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Nuclear Medicine Studies 9 Overview of Nuclear Medicine Studies / 669 • Principles of Nuclear Medicine / 669 • Principles of Imaging / 671 • General Procedure / 671 • Benefits and Risks / 672 • Clinical Considerations / 672 • Interventions / 672 • Pediatric Nuclear Medicine Considerations / 673 ● GASTROINTESTINAL STUDIES / 690 Hepatobiliary (Gallbladder, Biliary) Imaging With Cholecystokinin / 690 Gastroesophageal Reflux Imaging / 691 Gastric Emptying Imaging / 692 Gastrointestinal Bleeding Imaging / 694 Parotid (Salivary) Gland Imaging / 695 Liver/Spleen Imaging and Liver RBC Imaging / 696 Meckel’s Diverticulum Imaging / 697 ● CARDIAC STUDIES / 674 Myocardial Perfusion: Rest and Stress (Sestamibi/ Tetrofosmin/Thallium Stress Test) / 674 Myocardial Infarction (PYP) Imaging / 676 Multigated Acquisition (MUGA) Imaging: Rest and Stress / 677 Cardiac Flow Study (First-Pass Study; Shunt Imaging) / 678 ● NEUROLOGIC STUDIES / 698 Brain Imaging and Cerebral Blood Flow Imaging / 698 Cisternography (Cerebrospinal Fluid Flow Imaging) / 699 DaTscan Imaging / 700 ● ENDOCRINE STUDIES / 680 Thyroid Imaging / 680 Radioactive Iodine (RAI) Uptake Test / 681 Adrenal Gland (MIBG) Imaging / 683 Parathyroid Imaging / 685 ● GENITOURINARY STUDIES / 686 Renogram: Kidney Function and Renal Blood Flow Imaging (With Furosemide or Captopril/Enalapril) / 686 Testicular (Scrotal) Imaging / 687 ProstaScint Imaging / 688 Vesicoureteric Reflux (Bladder and Ureters) Imaging / 689 ● PULMONARY STUDIES / 701 Lung Scan (Ventilation and Perfusion Imaging) / 701 ● ORTHOPEDIC STUDIES / 703 Bone Imaging / 703 Bone Mineral Density (Bone Densitometry; Osteoporosis Imaging) / 705 ● TUMOR IMAGING STUDIES / 707 Gallium (67Ga) Imaging / 707 ● OVERVIEW OF MONOCLONAL ANTIBODY TUMOR IMAGING (ONCOSCINT, PROSTASCINT, OCTREOTIDE, AND OTHER PEPTIDES) / 709 Antibody and Peptide Tumor Imaging / 709 Iodine-131 Whole-Body (Total-Body) Imaging / 710 Breast Imaging (Scintimammography); Lymph Node Imaging (Lymphoscintigraphy) / 711 668 Fischbach_Ch09_printer_file.indd 668 11/4/13 10:27 PM ● ● INFLAMMATORY PROCESS IMAGING / 713 Leukocyte (WBC) Imaging (Indium- or CeretecLabeled WBCs) / 713 ● OVERVIEW OF RADIONUCLIDE (NON-RADIOIMMUNOASSAY) LABORATORY STUDIES / 714 Total Blood Volume; Plasma Volume; Erythrocyte (RBC) Volume / 714 Red Blood Cell (RBC) Survival Time Test / 716 Overview of Nuclear Medicine Studies 669 ● OVERVIEW OF POSITRON EMISSION TOMOGRAPHY (PET) IMAGING STUDIES / 717 Brain Imaging / 719 Cardiac Imaging / 720 Tumor Imaging / 721 OVERVIEW OF NUCLEAR MEDICINE STUDIES Nuclear medicine is a diagnostic modality that studies the physiology or function of any organ system in the body. Other diagnostic imaging modalities, such as ultrasound, magnetic resonance imaging (MRI), computed tomography (CT), and x-ray, generally visualize anatomic structures. A pharmaceutical is labeled with a radioactive isotope to form a radiopharmaceutical. The radioisotope emits gamma and positron rays. Radioisotopes are reactor produced (iodine-131 [131I]), cyclotron produced (fluorine-18 [18F] for positron emission tomography [PET]), or generator produced (technetium-99m [99mTc]). To visualize the function of an organ system, a radiopharmaceutical is administered. A time delay (in some cases, up to several hours) may be required for the radiopharmaceutical to reach its target site, and then the organ of interest is imaged with a gamma camera. Image formation technology involves the detection with very great density of a signal (gamma rays) emanating from the radioactive isotope. There is very little signal in the image that does not come from the radiopharmaceutical. The normal background level of radiation within the human body is minimal, with small amounts of radioactive potassium and some cesium. Routes of radiopharmaceutical administration vary with the specific study. Most commonly, a radiopharmaceutical is injected through a vein in the arm or hand. Other routes of administration include the oral, intramuscular, inhalation, intrathecal (within the subdural or subarachnoid space), subcutaneous, and intraperitoneal (within the peritoneal cavity) routes. See Table 9.1 for possible side effects of or adverse reactions to the administration of radiopharmaceuticals. Nuclear medicine studies are performed by certified nuclear medicine technologists, interpreted by radiologists or nuclear medicine physicians, and performed in a hospital or clinic-based nuclear medicine department. The collaborative approach to care is evidenced by interventions from pharmacists, laboratory personnel, and nurses, among others. Principles of Nuclear Medicine The radiopharmaceutical is generally made up of two parts: the pharmaceutical, which is targeted to a specific organ, and the radionuclide, which emits gamma rays (high-energy electromagnetic radiation; short wavelength) and allows the organ to be visualized by the gamma camera. Nuclear medicine imaging can yield quantitative as well as qualitative data. A measurement of the ejection fraction of the heart is an example of quantitative data derived from a multigated acquisition (MUGA) or a myocardial stress procedure. In general, nuclear medicine images visualize the distribution of a particular radiopharmaceutical, with hot, warm, or cold spots of activity indicating an abnormality. In a hot spot, there is an increased area of uptake of the radiopharmaceutical in diseased tissue compared with the distribution in normal tissue. Examples of this type of uptake can be seen on bone images. An example of a warm spot would be in a thyroid nodule. In a cold spot, there is an area of decreased uptake of the radiopharmaceutical compared with the distribution in normal tissue. Liver and lung imaging are examples of this Fischbach_Ch09_printer_file.indd 669 11/4/13 10:27 PM 670 CHAPTER 9 ● Overview of Nuclear Medicine Studies TABLE 9.1 Potential Side Effects in the Administration of Radiopharmaceuticals Radiopharmaceutical (Trade Name) Possible Side Effects Iodine-131 [131I] Chills, nausea, vomiting, headache, dizziness, diffuse rash, tachycardia Fluorine-18 [18F] None have been reported Thallium-201 [ Tl] Fever, flushing, diffuse rash, hypotension Technetium-99m [99mTc] 99mTc-pertechnetate (Minitec, UltratecKow) Chills, nausea, vomiting, headache, dizziness, diffuse rash, hypertension 201 99m Tc-tetrofosmin (Myoview) Angina, hypertension, hypotension, vomiting, dyspnea, dizziness, metallic taste, abdominal discomfort 99m Tc-pyrophosphate [99mTc-PYP] (Pyrolite, TechneScan PYP, Phosphotec) Chills, fever, nausea, vomiting, dizziness, diffuse rash, flushing, chest pain, syncope Tc-disofenin (Hepatolite) 99m Tc-mebrofenin (Choletec) None have been reported 99m Hives, urticaria Tc-sulfur colloid (AN-Sulfur Colloid, TechneColl, Tesuloid) Chills, fever, nausea, vomiting, headache, dizziness, diffuse rash, flushing, chest pain, vertigo, hypertension, hypotension, dyspnea 99m 99m Tc-bicisate dihydrochloride (Neurolite) Nausea, diffuse rash, dizziness, chest pain, seizures, syncope, vertigo 99m Tc methylenediphosphonate (MDP) (Osteolite, TechneScan) Chills, fever, nausea, vomiting, headache, dizziness, diffuse rash, flushing, chest pain, vertigo, hypertension, hypotension, syncope Tc-pentetate (diethylenetriaminepentaacetate [DTPA]) (TechneScan DTPA, Techneplex) Chills, fever, nausea, flushing, vomiting, headache, dizziness, diffuse rash, syncope, hypertension, hypotension, dyspnea 99m Tc-exametazime (Ceretec) Fever, flushing, diffuse rash, hypertension, hypotension, seizures, dyspnea 111 In-capromab pendetide (ProstaScint) Increase in bilirubin, hypotension, hypertension, injection site reactions, fever, rash, headache, production of human antimouse antibody (HAMA) Indium-111 [111In]-DTPA (MPI-DTPA) Fever, nausea, vomiting, flushing, headache, hypertension Indium oxine (111In) Fever 99m 123 I metaiodobenzylguanidine (MIBG) Nausea, flushing, hypertension, dizziness, vertigo, tachypnea Gallium citrate (67Ga) (Neoscan) Nausea, vomiting, flushing, diffuse rash, tachycardia, dizziness, vertigo, metallic or salty taste Cobalt (57Co) None have been reported Chromium-51 (51Cr) Flushing, hypertension, tachycardia Note: Most adverse drug reactions (ADRs) include such symptoms as nausea, vomiting, hypotension, rash, dyspnea, tachycardia, fever, and headaches; however, it is difficult to determine whether these are due to administration of the radiopharmaceutical or other medications the patient is taking. The ADR rate has been estimated at about 0.003% (3 per 100,000). The half-life of radiopharmaceuticals ranges from a couple of minutes to several days. Adapted from Silberstein EB, Ryan J, and Pharmacopeia Committee of the Society of Nuclear Medicine. Prevalence of Adverse Reactions in Nuclear Medicine. J Nucl Med. 1996;37:185–192. Fischbach_Ch09_printer_file.indd 670 11/4/13 10:27 PM ● Overview of Nuclear Medicine Studies 671 type of uptake. Prompt uptake in transplanted organs correlates with (1) adequate perfusion, such as reperfusion of the transplanted lungs or pancreas; (2) excretory function, such as in kidney transplants; and (3) evidence of cardiac viability and reinnervation. Poor uptake and nonvisualization of the transplanted organ are evidence of rejection. NOT E Units of measure: curie (Ci) or becquerel (Bq) ⫽ radiation emitted by a radioactive material (1 Ci ⫽ 3.7 ⫻ 1010 Bq) rad or gray (Gy) ⫽ radiation dose absorbed by a person (1 rad ⫽ 0.01 Gy) rem or sievert (Sv) ⫽ biological risk of exposure to radiation (1 rem ⫽ 0.01 Sv) Principles of Imaging Gamma cameras all have basically the same components. The camera may have one, two, or three heads, with the capability of imaging in multiple configurations. The camera is networked with a multitasking computer capable of acquiring and processing the data. Several methods of imaging are used: dynamic, static, whole-body, and single photon emission computed tomography (SPECT). These imaging capabilities are available on all current camera systems. Dynamic imaging allows serial display of multiple frames of data, each frame lasting 1 to 3 seconds, to visualize the blood flow associated with a particular organ. Static imaging is also known as planar imaging. The camera acquires one image at a time, covering the field of view. This image is twodimensional. Whole-body imaging acquires both anterior and posterior sweeps of the patient’s body. This type of imaging also gives two-dimensional information. SPECT imaging has revolutionized the field of nuclear medicine. SPECT imaging provides three dimensions of data. SPECT imaging increased the specificity and sensitivity of nuclear imaging through improved resolution and is often combined with CT scans. Recently, manufacturers have developed a combined gamma camera and CT scanner that allows both procedures to be performed without patient transfer. Therefore, positioning is not compromised, and both abnormal and normal areas are visualized without position change. General Procedure 1. Alert the patient that he or she may be required to follow a study-specific preparation regimen before imaging determined by the type of nuclear medicine procedure (e.g., nothing by mouth [Latin: nil per os, NPO], no caffeine for 24 hours, hydration, bowel preparation). 2. Administer a radiopharmaceutical through one of several routes: oral, inhalation, intravenous, intramuscular, intrathecal, or intraperitoneal. On occasion, additional pharmaceuticals may be administered to enhance the function of the organ of interest. 3. A time delay may be necessary for the radiopharmaceutical to reach the organ of interest. 4. Imaging time depends on: a. Specific study radiopharmaceutical used and the time that must be allowed for concentration in tissues b. Type of imaging equipment used c. Patient cooperation d. Additional views based on patient history and nuclear medicine protocol e. Patient’s physical size PROCEDURAL ALERT The nuclear medicine department should be notified if the patient may be pregnant or is breast-feeding or is younger than 18 years of age. Fischbach_Ch09_printer_file.indd 671 11/4/13 10:27 PM 672 CHAPTER 9 ● Overview of Nuclear Medicine Studies Benefits and Risks Benefits and risks should be explained before testing. Patients retain the radioisotope for a relatively short period. The radioactivity decays over time. Some of the radioisotope is eliminated in urine, feces, and other body fluids. 99m Tc, the most commonly used radiopharmaceutical, has a radioactive half-life of 6 hours. This means that half of the dose decays in 6 hours. Other radioisotopes, such as iodine, indium, thallium, and gallium, take 13 hours to 8 days for half of the dose to decay. 1. Benefits a. Nuclear medicine yields functional data that are not provided by other modalities. b. Nuclear imaging is relatively safe, painless (except for intravenous administration), and noninvasive. 2. Risks a. Radiation exposure is minimal; toxicity is nil. b. Hematoma at intravenous injection site. c. Reactions to the radiopharmaceutical (hives, rash, itching, constriction of throat, dyspnea, bronchospasm, anaphylaxis [rare]). Clinical Considerations The following information should be obtained before diagnostic nuclear imaging: 1. Pregnancy (confirmed or suspected). Pregnancy is a contraindication for most nuclear imaging. 2. Lactating women may be advised to stop nursing for a set period (e.g., 2 to 3 days with 99mTc). Most radiopharmaceuticals are excreted in the mother’s milk. 3. Radiopharmaceutical uptake from a recent nuclear medicine examination could interfere with interpretation of the current study. 4. The presence of any prostheses in the body must be recorded on the patient’s history because certain devices can shield the gamma rays from imaging. 5. Current medications, treatments, and diagnostic measures (e.g., telemetry, oxygen, urine collection, intravenous lines) 6. Age and current weight. This information is used to calculate the radiopharmaceutical dose to be administered. If the patient is younger than 18 years of age, notify the examining department before testing. The amount of radioactive substance administered is adjusted downward for anyone younger than 18 years of age. 7. Allergies. Past history of allergies, especially to contrast substances (e.g., iodine) used in diagnostic procedures. Interventions Pretest Patient Care and Standard Precautions for Nuclear Medicine Procedures 1. 2. 3. 4. 5. 6. 7. 8. Explain the purpose, procedure, benefits, and risks of the nuclear medicine procedure. Assess for allergies to substances such as iodine. Reassure the patient that the procedure is safe and painless. Inform the patient that the procedure is performed in the nuclear medicine department. Contact the department to determine the expected time and length of the procedure. Have the patient appropriately dressed. Obtain an accurate weight because the radiopharmaceutical dose may be calculated by weight. If a female patient is premenopausal, determine whether she may be pregnant. Pregnancy is a contraindication to most nuclear imaging. Irradiation of the fetus should be avoided whenever possible. Fischbach_Ch09_printer_file.indd 672 11/4/13 10:27 PM ● Overview of Nuclear Medicine Studies 673 CLINICAL ALERT 1. Nuclear medicine procedures are usually contraindicated in pregnant women. Lactating women may need to discard their breast milk for several days following the procedure. 2. These precautions are also to be followed for the radionuclide laboratory procedures and PET imaging. Posttest Patient Care and Standard Precautions for Nuclear Medicine Procedures 1. Use routine disposal procedures for body fluids and excretions unless directed otherwise by the nuclear medicine department. Special considerations for disposal must be followed for therapeutic procedures. 2. Record any problems that may have occurred during the procedure. 3. Monitor the injection site for signs of bruising, hematoma, infection, discomfort, or irritation. 4. Assess for side effects of radiopharmaceuticals. Pediatric Nuclear Medicine Considerations Many of the nuclear medicine procedures that are performed on adults may be indicated in children. Interventions Pediatric Pretest Care 1. Be aware that depending on hospital policy, a valid consent form may be requested to be signed by the parents or legal guardians of the patient. 2. Explain the procedure and its purpose, benefits, and risks to the parents or legal guardians and to the patient. Reassure the patient that the test is safe and painless. 3. Assess for allergy to medications. 4. Have the patient appropriately dressed, ensuring that there are no metal objects on the patient during the procedure. 5. Obtain an accurate weight; the dose is calculated based on the patient’s weight. Because pediatric patients have a different body metabolism than adults, a lower dose is given. Use of a “body surface area” (BSA) formula is recommended. The most commonly used is the DuBois formula: BSA ⫽ 0.007184 ⫻ W0.425 ⫻ H0.725 (W ⫽ weight in kg and H ⫽ height in cm) 6. Remember that immobilization techniques are often used during the imaging of pediatric patients. Wrapping an infant or small child is often necessary. Head clamps, arm boards, or sandbags may be used for patient immobilization. 7. Administer sedative drugs to reduce patient motion during the examination. Disadvantages of sedation may include nausea and vomiting. 8. Start an intravenous line for administration of radiopharmaceuticals. 9. Do not leave patients unattended during the procedure. 10. Pediatric patients need constant reassurance and emotional support. 11. Patient urination is often difficult to control. A urinary catheter may be required. 12. Verify that the adolescent female patient is not pregnant. Pediatric Posttest Care 1. Same as those stated for adults 2. Observe pediatric patients for adverse reactions to radiopharmaceuticals. Infants are more at risk for reactions. Fischbach_Ch09_printer_file.indd 673 11/4/13 10:27 PM 674 CHAPTER 9 ● Myocardial Perfusion: Rest and Stress CARDIAC STUDIES ● Myocardial Perfusion: Rest and Stress (Sestamibi/Tetrofosmin/ Thallium Stress Test) Tc sestamibi, thallium-201 (201Tl), and 99mTc tetrofosmin are the radioactive imaging agents available for myocardial perfusion imaging to diagnose ischemic heart disease and allow differentiation of ischemia and infarction. This test reveals myocardial wall defects and heart pump performance during increased oxygen demands. Nuclear medicine imaging may also be done before and after streptokinase treatment for coronary artery thrombosis, after surgery for great vessel translocation, and after transplantation to detect organ rejection and myocardial viability. Pediatric indications include evaluation for ventricular septal defects and congenital heart disease and postsurgical evaluation of congenital heart disease. Studies have shown the efficacy of performing SPECT imaging with 99mTc sestamibi when triaging diabetic patients arriving in the emergency department with symptoms suggestive of acute cardiac ischemia. 201 Tl is a physiologic analogue of potassium. The myocardial cells extract potassium, as do other muscle cells. 99mTc sestamibi is taken up by the myocardium through passive diffusion, followed by active uptake within the mitochondria. Unlike thallium, technetium does not undergo significant redistribution. Therefore, there are some procedural differences. Myocardial activity also depends on blood flow. Consequently, when the patient is injected during peak exercise, the normal myocardium has much greater activity than the abnormal myocardium. Cold spots indicate a decrease or absence of flow. A completely normal myocardial perfusion study may eliminate the need for cardiac catheterization in the evaluation of chest pain and nonspecific abnormalities of the electrocardiogram (ECG). SPECT imaging can accurately localize regions of ischemia. Administration of dipyridamole (Persantine) or regadenoson (Lexiscan) is indicated in adults and children who are unable to exercise to achieve the desired cardiac stress level and maximum cardiac vasodilation. This medication has an effect similar to that of exercise on the heart. Physical stress testing may be initiated in children beginning at 4 to 5 years. Candidates for drug-induced stress testing are those with lung disease, peripheral vascular disease with claudication, amputation, spinal cord injury, multiple sclerosis, or morbid obesity. Dipyridamole stress testing is also valuable as a significant predictor of cardiovascular death, reinfarction, and risk for postoperative ischemic events and to reevaluate unstable angina. Ejection fraction and wall motion can be assessed by computer analysis. 99m Reference Values Normal Normal stress test: ECG and blood pressure normal Normal myocardial perfusion under both rest and stress conditions Procedure 1. Myocardial perfusion general imaging a. There are two phases to this procedure: the rest imaging and the stress imaging. Either 201Tl, 99m Tc sestamibi, or 99mTc tetrofosmin may be used. (1) Rest imaging (a) Perform an intravenous injection of the radioisotope. Allow a 30- to 60-minute delay for the radioisotope to localize in the heart. (b) Perform SPECT imaging. Fischbach_Ch09_printer_file.indd 674 11/4/13 10:27 PM ● (2) Myocardial Perfusion: Rest and Stress 675 Stress imaging (a) The patient undergoes an exercise or a pharmacologic cardiac stress test. At the peak level of stress, inject the patient with the radioisotope. (b) SPECT imaging may begin 30 minutes after injection. PROCEDURAL ALERT Myocardial perfusion imaging protocols vary among nuclear medicine departments. Some departments use a rest-stress, stress-rest, dual-isotope, or 2-day protocol, separating the phases into 2 different days. b. Pharmacologic stress tests may be performed with any of three routine stressing agents: (1) Infuse dipyridamole over 4 to 6 minutes. Inject the radiopharmaceutical. Two minutes later, administer aminophylline, an antidote to the dipyridamole, at the nuclear medicine physician or cardiologist’s discretion. Patient monitoring may last 20 minutes. Contraindication: caffeine. (2) Infuse regadenoson over 20 seconds. Inject the radiopharmaceutical 3 minutes after the infusion. NOT E Regadenoson has an extremely short half-life: once the infusion has stopped, any symptoms will subside. Contraindications: caffeine and theophylline-based drugs. (3) 2. Infuse dobutamine until the predicted heart rate is achieved. The infusion protocol lasts 3 minutes at each dose increment. Tl a. During the cardiac stress test, the patient is monitored by a nuclear medicine physician, cardiologist, a registered nurse, an electrophysiologist, or an ECG technician. b. Have the patient begin walking on the treadmill. c. When the monitoring person determines that the patient has reached 85% to 95% of maximum heart rate, inject radioactive thallium. Take the patient for immediate imaging. d. SPECT imaging begins within 5 minutes of injection. e. Acquire a second image approximately 3 to 4 hours later, with the patient at rest, to determine redistribution of the thallium. f. See Chapter 1 guidelines for safe, effective, informed intratest care. 201 PROCEDURAL ALERT Some nuclear medicine protocols may require the patient to return 24 hours later for delayed imaging. 3. Tc sestamibi and 99mTc tetrofosmin a. Follow myocardial perfusion general imaging procedures. b. Observe standard precautions. 99m Clinical Implications 1. Imaging that is abnormal during exercise but remains normal at rest indicates transient ischemia. 2. Nuclear cardiac imaging that is abnormal both at rest and under stress indicates a past infarction. 3. Hypertrophy produces an increase in uptake. 4. The progress of disease can be estimated. 5. The location and extent of myocardial disease can be assessed. Fischbach_Ch09_printer_file.indd 675 11/4/13 10:27 PM 676 CHAPTER 9 ● Myocardial Infarction (PYP) Imaging 6. Specific and significant abnormalities in the stress ECG usually are indications for cardiac catheterization or further studies. Interfering Factors 1. Inadequate cardiac stress 2. Caffeine intake 3. Injection of dipyridamole in the upright or standing position or with isometric handgrip may increase myocardial uptake. Interventions Pretest Patient Care for Stress Testing 1. Explain test purpose and procedure, benefits, and risks. See standard nuclear medicine imaging pretest precautions. 2. Before the stress test has begun, start an intravenous line and prepare the patient. Perform a resting 12-lead ECG and blood pressure measurement. 3. Advise the patient that the exercise stress period will be continued for 1 to 2 minutes after injection to allow the radiopharmaceutical to be cleared during a period of maximum blood flow. 4. The patient should experience no discomfort during the imaging. 5. Alert the patient that fasting may be recommended for at least 2 hours before the stress test. Caffeine intake must be eliminated for 24 hours before the stress test. 6. For dipyridamole administration: a. Fasting may be required before the stress test, and avoidance of any caffeine products for at least 24 hours before the test is necessary. b. Blood pressure, heart rate, and ECG results are monitored for any changes during the infusion. Aminophylline may be given to reverse the effects of the dipyridamole. 7. See Chapter 1 guidelines for safe, effective, informed pretest care. CLINICAL ALERT 1. The stress study is contraindicated in patients who: a. Have a combination of right and left bundle branch block b. Have left ventricular hypertrophy c. Are taking digitalis or quinidine d. Are hypokalemic (because the results are difficult to evaluate) 2. Adverse short-term effects of dipyridamole may include nausea, headache, dizziness, facial flush, angina, ST-segment depression, and ventricular arrhythmia. Posttest Patient Care 1. Observe the patient for possible effects of dipyridamole infusion. 2. Interpret test outcomes, counsel, and monitor appropriately. 3. Refer to nuclear scan posttest precautions. 4. Follow Chapter 1 guidelines for safe, effective, informed posttest care. ● Myocardial Infarction (PYP) Imaging Tc pyrophosphate (99mTc-PYP) is the radioactive imaging agent used to evaluate the general location, size, and extent of myocardial infarction 24 to 96 hours after suspected myocardial infarction and as an indication of myocardial necrosis to differentiate between old and new infarcts. In some instances, the test is sensitive enough to detect an infarction 12 hours to 7 days after its occurrence. Acute infarction 99m Fischbach_Ch09_printer_file.indd 676 11/4/13 10:27 PM ● Multigated Acquisition (MUGA) Imaging: Rest and Stress 677 is associated with an area of increased radioactivity (hot spot) on the myocardial image. This test is useful when ECG and enzyme studies are not definitive. Reference Values Normal Normal distribution of the radiopharmaceutical in sternum, ribs, and other bone structures No myocardial uptake Procedure 1. Myocardial imaging involves a 4-hour delay before imaging after the intravenous injection of the radionuclide. During this waiting period, the radioactive material accumulates in the damaged heart muscle. 2. Alert the patient that imaging takes 30 to 45 minutes, during which time the patient must lie still on an imaging table. 3. See Chapter 1 guidelines for safe, effective, informed intratest care. Clinical Implications 1. Imaging that is entirely normal indicates that an acute infarction is not present and the myocardium is viable. 2. Myocardial uptake of the PYP is compared with the ribs (2⫹) and sternum (4⫹). Higher uptake levels (4⫹) reflect greater myocardial damage. 3. Larger defects have a poorer prognosis than small defects. Interfering Factors False-positive infarct-avid PYP can occur in cases of chest wall trauma, recent cardioversion, and unstable angina. Interventions Pretest Patient Care 1. Imaging can be performed at the bedside in the acute phase of infarction if the nuclear medicine department has a mobile gamma camera. 2. Explain the purpose, procedure, benefits, and risks of the nuclear medicine study. See standard pretest precautions. 3. Remember that imaging must occur within a period of 12 hours to 7 days after the onset of symptoms of infarction. Otherwise, false-negative results may be reported. 4. See Chapter 1 for additional guidelines for safe, effective, informed pretest care. Posttest Patient Care 1. Interpret the outcome and monitor appropriately. If heart surgery is needed, counsel the patient concerning follow-up testing after surgery. 2. Refer to standard precautions and posttest care. 3. Follow additional guidelines in Chapter 1 for safe, effective, informed posttest care. ● Multigated Acquisition (MUGA) Imaging: Rest and Stress The term gated refers to the synchronization of the imaging equipment and computer with the patient’s ECG to evaluate left ventricular function. The primary purpose of this test is to provide an ejection fraction (the amount of blood ejected from the ventricle during the cardiac cycle). Once injected, the distribution of radiolabeled red blood cells (RBCs) is imaged by synchronization of the recording of cardiac images with the ECG. This technique provides a means of obtaining Fischbach_Ch09_printer_file.indd 677 11/4/13 10:27 PM