Norm of Cerebral Computed Tomography
Normal-appearing skull and symmetry and size of cerebral or other brain tissue. Cerebrum appears with black-gray shadings, and bone or other very dense tissues appear white. There is normally no evidence of tumor, high-density to whitish hematoma, edema, or congenital abnormalities such as hydrocephalus.
Usage of Cerebral Computed Tomography
Brain tumor (astrocytoma, meningioma, metastatic or primary lesions); cerebral atrophy or infarction; cerebral edema; cerebrovascular accident (CVA); evaluation of neurologic symptoms; evaluation of effects of surgery, radiation, or chemotherapeutic treatment of intracranial tumors; head injury; hematoma (epidural, subdural); hydrocephalus; subarachnoid hemorrhage and other acute hemorrhage.
Description of Cerebral Computed Tomography
Computed tomography (CT) uses special radiographic equipment and computers to produce a series of images (or tomographs) of cross sections of the brain tissues. Images may be “slices” taken of the skull and brain across anteroposterior, horizontal, sagittal, or coronal planes. Although contrast medium may be used, the test is often noninvasive and therefore provides a safe, effective diagnostic tool for the study of tumors of the brain, evaluation of neurologic clinical changes, evaluation of CVA or intracranial bleeds, and assessment of clients with possible head injury for hematoma before symptoms are evident. For evaluation of vascular malformations, high-resolution CT (HRCT) is preferred. HRCT improves upon traditional CT technology by providing optimized spatial resolution of body structures and better differentiation of normal from abnormal blood vessels. For rapid evaluation after stroke symptoms appear, spiral (helical) CT is the preferred method. (See also Computed tomography of the body for further description of the different types of CT technology available.)
Professional Considerations of Cerebral Computed Tomography
Consent form IS required when contrast medium is injected as part of the study.
Allergic reaction to contrast media (itching, hives, rash, tight feeling in the throat, shortness of breath, bronchospasm, anaphylaxis, death), dehydration, renal toxicity, vomiting.
Claustrophobia; dehydration; severe liver or kidney disease; previous allergy to contrast medium, iodine, or shellfish; pregnancy (relative contraindication); and renal insufficiency if CT with contrast will be performed. Weight >136 kg, or >300 pounds, may exceed the capabilities of some scanners.
During pregnancy, risks of cumulative radiation exposure to the fetus from this and other previous or future imaging studies must be weighed against the benefits of the procedure. Although formal limits for client exposure are relative to this risk:benefit comparison, the United States Nuclear Regulatory Commission requires that the cumulative dose equivalent to an embryo/ fetus from occupational exposure not exceed 0.5 rem (5 mSv). Risk of exposure to the uterus from cerebral CT is <10 mrad. Radiation dosage to the fetus decreases as pregnancy progresses.
- Remove all jewelry, hairpins, wigs, or dentures.
- Establish intravenous access if contrast medium will be used.
- Have emergency equipment readily available for CT with contrast medium if necessary.
- Just before beginning the procedure, take a “time out” to verify the correct client, procedure, and site.
- The client is placed on a movable radiographic table in a supine position. The table has a specialized headrest with straps that are positioned to immobilize the head.
- The table head is moved into a circular CT scanner, which moves around the client's head, taking an extensive series of radiographs at each degree of a 180-degree arch.
- The automated computer then produces a reconstruction of the images, which shows slices through the skull and the brain.
- The study may then continue to include intravenous administration of contrast material. A second series of views is completed. The client is observed for rash or respiratory difficulty, which may indicate reaction to the contrast medium. Reactions develop within 30 minutes.
- None for CT without contrast.
- For CT with contrast, observe for side effects such as headache, nausea, and vomiting and delayed hypersensitivity reaction.
- Resume previous diet.
Client and Family Teaching
- You must lie very still for this test.
- If a contrast medium will be used, fast from midnight before the test.
- Results are normally available the same day.
- Inform CT personnel if you feel claustrophobic in enclosed spaces.
Factors That Affect Results
- Movement of the client's head interferes with the quality of the films.
- Metal objects such as jewelry or hairpins interfere with complete visualization.
- Intracerebral hemorrhage is higher among Hispanics as a result of chronic hypertension; therefore cerebral CT should be considered.