Patient Education - Lung Cancer Program at UCLA
yourself about lung cancer:
A chest MRI uses powerful magnets and radio waves to create pictures of the body.
Conventional radiography and computed tomographic (CT) imaging use potentially
harmful radiation (x-rays) that passes through a patient to generate images. Magnetic
resonance imaging (MRI) is based on the magnetic properties of atoms, and there is
no exposure to the same type of radiation used in x-rays and CT scans.
A powerful magnet generates a magnetic field roughly 10,000 times stronger than
the Earth's. A very small percentage of hydrogen atoms within the body will align
with this field. Radio wave pulses are broadcast towards the aligned hydrogen atoms
in tissues of interest, returning a signal of their own. The slight differences of
those signals from different tissues enables MRI to tell the difference between various
organs, and potentially, provide contrast between benign and malignant tissue.
Any imaging angle, 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.
Nuclear magnetic resonance - chest; Magnetic resonance imaging - chest; NMR -
chest; MRI of the thorax
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 that
slides into a large, tunnel-like tube within the scanner.
If contrast dye is used, it will be injected into 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.
Depending on the sequences performed and the possibility of the need for a contrast
dye, a complete scan may take up to a hour or more. Newer scanners with more powerful
magnets, updated software, and advanced sequences may complete the process in less
How to Prepare for the Test
No special tests, diets, or medications are usually needed. An MRI may be performed
immediately after other imaging studies.
Because of the strong magnets, certain metallic objects are not allowed into the
room. Items such as jewelry, watches, credit cards, and hearing aids can be damaged.
Pins, hairpins, metal zippers, and similar metallic items can distort the images.
Removable dental work should be taken out just prior to the scan. Pens, pocketknives,
and eyeglasses can become dangerous projectiles when magnet is activated and should
not accompany the patient into the scanner area.
Because the strong magnetic fields can displace or disrupt the action of implanted
metallic objects, people with cardiac pacemakers cannot be scanned and should not
enter the MRI area. MRI also should not be used for people with metallic objects
in their bodies such as inner ear (cochlear) implants, brain aneurysm clips, some
artificial heart valves, older vascular stents, and recently placed artificial joints.
The technologist will usually provide you with a questionnaire which lists the potentially
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 a sweatsuit
or similar clothing without metal fasteners.
How the Test Will Feel
There is no pain. The magnetic field and radio waves are not felt. Some people
experience a claustrophobic feeling from being inside the scanner. 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 the examination time pass.
Excessive movement can blur MRI images and cause errors in the image. If the patient
has difficulty lying still or is very anxious, they may be given medicine to relax
them (a sedative), by mouth or through a vein. There is no recovery, unless sedation
was necessary. After an MRI scan, you can resume normal diet, activity, and medications.
Why the Test is Performed
A chest MRI provides detailed pictures of tissues within the chest cavity, without
image blocking by overlying bone. It may be used to:
- Clarify findings from previous x-rays or CT scans
- Show the structures of the chest from multiple angles
- Help diagnose abnormal growths and provide information for the staging (such
as the size, extent, and spread) of tumors in the chest cavity; MRI can distinguish
tumors or other lesions from normal tissues
- Show lymph nodes and blood vessels
- Evaluate blood flow
- Avoid the dangers of angiography, or of repeated exposure to radiation.
A normal MRI would not show any abnormalities in the size or position of organs
in the chest cavity, as viewed from any angle. The MRI would not reveal any new growths
or lesions. Organs would appear to be functioning normally (for those organs where
MRI can show function).
What Abnormal Results Mean
The sensitivity of MRI depends, in part, on the experience of the radiologist.
A chest MRI may reveal disorders including:
- Thymus tumor
- Lung masses
- Esophageal mass (clumping together of cells in the esophagus)
- Other masses or tumors of the chest
- Abnormal lymph nodes
- Swollen glands and enlarged lymph nodes in any location of the chest
- Chronic Obstructive Pulmonary Disease (COPD)
- Bronchial abnormalities
- Cystic lung lesions
- Pleural abnormalities, including thickening or pleural effusion
- Abnormal pulmonary vessels
- Coarctation of the aorta
- Aortic stenosis
- Aortic dissection
- Pericardial effusion
- Thoracic aortic aneurysm
Additional conditions under which the test may be performed:
- Atrial myxoma
- Atrial septal defect
- Cardiac tamponade
- Ischemic cardiomyopathy
- Mitral regurgitation - acute
- Mitral regurgitation - chronic
- Staging of tumors including invasion of blood vessels
- Mitral valve prolapse
- Bacterial pericarditis
- Constrictive pericarditis
- Pericarditis after heart attack
- Pulmonary edema
- Restrictive cardiomyopathy
- Skin lesion of histoplasmosis
- SVC obstruction
There is no ionizing radiation involved in MRI. To date, there have been no documented
significant side effects of the magnetic fields and radio waves used on the human
body during an MRI scan.
The most common MR intravenous contrast agent, gadolinium, is very safe, and although
there have been documented allergic reactions to it, it is an extremely rare occurrence.
However, gadolinium should not be given if you are pregnant because of potential
harm to the fetus.
If sedation is used, there are associated risks of over-sedation. The technologist
monitors the patient's vital signs, including heart rate and breathing as needed.
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.
MRI is more accurate than CT scan or other tests for certain conditions, but less
accurate for others. The disadvantages include the high cost, long duration of the
scan, and sensitivity to movement. People with claustrophobia (fear of enclosed spaces),
or people who are confused or anxious, may have difficulty lying still for the relatively
long scan times.
MRI is not portable and is incompatible with some metallic implants, life support-devices,
traction apparatus, and similar equipment.
MRI is a superior technique in most cases where telling differences in soft tissues
is necessary. It can show organs without blockage by bone and foreign bodies. It
can show the tissues from multiple viewpoints and is a noninvasive way to evaluate
blood flow. Currently, MRI is not valuable in the evaluation of slight changes of
the lung tissue, since the lungs contain mostly air and are difficult to image.
Review Date: 10/25/2006
Reviewed By: Stuart Bentley-Hibbert, M.D., Ph.D., Department of Radiology, Weill
Cornell Medical Center, New York, NY. Review provided by VeriMed Healthcare Network.
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