What is an MRI scan?

An
MRI (or magnetic resonance imaging) scan is a radiology technique that
uses magnetism, radio waves, and a computer to produce images of body
structures. The MRI scanner is a tube surrounded by a giant circular
magnet. The patient is placed on a moveable bed that is inserted into
the magnet. The magnet creates a strong magnetic field that aligns the
protons of hydrogen atoms, which are then exposed to a beam of radio
waves. This spins the various protons of the body, and they produce a
faint signal that is detected by the receiver portion of the MRI
scanner. The receiver information is processed by a computer, and an
image is produced.

The
image and resolution produced by MRI is quite detailed and can detect
tiny changes of structures within the body. For some procedures,
contrast agents, such as gadolinium, are used to increase the accuracy
of the images.

When are MRI scans used?

What are the risks of an MRI scan?

An
MRI scan is a painless radiology technique that has the advantage of
avoiding x–ray radiation exposure. There are no known side effects of
an MRI scan. The benefits of an MRI scan relate to its precise accuracy
in detecting structural abnormalities of the body. Patients who have
any metallic materials within the body must notify their physician
prior to the examination or inform the MRI staff. Metallic chips,
materials, surgical clips, or foreign material (artificial joints,
metallic bone plates, or prosthetic devices, etc.) can significantly
distort the images obtained by the MRI scanner. Patients who have heart
pacemakers, metal implants, or metal chips or clips in or around the
eyeballs cannot be scanned with an MRI because of the risk that the
magnet may move the metal in these areas. Similarly, patients with
artificial heart valves, metallic ear implants, bullet fragments, and
chemotherapy or insulin pumps should not have MRI scanning.

During
the MRI scan, patients lie in a closed area inside the magnetic tube.
Some patients can experience a claustrophobic sensation during the
procedure. Therefore, patients with any history of claustrophobia
should relate this to the practitioner who is requesting the test, as
well as the radiology staff. A mild sedative can be given prior to the
MRI scan to help alleviate this feeling. It is customary that the MRI
staff will be nearby during MRI scan. Furthermore, there is usually a
means of communication with the staff (such as a buzzer held by the
patient) which can be used for contact if the patient cannot tolerate
the scan.

How does a patient prepare for an MRI scan and how is it performed?

All
metallic objects on the body are removed prior to obtaining an MRI
scan. Occasionally, patients will be given a sedative medication to
decrease anxiety and relax the patient during the MRI scan. MRI
scanning requires that the patient lie still for best accuracy.
Patients lie within a closed environment inside the magnetic machine.
Relaxation is important during the procedure and patients are asked to
breathe normally. Interaction with the MRI technologist is maintained
throughout the test. There are loud, repetitive clicking noises which
occur during the test as the scanning proceeds. Occasionally, patients
require injections of liquid intravenously to enhance the images which
are obtained. The MRI scanning time depends on the exact area of the
body studied, but ranges from half an hour to an hour and a half.

How does a patient obtain the results of the MRI scan?

After
the MRI scanning is completed, the computer generates visual images of
the area of the body that was scanned. These images can be transferred
to film (hard copy). A radiologist is a physician who is specially
trained to interpret images of the body. The interpretation is
transmitted in the form of a report to the practitioner who requested
the MRI scan. The practitioner can then discuss the results with the
patient and/or family.

Future

Scientists
are developing newer MRI scanners that are smaller, portable devices.
These new scanners apparently can be most useful in detecting
infections and tumors of the soft tissues of the hands, feet, elbows,
and knees. The application of these scanners to medical practice is now
being tested.

MRI Scan At A Glance

• MRI scanning uses magnetism, radio waves, and a computer to produce images of body structures.

• MRI scanning is painless and does not involve x–ray radiation.

• Patients
  with heart pacemakers, metal implants, or metal chips or clips in or
  around the eyes cannot be scanned with MRI because of the effect of the
  magnet.

• Claustrophobic sensation can occur with MRI scanning.