Nuclear medicine is an imaging modality that involves injection, inhalation or injection of radioactive tracers to visualize various organs. The tracer or radiopharmaceutical is produced through addition of a radioactive isotope to a pharmaceutical specific to the organ being imaged. The radioactive tracer emits gamma radiation, which is then imaged using a gamma camera.
The gamma camera consists of a radiation sensitive crystal which detects the distribution of the tracer within the patient’s body. The information is converted to a digital format to produce a two or three dimensional image on a screen. The latest generations of gamma camera are hybrid machines including a CT to allow for fusion of Nuclear Medicine and CT images.
The field of Nuclear Medicine also incorporates therapy procedures. A high dose of therapeutic radiation is delivered through administration of a radiopharmaceutical specific to the diseased target organ. This is of benefit to treat cancer or over functioning thyroid gland.
Nuclear medicine in diagnosis:
A radiologist is a qualified doctor who specializes in radiology. Nuclear medicine is used to diagnose a wide range of conditions.
The patient will inhale, swallow, or be injected with a radiopharmaceutical. This is a radioactive material. After taking the substance, the patient will normally lie down on a table, while a camera takes pictures.
The camera will focus on the area where the radioactive material is concentrated, and this will show the doctor what kind of a problem there is, and where it is.
Types of imaging techniques include positon emission tomography (PET) and single-photon emission computed tomography (SPECT). PET and SPECT scans can provide detailed information about how a body organ is functioning. This type of imaging is particularly helpful for diagnosing thyroid disease, gall bladder disease, heart conditions, and cancer. It can also help diagnose Alzheimer’s disease and other types of dementia and brain conditions. In the past, diagnosing internal problems often needed surgery, but nuclear medicine makes this unnecessary. After diagnosis, and when treatment starts, PET and SPECT can show how well the treatment is working. PET and SPECT are also offering new insights into psychiatric conditions, neurological disorders, and addiction. Other types of imaging involved in nuclear medicine include targeted molecular ultrasound, which is useful in detecting different kinds of cancer and highlighting blood flow; and magnetic resonance sonography, which has a role in diagnosing cancer and metabolic disorders.
Nuclear medicine in treatment:
Radioactive agents may be swallowed in pill form, inhaled, or injected as part of a person’s treatment.
Radioactive techniques are also used in treatment. The same agents that are used in nuclear imaging can be used to deliver treatment. The radiopharmaceutical can be swallowed, injected, or inhaled.
One example is radioactive iodine (I-131). It has been used for over 50 years to treat thyroid cancer and hyperthyroidism, or an overactive thyroid. Now, it is also used to treat non-Hodgkin lymphoma and bone pain from some kinds of cancer.
Iodine-131 (I-131) targeted radionuclide therapy (TRT) introduces radioactive iodine into the body. As the thyroid cells or cancer cells absorb this substance, it kills them. I-131 can be given as capsules or in liquid form.
In the future, it may be possible to embed chemotherapy into medication imaging agents that will attach only to cancer cells. In this way, the chemotherapy would kill only the target cells and not the nearby healthy tissue. This would reduce some of the adverse effects of chemotherapy.
Radioimmunotherapy (RIT) combines nuclear medicine (radiation therapy) with immunotherapy. Immunotherapy is a treatment that mimics cellular activity in the body. Combining the two types of treatment means the nuclear medicine can be targeted more directly to the cells that need it.
Various radionuclides are used. The most common one is I-131, or radioactive iodine therapy (RAI). Other options include 90Y-ibritumomab tiuxetan, or Zevalin, which is used to treat different types of lymphoma. 131-I-tositumomab, or Bexxar, is used to treat lymphoma and multiple myeloma.
Experts in nanotechnology, advanced polymer chemistry, molecular biology, and biomedical engineering are investigating ways to deliver the drugs to the correct site without affecting surrounding tissues.
Theranostics is an approach that integrates nuclear medicine techniques for diagnosis and imaging with those for treatment. By combining molecular targeting vectors, such as peptides, with radionuclides, it can direct the radioactive substance to the target area to diagnose and deliver treatment at the same time.
Common Clinical Applications
- Bone scan; to assess metabolic activity of the bones. Commonly used for oncology staging, arthritis, fractures.
- Myocardial Perfusion scan; to compare the blood flow to the myocardium at exercise and rest allowing for differentiation of ischaemia and infarction.
- Renal scan; to determine the perfusion and drainage of the kidneys and allow for calculation of differential function.
- Lung scan (VQ); to allow for comparison of ventilation and perfusion of the lungs to diagnose pulmonary embolism.
- Thyroid scan; to assess the appearance and function of the thyroid gland.
- Pregnancy status must be established prior to procedure. Performance of a Nuclear Medicine study on a pregnant woman must be clinically justified, with the administered dose minimized.
- Breast feeding women may need to cease breast feeding dependent on the procedure being performed. This is due to excretion of the radiotracer in the breast milk.
- Children are particularly radiosensitive; therefore non radiation imaging modalities such as ultrasound and MRI should be utilized if possible. When performing Nuclear Medicine studies on pediatric patients the radioactive dose is scaled according to the patient’s weight.
- To aid excretion of the tracer via the urinary tract, the patient may be instructed to remain well hydrated and urinate frequently to reduce radiation dose.
- Patients undergoing therapy procedures will be given specific instructions regarding radiation safety.