Nuclear medicine is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease.
Nuclear medicine, in a sense, is "radiology done inside out" or "endoradiology" because it records radiation emitting from within the body rather than radiation that is generated by external sources like X-rays.
In addition, nuclear medicine scans differ from radiology as the emphasis is not on imaging anatomy but the function and for such reason, it is called a physiological imaging modality.
Single photon emission computed tomography(SPECT)
Positron emission tomography (PET) scans
HOW IT WORKS-DIAGNOSTIC
Nuclear medicine imaging uses small amounts of radioactive materials called radiotracers that are typically injected into the bloodstream, inhaled or swallowed. The radiotracer travels through the area being examined and gives off energy in the form of gamma rays which are detected by a external cameras and a computer to create images of the inside the body. Nuclear medicine imaging provides unique information that often cannot be obtained using other imaging procedures and offers the potential to identify disease in its earliest stages.
Diagnostic tests primarily show the physiological function of the system being investigated as opposed to traditional anatomical imaging such as CT or MRI
Studies are generally more organ-, tissue- or disease-specific than those in conventional radiology imaging, which focus on a particular section of the body
There are nuclear medicine studies that allow imaging of the whole body based on certain cellular receptors or functions (whole body PET scans or PET/CT scans, gallium scans, indium white blood cell scans, MIBG and octreotide scans)
Diagnostic tests in nuclear medicine exploit the way that the body handles substances differently when there is disease or pathology present.
The radionuclide introduced into the body is often chemically bound to a complex that acts characteristically within the body; this is commonly known as a tracer.
In the presence of disease, a tracer will often be distributed around the body and/or processed differently. For example, the ligand methylene-diphosphonate (MDP) can be preferentially taken up by bone. By chemically attaching technetium-99m to MDP, radioactivity can be transported and attached to bone via the hydroxyapatite for imaging. Any increased physiological function, such as due to a fracture in the bone, will usually mean increased concentration of the tracer. This often results in the appearance of a "hot spot", which is a focal increase in radio accumulation or a general increase in radio accumulation throughout the physiological system.
Some disease processes result in the exclusion of a tracer, resulting in the appearance of a "cold spot". Many tracer complexes have been developed to image or treat many different organs, glands, and physiological processes.
2D: Scintigraphy ("scint") is the use of internal radionuclides to create two-dimensional images
3D: SPECT is a 3D tomographic technique that uses gamma camera data from many projections and can be reconstructed in different planes
Positron emission tomography (PET) uses coincidence detection to image functional processes.
WHEN IS IT USED-DIAGNOSTIC
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)
scan lungs for respiratory and blood flow problems
assess differential lung function for lung reduction or transplant surgery
detect lung transplant rejection
evaluate bones for fractures, infection and arthritis
evaluate for metastatic bone disease
evaluate painful prosthetic joints
evaluate bone tumors
identify sites for biopsy
investigate abnormalities in the brain in patients with certain symptoms or disorders, such as seizures, memory loss and suspected abnormalities in blood flow
detect the early onset of neurological disorders such as Alzheimer's disease
assist in surgical planning and localize seizure foci
evaluate for abnormalities in a chemical in the brain involved in controlling movement in patients with suspected Parkinson's disease or related movement disorders
evaluation for suspected brain tumor recurrence, surgical or radiation planning or localization for biopsy
identify inflammation or abnormal function of the gallbladder
identify bleeding into the bowel
assess post-operative complications of gallbladder surgery
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
HOW IT WORKS-INTERVENTIONAL
Radionuclide therapy can be used to treat conditions such as hyperthyroidism, thyroid cancer, and blood disorders.
In nuclear medicine therapy, the radiation treatment dose is administered internally (e.g. intravenous or oral routes) rather than from an external radiation source.
The radiopharmaceuticals used in nuclear medicine therapy emit ionizing radiation that travels only a short distance, thereby minimizing unwanted side effects and damage to noninvolved organs or nearby structures. Most nuclear medicine therapies can be performed as outpatient procedures since there are few side effects from the treatment and the radiation exposure to the general public can be kept within a safe limit.
RISKS AND BENEFITS
Nuclear medicine examinations provide unique information—including details on both function and anatomic structure of the body that is 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.
PET scans may provide additional information that is used for radiation therapy planning.
Because the doses of radiotracer administered are small, diagnostic nuclear medicine procedures result in relatively low radiation exposure to the patient, 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.
The use of internal radionuclides to create two-dimensional images
A nuclear medicine whole body bone scan. The nuclear medicine whole body bone scan is generally used in evaluations of various bone-related pathology, such as for bone pain, stress fracture, nonmalignant bone lesions, bone infections, or the spread of cancer to the bone.
Nuclear medicine myocardial perfusion scan with thallium-201 for the rest images (bottom rows) and Tc-Sestamibi for the stress images (top rows). The nuclear medicine myocardial perfusion scan plays a pivotal role in the noninvasive evaluation of coronary artery disease. The study not only identifies patients with coronary artery disease; it also provides overall prognostic information or overall risk of adverse cardiac events for the patient.
A nuclear medicine parathyroid scan demonstrates a parathyroid adenoma adjacent to the left inferior pole of the thyroid gland. The above study was performed with Technetium-Sestamibi (1st column) and iodine-123 (2nd column) simultaneous imaging and the subtraction technique (3rd column).
Normal hepatobiliary scan (HIDA scan). The nuclear medicine hepatobiliary scan is clinically useful in the detection of the gallbladder disease.