NUCLEAR IMAGING

What is Nuclear Imaging ?
• The process involves injecting into the body a small amount of chemical substance tagged with a short lived radioactive tracer. Depending on the chemical substance used, the radiopharmaceutical concentrates in the part of the body being investigated and gives off gamma rays. A gamma camera then detects the source of the radiation to build a picture. These are called scans.
Radioisotope Treatments or Therapy :
• Radiotherapy using external beam treatment is used commonly for treatment of cancers (see Oncology). However the use of unsealed, liquid sources in the treatment of disease is important in a few, specialized situations. For example Iodine-131 is taken orally to treat overactive thyroid and cancer of the thyroid.
Nuclear Imaging Scans:
• Brain Scans These investigate blood circulation and diseases of the brain such as infection, stroke or tumor. Technetium is injected into the blood so the image is that of blood patterns.
• Thyroid Uptakes and Scans These are used to diagnose disorders of the thyroid gland. Iodine 131 is given orally , usually as sodium iodide solution. It is absorbed into the blood through the digestive system and collected in the thyroid.
• Lung Scans These are used to detect blood clots in the lungs. Albumen, which is part of human plasma, can be coagulated, suspended in saline and tagged with technetium.
• Cardiac Scans These are used to study blood flow to the heart and can indicate conditions that could lead to a heart attack. Imaging of the heart can be synchronised with the patient's ECG allowing assessment of wall motion and cardiac function.
• Bone Scans These are used to detect areas of bone growth, fractures, tumors, infection of the bone etc. A complex phosphate molecule is labeled with technetium. If cancer has produced secondary deposits in the bone, these show up as increased uptake or hot spots.
Radioisotopes Used in Nuclear Medicine:
• For imaging Technetium is used extensively, as it has a short physical half life of 6 hours. However, as the body is continually eliminating products the biological half life may be shorter. Thus the amount of radioactive exposure is limited.
• Technetium is a gamma emitter. This is important as the rays need to penetrate the body so the camera can detect them.
Because it has such a short half life, it cannot be stored for very long because it will have decayed. It is generated by a molybdenum source (parent host) which has a much greater half life and the Tc extracted on the day it is required. The molybdenum is obtained from a nuclear reactor and imported. For treatment of therapy, beta emitters are often used because they are absorbed locally.