Nuclear Scanning

Reasons for Performing Nuclear Medicine Studies

With the administration of a radiopharmaceutical and subsequent detection of the photons emitted from a particular organ, anatomic and functional abnormalities of various body areas can be detected. Nuclear medicine studies do not identify the specific cause (disease) of the abnormality. They provide supportive information to be used in conjunction with other diagnostic modalities. There are many indications for nuclear scanning, some of which are listed below:

The radionuclides used in diagnostic medicine are artificially produced by either a nuclear reactor or a charged particle accelerator (cyclotron) by irradiating the nuclei and causing them to be unstable. Because of this instability, the nucleus of the radionuclide atom emits radioactive particles (photons in the gamma radiation range). The radionuclides used in nuclear scanning have short half-lives, which refers to the time required for 50% of the radioactive atoms to undergo decay. Technetium-99m (^99mTc) is used extensively in nuclear scanning because its half-life is 6 hours and it emits low levels of gamma rays. Other commonly used radionuclides include gallium, thallium, and iodine.

To get to the desired organ, radionuclides are combined with a transport molecule. This combination of radionuclide and transport molecule is called a radiopharmaceutical. A radiopharmaceutical is the compound, labeled with the radionuclide that is administered to the patient and localized in the organ to be studied. For most nuclear scans, radiopharmaceuticals are given intravenously. Less commonly used methods of administration include the oral and inhalation routes. Radiopharmaceuticals concentrate in target organs by various mechanisms. For example, some labeled compounds, such as iodohippurate sodium ¹³¹I (Hippuran ¹³¹I), are cleared from the blood and excreted by the kidneys. Some phosphate compounds concentrate in the bone and infarcted tissue. Lung function can be studied by imaging the distribution of inhaled gases and aerosols. Other radiopharmaceuticals (such as FDG) are selectively taken up by cancers.

After the radioisotope concentrates in the desired area, it emits gamma rays. The area is scanned with a gamma camera or a scintillation scanner that detects and records the emission of gamma rays. With each gamma ray detected, a light particle is emitted from the scintillation scanner. A computer translates these light readings into a two-dimensional image or scan (scintigram) that is printed in various shades of gray. Using multiple scanners, a three-dimensional image (SPECT) can be obtained. Scintigrams can now be produced in color. The shades of gray or color show the distribution of the radionuclide in the organ. When superimposed on a baseline computerized tomogram (PET/CT), accurate anatomy can be created. Hot spots are areas of increased uptake, and cold spots are areas with decreased uptake of the radionuclide. Normally the uptake of the radionuclide in an organ is diffuse and homogeneous. Hot and cold spots may mean different things on different scans. For example, a cold spot identified in the liver, spleen, or brain would indicate tumor, abscess, or some other space-occupying lesion. A cold spot detected on a thallium scan of the heart would not be suggestive of tumor but rather indicates an area of ischemia or infarction. On bone scan, hot spots may indicate areas of osteoblastic activity surrounding tumor. Arthritis or fracture may also be evident as hot spots. The scanning usually takes place in the nuclear medicine department.

Scanning can be static, which means that the patient and the camera are held in one position until an image is completed. Often the patient is rotated into another position for a static image of another view of the same organ. Dynamic scanning can also be performed and allows one to evaluate the blood flow to a certain organ, such as the brain or the liver. Single-photon emission computed tomography (SPECT) is a technique in which a gamma camera is serially placed at multiple angles around the entire circumference of the patient. With this method, three-dimensional images can be obtained of the organ to be studied. Increased sensitivity is obtained. Positron emission tomography (PET) scanning can demonstrate anatomic, functional, and biochemical abnormalities in an organ.

Although nuclear scanning includes a risk of radiation for the patient, the risk associated with most radionuclides is much less than that of an x-ray study. The half-lives of the radioisotopes are short, resulting in minimal radiation contamination by way of fecal and urine wastes. Unless the benefit outweighs the risk, nuclear scans are contraindicated in pregnant women and nursing mothers because of the risk of injury to the fetus or infant. To help protect patients and others, patients should take some precautions for 12 hours after injection of radionuclides. Whenever possible, a toilet should be used, rather than a urinal. The toilet should be flushed several times after each use. Spilled urine should be cleaned up completely. After each voiding or fecal elimination, patients should thoroughly wash their hands. All urine- or fecal-soiled clothes should be washed separately.

Procedural Care for Nuclear Scans

Reporting of Results

Most tests are performed by a nuclear medicine technologist in the nuclear medicine department. A physician trained in diagnostic nuclear medicine interprets the test results.

Normal Findings

Indications

The bone scan is used to identify metastatic cancer involving the bone. It is often performed on cancer patients as a routine part of staging before and after treatment. To a lesser degree, bone scanning is used to identify pathologic bone conditions that cannot be identified on plain films of the bone (e.g., osteomyelitis, hairline fractures).

Test Explanation

The bone scan permits examination of the skeleton by a scanning camera after intravenous (IV) injection of a radionuclide material. Usually technetium-99m (^99mTc) is the radionuclide utilized. After injection of the ^99mTc, the radiopharmaceutical is taken up by the bone. Gamma rays are emitted from the ^99mTc through the body and are detected by a scintillation scanner. The scintillation scanner emits light with each photon it receives from the gamma ray. When these light patterns are arranged in a spatial order, a realistic image of the bones is apparent.

The degree of radionuclide uptake is related to the metabolism of the bone. Normally a uniform concentration should be seen throughout the bones of the body. There is symmetric distribution of activity throughout the skeletal system in healthy adults. Urinary bladder activity, faint renal activity, and minimal soft-tissue activity are also normally present. An increased uptake of isotope is abnormal and may represent tumor, arthritis, fracture, degenerative bone and joint changes, osteomyelitis, bone necrosis, osteodystrophy, or Paget disease (Figure 8-1). These areas of concentrated radionuclide uptake are often called hot spots and are detectable months before an ordinary x-ray film can reveal the pathologic condition. Hot spots occur because new bone growth is usually stimulated around areas of abnormality. If a pathologic condition exists and there is no new bone formation around the lesion, the scan will not pick up the abnormality. Increased uptake of radionuclide is also seen in the normal physiologic active epiphyses of children (growth plates).

The major reason a bone scan is performed is to detect metastatic cancer to the bone. All malignancies capable of metastasis may reach the bone, especially those of the prostate, breast, lung, kidney, urinary bladder, and thyroid gland. Bone scans are also useful in staging primary bone tumors such as osteogenic sarcomas and Ewing sarcoma. Bone scans may be serially repeated to monitor tumor response to antineoplastic therapy.

Bone scans also provide valuable information for the evaluation of patients with trauma or unexplained pain. Bone scanning is much more sensitive than routine x-ray films in detecting small and difficult-to-find fractures, especially in the spine, ribs, face, and small bones of the extremities. Bone scans are used to determine the age of a fracture as well. If a fracture line is seen on a plain x-ray film and the uptake around that fracture is not increased on a bone scan, the injury is said to be an “old” fracture, exceeding several months in age.

Although the bone scan is extremely sensitive, unfortunately it is not very specific. Fractures, infections, tumors, and arthritic changes all appear similar in this scan. When plain films fail to identify the classic findings of bone infection (osteomyelitis), bone scans are helpful.

A three-phase bone scan may be performed if inflammation (arthritis) or infection (osteomyelitis, septic arthritis) is suspected. In a three-phase bone scan, imaging is performed at three different times after injection of the radionuclide. Early uptake of the radionuclide would indicate infection or inflammation rather than neoplasm. Uptake of the radionuclide on delayed imaging that had not been present on early imaging would indicate neoplasm.

When the metastasis process is diffuse, virtually all of the radiotracer is concentrated in the skeleton, with little or no activity in the soft tissues or urinary tract. The resulting pattern, which is characterized by excellent bone detail, is frequently referred to as a “superscan.” A superscan may also be associated with metabolic bone diseases such as Paget disease, renal osteodystrophy, or osteomalacia. Unlike in metastatic disease, however, the uptake in metabolic bone disease is more uniform in appearance and extends into the distal appendicular skeleton. Intense calvarial uptake disproportionate to that in the remainder of the skeleton is another feature of a metabolic superscan.

The bone scan is performed by a nuclear medicine technologist in 30 to 60 minutes. It is interpreted by a physician trained in nuclear medicine imaging. The injection of the radioisotope causes slight discomfort. There may be some pain caused by lying on the hard scanning table for an hour. In many circumstances, magnetic resonance imaging (MRI) is used in place of bone scans. It is more specific in indicating disease pathology.

Contraindications

Procedure and Patient Care

Test Results and Clinical Significance

Related Tests

Normal Findings

No areas of altered radionuclide uptake within the brain

Indications

The usefulness of nuclear brain scan is narrow when compared to CT, MRI, and PET scans of the brain. The cost of these newer scans sometimes precludes their utilization and nuclear brain scanning may be preferably used. This test can be used to identify pathologic conditions (tumor, infarction, infection) involving the cortex. It is used for patients with headaches, epilepsy, and other neurologic symptoms. The nuclear cerebral blood flow brain scan is used to support the diagnosis of cerebral brain death.

Test Explanation

The brain scan permits examination of the brain by a scanning camera after intravenous (IV) injection of a radionuclide material (Figure 8-3). A technetium-99m (^99mTc) radionuclide, such as hexamethylpropyleneamine (Tc-HMPAO) or ethyl cysteinate dimer (Tc-ECD), bicisate, or Neurolite, is most commonly used.

Primarily, nuclear brain scan is used to indicate complete and irreversible cessation of brain function (brain death). This determination, when combined with appropriate clinical data, allows for cessation of medical therapy and opportunity for the harvest of potential donor organs. With brain death, there is complete absence of blood perfusion to the brain. In cerebral blood flow scanning, one normally sees an early “arterial visualization phase” followed by a “blood pool phase” in which the venous sinuses but not the brain tissue are seen. In severe brain damage or death, there is usually asymmetric or no blood flow noted on the angiographic phase and an abnormal blood pool phase.

The brain scan can also be used to indicate cerebral vascular occlusion or stenosis. With the use of Diamox (acetazolamide), an accurate assessment of local cerebral blood flow can be determined. Diamox is carbonic anhydrase inhibitor that results in the elevation of PCO₂ in the bloodstream. Normally this causes dilatation of the cerebral blood vessels. If asymmetric blood flow is noted after Diamox injection, cerebral vascular occlusion or stenosis can be suspected.

The brain scan can also document successful therapeutic disruption of the normal blood-brain barrier to inject chemotherapeutic agents into localized brain tumors. Furthermore this scan has been used in the evaluation of patients with seizure disorders, psychiatric disease, and dementia. Although not nearly as accurate as an MRI or PET scan, the nuclear brain scan is able to identify primary brain neoplasms (e.g., gliomas, astrocytomas primary lymphoma) and metastatic tumors. Because sometimes nuclear medicine can indicate tissue viability, nuclear brain scanning is used to differentiate radiation necrosis from recurrent brain viable tumor.

Brain scans are also used to investigate the ventricular system (cisternogram) of the central nervous system. Normal pressure hydrocephalus and ventricular shunt dysfunction can be identified and located. Cisternogram may be performed by injecting radioactive material into the subarachnoid space and then taking serial scans of the head. These scans are useful in evaluating ventricular size and patency of the cerebrospinal fluid (CSF) pathways and reabsorption. Because only a small amount of CSF enters the ventricles, their uptake of radioactive material normally should be minimal. Blocks in the CSF pathways may prevent this reabsorption, however; thus large amounts of isotopes may appear in the ventricles. A cisternogram may also be used to evaluate CSF leakage (e.g., into the nasal sinuses) in patients with recurrent meningitis and to evaluate hydrocephalus.

The technique of single-photon emission computed tomography (SPECT) has significantly improved the quality of brain scanning. With SPECT scanning, the radionuclide is injected and the scintillation cameras are placed to receive images from multiple angles (around the circumference of the head). This technique greatly increases the usefulness of nuclear brain scanning. In general, CT scans, MRI scans, and carotid duplex scans have replaced the brain scan in diagnostic neurology. However, a host of traumatic, inherited, and acquired diseases can be identified with nuclear brain scanning.

A SPECT brain scan using isoflurane I¹²³ (also known as phenyltropane) can be helpful in the diagnosis of Parkinson disease. This test is often referred to as a DaT scan. Patients with Parkinson's disease experience degeneration of presynaptic dopamine neurotransmitter cells first in the basal ganglia of the brain and then other parts of the brain. Isoflurane tags these neurons with I¹²³. In a healthy brain, isoflurane I¹²³ is seen concentrated in the basal ganglia. This is demonstrated as hot spots. In these parts of the brain in which dopamine cells should be remain dark on the brain SPECT scan, Parkinson disease is suspected. These changes may be subtle. There are commonly identified patterns that can separate out Parkinson disease from other forms of brain deterioration or aging.

Contraindications

Interfering Factors

Procedure and Patient Care

Test Results and Clinical Significance

Related Tests

Normal Findings

Negative: Minimal, symmetric, bilateral, and uniform breast uptake equal to soft-tissue uptake

Indications

This test is used to identify breast cancer, especially in young women with dense breasts in whom the accuracy of mammography is diminished.

Test Explanation

Nuclear scans of the breast, using technetium (^99mTc)-labeled sestamibi or tetrofosmin as a radiotracer, are used to identify breast cancer in patients whose dense breast tissue precludes accurate evaluation by conventional mammography. To conduct BSGI, patients are given an intravenous injection with a small dose of a tracing agent (Technetium ^99mTc) that emits gamma rays. The radioisotope is transported by passive diffusion into the cell and is sequestered within the mitochondria. Thus cancer cells that usually contain a large number of mitochondria will show an increased uptake of ^99mTc as compared with noncancerous cells. BSGI is a functional scan that indicates physiologic behavior of cells. Cancerous areas show up as “hot spots” on breast specific specialized high-resolution, small field-of-view gamma cameras. The cameras are compact and maneuverable and they can be placed close to the chest to image deep within the breast.

This test has also been used as an adjunct in patients with an indeterminate mammogram abnormality and in women with indeterminate palpable breast masses. However this scan may miss as many as 10% to 15% of cancers, and the false-positive rate is about 15% to 25%. Areas of benign cellular hyperplasia also trap the radiotracer. Because cellular hyperplasia is a common finding in the breast just before menses, imaging at this time in the menstrual cycle should be avoided.

Breast nuclear scans will not replace the role of mammography in breast imaging. Nor will they ever be an effective screening tool for the early detection of breast cancer among large populations. Other technologies currently used for similar post-mammography evaluation include ultrasound (p. 871) and magnetic resonance imaging (MRI) (p. 1106). Each of these technologies has its advantages and limitations. Ultrasound is well tolerated, it does not use ionizing radiation or require intravenous contrast administration, and it is able to identify small lesions in dense breast tissue. MRI of the breast offers accuracy similar to ultrasound and BSGI. However, MRI is not suitable for many patients, such as women with pacemakers, who are claustrophobic, and who cannot lie prone for the required length of the exam. BSGI is not without limitations; it is limited by its inability to reliably image cancers smaller than 1 cm.

Contraindications

Procedure and Patient Care

Test Results and Clinical Significance

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Normal Findings

Indications

This test is used for the evaluation of:

Test Explanation

See Table 8-1 for an overview of cardiac nuclear scanning. A cardiac perfusion scan measures the coronary blood flow at rest and during exercise. It is often used to evaluate the cause of chest pain. It may be done after a coronary ischemic event to evaluate coronary patency or heart muscle function.

In this test, radionuclide is injected intravenously into the patient. Myocardial perfusion images are then obtained while the patient is lying down under a single-photon emission computed tomography (SPECT) camera that generates a picture of the radioactivity coming from the heart. This scan can be performed at rest or with exercise such as treadmill or bicycling (myocardial nuclear stress testing). Medications may be administered that duplicate exercise stress testing. Vasodilators (dipyridamole, adenosine and Regadenoson) or chronotropic agents (dobutamine) are commonly used. Regadenoson is the most recent A_2A adenosine receptor agonist that instigates coronary vasodilatation. It is associated with fewer side effects (e.g., heart block, bronchospasm) and can be injected more quickly.

Although the initial radioisotope used was thallium (thus the name thallium scan), technetium agents such as tetrofosmin and sestamibi (isonitrile) are more commonly used today. The uptake of these agents is proportional to the myocardial coronary flow (Figure 8-5). At rest, a coronary stenosis must exceed 90% of the normal diameter before blood flow is impaired enough to see it on the perfusion scan. With exercise stress testing, however, stenosis of 50% becomes obvious. Often stenosis or coronary obstruction is noted by a normal resting perfusion scan followed by stress perfusion scan that demonstrates cold spots compatible with decreased coronary perfusion. Myocardial perfusion scans can be synchronized by gating the images with the cardiac cycle and thereby allowing the visualization and evaluation of cardiac muscle function. The contractility of the muscle wall can be evaluated at the same time. Prior muscle injury is demonstrated by reduced muscle wall motion. Most often, nuclear myocardial scans include both perfusion and gated wall motion images. Cardiac ejection fraction, the end-systolic volume of the left ventricle can be calculated.

Cardiac nuclear stress testing is more accurate than echocardiography stress testing (p. 877) or radiographic stress ventriculography (p. 1008). The nuclear myocardial scan is the best initial imaging study for the detection of myocardial ischemia; however, stress echocardiography is performed more often because it is more readily available and many cardiologists are better trained in echocardiography and are more comfortable with echocardiography. The assessment of myocardial perfusion and function using PET and hybrid positron emission tomography (PET)/CT imaging (p. 822) is becoming more available as the cost of the technology decreases and as positron-emitting radiopharmaceuticals become more available. Myocardial PET scanning provides better cardiac and coronary imaging.

Cardiac nuclear imaging when gated to the cardiac cycle (Multi Gated Acquisition Scan [MUGA], gated blood pool scan) can provide an accurate measure of ventricular function through the calculation of the ventricular ejection fraction (Figure 8-6). In this scan the patient's red blood cells are tagged with technetium. Red blood cell binding with technetium can be performed in vivo or in vitro. In vivo techniques are more convenient and less time-consuming but in vitro labeling is more efficient, especially in patients who have large indwelling venous access.

Ventricular volumes can be calculated and used to accurately calculate the amount of blood that is ejected from the ventricle with each contraction (ejection fraction). This is used in the initial assessment of cardiac function and subsequently to monitor therapy designed to improve cardiac function. Patients with cardiomyopathies (ischemic, infiltrative, inflammatory), cardiac transplant, or drug-induced cardiac muscle toxicity (from doxorubicin or Herceptin) require frequent evaluation of ventricular ejection fraction.

This test is usually performed in a few hours in the nuclear medicine department by a technologist and interpreted by a nuclear medicine physician. Delayed images may be required 24 hours later.

Contraindications^∗

Interfering Factors

Procedure and Patient Care

Test Results and Clinical Significance

Related Tests

Normal Findings

Indications

Cholescintigraphy is valuable in evaluating patients for suspected gallbladder disease. The primary use of this study is to diagnose acute cholecystitis in patients who have acute right upper quadrant abdominal pain. When gallbladder ejection fraction is calculated, chronic cholecystitis can be diagnosed. This study is also used to assist in the diagnosis of extrahepatic biliary obstruction.

Test Explanation

Through the use of iminodiacetic acid analogues (IDAs) labeled with technetium-99m (^99mTc), the biliary tract can be evaluated in a safe, accurate, and noninvasive manner. These radionuclide compounds are extracted by the liver and excreted into the bile. Gamma rays are emitted from the ^99mTc in the bile through the body and are detected by a scintillation camera. The scintillation camera emits light with each photon it receives from the gamma ray. When these light patterns are arranged in a spatial order, a realistic image of the biliary tree is apparent.

Failure to visualize the gallbladder 60 to 120 minutes after injection of the radionuclide is virtually diagnostic of an obstruction of the cystic duct, which instigates the pathophysiology of acute cholecystitis. Delayed filling of the gallbladder is associated with chronic or acalculous cholecystitis. This procedure is also helpful in diagnosing biliary duct obstructions. The identification of the radionuclide in the biliary tree but not in the bowel is diagnostic of common bile duct obstruction.

This procedure is superior to oral cholecystography, intravenous (IV) cholangiography, ultrasonography, and computed tomography (CT) of the gallbladder in the detection of cholecystitis (Table 8-2). Also, with cholescintigraphy, gallbladder function can be numerically determined by calculating the capability of the gallbladder to eject its contents. It is believed that an ejection fraction below 35% indicates primary gallbladder disease. To a large degree, abdominal ultrasound (p. 866) has replaced this test in the diagnosis of acute cholecystitis.

Occasionally, morphine sulfate is given intravenously during nuclear scanning. The morphine causes increased ampullary contraction. Not only can this reproduce the patient's symptoms of biliary colic, but it also serves to force the bile containing the radionuclide into the gallbladder. If no radionuclide is seen in the gallbladder with the use of morphine within 15 to 60 minutes, the diagnosis of acute cholecystitis is nearly certain. This greatly decreases the scanning time because without morphine it requires 4 hours to obtain a definitive diagnosis of acute cholecystitis.

A nuclear medicine technologist performs this study in 1 to 4 hours in the nuclear medicine department. A physician trained in interpretation of diagnostic nuclear medicine interprets the test in a few minutes. The only discomfort associated with this procedure is the IV injection of radionuclide.

Contraindications

Interfering Factors

Procedure and Patient Care

Test Results and Clinical Significance

Related Tests

Normal Findings

Indications

Gallium becomes concentrated in areas of the body where white blood cells (WBCs) tend to congregate (areas of tumor, infection, and inflammation). It is used to stage gallium-avid tumors (those that attract high concentrations of gallium; e.g., lymphomas, lung cancer). It is used to locate infection or inflammation in patients with fever of unknown origin. Finally, it is used to monitor response to treatment of infection, inflammation, or tumor.

Test Explanation

A gallium scan of the total body is usually performed 24, 48, and 72 hours after an intravenous (IV) injection of radioactive gallium. Most commonly, however, a single scan is performed 2 to 4 days after injection of the gallium. Gallium is a radionuclide that is concentrated in areas of inflammation and infection, by abscesses, and by benign and malignant tumors. Not all types of tumors, however, will concentrate gallium. Lymphomas are particularly gallium avid. Other tumors that can be detected by a gallium scan include sarcomas, hepatomas, and carcinomas of the gastrointestinal (GI) tract, kidney, uterus, stomach, and testicle.

This test is useful in detecting metastatic tumor, especially lymphoma, even when other diagnostic imaging tests are normal. To a large degree, PET scans (p. 821) have replaced the use of gallium scans for the identification of malignancy. The gallium scan also is useful in demonstrating a source of infection in patients with a fever of unknown origin. Gallium can be used to identify noninfectious inflammation within the body in patients who have an elevated sedimentation rate. Unfortunately, this test is not specific enough to differentiate among tumor, infection, inflammation, and abscess. Although a gallium scan is better able to detect sites of chronic inflammation, PET scans are more commonly used to identify areas of acute infection.

Some organs (liver, spleen, bone, colon) normally retain gallium. Therefore a normal total-body gallium scan study would demonstrate some uptake in these organs, but this uptake is much less concentrated than in pathologic areas (e.g., tumor, inflammation).

Another method of scanning is called SPECT (single-photon emission computed tomography). With SPECT scanning, the patient lies supine on the table surrounded by a donut-like gantry. The photon detection camera rotates around the patient to obtain photon counts from 360 degrees. This provides a more detailed image.

A nuclear medicine technologist performs each scan in approximately 30 to 60 minutes. Repeated scanning is required. Repeated injections are not necessary. The test results are interpreted by a physician trained in nuclear medicine and are usually available 72 hours after the injection. No pain or discomfort is associated with this procedure other than the IV injection. However, it occasionally can be uncomfortable to lie still on a hard table for the duration required.

Contraindications

Interfering Factors

Procedure and Patient Care

Test Results and Clinical Significance

Normal Findings

Normal values are determined by type and quantity of radiolabeled ingested food.

Values lower than normal represent abnormally fast gastric emptying. Values higher than upper limits represent delayed gastric emptying.

Indications

This scan is used to determine the rate of gastric emptying. It is used to diagnose gastroparesis or gastric obstruction in patients who have postcibal nausea, vomiting, bloating, early satiety, belching, or abdominal pain.

Test Explanation

In this study the patient ingests a solid or liquid “test meal” containing a radionuclide such as technetium (Tc). The stomach is then scanned until gastric emptying is complete (Figure 8-8). This study is used to assess the stomach's ability to empty solids or liquids and to evaluate disorders that may cause a delay in gastric emptying, such as obstruction (caused by peptic ulcers or gastric malignancies) and gastroparesis. This scan is also useful in determining the patency of a gastrointestinal (GI) surgical anastomosis.

This procedure lasts approximately 4 hours, depending on the gastric emptying time. The test is interpreted by a nuclear medicine physician. Results are available the same day. There is no discomfort associated with the test.

Contraindications

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Procedure and Patient Care

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Related Test

Normal Findings

Indications

This scan is performed on patients who complain of heartburn, reflux of food, water brash (sour taste in the mouth), aspiration, or paroxysmal nocturnal dyspnea (from nocturnal aspiration). It can detect gastroesophageal reflux and/or aspiration.

Test Explanation

GE reflux scans are used to evaluate patients with symptoms of heartburn, regurgitation, vomiting, and dysphagia. Also, these scans are used to evaluate the medical or surgical treatment of patients with GE reflux. Finally, aspiration scans may be used to detect aspiration of gastric contents into the lungs and to evaluate swallowing function.

This procedure is performed in the nuclear medicine department in approximately 30 minutes. There is no discomfort associated with this test.

Contraindications

Procedure and Patient Care

Test Results and Clinical Significance

Related Test

Normal Findings

Indications

This study is mainly used to localize sites of GI bleeding.

Test Explanation

The GI bleeding scan is a test used to localize the site of bleeding in patients who are having active GI hemorrhage. The scan also can be used in patients who have suspected intraabdominal (nongastrointestinal) hemorrhage from an unknown source. Localization of the source of GI or other bleeding can be quite difficult. When surgery is required under these circumstances, it is difficult, cumbersome, and prolonged. The surgeon may have extreme difficulty finding the source of bleeding. The bleeding scan helps localize the bleeding for the surgeon.

Box 8-1 provides an overview of the diagnostic procedures used in evaluating GI bleeding. Many of these studies have limitations that warrant the use of the GI bleeding scan. For example, endoscopy has proved to be extremely useful in determining the source of intestinal bleeding; however, endoscopy is not helpful if the source is within the small intestine or the colon. Although colonoscopy allows excellent visualization of the colon when it is cleared out, it is extremely difficult to see when acute, active intestinal bleeding is occurring. Arteriography has three limitations in its evaluation of GI bleeding. First, arteriography can determine the site of bleeding, but the rate of bleeding must exceed 0.5 mL/min for detection. Second, if GI bleeding is intermittent, the results of the arteriogram can be falsely negative. Third, arteriography visualizes only the blood vessels to the small bowel, right colon, and transverse colon through a superior mesenteric angiogram. If the left colon and sigmoid vessels are to be visualized (most bleeding comes from these areas), an inferior mesenteric angiogram must be requested. This is more difficult to perform.

The GI bleeding scan has several advantages over arteriography. The GI bleeding scan can detect bleeding if the rate is in excess of 0.05 mL/min. Also, with the use of technetium-labeled RBCs, delayed films (as long as 24 hours) can be obtained to indicate the site of an intermittent or extremely slow intestinal bleed.

A GI scintigram is much more sensitive in locating the site of GI bleeding; however, it is not very specific in pinpointing the site or the cause of bleeding. Usually, when the results of a GI scintigram are positive, the exact source of bleeding cannot be localized any more accurately than indicating the affected quadrant of the abdomen (e.g., right upper, left lower). This test is usually performed by injecting sulfur colloid labeled with technetium-99m (^99mTc) or ^99mTc-labeled red blood cells (RBCs) into the patient. If the patient is bleeding at a rate in excess of 0.05 mL/min, pooling of the radionuclide will ultimately be detected in the abnormal segment of the intestine. Few false-positive results occur. Again, it is important to recognize that the test will only localize the bleeding; it will not indicate the exact pathologic condition causing the bleeding. With this test result, if surgery is required, the surgeon is directed to the abnormal area and hopefully can detect and resect the pathologic bleeding source.

It is important to realize that this test can take at least 1 to 4 hours to obtain useful information. Unstable patients should not leave the intensive care environment for that long. Furthermore, the unstable patient may need to go to surgery in minutes and the surgeon may not have the luxury of taking several hours to determine the region of active bleeding.

Contraindications

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Procedure and Patient Care

Test Results and Clinical Significance

Related Tests

Normal Findings

Indications

This test allows for visualization of the liver and spleen. It is indicated in patients with cancer to rule out metastatic tumor to the liver. It is a routine part of tumor staging. It is also indicated in patients with primary tumors (hepatomas) or in patients with cirrhosis who are at high risk for the development of primary hepatomas. Patients with abnormal liver enzymes will also have their liver visualized. Liver scanning is used to monitor liver diseases and response to therapy.

Test Explanation

This radionuclide procedure is used to outline and detect structural changes of the liver and spleen. A radionuclide, usually technetium-99m (^99mTc)-labeled sulfur colloid, is administered intravenously. Later, a scintillation camera is placed over the right upper and left upper quadrants of the patient's abdomen. This records the distribution of the radioactive particles emitted from the liver and spleen. Images are obtained that are comparable to the gamma ray emission and are recorded digitally or on an analog film.

Because the scan can demonstrate only filling defects greater than 2 cm in diameter, false-negative results may occur in patients with space-occupying lesions (e.g., tumors, cysts, granulomas, abscesses) smaller than 2 cm. The scan may be incorrectly interpreted as positive for filling defects in patients with cirrhosis because of the distortion of the patient's liver parenchyma. The liver scan can detect tumors, cysts, granulomas, abscesses, and diffuse infiltrative processes affecting the liver (e.g., amyloidosis, sarcoidosis).

When a liver filling defect is observed, the most common cause is a benign hemangioma. This can be differentiated from tumor with the use of Tc-labeled red blood cells (RBCs). The patient's own RBCs are labeled with Tc and reinjected into the patient. Immediate uptake of the radionuclide by the filling defect is suggestive of a hemangioma, for which no therapy is usually required.

In general, computed tomography (CT) scans and magnetic resonance imaging (MRI) scans have replaced the liver scan in diagnostics. Single-photon emission computed tomography (SPECT) has significantly improved the quality and accuracy of liver scanning. With SPECT scanning the radionuclide is injected and the scintillation camera is placed to receive images from multiple angles (around the circumference of the liver). This greatly increases the usefulness of nuclear liver scanning. With the use of radioactive carbon, nitrogen, fluorine, or oxygen, anatomic and biochemical changes can be visualized within the liver. This method of liver scanning is called positron emission tomography (PET) scanning (p. 821).

The liver scan can also identify portal hypertension. Normally, most of the radionuclide administered during a liver scan is taken up by the liver. If the liver-to-spleen ratio is reversed (i.e., the spleen takes up more of the radionuclide), reversal of hepatic blood flow exists as a result of portal hypertension.

Splenic hematoma, abscess, cyst, tumor, infarction, and infiltrate processes such as granulomas can be detected. SPECT scanning can also be used to improve visualization of the spleen.

Contraindications

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Procedure and Patient Care

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Related Tests

Normal Findings

Indications

The lung scan is very helpful in making the diagnosis of pulmonary embolism (PE). It is easily and rapidly performed on patients who have sudden onset of noncardiac chest pain or shortness of breath. It is often performed on patients who have unexplained tachycardia or hypoxemia (Box 8-2).

Test Explanation

This nuclear medicine procedure is used to identify defects in blood perfusion of the lung in patients with suspected PE. Blood flow to the lungs is evaluated using a macroaggregated albumin (MAA) tagged with technetium (Tc), which is injected into the patient's peripheral vein. Because the diameter of the radionuclide aggregates is larger than that of the pulmonary capillaries, the aggregates become temporarily lodged in the pulmonary vasculature. A scintillation camera detects the gamma rays from within the lung microvasculature. With the use of light conversion a realistic image of the lung is obtained on film.

A homogeneous uptake of particles that fills the entire pulmonary vasculature conclusively rules out PE. If a defect in an otherwise smooth and diffusely homogeneous pattern is seen, a perfusion abnormality exists (Figure 8-10). This can indicate PE. Unfortunately, many other serious pulmonary parenchymal lesions (e.g., pneumonia, pleural fluid, emphysematous bullae) also cause a defect in pulmonary blood perfusion. Therefore, although the scan may be sensitive, it is not specific because many different pathologic conditions can cause the same abnormal results.

The chest x-ray film aids in the interpretation of the perfusion scan because a defect on the perfusion scan seen in the same area as a pulmonary parenchymal abnormality on the chest x-ray film does not indicate PE. Rather, the defect may represent pneumonia, atelectasis, effusion, and so on. When a perfusion defect occurs in an area of the lung that is normal on a chest x-ray study, however, PE is very likely.

Specificity of a perfusion scan also can be enhanced by the concomitant performance of a ventilation lung scan, which detects parenchymal abnormalities in ventilation (e.g., pneumonia, pleural fluid, emphysematous bullae). The ventilation scan reflects the patency of the pulmonary airways using xenon gas or technetium (Tc) diethylenetriamine pentaacetic acid (DTPA) as an aerosol. When vascular obstruction (embolism) is present on a perfusion scan, ventilation scans will demonstrate a normal wash-in and a normal wash-out of radioactivity from the embolized lung area. If parenchymal disease (e.g., pneumonia) is responsible for the perfusion abnormality, however, wash-in or wash-out will be abnormal. Therefore the “mismatch” of perfusion and ventilation is characteristic of embolic disorders, whereas the “match” is indicative of parenchymal disease. When ventilation and perfusion scans are performed synchronously, this is called a ventilation/perfusion (V/Q) scan.

Most nuclear physicians place the lung scan results in one of several categories: negative for PE, low probability of PE, high probability of PE, or positive for PE.

With the increased availability of rapid access spatial CT scanning of the chest (see p. 1029), the diagnosis of PE is now more easily made with CT scanning of the chest using CT angiography. CT angiography is faster and more accurate than ventilation/perfusion lung scans and is less invasive than pulmonary angiography.

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This scan is designed to identify a Meckel diverticulum that contains ectopic gastric mucosa. It is indicated in patients who have recurrent lower abdominal pain or in pediatric or young adult patients who have occult gastrointestinal (GI) bleeding.

Test Explanation

Meckel diverticulum is the most common congenital abnormality of the intestinal tract. It is a persistent remnant of the omphalomesenteric tract. The diverticulum usually occurs in the ileum, approximately 2 feet proximal to the ileocecal valve. Approximately 20% to 25% of Meckel diverticula are lined internally by ectopic gastric mucosa. This gastric mucosa can secrete acid and cause ulceration of the intestinal mucosa nearby. Bleeding, inflammation, and intussusception are other potential complications of this congenital abnormality. The majority of these complications occur by 2 years of age.

Both normal gastric mucosa within the stomach and ectopic gastric mucosa in Meckel diverticulum concentrate technetium-99m pertechnetate. When this radionuclide is injected intravenously, it is concentrated in the ectopic gastric mucosa of Meckel diverticulum. One can then expect to see a hot spot in the right lower quadrant of the abdomen at about the same time as the normal stomach mucosa is visualized. This is a very sensitive and specific test for this congenital abnormality.

It is possible that Meckel diverticulum is present but contains no ectopic gastric mucosa within. Usually this is not symptomatic. No concentration of radionuclide will occur within the diverticulum. This test is not helpful in these cases.

Other conditions can simulate a hot spot compatible with Meckel diverticulum containing ectopic gastric mucosa. Usually these are associated with inflammatory processes within the abdomen (e.g., appendicitis, Crohn disease, or ectopic pregnancy).

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Octreotide scans are used to identify and localize neuroendocrine primary and metastatic tumors. This scan is indicated in patients with known neuroendocrine tumors (e.g., carcinoid tumors and gastrinomas). It is used preoperatively to direct the surgeon to primary and metastatic tumors. This scan is also used to monitor therapy of these tumors.

Test Explanation

Octreotide scan is a specific example of nuclear peptide scanning that is increasingly being used to identify neoplasms by their altered state of physiology. Using peptides for which tumors have an increased uptake because of cellular membrane receptors or idiosyncratic physiology (glycolysis, proliferation, angiogenesis, or oxidation) will allow anatomic localization of many previously hidden tumors. These molecular imaging techniques can also provide information regarding the effect of anticancer therapy on tumor growth and survival.

Most neuroendocrine cells have a somatostatin receptor on the cellular membrane. Neuroendocrine tumors retain these receptors. Octreotide is an analogue of somatostatin. When combined with a radiopharmaceutical (such as indium-111 DTPA), the radiolabeled octreotide will attach to the somatostatin receptors of the neuroendocrine tumor cells. With the use of a scintillation camera the uptake can be observed and localized. In pediatrics, metaiodobenzylguanidine (MIBG) is used more frequently than octreotide as the radioisotope for identification of neuroendocrine tumors.

In patients with known neuroendocrine tumors, this test is used to direct the surgeon to the primary and metastatic sites within the body (especially the abdomen). This test is also used in the surveillance of patients who have been or are being treated for these neuroendocrine tumors. When this test is used as a monitor of disease, recurrence or progression can be identified quite easily and accurately. The liver, however, is more difficult to evaluate with octreotide scanning. The use of single-photon emission computed tomography (SPECT) imaging improves the sensitivity of this test. Many different types of hormone-producing tumors can be detected by this scan. Most notable include carcinoid, gastrinoma, insulinoma, glucagonoma, pheochromocytoma, and small cell lung cancer. Other abnormalities can pick up octreotide, including granulomatous infections (such as sarcoidosis or tuberculosis), rheumatoid arthritis, and nonhormonal cancers (breast, lymphoma, and non–small cell lung cancers).

The imaging procedure is performed by a trained technologist in approximately 30 minutes. A physician trained in nuclear medicine interprets the results. The only discomfort associated with this procedure is the intravenous (IV) injection of the radionuclide.

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This test is used to locate the parathyroid glands before surgery. It also indicates the cause of the hyperparathyroidism.

Test Explanation

Hypercalcemia can be caused by hyperparathyroidism. Parathyroid hyperplasia, adenoma, or cancer can cause hyperparathyroidism. It is important for the surgeon planning resection of the parathyroid abnormality to know how many parathyroid glands are involved and their locations. Preoperative parathyroid scanning is the most accurate method of providing this information. Parathyroid hyperplasia causes enlargement of all four parathyroid glands. A parathyroid adenoma or cancer, however, causes enlargement of only one parathyroid gland and suppression (decrease in size) of the other three glands. Based on the parathyroid scan, the surgeon will know whether to suspect disease in one or all four of the glands.

Parathyroids are located most commonly on the lateral borders of the thyroid lobes—two on each side. However, parathyroid anatomic location varies considerably, and they may be located anywhere from the upper neck to the lower mediastinum. Parathyroid scanning is also done immediately before surgery to help the surgeon identify the parathyroid glands and particularly the pathologic glands. In this test, the scan is performed on the parathyroid glands as described previously. In the operating room, the surgeon scans the entire anterior neck with a hand-held gamma ray detector. Increased counts are noted in the regions where the parathyroids are located.

Scanning is now done more frequently in newly diagnosed patients. In some centers, scanning is reserved for those patients in whom an initial neck exploration failed to identify all four parathyroid glands and the hypercalcemia persisted after the operation.

There are two methods of parathyroid scanning. The first is the single tracer double phase (STDP) test using technetium-99m (^99mTc) sestamibi or ^99mTc tetrofosmin. With this method, the patient is injected with the sestamibi tracer. Images are obtained at 15 minutes and 3 hours. The tracer initially lights up both the thyroid and the parathyroid glands. At 3 hours, however, the tracer is washed out of all normal endocrine tissue and remains only in the pathologic parathyroid tissue.

The second method is the dual isotope subtraction test in which ^99mTc pertechnetate or iodine 123 (¹²³I) is administered. Only the thyroid gland takes up either of these two later tracers. Scanning is performed. ^99mTc sestamibi is then administered and is taken up by both the thyroid and the parathyroid glands. Scanning is repeated and that first image is then “subtracted” from the second image leaving an image of only the parathyroid glands.

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PET scanning is used in many areas of medicine, most commonly for evaluation of the heart and brain. It is also commonly used in many aspects of oncology.

Test Explanation

In PET scanning, radioactive chemicals are administered to the patient. These chemicals are used in the normal metabolic process of the cells of the particular organ being imaged. Positrons emitted from the radioactive chemicals in the organ are sensed by a series of detectors positioned around the patient. Positron counts are received by these detectors and—with the combination of computed tomography—the positron emissions are recorded into a high-resolution three-dimensional image indicating a particular metabolic process in a specific anatomic site (Figure 8-12). Therefore PET provides images representing not only anatomy but also physiology. Like CT scans, MRI merely produces images of the body's anatomy or structure—not its metabolism. In most disease states, physiologic changes precede anatomic changes. Still in other disease states, such as Alzheimer disease, no anatomic changes occur—yet PET can identify classic physiologic changes that are diagnostic of the disease. Depending on the particular radionuclide used, PET can demonstrate the glucose metabolism, oxygenation, blood flow, and tissue perfusion of any specific area. Pathologic conditions are recognized and diagnosed by alterations in the normal metabolic process.

Certain radioactive chemical compounds provide specific information depending on the information required and the organ being evaluated. A cyclotron is used to create the radioactive chemical. Radioactive oxygen is used to make radioactive water (H₂¹⁵O). This is used to evaluate blood flow and tissue perfusion of an organ.

Radioactive fluorine is applied to a glucose analog and called fluorodeoxyglucose (FDG). Because most cells use glucose as an energy source, FDG is particularly useful in concentrating in regions of high metabolic activity of a particular organ. Radioactive carbon-labeled glucose is also useful for this purpose. Radioactive nitrogen is used in radioactive ammonia, which can be used in evaluating the liver. Other applications of radionuclides are listed in Table 8-3. PET scanning is becoming more widely applied and commonly used as research continues. Its greatest use thus far has been in the fields of neurology, cardiology, and oncology.

In many centers, PET images can be superimposed with computed tomography (CT) or magnetic resonance imaging (MRI) to produce an anatomically accurate image showing the physiology/metabolism of the organ imaged. With newer units, PET/CT imaging can be performed by the same machine (Figure 8-13). This is called PET/CT image fusion or PET/CT co-registration. These composite views, which allow the information from two different studies to be digitally correlated and superimposed onto one image, lead to more precise information and accurate diagnoses. The CT images are acquired with the use of iodine contrast. In less than 60 minutes after the FDG is administered, the PET scan is performed in the same unit. The images are imposed on each other. The combined PET/CT scans provide images that pinpoint the location of abnormal metabolic activity within the body.

Neurology

Most brain imaging is performed with FDG. The brain uses glucose as its sole metabolic fuel. Pathologic areas of the brain that are more metabolically active (such as cancers) more avidly take up FDG than do normal areas. Because of the high physiologic rate at which glucose is metabolized by normal brain tissue, the detectability of tumors with only modest increases in glucose metabolism, such as low-grade tumors and, in some cases, recurrent tumors, is difficult with FDG. Another radioactive marker that is being used is 3,4-dihydroxy-6-18F-fluoro-L-phenylalanine (18F-FDOPA). This seems to improve visibility of low-grade brain tumors.

Epilepsy, Parkinson disease, and Huntington disease are identified as localized areas of increased metabolic activity indicating rapid nerve firing. Brain trauma resulting in a hematoma or bleeding is evident as decreased metabolic activity in the area of trauma. Stroke can also be identified and its extent determined. With the use of radioactive water (H₂¹⁵O), brain blood flow can be determined. Areas of decreased blood flow take up less (H₂¹⁵O) than normal areas and represent areas at risk for stroke.

Alzheimer disease can be recognized by identifying hypometabolism in multiple areas of the brain (temporal and parietal lobe) as scanning is performed during cognitive exercises. PET scanning with amyloid imaging using radioactive markers such as Pittsburgh agent compound B (PiB), flutemetamol, or fluorine-18 has been very helpful in identifying amyloid protein precursors (p. 639) in the brain. These agents bind to the beta-amyloid plaques that are increased in patients with Alzheimer disease. A negative PET scan with amyloid imaging eliminates the possibility of Alzheimer disease in a patient with cognitive impairment. Because other neurologic conditions (especially in elderly people) are also associated with amyloid neuritic plaques, a positive scan does not certainly establish the diagnosis of Alzheimer disease.

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No increased uptake outside the prostate gland

Indications

This test is used to identify and accurately stage prostate cancer.

Test Explanation

By using a radionuclide that is able to attach to prostate cancer cells only, metastatic prostate cancer outside the prostate gland can be easily identified. In this scan, mouse monoclonal antibody (capromab) directed against prostate specific membrane antigen (PSMA) is tagged with indium¹¹¹. PSMA, located in the cytoplasm of prostate cancer (or transitional cell urogenital cancer), is detected on radionuclide scan images. Disease outside the prostate (e.g., retroperitoneum, liver, lung, bone) indicates metastatic prostate cancer. Other radionuclides, such as technetium labeled red blood cells, can be used, but the images provide less accurate results.

This scan is helpful in staging newly diagnosed prostate cancer patients who are at high risk for metastatic disease to the lymph nodes or other organs. This test can also be used to identify recurrent or metastatic disease after curative therapy. This test can document completeness of anti-prostate cancer therapy. Finally this scan helps elucidate abnormalities that may be noted on other diagnostic imaging tests, such as CT scan (especially in patients with prior prostate cancer).

The ProstaScint scan is usually performed in conjunction with other diagnostic testing, such as CT scan, PET scan, or ultrasound. Because of cost and labor intensity, this test is not used routinely for prostate screening.

This test takes about 30 minutes (per day for as many as 5 days) and is performed by a nuclear medicine technologist. It is interpreted by a nuclear medicine physician. There is no discomfort associated with this test other than an intravenous injection.

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Renal scans are used to indicate the perfusion, function, and structure of the kidneys. They are also used to indicate the presence of obstruction or renovascular hypertension. Because this study uses no iodinated dyes, it is safe to use on patients who have iodine allergies or compromised renal function. Renal scans are used to monitor renal function in patients with known renal disease. This scan also plays a large part of the diagnosis of renal transplant rejection.

Test Explanation

This nuclear medicine procedure provides visualization of the urinary tract after intravenous administration of a radioisotope. The radioactive material is detected by a scintillation camera, which can detect the gamma rays emitted by the radionuclide in the kidney. The scintillation camera information can be translated into light and thereby create a realistic image of the renal structure. That information is collated by a computer, and the amount of gamma ray emission per unit of time can be calculated to determine renal function, vascular insufficiency, or renal obstruction. Scans do not interfere with the normal physiologic process of the kidney. The resultant image (scan) indicates distribution of the radionuclide within the kidney and ureters.

There are several different types of renal scans, depending on what information is needed (Table 8-4). Different isotopes may be more suitable for different scans, based on the manner in which the kidney handles the radioisotope.

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This test is used to evaluate patients with xerostomia (dry mouth), salivary gland pain, tumors, or possible parotid duct obstruction.

Test Explanation

The ability of the epithelial cells of the salivary glands to transport large pertechnetate from the blood and to secrete it into the saliva provides the principle for imaging the salivary glands. The functional capabilities, structural integrity, and location of the glands can be assessed. Most usually, the parotid gland alone is visualized. Occasionally, the submandibular glands can be seen.

By following the radionuclide immediately after injection, blood flow can be evaluated. Because this blood flow comes from the cerebral arteries, this test is a measure of the patency of those vessels. Tumors have increased blood flow that can be identified during this part of the study. Patients with acute inflammation will also have increase blood flow during the early stages of the test.

In about 10 to 20 minutes after injection, gland function becomes obvious by uptake of the nuclide into the gland. This uptake is usually compared to the thyroid, which is visualized at the same time. Function will be diminished in patients with severe inflammation or autoimmune diseases, such as Sjögren syndrome. Five to 10 minutes later, one should see secretion of nuclear material into the mouth. Salivary calculi will impede excretion and wash-out of the radionuclide because of obstruction of the excretory duct.

Wash-out demonstrates complete salivary gland excretion. Usually the patient is asked to suck on a lemon to encourage rapid wash-out. Static lateral pictures of the salivary glands can demonstrate tumors or cysts. Most commonly the parotid gland is affected by tumors, and usually they are benign. In neoplasm of the salivary glands, wash-out is slow (i.e., the tumor may remain “hot” [retain radionuclide]) for longer periods of time. Nearly 50% of the benign tumors are hot. A cold tumor (does not take up radionuclide as well as “cold” surrounding tissue) is common in malignant tumors.

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Indications

Scrotal imaging is helpful in the diagnosis of patients with a sudden onset of unilateral testicular swelling and pain. Scrotal imaging can differentiate unilateral testicular torsion from other causes of testicular pain (e.g., acute epididymitis, torsion of the testicular appendage, orchitis, strangulated hernia, testicular hemorrhage). This test is not used frequently because scrotal ultrasound can reliably provide the same information more rapidly and more cheaply.

Test Explanation

Testicular torsion is a surgical emergency requiring prompt surgical exploration to salvage the involved testicle. To provide immediate surgical care, the surgeon must differentiate the condition from other causes of painful testicular swelling that do not require surgery. Use of radionuclide scrotal imaging enables the surgeon to diagnose testicular torsion. This study is usually performed on an emergency basis and in the nuclear medicine department.

The patient is positioned under the gamma camera with the scrotum supported between the abducted thighs. Technetium-99m (^99mTc) pertechnetate is administered, and a dynamic radionuclide nuclear angiogram is obtained. Static images are obtained immediately afterward. An area of decreased perfusion corresponding to the involved testes indicates a high probability of torsion of the testicle. If the clinically involved testis is normally perfused or hypervascular, a disease other than torsion of the testicle (as described earlier) exists.

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Lymphoscintigraphy is used to identify the “sentinel” lymph node—the one most likely to contain metastasis from a nearby primary tumor. It is used to map the lymphatic drainage of a primary cancer so that surgery can be directed for diagnostic and possibly therapeutic resection of lymph nodes. It is primarily used in breast cancer and melanoma.

Test Explanation

With this procedure, the first (sentinel) lymph node in line to catch metastatic tumor cells from a primary tumor is identified and biopsied. To stage most breast or melanoma cancers, a lymph node draining the primary site must be evaluated microscopically. With the use of SLNB, the first lymph node in the chain of lymph nodes can be identified and biopsied. If results are negative, as is the case in most patients with small tumors, the rest of the axillary lymph contents can be safely assumed to be free of tumor and are not removed. This saves women from the potential complications associated with a full lymph node dissection including arm swelling, cellulitis, postoperative pain, and reduced range of motion. Furthermore this test can identify unusual locations for lymph node metastasis that would not normally be identified by the surgeon.

To summarize the procedure, a tracer (isosulfan blue dye or technetium [^99mTc] sulfur colloid) is injected into the skin or tissue near the tumor. If technetium is used, a lymphoscintigraphy scan is performed about 1 to 2 hours after the injections. There are specific protocols depending on the lymph node basin being studied and on the primary tumor site. Lymph nodes that take up the radionuclide are the sentinel lymph nodes that the surgeon will identify and remove. In the operating room, using a hand-held gamma detector, the surgeon is able to identify the region of maximum radioactivity. These are removed and sent to the pathologists for immediate evaluation. If isosulfan or methylene blue dye is injected, a stained lymphatic vessel is identified by the surgeon in the subcutaneous tissue and followed to the first blue-colored node. The sentinel lymph nodes are the blue, or “hot,” nodes closest to the primary tumor.

If the sentinel lymph node is negative on frozen section or imprint cytology (touch prep) pathologic study, the lymph node dissection procedure is not required. If the sentinel lymph node is positive, a full lymph node dissection may be performed. In some instances light microscopy may be negative but subsequent immunohistochemical staining may indicate the presence of cancer in the node. The sentinel lymph node can also be evaluated right in the operating room by using molecular assays for epithelial cell specific components such as cytokeratin or mammaglobin.

This test is quickly becoming an important part of the standard treatment for breast and melanoma cancer surgery. The only discomfort associated with the test is the preoperative injections required around the tumor. The technetium injection and subsequent scanning are usually performed in the nuclear medicine department. When isosulfan blue is used as the lymph node tracer, the injection is administered in the operating room under anesthesia.

Nuclear lymphoscintigraphy is also used to evaluate the lymph node status in patients with Hodgkin disease and other lymphomas. Patients with chronic lymphedema of an extremity may also be evaluated by lymphoscintigraphy.

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Indications

This test is used to visualize the thyroid gland when disease of the thyroid is suspected. It is particularly useful in the evaluation of patients with a suspected thyroid nodule. With thyroid nuclear scanning the nodule can be classified and more appropriately treated.

Test Explanation

Thyroid scanning allows the size, shape, position, and physiologic function of the thyroid gland to be determined with the use of radionuclear scanning. A radioactive substance such as technetium-99m (^99mTc) or Iodine¹³¹ is given to the patient to visualize the thyroid gland. A scintigraphy camera is passed over the neck area, and an image is recorded (Figure 8-16).

Thyroid nodules are easily detected by this technique. Nodules are classified as functioning (warm/hot) or nonfunctioning (cold) depending on the amount of radionuclide taken up by the nodule (Figure 8-17). A functioning nodule could represent a benign adenoma or a localized toxic goiter. A nonfunctioning nodule may represent a cyst, carcinoma, nonfunctioning adenoma or goiter, lymphoma, or localized area of thyroiditis.

Scanning is useful in patients with the following clinical conditions:

Another form of thyroid scan is called the whole-body thyroid scan. This scan is performed on patients who have previously had a thyroid cancer treated. Iodine¹³¹ is administered orally, and the entire body is scanned to look for metastatic thyroid tissue. A hot spot would indicate recurrent tumor. Before this test can be performed, all of the thyroid tissue in the neck must be either surgically excised or ablated with radioactive ¹³¹I. If the patient is receiving thyroid replacement therapy, the thyroid medicine must be discontinued at least 6 weeks before testing. This makes any metastatic thyroid tissue, particularly iodine, avid. A high thyroid-stimulating hormone blood level ensures that any thyroid cancer tissue will take up the administered radioactive iodine. This test is performed routinely (every 1 to 2 years) on patients who have had a thyroid cancer larger than 1 cm. Smaller cancers are unlikely to metastasize. Much of the procedure is similar to thyroid scanning.

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Normal Findings

No deviation from normal

Indications

Total blood volume measurement may be useful in the following clinical circumstances:

Test Explanation

Measurement of total blood volume is an accurate indicator of true plasma (liquid components of blood) measurement. Based on the patient's height, weight, gender, and body composition, a TBV can determine whether the measured volumes are normal, high, or low compared with what would be ideal for the particular patient. The report indicates actual volumes for TBV and RBCs that deviate from normal.

To maintain blood volume within a normal range, the kidneys regulate the amount of water and sodium lost into the urine. For example, if excessive water and sodium are ingested, the kidneys normally respond by excreting more water and sodium into the urine. This auto adjustment is mediated through the renin-angiotensin-aldosterone system. Both angiotensin and aldosterone, although by different mechanisms, stimulate distal tubular sodium reabsorption and decrease sodium and water loss by the kidney and thereby adjust blood volume. Another important hormone in regulating blood volume is vasopressin (antidiuretic hormone [ADH]). This hormone is released by the posterior pituitary. One of its actions is to stimulate water reabsorption in the collecting duct of the kidney, thereby decreasing water loss and increasing blood volume. Blood volume affects cardiac output and blood pressure.

Radioiodine labeled albumin is injected intravenously. Blood is withdrawn every 5 minutes for five samples. The radioactivity is counted and compared with what would be considered normal. A lower amount of the radioactivity in the sample indicates a higher plasma volume. The hematocrit is then used to derive the red cell volume. The total blood volume is obtained by adding the plasma volume and the red cell volume.

Test Results and Clinical Significance

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Indications

This scan is used to identify and localize occult inflammation or infection. It is used for patients who have a fever of unknown origin, suspected osteomyelitis, or inflammatory bowel disease. It is used to indicate whether or not an abnormal mass (e.g., a pancreatic pseudocyst) is infected.

Test Explanation

This test is based on the fact that WBCs are attracted to areas of infection or inflammation. When the patient has a suspected infection or inflammation, yet the site cannot be localized, the injection of radiolabeled WBCs may identify and localize that area of inflammation or infection. Appropriate treatment can then be performed. This is especially helpful in patients who have a fever of unknown origin, suspected occult intraabdominal infection, or suspected (yet radiographically unapparent) osteomyelitis. The scan can differentiate infectious from noninfectious processes. Areas of noninfectious inflammation (e.g., inflammatory bowel disease) also take up the radiolabeled WBCs.

This scan requires drawing about 40 to 50 mL of blood from the patient, separating out the WBCs, labeling the WBCs with technetium or indium, and reinjecting them into the patient. Four to 24 hours later, imaging of the whole body may show an area of increased radioactivity suggestive of accumulation of the radiolabeled WBCs in an area of infection or inflammation.

The imaging procedure is performed by a trained technologist in approximately 30 minutes. A physician trained in nuclear medicine interprets the results. The only discomfort associated with this procedure is the intravenous (IV) injection of the radionuclide.

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