Computed Tomography, Brain

Computed Tomography, Brain

Synonym/acronym: Computed axial tomography (CAT) of the head, computed transaxial tomography (CTT) of the head, brain CT, helical/spiral CT.

Common use

To visualize and assess the brain to assist in diagnosing tumor, bleeding, infarct, infection, structural changes, and edema. Also valuable in evaluation of medical, radiation, and surgical interventions.

Area of application



With or without IV iodinated contrast medium.


Computed tomography (CT) of the brain is a noninvasive procedure used to assist in diagnosing abnormalities of the head, brain tissue, cerebrospinal fluid, and blood circulation. It becomes invasive if contrast medium is used. During the procedure, the patient lies on a motorized table. The table is moved in and out of a circular opening in a doughnut-like device called a gantry, which houses the x-ray tube and associated electronics. A beam of x-rays irradiates the patient as the table moves in and out of the scanner in a series of phases. Multiple detectors rotate around the patient to produce cross-sectional views or slices. The slices can be viewed individually or as a three-dimensional image. Multislice or multidetector CT (MDCT) scanners continuously collect images in a helical or spiral fashion instead of a series of individual images as with standard scanners. Helical CT is capable of collecting many images over a short period of time (seconds), is very sensitive in identifying small abnormalities, and produces high-quality images. Differences in tissue density are detected and recorded and are viewable as computerized digital images. Slices or thin sections of certain anatomic views of the brain and associated vascular system are viewed to allow differentiations of solid, cystic, inflammatory, or vascular lesions, as well as identification of suspected aneurysms, intracranial bleeds, and subdural or epidural hematomas. The procedure may be repeated after intravenous injection of iodinated contrast medium for vascular evaluation. Tumor progression, before and after therapy, and effectiveness of medical interventions may be monitored by CT scanning. Xenon-enhanced CT scanning is an imaging method used to assess cerebral blood flow. Xenon-133 is an odorless, colorless, radioactive gas that can either be inhaled or injected. The isotope moves rapidly through the blood into the brain. The diffused gas demonstrates how much blood goes to each area of the brain. Sensitivity of stroke detection in the acute phase is increased by using Xenon.

This procedure is contraindicated for

  • high alertPatients who are pregnant or suspected of being pregnant, unless the potential benefits of a procedure using radiation far outweigh the risk of radiation exposure to the fetus and mother.
  • high alertPatients who are claustrophobic.
  • high alertPatients with conditions associated with adverse reactions to contrast medium (e.g., asthma, food allergies, or allergy to contrast medium). Although patients are still asked specifically if they have a known allergy to iodine or shellfish, it has been well established that the reaction is not to iodine, in fact an actual iodine allergy would be very problematic because iodine is required for the production of thyroid hormones. In the case of shellfish the reaction is to a muscle protein called tropomyosin; in the case of iodinated contrast medium the reaction is to the noniodinated part of the contrast molecule. Patients with a known hypersensitivity to the medium may benefit from premedication with corticosteroids and diphenhydramine; the use of nonionic contrast or an alternative noncontrast imaging study, if available, may be considered for patients who have severe asthma or who have experienced moderate to severe reactions to ionic contrast medium.
  • high alertPatients with conditions associated with preexisting renal insufficiency (e.g., renal failure, single kidney transplant, nephrectomy, diabetes, multiple myeloma, treatment with aminoglycosides and NSAIDs) because iodinated contrast is nephrotoxic.
  • high alertElderly and compromised patients who are chronically dehydrated before the test, because of their risk of contrast-induced renal failure.
  • high alertPatients with pheochromocytoma, because iodinated contrast may cause a hypertensive crisis.
  • high alertPatients with bleeding disorders or receiving anticoagulant therapy because the puncture site may not stop bleeding.


  • Detect brain infection, abscess, or necrosis, as evidenced by decreased density on the image
  • Detect ventricular enlargement or displacement by increased cerebrospinal fluid
  • Determine benign and cancerous intracranial tumors and cyst formation, as evidenced by changes in tissue densities
  • Determine cause of increased intracranial pressure
  • Determine presence and type of hemorrhage in infants and children experiencing signs and symptoms of intracranial trauma or congenital conditions such as hydrocephalus and arteriovenous malformations (AVMs)
  • Determine presence of multiple sclerosis, as evidenced by sclerotic plaques
  • Determine lesion size and location causing infarct or hemorrhage
  • Differentiate hematoma location after trauma (e.g., subdural, epidural, cerebral) and determine extent of edema, as evidenced by higher blood densities
  • Differentiate between cerebral infarction and hemorrhage
  • Evaluate abnormalities of the middle ear ossicles, auditory nerve, and optic nerve
  • Monitor and evaluate the effectiveness of medical, radiation, or surgical therapies

Potential diagnosis

Normal findings

  • Normal size, position, and shape of intracranial structures and vascular system

Abnormal findings related to

  • Abscess
  • Alzheimer’s disease
  • Aneurysm
  • AVMs
  • Cerebral atrophy
  • Cerebral edema
  • Cerebral infarction
  • Congenital abnormalities
  • Craniopharyngioma
  • Cysts
  • Hematomas (e.g., epidural, subdural, intracerebral)
  • Hemorrhage
  • Hydrocephaly
  • Increased intracranial pressure or trauma
  • Infection
  • Sclerotic plaques suggesting multiple sclerosis
  • Tumor
  • Ventricular or tissue displacement or enlargement

Critical findings

  • Abscess
  • Acute hemorrhage
  • Aneurysm
  • Infarction
  • Infection
  • 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, dentures, body rings) within the examination field, which may inhibit organ visualization and cause unclear images.
    • Patients who are very obese or who may exceed the weight limit for the equipment.
    • Patients with extreme claustrophobia unless sedation is given before the study.
    • Patient who are unable to cooperate or remain still during the procedure because of age, significant pain, or mental status.
  • Other considerations

    • The procedure may be terminated if chest pain or severe cardiac arrhythmias occur.
    • Failure to follow dietary restrictions and other pretesting preparations may cause the procedure to be canceled or repeated.
    • Consultation with the HCP should occur before the procedure for radiation safety concerns regarding younger patients or patients who are lactating. Pediatric & Geriatric Imaging Children and geriatric patients are at risk for receiving a higher radiation dose than necessary if settings are not adjusted for their small size. Pediatric Imaging Information on the Image Gently Campaign can be found at the Alliance for Radiation Safety in Pediatric Imaging (
    • Risks associated with radiation overexposure can result from frequent x-ray procedures. Personnel in the room with the patient should wear a protective lead apron, stand behind a shield, or leave the area while the examination is being done. Personnel working in the examination area should wear badges to record their level of radiation exposure.

Nursing Implications and Procedure


  • 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, or contrast medium.
  • Obtain a history of the patient’s musculoskeletal system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Ensure results of coagulation testing are obtained and recorded prior to the procedure; BUN and creatinine results are also needed if contrast medium is to be used.
  • Note any recent procedures that can interfere with test results, including examinations using barium- or iodine-based contrast medium. Ensure that barium studies were performed more than 4 days before the CT scan.
  • 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 anticoagulants, aspirin and other salicylates, herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus). Note the last time and dose of medication taken.
  • Note that if iodinated contrast medium is scheduled to be used in patients receiving metformin (Glucophage) for non-insulin-dependent (type 2) diabetes, the drug should be discontinued on the day of the test and continue to be withheld for 48 hr after the test. Iodinated contrast can temporarily impair kidney function, and failure to withhold metformin may indirectly result in drug-induced lactic acidosis, a dangerous and sometimes fatal side effect of metformin related to renal impairment that does not support sufficient excretion of metformin.
  • Review the procedure with the patient. Address concerns about pain and explain that there may be moments of discomfort and some pain experienced during the test. Inform the patient the procedure is usually performed in a radiology suite by an HCP specializing in this procedure, with support staff, and takes approximately 15 to 30 min.
  • 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 (e.g., normal saline), contrast medium, dye, or sedatives.
  • Inform the patient that he or she may experience nausea, a feeling of warmth, a salty or metallic taste, or a transient headache after injection of contrast medium.
  • Instruct the patient to remove dentures and jewelry and other metallic objects from the area to be examined.
  • Note that there are no food or fluid restrictions unless by medical direction. Instruct the patient to avoid taking anticoagulant medication or to reduce dosage as ordered prior to the procedure. Protocols may vary among facilities.
  • Make sure a written and informed consent has been signed prior to the procedure and before administering any medications.


  • Potential complications:
  • Injection of the contrast through IV tubing into a blood vessel 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 insertion of the IV needle, or infection that might occur if bacteria from the skin surface is introduced at the IV needle insertion site.

  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient.
  • Ensure the patient has complied with medication restrictions and pretesting preparations.
  • Ensure the patient has removed dentures and 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. Use nonionic contrast medium for the procedure.
  • 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 cooperate fully and to follow directions. Instruct the patient to remain still throughout the procedure because movement produces unreliable results.
  • Establish an IV fluid line for the injection of contrast medium, emergency drugs, and 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.
  • Place the patient in the supine position on an examination table.
  • If contrast media is used, a rapid series of images is taken during and after injection.
  • 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) if contrast is used.
  • The needle is removed, and a pressure dressing is applied over the puncture site.
  • Observe/assess the needle insertion site for bleeding, inflammation, or hematoma formation.


  • 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.
  • Instruct the patient to resume medications and activity, as directed by the HCP. Renal function should be assessed before metformin is resumed, if contrast was used.
  • Monitor vital signs and neurological status every 15 min for 1 hr, then every 2 hr for 4 hr, and then as ordered by the HCP. Monitor temperature every 4 hr for 24 hr. Monitor intake and output at least every 8 hr. Compare with baseline values. Notify the HCP if temperature is elevated. Protocols may vary among facilities.
  • If contrast was used, observe for delayed allergic reactions, such as rash, urticaria, tachycardia, hyperpnea, hypertension, palpitations, nausea, or vomiting.
  • 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.
  • Observe/assess the needle insertion site for bleeding, inflammation, or hematoma formation.
  • Instruct the patient in the care and assessment of the site.
  • Instruct the patient to apply cold compresses to the puncture site as needed, to reduce discomfort or edema.
  • Instruct the patient to increase fluid intake to help eliminate the contrast medium, if used.
  • Inform the patient that diarrhea may occur after ingestion of oral contrast medium.
  • 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 needed 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 angiography carotid, audiometry hearing loss, BUN, CSF analysis, CBC, CBC hematocrit, CBC hemoglobin, CT angiography, creatinine, EEG, EMG, evoked brain potentials, MR angiography, MRI brain, nerve fiber analysis, otoscopy, PET brain, PT/INR, spondee speech reception threshold, and tuning fork tests.
  • Refer to the Musculoskeletal System table at the end of the book for related tests by body system.
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