Positron Emission Tomography, Brain

Positron Emission Tomography, Brain

Synonym/acronym: PET scan of the brain.

Common use

To assess blood flow and metabolic processes of the brain to assist in diagnosis of disorders such as ischemic or hemorrhagic stroke or cancer and to evaluate head trauma.

Area of application

Brain.

Contrast

IV radioactive material (fluorodeoxyglucose [FDG]).

Description

Positron emission tomography (PET) combines the biochemical properties of nuclear medicine with the accuracy of computed tomography (CT). PET uses positron emissions from specific radionuclides (oxygen, nitrogen, carbon, and fluorine) to produce detailed functional images within the body. After the radionuclide becomes concentrated in the brain, PET images of blood flow or metabolic processes at the cellular level can be obtained. Fluorine-18, in the form of fluorodeoxyglucose (FDG), is one of the more commonly used radionuclides. FDG is a glucose analogue, and because every cell uses glucose, the metabolic activity occurring in neurological conditions can be measured. There is little localization of FDG in normal tissue, allowing rapid detection of abnormal disease states. The brain uses oxygen and glucose almost exclusively to meet its energy needs, and therefore the brain’s metabolism has been studied widely with PET.

The positron radiopharmaceuticals generally have short half-lives, ranging from a few seconds to a few hours, and therefore they must be produced in a cyclotron located near where the test is being done. The PET scanner translates the emissions from the radioactivity as the positron combines with the negative electrons from the tissues and forms gamma rays that can be detected by the scanner. This information is transmitted to the computer, which determines the location and its distribution and translates the emissions as color-coded images for viewing, quantitative measurements, activity changes in relation to time, and three-dimensional computer-aided analysis. Each radionuclide tracer is designed to measure a specific body process, such as glucose metabolism, blood flow, or brain tissue perfusion. The radionuclide can be administered IV or inhaled as a gas. PET has had the greatest clinical impact in patients with epilepsy, dementia, neurodegenerative diseases, inflammation, cerebrovascular disease (indirectly), and brain tumors.

The expense of the study and the limited availability of radiopharmaceuticals limit the use of PET even though it is more sensitive than traditional nuclear scanning and single-photon emission computed tomography (SPECT). Changes in reimbursement and the advent of mobile technology have increased the availability of this procedure in the community setting.

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.

Indications

  • Detect Parkinson’s disease and Huntington’s disease, as evidenced by decreased metabolism
  • Determine the effectiveness of therapy, as evidenced by biochemical activity of normal and abnormal tissues
  • Determine physiological changes in psychosis and schizophrenia
  • Differentiate between tumor recurrence and radiation necrosis
  • Evaluate Alzheimer’s disease and differentiate it from other causes of dementia, as evidenced by decreased cerebral flow and metabolism
  • Evaluate cranial tumors pre- and postoperatively and determine stage and appropriate treatment or procedure
  • Identify cerebrovascular accident or aneurysm, as evidenced by decreased blood flow and oxygen use
  • Identify focal seizures, as evidenced by decreased metabolism between seizures

Potential diagnosis

Normal findings

  • Normal patterns of tissue metabolism, blood flow, and radionuclide distribution

Abnormal findings related to

  • Alzheimer’s disease
  • Aneurysm
  • Cerebral metastases
  • Cerebrovascular accident
  • Creutzfeldt-Jakob disease
  • Dementia
  • Head trauma
  • Huntington’s disease
  • Migraine
  • Parkinson’s disease
  • Schizophrenia
  • Seizure disorders
  • Tumors

Critical findings

  • Aneurysm
  • Cerebrovascular accident
  • 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

    • Inability of the patient to cooperate or remain still during the procedure because of age, significant pain, or mental status.
    • Drugs that alter glucose metabolism, such as tranquilizers or insulin, because hypoglycemia can alter PET results.
    • The use of alcohol, tobacco, or caffeine-containing drinks at least 24 hr before the study, because the effects of these substances would make it difficult to evaluate the patient’s true physiological state (e.g., alcohol is a vasoconstrictor and would decrease blood flow to the target organ).
    • Metallic objects (e.g., jewelry, body rings) within the examination field, which may inhibit organ visualization and cause unclear images.

  • Other considerations

    • Failure to follow dietary restrictions before the procedure may cause the procedure to be canceled or repeated.
    • Improper injection of the radionuclide that allows the tracer to seep deep into the muscle tissue produces erroneous hot spots.
    • False-positive findings may occur as a result of normal gastrointestinal tract uptake and uptake in areas of infection or inflammation.
    • Consultation with a 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 (www.pedrad.org/associations/5364/ig/).
    • Risks associated with radiation overexposure can result from frequent x-ray or radionuclide procedures. Personnel working in the examination area should wear badges to record their level of radiation exposure.

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 that this procedure can assist in assessing blood flow to the brain and brain tissue metabolism.
  • Obtain a history of the patient’s complaints or clinical symptoms, including a list of known allergens, especially allergies or sensitivities to latex, anesthetics, sedatives, or radionuclides.
  • Obtain a history of the patient’s musculoskeletal system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • 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 some pain may be experienced during the test, or there may be moments of discomfort. Reassure the patient that radioactive material poses minimal radioactive hazard because of its short half-life and rarely produces side effects. Inform the patient that the procedure is performed in a special department, usually in a radiology suite, by an HCP specializing in this procedure, with support staff, and takes approximately 60 to 120 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 such as normal saline, anesthetics, sedatives, radionuclides, medications used in the procedure, or emergency medications.
  • Sometimes FDG examinations are done after blood has been drawn to determine circulating blood glucose levels. If blood glucose levels are high, insulin may be given.
  • Instruct the patient to remove jewelry and other metallic objects from the area to be examined prior to the procedure.
  • Instruct the patient to avoid taking anticoagulant medication or to reduce dosage as ordered prior to the procedure.
  • Instruct the patient to restrict food for 4 hr; restrict alcohol, nicotine, or caffeine-containing drinks for 24 hr; and withhold medications for 24 hr before the test. Protocols may vary among facilities.
  • Make sure a written and informed consent has been signed prior to the procedure and before administering any medications.

Intratest

  • Potential complications:

  • Although it is rare, there is the possibility of allergic reaction to the radionuclide. Have emergency equipment and medications readily available. If the patient has a history of allergic reactions to any substance or drug, administer ordered prophylactic steroids or antihistamines before the procedure.

  • Establishing an IV site and injecting radionuclides is an invasive procedure. Complications are rare but do include bleeding from the puncture site related to a bleeding disorder, or the effects of natural products and medications known to act as blood thinners; hematoma related to blood leakage into the tissue following needle insertion; infection that might occur if bacteria from the skin surface is introduced at the puncture site; or nerve injury that might occur if the needle strikes a nerve.

  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient.
  • Ensure that the patient has complied with dietary, fluid, and medication restrictions and pretesting preparations.
  • Ensure the patient has removed all jewelry and external metallic objects from the area to be examined prior to 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 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. Ask the patient to remain still throughout the procedure because movement produces unreliable results.
  • Record baseline vital signs and assess neurological status. Protocols may vary among facilities.
  • Establish an IV fluid line for the injection of saline, anesthetics, sedatives, radionuclides, or emergency medications.
  • Place the patient in the supine position on an examination table.
  • The radionuclide is injected, and imaging is started after a 30-min delay. If comparative studies are indicated, additional injections may be needed.
  • The patient may be asked to perform different cognitive activities (e.g., reading) to measure changes in brain activity during reasoning or remembering.
  • The patient may be blindfolded or asked to use earplugs to decrease auditory and visual stimuli.
  • 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.
  • Instruct the patient to resume pretest diet, fluids, medications, or activity.
  • 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/catheter insertion site for bleeding, inflammation, or hematoma formation.
  • Instruct the patient in the care and assessment of the injection site.
  • Instruct the patient to apply cold compresses to the puncture site as needed to reduce discomfort or edema.
  • Instruct the patient to drink increased amounts of fluids for 24 to 48 hr to eliminate the radionuclide from the body, unless contraindicated. Educate the patient that radionuclide is eliminated from the body within 6 to 24 hr.
  • Instruct the patient to flush the toilet immediately after each voiding and to meticulously wash hands with soap and water for 24 hr after the procedure.
  • Instruct all caregivers to wear gloves when discarding urine for 24 hr after the procedure. Wash gloved hands with soap and water before removing gloves. Then wash hands after the gloves are removed.
  • If a woman who is breastfeeding must have a nuclear scan, she should not breastfeed the infant until the radionuclide has been eliminated, about 3 days. Instruct her to express the milk and discard it during the 3-day period to prevent cessation of milk production.
  • No other radionuclide tests should be scheduled for 24 to 48 hr after this procedure.
  • Recognize anxiety related to test results, and be supportive of perceived loss of independent function. 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 Alzheimer’s disease markers, CT brain, EEG, MRI brain, and US arterial Doppler of the carotids.
  • Refer to the Musculoskeletal System table at the end of the book for related tests by body system.