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Introduction ⬇

A brain perfusion scan provides information about regional perfusion and brain function, whereas CT and MRI show structural changes. Developments in radiopharmaceuticals and SPECT have rejuvenated brain imaging. Technetium complexes, such as 99mTc bicisate (ethyl cysteinate dimer) and 99mTc exametazime, are radiopharmaceuticals that cross the blood–brain barrier. The blood–brain barrier is not an anatomic structure but a complex system of select mechanisms that oppose the passage of most ions and high-molecular-weight compounds from the blood to the brain tissue. This complex system includes capillary endothelium with closed intracellular clefts, a small or absent extravascular fluid space between endothelium and glial sheaths, and the membrane of the neurons themselves. SPECT technology allows for three-dimensional slices, providing depth resolution from different angles.

Although PET imaging is more effective in functional diagnosis, SPECT is less expensive and more readily available. This test is indicated in both adults and children to determine brain death or the presence of encephalitis; it is also used in children with hydrocephalus, to localize epileptic foci, to assess metabolic activity, to evaluate brain tumors, and for the assessment of childhood development disorders.

Procedure ⬆ ⬇

  1. Inject the radionuclide intravenously. Prior to the injection, have the patient in a relaxed, controlled environment to minimize anxiety. For uncooperative children, do not use sedation until after the injection because it may affect brain activity. Secure the patient’s head during the scan.

  2. Begin imaging immediately after administration of the radiopharmaceutical agent or after a 1-hour delay. The test takes about 1 hour to complete.

  3. With the patient in the supine position, obtain SPECT images around the circumference of the head.

  4. With administration of iodoamphetamines, some departments require a dark and quiet environment.

  5. See Chapter 1 guidelines for safe, effective, informed intratest care.

Procedural Alert

For children, to localize of the area in the brain where a seizure originates, the radiopharmaceutical agent is injected at the time of a seizure (20-second window), and the child is immediately transported to the nuclear medicine department to obtain SPECT images. This scan is done under a controlled environment in which the child has been previously weaned from medication and under continuous observation by healthcare professionals

Clinical Implications ⬆ ⬇

  1. Abnormal radionuclide distribution patterns indicate:

    1. Alzheimer disease

    2. Stroke

    3. Dementia

    4. Seizure disorders

    5. Epilepsy

    6. Systemic lupus erythematosus

    7. Huntington disease

    8. Parkinson disease

    9. Psychiatric disorder (schizophrenia)

  2. The brain perfusion scan for a patient with suspected brain death shows a very distinct image: There is a lack of tracer uptake in the anterior and middle cerebral arteries and in the cerebral hemisphere, but perfusion is present in the scalp veins.

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain the purpose, procedure, benefits, and risk to patient or family, as indicated.

  2. Refer to standard NMI pretest precautions.

  3. Because precise head alignment is crucial, advise the patient to remain quiet and still.

  4. Obtain a careful neurologic history before testing.

  5. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Refer to standard NMI posttest precautions.

  2. Review test results; report and record findings. Modify the nursing care plan as needed. Monitor patient appropriately, especially if sedation is used.

  3. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆ ⬇

  1. Any patient motion (e.g., coughing, leg movement) can alter cerebral alignment.

  2. Sudden distractions or loud noises can alter the distribution of the radionuclide.

Reference Values ⬆

Normal

Normal extracranial and intracranial blood flow

Normal distribution, with highest uptake in the gray matter, basal ganglia, thalamus, and peripheral cortex and less activity in the central white matter and ventricles