bone scan can show problems such as bone tumors, infection, and fractures of the spine. It can also be used to determine bone density and the bone-thinning condition of osteoporosis.

How is it done?

An intravenous line (IV) is started in your hand or arm. The chemical tracer is injected into the bloodstream through the IV. There is a waiting period of two to three hours, while the chemical attaches itself to any areas of bone that are undergoing rapid changes. Usually, you are free to leave and come back after this period.

You will then be asked to lie or sit underneath a large “camera” that takes pictures of your skeleton. Since the chemical tracer is radioactive, it sends out radiation that can be captured by a special camera. The camera is similar to a “Geiger counter” in that it uses film to capture the radioactivity. The procedure takes 30-90 minutes.

What are the limitations?

The bone scan does not show details of the bones or soft tissue. It simply shows how much the bone around a specific area is reacting to the problem.

What are the risks?

There is always the risk of an allergic reaction to anything injected into the bloodstream. In this case, an allergic reaction to the chemical is uncommon. The chemical is radioactive, but it disappears from the body very rapidly-within hours.

Myelogram

What is it?

A myelogram is an older test that is still used to examine the spinal canal and spinal cord. A special dye is placed into the spinal sac that shows up on X-rays to indicate any abnormalities. Before there were CT and MRI scans, the myelogram was the best test to determine the cause of pressure on the spinal cord or spinal nerves. Today the myelogram is used only for very special purposes, such as for complicated revision spine surgeries. It is rarely the first test used if your doctor suspects you have a herniated disc.

Why is it done?

The dye used during a myelogram outlines the spinal cord and nerve roots. This helps your doctor determine if there are any unusual indentations or abnormal shapes in the spinal cord. Anything that is pushing into the nerves shows up as an indentation into the spinal sac. This indentation could be from a herniated or bulging disc, a tumor, or an injury to the spinal nerve roots. The myelogram is useful for patients who have metal plates and screws in their spine, which prevents them from having either a CT or MRI scan.

How is it done?

The doctor must perform a spinal tap to inject dye into the spinal sac. The dye mixes with the spinal fluid so that it will show up on X-rays. You will be asked to lie on a tilting table while multiple X-rays are taken to show the flow of the dye through the spine. The myelogram is usually combined with a CT scan to get a better view of the spine in cross section and to check the health of the bones and nerves.

What are the limitations?

A myelogram does not show the soft tissues. It shows only the bones and the spinal fluid where the dye has mixed with the fluid.

What are the risks?

Because the myelogram requires a spinal tap, there are more risks associated with it than most other tests. This is one reason that doctors prefer to use “noninvasive” tests first, such as the MRI and CT scan. The risks associated with a spinal tap include meningitis (infection of the spinal fluid), spinal headache, and allergic reaction to the dye. There is also a very small chance that the needle will cause bleeding around the spinal sac. The myelogram requires X-rays, which use radiation. Large doses of radiation can increase the risk of cancer. The vast majority of patients who have X-rays taken will never get enough radiation to worry about cancer. Only patients who have large numbers of X-rays-hundreds-over many years need to be concerned.

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