Magnetic Resonance Imaging
A medical imaging technique that
is used to visualize internal body
structures. It uses nuclear
magnetic resonance (NMR) to
image nuclei of atoms inside the
body.
A MRI scan produces images or
“slices” that can be digitally
displayed or printed on film.
How it Works
The patient lies on a table that
slides into the tunnel shaped
scanner. Via the use of a moving/varying magnetic field facilitated by an alternative radio
frequency transmitter, the machine systematically alters the alignment of the magnetization
of the atomic nuclei of cells. The scanner is able to detect these changes and use this
information to map the structures scanned.
Small devices, called coils, may be placed around the scan area to be to help send and receive
the radio waves, and improve the quality of the images.
Contrast agents can be used with MRI and are injected intravenously to enhance the
appearance of blood vessels, tumors, tissue damage, or inflammation.
The most common type of contrast/dye used is gadolinium. It is very safe, allergic reactions
rarely occur. Though gadolinium can be harmful to patients with kidney problems.
A radiologist will analyze the MRI scans and send a report to provider who shares the results
with the patient.
Risks
To date no side effects from the magnetic fields and radio waves have been reported.
The strong magnetic fields created during an MRI scan can cause damage to metal implants.
It can also cause a piece of metal inside your body to move or shift.
Normal values
A normal result means the body area being studied looks normal.
What Abnormal Results Mean
Results depend on the part of the body being examined and the nature of the problem.
Different types of tissues send back different MRI signals. For example, healthy tissue sends
back a slightly different signal than cancerous tissue.
PROS/ Benefits
 It provides good contrast between soft tissues.
 It is used to determine pathological tissues (ie brain tumor) from normal tissues.
 It’s non invasive and harmless to patient.
 It’s safe to use during pregnancy, no fetal harm caused.
 There is no ionizing radiation like CT and X-Ray scans which cause biological damage.
CONS/ Considerations
 It is very expensive
 You cannot scan a patient if they have irremovable metal implants, objects, etc.
o Aneurism coils/clips, cochlear implant, pace maker, heart valve, shrapnel, etc.
 The MRI machine is very loud!
 The scan process can take from 30 minutes to 2 hours depending on type.
 Most MRI machines enclose the patient in a small space and can cause claustrophobia.
 The patient must remain still during the scan and remaining immobile and in a position
ideal for the scan may cause patient discomfort.
Precautions/Safety
 Have pt wear hospital gown or clothing without metal fasteners
 Ear protection headphones should be worn by patient during scan.
 Metal objects in the room will fly toward the opening of the machine where the patient is
at high speeds and cause injury when scan is being done.
MRI scans provide the ability to distinguish separate structures a small distance apart from
each other (spatial resolution) similarly to a CT scan however the MRI scan provides the
ability to distinguish the differences between two similar but not identical tissues (contrast
resolution). X-ray does not clearly distinguish soft tissue.
MRI
CT Scan
X- Ray
References
http://www.nlm.nih.gov/medlineplus/ency/article/003335.htm
www.mayoclinic.com/health/mri/MY00227