Positron Emission Tomography, FDG

Positron Emission Tomography, FDG

Synonym/acronym: Fluorodeoxyglucose (FDG)-positron emission tomography (PET).

Common use

To assist in assessment, staging, and monitoring of metabolically active malignant lesions in the breast, abdomen, brain, and heart, such as breast cancer, Parkinson’s disease, and Alzheimer’s disease.

Area of application

Abdomen, brain, breast, heart, pelvis.

Contrast

IV radioactive material fluorodeoxyglucose (FDG).

Description

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 positron emission tomography (PET). The role of this procedure is to detect metabolically active malignant lesions. FDG-PET scan may also be used to stage and monitor the response to the malignant disease.

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. 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.

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. 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 physiological changes in psychosis and schizophrenia
  • Evaluate Alzheimer’s disease and differentiate it from other causes of dementia, as evidenced by decreased cerebral flow and metabolism
  • Evaluate coronary artery disease (CAD), as evidenced by decreased myocardial blood flow and myocardial perfusion
  • Evaluate myocardial viability, as evidenced by low glucose metabolism
  • Evaluate tumors preoperatively and postoperatively and determine grade, 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
  • Brain trauma
  • Breast cancer
  • Colorectal cancer
  • CAD
  • Epilepsy
  • Heart muscle dysfunction
  • Huntington’s disease
  • Infections
  • Lung cancer
  • Lymphoma
  • Melanoma
  • Metastatic disease
  • Myeloma
  • Ovarian cancer
  • Pancreatic cancer
  • Parkinson’s disease

Critical findings

    N/A

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, sedatives, 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, 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).
    • Excessive exercise in the preceding 3 days, which can cause factitious uptake of the contrast material in the musculature.
    • Excessive anxiety may affect valuation of brain function.
    • 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.
    • Consultation with a health-care provider (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 this test can assist in assessing blood flow and 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 cardiovascular, hematopoietic, neuromuscular, and reproductive systems; 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 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 the radionuclide poses no radioactive hazard and rarely produces side effects. Inform the patient that the procedure is performed in a nuclear medicine department, by an HCP specializing in this procedure, with support staff, and takes approximately 1 to 3 hr.
  • 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.
  • Instruct patients with diabetes to take their pretest dose of insulin at a meal 4 hr before the test.
  • 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 restrict food for 4 to 6 hr; restrict alcohol, nicotine, or caffeine-containing drinks for 24 hr; and withhold medications for 24 hr before the test. The exception is that there are no dietary restrictions for patients undergoing cardiac imaging. 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 prior to the procedure.
  • Ensure that the patient has removed 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.
  • 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.
  • Instruct the patient to cooperate fully and to follow directions. Instruct 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.
  • Cardiac imaging patients may be asked to drink glucose prior to the radionuclide injection.
  • Place the patient in the supine position on an examination table.
  • The radionuclide is injected, and imaging is started after a 30-min delay. Images may be recorded for up to 3 hr postinjection.
  • 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, and 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.
  • Nutritional Considerations: Abnormal findings may be associated with cardiovascular disease. Nutritional therapy is recommended for the patient identified to be at risk for developing CAD or for individuals who have specific risk factors and/or existing medical conditions (e.g., elevated LDL cholesterol levels, other lipid disorders, insulin-dependent diabetes, insulin resistance, or metabolic syndrome). Other changeable risk factors warranting patient education include strategies to encourage patients, especially those who are overweight and with high blood pressure, to safely decrease sodium intake, achieve a normal weight, ensure regular participation in moderate aerobic physical activity three to four times per week, eliminate tobacco use, and adhere to a heart-healthy diet. If triglycerides also are elevated, the patient should be advised to eliminate or reduce alcohol. The 2013 Guideline on Lifestyle Management to Reduce Cardiovascular Risk published by the American College of Cardiology (ACC) and the American Heart Association (AHA) in conjunction with the National Heart, Lung, and Blood Institute (NHLBI) recommends a “Mediterranean”-style diet rather than a low-fat diet. The new guideline emphasizes inclusion of vegetables, whole grains, fruits, low-fat dairy, nuts, legumes, and nontropical vegetable oils (e.g., olive, canola, peanut, sunflower, flaxseed) along with fish and lean poultry. A similar dietary pattern known as the Dietary Approaches to Stop Hypertension (DASH) diet makes additional recommendations for the reduction of dietary sodium. Both dietary styles emphasize a reduction in consumption of red meats, which are high in saturated fats and cholesterol, and other foods containing sugar, saturated fats, trans fats, and sodium.
  • No other radionuclide tests should be scheduled for 24 to 48 hr after this procedure.
  • 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. Decisions regarding the need for and frequency of breast self-examination, mammography, magnetic resonance imaging (MRI) of the breast, or other cancer screening procedures should be made after consultation between the patient and HCP. The most current guidelines for breast cancer screening of the general population as well as of individuals with increased risk are available from the American Cancer Society (www.cancer.org), the American College of Obstetricians and Gynecologists (ACOG) (www.acog.org), and the American College of Radiology (www.acr.org). 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 AFP, Alzheimer’s disease markers, amino acid screen, amylase, barium enema, biopsy breast, biopsy lung, bronchoscopy, calcitonin, cancer antigens, CBC WBC count and differential, CSF analysis, colonoscopy, CT abdomen, CT brain, CT pancreas, CT pelvis, cytology sputum, evoked brain potentials, exercise stress test, fecal analysis, gallium scan, laparoscopy abdominal, laparoscopy gyn, lymph-angiogram, mammography, MRI abdomen, MRI brain, MRI breast, MRI pelvis, myocardial perfusion heart scan, peritoneal fluid analysis, PET brain, PET heart, PET pelvis, proctosigmoidoscopy, stereotactic breast biopsy, US breast, US pancreas, US pelvis gyn, and WBC scan.
  • Refer to the Cardiovascular, Musculoskeletal, and Reproductive systems tables at the end of the book for related tests by body system.