What is an MRI?

Magnetic resonance imaging (MRI) also known as nuclear magnetic resonance (NMR) imaging is a non-invasive way to take pictures of the body. It is primarily used in Radiology to visualize the structure and function of the body. It is a noninvasive medical test that provides detailed images of the body in any plane. MRI provides much greater contrast between the different soft tissues of the body than does computed tomography (CT), making it especially useful in spinal, neurological (brain), musculoskeletal, cardiovascular, and oncological (cancer) imaging.

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 called CT or CAT scanning).

MRI of the Spine

Magnetic resonance imaging (MRI) of the spine is a noninvasive procedure that uses powerful magnets and radio waves to create pictures of the spine area, including the spine bones (vertebrae), the spinal cord, and the spaces between the vertebrae through which the nerves travel.

Currently, MRI is the most sensitive imaging test of the spine in routine clinical practice.

How does the MRI work?

MR imaging uses a powerful magnetic field, radio waves and a computer to produce detailed pictures of organs, soft tissues, bone and virtually all other internal body structures. The images can then be examined on a computer monitor or printed.

When a person is in the scanner, the hydrogen nuclei (i.e., protons) found in abundance in the human body in water molecules, align with the strong magnetic field. A radio wave at just the right frequency for the protons to absorb energy pushes some of the protons out of alignment. The protons then snap back to alignment, producing a detectable rotating magnetic field as they do so. Since protons in different tissues of the body (e.g., fat vs. muscle) realign at different speeds, the different structures of the body can be revealed.

Gradient fields in the three dimensions allow the scanner to work only with protons from a "slice" at a time, allowing the creation of a whole volume that can be looked at in three dimensions.

Contrast agents may be injected intravenously to enhance the appearance of blood vessels, tumors or inflammation. Unlike CT scanning MRI uses no ionizing radiation (x-rays) and is generally a very safe procedure. Patients with some metal implants and cardiac pacemakers are prevented from having an MRI due to effects of the powerful magnetic field and powerful radio waves.

Applications of spine MRI

MR imaging of the spine is performed to:
•  assess and evaluate the spinal anatomy.
•  visualize anatomical variations and identify diseased tissue in the spine.
•  help plan for spinal surgeries like spinal fusion or decompression of a pinched nerve.
•  monitor changes in the spine after a surgery, such as scarring or infection.
•  guide the injection of steroids to help relieve spinal pain.
•  explore possible causes in patients with back pain (compression fracture for example).
•  evaluate compressed (or pinched) and inflamed nerves.
•  assess the disks - bulging, degenerated or herniated intervertebral disk - a frequent cause of severe lower back pain and sciatica.
•  show the exact location of tumors or other problems of the spine, spinal cord, or disks.
•  assess children with daytime wetting and an inability to fully empty the bladder.

Procedure details of spine MRI

Spine MRI exams are performed on an outpatient basis.

You will be asked to lie on a narrow table, which slides into a large tunnel-like tube. The health care provider may inject a dye through one of your veins. This helps certain diseases and organs show up better on the images.

Unlike computed tomography (CT) scans, MRI does not use radiation. Instead, it uses powerful magnets and radio waves. The magnetic field produced by an MRI forces atoms in your body to line up in a certain way. It's similar to how the needle on a compass moves when you hold it near a magnet.

Depending on the location of symptoms, only part of the spine may be imaged: the cervical (neck) portion, the thoracic (chest) spine or the lumbar (lower) spine.

The radio waves are sent toward these atoms and bounce back, and a computer records the signal. Different types of tissues send back different signals. For example, healthy tissue sends back a slightly different signal than cancerous tissue.

A technologist will operate the machine from a room next door and watch you during the entire study.

Several sets of images are usually needed. Each one takes about 2 - 15 minutes. A complete scan can take up to 1 hour. Newer scanners may complete the process in less time.

MR spectroscopy, which provides additional information on the chemicals present in the body's cells, may also be performed during the MRI exam.

Risks

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 common type of contrast (dye) used is gadolinium. It is very safe. However, you should not receive gadolinium if you are pregnant because it can potentially harm your unborn baby. Allergic reactions to gadolinium rarely occur. The person operating the machine will monitor your heart rate and breathing as needed.

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.

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.

Cost of treatment

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