NUCLEAR MEDICINE

Nuclear medicine is a branch of medical imaging that uses small amounts of radioactive material to diagnose and determine the severity of or treat a variety of diseases, including many types of cancers, heart disease, gastrointestinal, endocrine, neurological disorders and other abnormalities within the body. Because nuclear medicine procedures are able to pinpoint molecular activity within the body, they offer the potential to identify disease in its earliest stages as well as a patient’s immediate response to therapeutic interventions.

Diagnosis

Nuclear medicine, or radionuclide, diagnostic imaging procedures are noninvasive and, with the exception of intravenous injections, are usually painless medical tests that help physicians diagnose and evaluate medical conditions. These imaging scans use radioactive materials called radiopharmaceuticals or radiotracers.

Depending on the type of nuclear medicine exam, the radiotracer is either injected into the body, swallowed or inhaled as a gas and eventually accumulates in the organ or area of the body being examined. Radioactive emissions from the radiotracer are detected by a special camera or imaging device that produces pictures and detailed molecular information.

In many centers, nuclear medicine images can be superimposed with computed tomography (CT) or magnetic resonance imaging (MRI) to produce special views, a practice known as image fusion or co-registration. These views allow the information from two different exams to be correlated and interpreted on one image, leading to more precise information and accurate diagnoses. In addition, manufacturers are now making single photon emission computed tomography/computed tomography (SPECT/CT) and positron emission tomography/computed tomography (PET/CT) units that are able to perform both imaging exams at the same time. An emerging imaging technology, but not readily available at this time is PET/MRI.

Therapy

Nuclear medicine also offers therapeutic procedures, such as radioactive iodine (I-131) therapy that use small amounts of radioactive material to treat cancer and other medical conditions affecting the thyroid gland, as well as treatments for other cancers and medical conditions.

Non-Hodgkin's lymphoma patients who do not respond to chemotherapy may undergo radioimmunotherapy (RIT).

Radioimmunotherapy (RIT) is a personalized cancer treatment that combines radiation therapy with the targeting ability of immunotherapy, a treatment that mimics cellular activity in the body's immune system.

Use:

Clinicians use radionuclide imaging procedures to visualize the structure and function of an organ, tissue, bone or system within the body in order to:

Cancer

• stage cancer by determining the presence or spread of cancer in various parts of the body localize sentinel lymph nodes before surgery in patients with breast cancer or melanoma 
• plan treatment
• evaluate response to therapy
• detect the recurrence of cancer
• detect rare tumors of the pancreas and adrenal glands

Renal

• analyze native and transplant kidney function
• detect urinary tract obstruction
• evaluate for hypertension related to the kidney arteries
• evaluate kidneys for infection versus scar
• evaluate and follow-up urinary reflux in pediatric patients

Heart

• visualize heart blood flow and function (such as a myocardial perfusion scan)
• detect coronary artery disease and the extent of coronary stenosis
• assess damage to the heart following a heart attack
• evaluate treatment options such as bypass heart surgery and angioplasty
• evaluate the results of revascularization procedures
• detect heart transplant rejection
• evaluate heart function before and after chemotherapy (MUGA)

Lungs

• scan lungs for respiratory and blood flow problems
• assess differential lung function for lung reduction or transplant surgery
• detect lung transplant rejection

Bones

• evaluate bones for fractures, infection and arthritis
• evaluate for metastatic bone disease
• evaluate painful prosthetic joints
• evaluate bone tumors
• identify sites for biopsy

Brain

• investigate abnormalities in the brain, such as seizures, memory loss and abnormalities in blood flow
• detect the early onset of neurological disorders such as Alzheimer disease
• plan surgery and localize seizure foci
• evaluate post-concussion syndrome

Other Systems

• identify inflammation or abnormal function of the gallbladder
• identify bleeding into the bowel
• assess post operative complication of gallbladder surgery
• evaluate lymphedema
• evaluate fever of unknown origin
• locate the presence of infection
• measure thyroid function to detect an overactive or underactive thyroid
• help diagnose hyperthyroidism and blood cell disorders
• evaluate for hyperparathyroidism
• evaluate stomach emptying
• evaluate spinal fluid flow and potential spinal fluid leaks

Nuclear medicine therapies include:

• Radioactive iodine (I-131) therapy used to treat some causes of hyperthyroidism (overactive thyroid gland, for example, Graves' disease) and thyroid cancer
• Radioactive antibodies used to treat certain forms of lymphoma (cancer of the lymphatic system)
• Radioactive phosphorus (P-32) used to treat certain blood disorders
• Radioactive materials used to treat painful tumor metastases to the bones
• I-131 MIBG (radioactive iodine laced with metaiodobenzylguanidine) used to treat adrenal gland tumors in adults and nerve tissue tumors in children.

Benefits

• Nuclear medicine examinations offer information that is unique—including details on both function and structure—and often unattainable using other imaging procedures.
• For many diseases, nuclear medicine scans yield the most useful information needed to make a diagnosis or to determine appropriate treatment, if any.
• Nuclear medicine is less expensive and may yield more precise information than exploratory surgery.
• Nuclear medicine offers the potential to identify disease in its earliest stage, often before symptoms occur or abnormalities can be detected with other diagnostic tests.
• By detecting whether lesions are likely benign or malignant, PET scans may eliminate the need for surgical biopsy or identify the best biopsy location.

Risks

• Because the doses of radiotracer administered are small, diagnostic nuclear medicine procedures result in low radiation exposure, acceptable for diagnostic exams. Thus, the radiation risk is very low compared with the potential benefits.
• Nuclear medicine diagnostic procedures have been used for more than five decades, and there are no known long-term adverse effects from such low-dose exposure.
• The risks of the treatment are always weighed against the potential benefits for nuclear medicine therapeutic procedures. You will be informed of all significant risks prior to the treatment and have an opportunity to ask questions.
• Allergic reactions to radiopharmaceuticals may occur but are extremely rare and are usually mild. Nevertheless, you should inform the nuclear medicine personnel of any allergies you may have or other problems that may have occurred during a previous nuclear medicine exam.
• Injection of the radiotracer may cause slight pain and redness which should rapidly resolve.
• Women should always inform their physician or radiology technologist if there is any possibility that they are pregnant or if they are breastfeeding. See the Safety page for more information about pregnancy, breastfeeding and nuclear medicine exams.

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Akshaya Srikanth Bhagavathula

Hyderabad, India