Patient Education - Lung Cancer Program at UCLA
yourself about lung cancer:
MRI of the head
An MRI of the head is a noninvasive procedure that uses powerful magnets and
radio waves to construct clear, detailed pictures of brain tissues.
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. These errors are called artifacts.
Nuclear magnetic resonance - cranial; Magnetic resonance imaging - cranial; Head
MRI scan; MRI - cranial; NMR - cranial; Cranial MRI
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.
You will lie on a narrow table which slides into a large tunnel-like tube within
the scanner. In addition, a small device may be placed around the head. This is a
special body coil which sends and receives the radio wave pulses. It is designed
to improve the quality of the images.
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 sweat suit 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
MRI provides detailed pictures of the brain and nerve tissues from multiple angles
without obstruction by overlying bone. In fact, about 90% of all MRI scans are for
brain or spine disorders.
MRI is the procedure of choice for most brain disorders. MRI is particularly useful
in brain and neurological disorders, because it can clearly show different types
of nerve tissue. It provides clear pictures of the brainstem and posterior brain,
which are difficult to view on CT scan. It is also useful for the diagnosis of demyelinating
disorders. These are disorders such as multiple sclerosis, which cause destruction
of the myelin covering of the nerve.
MRI is a noninvasive procedure that can evaluate blood flow and the flow of cerebrospinal
fluid (CSF). MRI can distinguish tumors or other lesions from normal tissues. MRI
is sometimes used to avoid the dangers of angiography or of repeated exposure to
What Abnormal Results Mean
The sensitivity of an MRI depends, in part, on the experience of the radiologist.
An MRI of the head may reveal disorders including:
- Primary brain tumors
- Metastatic brain tumors
- Structural abnormalities of the brain, brain ventricles, and pituitary gland
- Pituitary masses
- Lesions or masses (any location)
- Acoustic neuroma
- Optic glioma
- Arteriovenous malformations of the head
- Brain aneurysms
- Damage to basal ganglia (an area of the brain that regulates movement)
- Subdural hematoma, blood clots
- Intracranial hemorrhage (more than 48 hours old)
- Radiation damage to the brain
- Brain swelling
- Demyelinating diseases
- Tissue destruction in the brain
- Brain abscess
- Abnormalities of blood flow (such as carotid artery stenosis)
Additional conditions under which the test may be performed:
- Amyotrophic lateral sclerosis
- Throat cancer
- Chronic subdural hematoma
- Cushing's syndrome
- Deep intracerebral hemorrhage
- Dementia due to metabolic causes
- Diabetes insipidus; central
- Hemorrhagic (bleeding) stroke
- Huntington's disease
- Hypertensive intracerebral hemorrhage
- Intracerebral hemorrhage
- Lobar intracerebral hemorrhage
- Melanoma of the eye
- Meniere's disease
- Multi-infarct dementia
- Multiple endocrine neoplasia (MEN) I
- Multiple sclerosis
- Normal pressure hydrocephalus (NPH)
- Partial (focal) seizure
- Partial complex seizure
- Petit mal seizure
- Pituitary Cushing's (Cushing's disease)
- Reye's syndrome
- Senile cerebral amyloid angiopathy
- Senile dementia/Alzheimer's type
- Acute sinusitis
- Chronic sinusitis
- Stroke secondary to atherosclerosis
- Stroke secondary to cardiogenic embolism
- Stroke secondary to FMD
- Stroke secondary to syphilis
- Temporomandibular joint (TMJ) syndrome
- Transient ischemic attack (TIA)
- Wernicke-Korsakoff syndrome
- Wilson's disease
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 superior to computed tomography (CT) in most cases where differentiation of
soft tissues is necessary. It can view organs without obstruction by bone and foreign
bodies. It is capable of showing the tissues from multiple viewpoints and is a noninvasive
way to evaluate blood flow.
A CT scan may be preferred for:
- Acute trauma of the head and face
- Acute (less than 72 hours) neurological dysfunction
- Early symptoms of stroke
- Subarachnoid or intracranial hemorrhage (within the first 24 - 48 hours)
- Skull bone disorders, disorders involving the bones of the ear
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.
Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission
(www.urac.org). URAC's accreditation program is an independent audit to verify that
A.D.A.M. follows rigorous standards of quality and accountability. A.D.A.M. is among
the first to achieve this important distinction for online health information and
services. Learn more about A.D.A.M.'s editorial policy, editorial process and privacy
policy. A.D.A.M. is also a founding member of Hi-Ethics and subscribes to the principles
of the Health on the Net Foundation (www.hon.ch).
The information provided herein should not be used during any medical emergency or for
the diagnosis or treatment of any medical condition. A licensed medical professional should
be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for
all medical emergencies. Links to other sites are provided for information only -- they do
not constitute endorsements of those other sites. © 1997- 2007 A.D.A.M., Inc. Any duplication
or distribution of the information contained herein is strictly prohibited.