Nuclear Imaging

Nuclear medicine uses small amounts of short-lived radioactive material to diagnose or treat diseases and to give information on how tissues and organs work. Nuclear medicine can detect diseases such as heart disease, arthritis, and cancer. Areas of the body most often studied include the brain, thyroid gland, heart, lungs, kidneys, gallbladder, liver, and bones.

Before having a nuclear medicine procedure performed, patients are given a radioactive material called an isotope. Isotopes can be injected, inhaled, or swallowed in liquid or capsule form. Once the isotope is inside the body, it travels to the target organs or tissues and gives off gamma rays. Images are then taken of the body with special equipment that can detect the gamma rays. These images are interpreted by a radiologist with special training in nuclear medicine. Various types of equipment are used for nuclear medicine studies depending on the procedure.  Gamma probes, stationary gamma cameras, and single photon emission computed tomography (SPECT) cameras.

Indications

  • Screen for bone metastasis in patients with known or suspected cancer.
  • Infection (osteomyelitis)
  • Evaluation of suspected fractures, including stress fractures
  • Evaluate response to therapy, chemotherapy or radiation therapy for cancer.
  • Evaluation of joint prosthesis for loosening or infection.
  • Evaluation of nonspecific bone pain, or abnormal x-ray appearance of bone.
  • Evaluation of metabolic bone disease.
  • Evaluation of the diagnosis of RSD or reflex sympathetic dystrophy.
  • Evaluation of avascularity of bone and post traumatic hetertopic bone formation.

A bone scan is an imaging test that shows areas of increased or decreased bone turnover (metabolism). It is used to diagnose a bone tumor, cancer, bone infection, and evaluate metabolic disorders. The procedure involves injecting a radioactive material (radiotracer) into a vein. The substance travels through the bloodstream to the bones and organs. As it wears away, it gives off radiation. This radiation is detected by a camera that slowly scans your body. Some risks involved are anaphylaxis, rash, swelling, infection and bleeding when the needle is inserted into a vein.

Indications

  • Detection of abscess or acute infection.
  • Evaluation of fever of unknown origin.
  • Acute or chronic osteomyelitis.
  • Evaluation of prosthesis or graft infection.
  • Evaluation of inflammatory bowel disease.
  • Evaluation of medication induced lung toxicity.

A gallium scan is a test that uses radioactive material to look for infection in the body. The test is performed to search for an unknown source of fevers. Gallium collects in areas of inflammation which may be due to an abscess or tumor. Combined with other imaging, such as CT, hidden disease may be detected. The procedure involves tying a rubber band around your upper arm, and the health provider injects a radioactive material called gallium into a vein. It then travels through the blood and collects in the bones and certain organs. Your healthcare provider will tell you to return at a later time to be scanned. If your healthcare provider thinks you have an acute inflammatory disease, the scan is done 4-6 hours after the injection. Otherwise, the scan is taken 24-48 hours (occasionally 72 hours) after the injection. There is minimal risk of radiation exposures (less than with x-rays or CT scans). Radiation exposure of any sort is not usually recommended for pregnant or nursing women or young children unless the benefits of the test exceed the risks.

Indications

  • Abscess or inflammatory localization.
  • Evaluation of osteomyelitis.

There is a very slight exposure to radiation from the radioisotope. The spleen normally receives the highest dose of radiation because white blood cells normally accumulate in the spleen. The radiation from these materials is very slight, and the materials decompose (become no longer radioactive) in a very short time. Virtually all radioactivity is gone within 1 or 2 days. There are no documented cases of injury from exposure to radioisotopes. The scanner only detects radiation – it does not emit any radiation.

However, because of the slight radiation exposure, most nuclear scans (including WBC scan) are not recommended for women who are pregnant or breastfeeding.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associate with having blood drawn are slight but may include: Excessive bleeding, fainting or feeling light headed, hematoma (blood accumulating under the skin), and infection (a slight risk any time the skin is broken.

Extremely rarely, a person may experience an allergic reaction to the radioisotope. This may include anaphylaxis if the person is extremely sensitive to the substance.

Indications

  • Evaluation of acute cholecystitis (cystic or common bile duct obstruction).
  • Evaluation of bile duct leakage following surgery.
  • Evaluation of congenital bile duct abnormalities.
  • Evaluation of biliary dyskinesia.

There is a small risk to pregnant or nursing mother, because the fetus or small child has a greater sensitivity to radioactive chemicals. Unless it is absolutely necessary, the scan will be delayed. The amount of radiation is small (less than that of a conventional x-ray) and is virtually gone from the body within 1 or 2 days. With an increased number of scans, there is some radiation risk.

Indications

  • Evaluation of renal perfusion and function.
  • Evaluation of renal trauma
  • Diagnosis of renovascular hypertension.
  • Evaluation of renal collecting system for obstruction.
  • Evaluation of renal transplant patients.
  • Diagnosis of acute tubular necrosis.
  • Renal evaluation in those with allergy to radiographic contrast.
  • Evaluation of ureterovesical reflux.
  • Evaluation of kidney function/scarring post renal infection.

A renal scan is an exam in which a small amount of radioactive material (radioisotope) is used to measure the function of the kidneys. This procedure reveals the size, position, shape, and function of the kidneys. A renal scan is usually performed after a kidney transplant to check kidney function and to look for signs of transplant rejection. The type of scan may vary due to a patient’s specific needs. You will lie on scanner table and the healthcare provider will place a tourniquet or blood pressure cuff to the upper arm, which creates pressure and enlarges your arm veins. The inner elbow is scrubbed with a numbing medicine (antiseptic) and a small amount of radioisotope is injected in a vein. The pressure on the upper arm is released, which allows the radioactive material to travel through the bloodstream. The kidneys are scanned a short time later. Several images are taken, each lasting 1 or 2 seconds. The total scan time takes about 30 minutes to an hour. A computer analyzes the images and provides detailed information about particular kidney functions. The scan requires no recovery time and be sure to drink plenty of fluids and urinate frequently to help remove the radioactive material from the body. Some risks may include from the needle stick bleeding and infection. In rare cases, a person will exhibit an allergic reaction to the radioisotope, which may include severe anaphylaxis.

Indications

  • Determination of thyroid size
  • Evaluation of functional status of thyroid nodules.
  • Evaluation of thyroid and neck masses.
  • Evaluation of patients with history of head and neck irradiation.
  • Quantitative thyroid uptake.
  • Detection of ectopic or substernal thyroid tissue.
  • Evaluation of thyroid patients following ablation for thyroid cancer.
  • Treatment of hyperthyroidism.

A thyroid scan is a nuclear medicine examination that uses a radioactive iodine tracer to see how well the thyroid gland is working. This test is done to check for hyperthyroidism, thyroid cancer, and thyroid nodules or other growths. Before the procedure begins, a pill will be given to you that contain radioactive iodine. The first scan is usually done 4-6 hours after the iodine pill is taken. Another scan may be taken 24 hours later. Other scans may be done by using a substance containing technetium. After the radioactive iodine has been absorbed by the thyroid, you will lie on your back on a movable table with your neck and chest under the scanner. The scanner detects the location and intensity of the rays given off by the radioactive material. During this part of the procedure, you must lie still to let the scanner get a clear image. A computer displays images of the thyroid gland. All radiation has possible side effects. There is a very small amount of radiation in the tracer swallowed during the test. Women who are nursing or pregnant should discuss the risks to the fetus or infant with their healthcare providers before taking this test.

Indications

  • Diagnosis of pulmonary embolism.
  • Evaluation of regional pulmonary perfusion and ventilation in acquired pulmonary disease (COPD, asthma, carcinoma).
  • Pre-op evaluation of lung function prior for thoracotomy. Quantitative lung evaluation.
  • Assessment of congenital pulmonary abnormalities and cardiac shunts

A pulmonary ventilation/perfusion is a pair of nuclear scan tests. These tests use inhaled and injected radioactive material (radioisotopes) to measure breathing (ventilation) and circulation (perfusion) in all areas of the lungs. A ventilation and perfusion scan is most often done to detect a pulmonary embolus, abnormal circulation (shunts) in the blood vessels of the lungs (pulmonary vessels), and to test lung function in people with advanced pulmonary disease such as COPD.

A pulmonary ventilation/perfusion scan is actually two tests. These tests may be performed separately or together. During the perfusion scan, a healthcare provider injects radioactive albumin into your vein. You are placed on a movable table that is under the arm of a scanner. The machine scans your lungs as blood flows through them to find the location of the radioactive particles. During the ventilation scan, you breathe in radioactive gas through a mask while you are sitting or lying on a table under the scanner arm. The risks are about the same as for x-rays (radiation) and needle pricks. This may include some exposure to radiation from the isotope, infection or bleeding from the site where the needle was inserted.

Indications

  • Determination of sentinel node for evaluation of metastatic breast cancer and malignant melanoma.

Lymphoscintigraphy is imaging that provides pictures called scintigrams of the lymphatic system. It is a network of small channels similar to blood vessels that circulate the fluid (called lymphs) and cells (lymphocytes) of the immune system throughout the body. Lymph nodes, which act like a filter to foreign bodies such as germs, viruses and pollen, are located along this network. Physicians perform this procedure to identify the sentinel lymph node, points of blockage in the lymphatic system, and plan a biopsy or surgery that will help assess the stage of cancer and create a treatment plan, and. The risks included are radiation exposure (small amount) and allergic reaction.

Indications

  • Evaluation for gastroparesis.

Gastroparesis is a condition that affects the ability of the stomach to empty its contents, but there is no blockage (obstruction). The cause of gastroparesis is unknown, but it may be caused by a disruption of nerve signals to the intestine. The condition is a common complication of diabetes and can be a complication of some surgeries. Risk factors include diabetes, gastrectomy, systematic sclerosis, and use of medication that inhibits certain nerve signals (anticholinergic medication).

PET is a nuclear medicine technique using a camera, which captures powerful images of the human body’s function and reveals information of health and disease. Compounds normally existing in the body, like simple sugars, are labeled with radioactive tracers, which emit signals and are injected into the body intravenously. The scanner records the signals that the tracer emits as it journeys through the body and as it collects in targeted organs. A powerful computer reassembles the signals into actual images, which then show biological maps of normal organ function and failure of organ systems in disease.

The reason why PET is so successful is that no other imaging technique shows the internal chemistry of the body so well. Conventional imaging techniques such as X-ray, CAT scans, and Magnetic Imaging Resonance shows anatomy. PET detects chemical and metabolic changes in disease states, such as cancer, before anatomic and structural changes (detected by conventional imaging) have time to develop. Therefore PET can detect diseases when anatomic imaging studies are still normal, and may be informative in differentiating benign from malignant process. PET evaluation of tissue metabolism can indicate the probable presence or absence of malignancy based on differences of biological activity, whereas anatomic imaging depends on size and radiographic characteristics of lesions to determine the likelihood of malignancy. In addition, whole body imaging with PET provides a means to examine all the organ systems in the entire body for both primary and metastatic disease in one procedure.

Utilizing a dedicated imaging workstation, we are able to overlay PET data with CT/MRI images, allowing precise localization of tumor.

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Image fusion readily localized tumor location in the spleen (arrow) in this patient with lymphoma (green arrowheads indicate normal physiologic activity in the bowel and kidney).

[CT data above left, PET data above right. Image fusion below.]

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The combined CT & PET data effectively increases specificity and sensitivity of each exam. Lymphoma in the axilla (green on fused CT image of the upper chest on image below) could be easily overlooked when evaluated by CT alone.

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A different patient (below) with locoregional recurrence of breast carcinoma along the right anterior chest wall.

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Thallium

Fixed defects anterior wall, inferior wall, inferolateral wall & apex & diffuse thinning of septum without SPECT evidence of ischemia

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PET

Increased uptake at inferolateral wall indicating hibernating, metabolically active myocardium which is still amenable to cardiovascular revasculartization (with stenting or surgical bypass)

In Neurology, PET plays a vital non-invasive role:

(1) Pre-surgical assessment of patients with refractory epilepsy. PET has greatly diminished the need for deep electrode monitoring, with all its attendant morbidity.

(2) PET is the only clear non-invasive way to distinguish between tumor recurrence and radiation necrosis in the brain of post surgical patients.

(3) Provides the earliest positive diagnosis of Alzheimer’s Dementia and in differentiating Alzheimer’s Dementia from other forms of dementia. All present treatments of Alzheimer’s and probably all future ones will require early detection to be effective.

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Images of the brain show exquisite anatomic detail with abnormal activity in the right temporal lobe (arrow) in an epileptic patient

The bottom line is that patients are managed differently when PET is used. Fewer diagnostic and fewer surgical procedures need to be done when PET is used in the diagnostic and surgical work up of patients with primary and recurrent carcinoma. Patients are spared the morbidity and mortality associated with diagnostic and surgical procedures that will have little or no benefit to them, and the insurance companies and the healthcare system are saved the cost of these unnecessary exams.

Learn about Positron Emission Mammography (PEM) for evaluation of breast cancer

Links to other PET scan websites:

http://www.petscan.org/

http://www.icppet.org/

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