Magnetic Resonance Imaging, Brain

Magnetic Resonance Imaging, Brain

Synonym/acronym: Brain MRI.

Common use

To visualize and assess intracranial abnormalities related to tumor, bleeding, lesions, and infarct such as stroke.

Area of application

Brain area.

Contrast

Can be done with or without IV contrast medium (gadolinium).

Description

Magnetic resonance imaging (MRI) is very useful when the area of interest is soft tissue. The technology does not involve radiation exposure and is considered safer than other imaging methods such as radiographs and computed tomography (CT). MRI uses a magnet and radio waves to produce an energy field that can be displayed as an image of the anatomic area of interest based on the water content of the tissue. The magnetic field causes the hydrogen atoms in tissue to line up, and when radio waves are directed toward the magnetic field, the hydrogen atoms absorb the radio waves and change their position. This change in the energy field is detected by the equipment, and an image is generated by the equipment's computer system. MRI produces cross-sectional images of pathological lesions of the brain in multiple planes without the use of ionizing radiation or the interference of bone or surrounding tissue. Images can be obtained in two-dimensional (series of slices) or three-dimensional sequences. Standard or closed MRI equipment has the appearance of an open tube or tunnel; open MRI equipment has no sides and provides an alternative for people who suffer from claustrophobia, pediatric patients, or patients who are obese. IV gadolinium-based contrast media may be used to better visualize the vessels and tissues in the area of interest. Clear, high-quality images of abnormalities and disease processes significantly improve the diagnostic value of the study.

Standard brain MRI can distinguish solid, cystic, and hemorrhagic components of lesions. This procedure is done to aid in the diagnosis of intracranial abnormalities, including tumors, ischemia, infection, and multiple sclerosis, and in assessment of brain maturation in pediatric patients. Rapidly flowing blood on spin-echo MRI appears as an absence of signal or a void in the vessel’s lumen. Blood flow can be evaluated in the cavernous and carotid arteries. Contrast-enhanced imaging is effective for enhancing differences between normal and abnormal tissues. Aneurysms may be diagnosed without traditional iodine-based contrast angiography, and old clotted blood in the walls of the aneurysm appear white. MRI uses the noniodinated contrast medium gadopentetate dimeglumine (Magnevist), which is administered IV.

Functional MRI (fMRI) is a neuroimaging application of MRI used to study how the brain is working. It identifies changes in blood flow, reflected by changes in the level of blood oxygenation, in response to activity. fMRI can identify metabolic changes in normal, diseased, or injured brain tissue. It is also used in research to study which parts of the brain are responsible for speech, physical movement, thought, and sensations; this type of research is also called brain mapping that has significant implications in understanding and managing the effects of stroke, brain tumors, and diseases like Alzheimer's. fMRI is based on the blood oxygen level–dependent (BOLD) contrast mechanism that takes advantage of the inherent paramagnetic quality of deoxyhemoglobin. In a properly performed study, the patient is asked to perform a task; the MRI scanner detects changes in the signal strength of brain water protons produced as blood oxygen levels change, and the corresponding strength of the natural paramagnetic signal of deoxyhemoglobin changes.

This procedure is contraindicated for

  • high alert Patients who are pregnant or suspected of being pregnant, unless the potential benefits of the MRI far outweigh the risks to the fetus and mother. In pregnancy, gadolinium-based contrast agents (GBCAs) cross the placental barrier, enter the fetal circulation, and pass via the kidneys into the amniotic fluid. Although no definite adverse effects of GBCA administration on the human fetus have been documented, the potential bioeffects of fetal GBCA exposure are not well understood. GBCA administration should therefore be avoided during pregnancy unless no suitable alternative imaging is possible and the benefits of contrast administration outweigh the potential risk to the fetus.
  • high alert Patients with moderate to marked renal impairment (glomerular filtration rate less than 30 mL/min/1.73 m2). Patients should be screened for renal dysfunction prior to administration. The use of GBCAs should be avoided in these patients unless the benefits of the studies outweigh the risks and if essential diagnostic information is not available using non–contrast-enhanced diagnostic studies.
  • high alert Patients with cardiac pacemakers that can be deactivated by MRI.
  • high alert Patients with metal in their body, such as dental amalgams, metallic body piercing items, tattoo inks containing iron (including tattooed eyeliners), shrapnel, bullet, ferrous metal in the eye, certain ferrous metal prosthetics, valves, aneurysm clips, IUD, inner ear prostheses, or other metallic objects; these items can impair image quality. Metallic objects are also a significant safety issue for patients and health-care staff in the examination room during performance of an MRI. The MRI equipment consists of an extremely powerful magnet that can inactivate, move, or shift metallic objects inside a patient. Many metallic objects currently used in health-care procedures are made of materials that do not interfere with MRI studies; it is important for patients to provide specific information regarding medical procedures they have undergone in order to identify whether their device is safe to undergo MRI. Required information includes the date of the procedure and identification of the device. Metallic objects are not allowed inside the room with the MRI equipment because items such as watches, credit cards, and car keys can become dangerous projectiles.
  • high alert Patients with transdermal patches containing metallic components. The patch's liner contains a metal that controls absorption of the substance from the patch (e.g., drugs, nicotine, steroids, hormones). The patch may cause burns to the skin related to energy conducted through the metal which is converted to heat during the MRI. Other metallic objects on the skin may also cause burns.
  • high alert Patients who are claustrophobic.

Indications

  • Detect and locate brain tumors
  • Detect cause of cerebrovascular accident, cerebral infarct, or hemorrhage
  • Detect cranial bone, face, throat, and neck soft tissue lesions
  • Evaluate the cause of seizures, such as intracranial infection, edema, or increased intracranial pressure
  • Evaluate cerebral changes associated with dementia
  • Evaluate demyelinating disorders
  • Evaluate intracranial infections
  • Evaluate optic and auditory nerves
  • Evaluate the potential causes of headache, visual loss, and vomiting
  • Evaluate shunt placement and function in patients with hydrocephalus
  • Evaluate the solid, cystic, and hemorrhagic components of lesions
  • Evaluate vascularity of the brain and vascular integrity
  • Monitor and evaluate the effectiveness of medical or surgical interventions, chemotherapy, radiation therapy, and the course of disease

Potential diagnosis

Normal findings

  • Normal anatomic structures, soft tissue density, blood flow rate, face, nasopharynx, neck, tongue, and brain

Abnormal findings related to

  • Abscess
  • Acoustic neuroma
  • Alzheimer’s disease
  • Aneurysm
  • Arteriovenous malformation
  • Benign meningioma
  • Cerebral aneurysm
  • Cerebral infarction
  • Craniopharyngioma or meningioma
  • Granuloma
  • Intraparenchymal hematoma or hemorrhage
  • Lipoma
  • Metastasis
  • Multiple sclerosis
  • Optic nerve tumor
  • Parkinson’s disease
  • Pituitary microadenoma
  • Subdural empyema
  • Ventriculitis

Critical findings

  • Abscess
  • Cerebral aneurysm
  • Cerebral infarct
  • Hydrocephalus
  • Skull fracture or contusion
  • Tumor with significant mass effect

  • It is essential that a critical finding be communicated immediately to the requesting health-care provider (HCP). A listing of these findings varies among facilities.

  • Timely notification of a critical finding for lab or diagnostic studies is a role expectation of the professional nurse. Notification processes will vary among facilities. Upon receipt of the critical value the information should be read back to the caller to verify accuracy. Most policies require immediate notification of the primary HCP, Hospitalist, or on-call HCP. Reported information includes the patient’s name, unique identifiers, critical value, name of the person giving the report, and name of the person receiving the report. Documentation of notification should be made in the medical record with the name of the HCP notified, time and date of notification, and any orders received. Any delay in a timely report of a critical finding may require completion of a notification form with review by Risk Management.

Interfering factors

  • Factors that may impair clear imaging

    • Metallic objects (e.g., jewelry, body rings, dental amalgams) within the examination field, which may inhibit organ visualization and cause unclear images.
    • Inability of the patient to cooperate or remain still during the procedure because of age, significant pain, or mental status.
    • Patients with extreme cases of claustrophobia, unless sedation is given before the study or an open MRI is utilized.

  • Other considerations

    • If contrast medium is allowed to seep deep into the muscle tissue, vascular visualization will be impossible.

Nursing Implications and Procedure

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this procedure can assist in assessing the brain.
  • Obtain a history of the patient’s complaints or clinical symptoms, including a list of known allergens, especially allergies or sensitivities to latex, anesthetics, contrast medium, or sedatives. Patients with a known hypersensitivity to contrast medium may benefit from premedication with corticosteroids and diphenhydramine.
  • Obtain a history of the patient’s cardiovascular and neuromuscular systems, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures. Obtain a history of renal dysfunction if the use of GBCA is anticipated.
  • Ensure the results of BUN, creatinine, and eGFR (estimated glomerular filtration rate) are obtained if GBCA is to be used.
  • Determine if the patient has ever had any device implanted into his or her body, including copper intrauterine devices, pacemakers, ear implants, and heart valves.
  • Obtain occupational history to determine the presence of metal in the body, such as shrapnel or flecks of ferrous metal in the eye (which can cause retinal hemorrhage).
  • Note any recent procedures that can interfere with test results, including examinations using barium- or iodine-based contrast medium.
  • Record the date of the last menstrual period and determine the possibility of pregnancy in perimenopausal women.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
  • Review the procedure with the patient. Address concerns about pain related to the procedure and explain that no pain will be experienced during the test, but there may be moments of discomfort. Reassure the patient that if contrast is used, it poses no radioactive hazard and rarely produces side effects. Inform the patient the procedure is performed in an MRI department, usually by an HCP who specializes in this procedure, with support staff, and takes approximately 30 to 60 min.
  • Inform the patient that the technologist will place him or her in a supine position on a flat table in a large cylindrical scanner.
  • Tell the patient to expect to hear loud banging from the scanner and possibly to see magnetophosphenes (flickering lights in the visual field); these will stop when the procedure is over.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Explain that an IV line may be inserted to allow infusion of IV fluids such as saline, anesthetics, contrast medium, or sedatives.
  • Instruct the patient to remove jewelry and all other metallic objects from the area to be examined prior to the procedure.
  • Note that there are no food, fluid, or medication restrictions unless by medical direction.

Intratest

  • Potential complications:

  • Injection of the contrast is an invasive procedure. Complications are rare but do include risk for allergic reaction related to contrast reaction; cardiac arrhythmias; hematoma related to blood leakage into the tissue following needle insertion; bleeding from the puncture site related to a bleeding disorder, or the effects of natural products and medications known to act as blood thinners; vascular or nerve injury that might occur if the needle strikes a nerve or nearby blood vessel; or infection that might occur if bacteria from the skin surface is introduced at the puncture site.

  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient.
  • Ensure that the patient has removed all external metallic objects from the area to be examined prior to the procedure.
  • Administer ordered prophylactic steroids or antihistamines before the procedure if the patient has a history of allergic reactions to any substance or drug.
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Have emergency equipment readily available.
  • Instruct the patient to void prior to the procedure and to change into the gown, robe, and foot coverings provided.
  • Instruct the patient to cooperate fully and to follow directions. Instruct the patient to remain still throughout the procedure because movement produces unreliable results.
  • Supply earplugs to the patient to block out the loud, banging sounds that occur during the test. Instruct the patient to communicate with the technologist during the examination via a microphone within the scanner.
  • Apply MRI-safe electrodes to the appropriate sites if an electrocardiogram or respiratory gating is to be performed in conjunction with the scan.
  • Establish IV fluid line for the injection of IV fluids such as saline, anesthetics, contrast medium, or sedatives.
  • Administer an antianxiety agent, as ordered, if the patient has claustrophobia. Administer a sedative to a child or to an uncooperative adult, as ordered.
  • Assist the patient onto the examination table and into the appropriate position for imaging to begin.
  • Imaging can begin shortly after the injection, if contrast is used.
  • Ask the patient to inhale deeply and hold his or her breath while the images are taken and then to exhale after the images are taken.
  • Instruct the patient to take slow, deep breaths if nausea occurs during the procedure.
  • Monitor the patient for complications related to the procedure (e.g., allergic reaction, anaphylaxis, bronchospasm).
  • Remove the needle or catheter and apply a pressure dressing over the puncture site.
  • Observe/assess the needle/catheter insertion site for bleeding, inflammation, or hematoma formation.

Post-Test

  • Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Observe for delayed allergic reactions, such as rash, urticaria, tachycardia, hyperpnea, hypertension, palpitations, nausea, or vomiting, if contrast medium was used.
  • Instruct the patient to immediately report symptoms such as fast heart rate, difficulty breathing, skin rash, itching, chest pain, persistent right shoulder pain, or abdominal pain. Immediately report symptoms to the appropriate HCP.
  • Instruct the patient to apply cold compresses to the puncture site as needed to reduce discomfort or edema.
  • Recognize anxiety related to test results. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include Alzheimer’s disease markers, angiography of the carotids, BUN, CSF analysis, CT brain, creatinine, EMG, evoked brain potentials, and PET brain.
  • Refer to the Cardiovascular and Musculoskeletal systems tables at the end of the book for related tests by body system.