Question

b) State two examples of radioisotopes used in imaging. Name the particular condition, and state which radioisotope would be used.

  

c) A radiologist in the laboratory has had an accident and been exposed to alpha, beta and gamma radiation. Explain the potential consequences of this careless action giving scientific reasons behind your discussion. Consider the effects of different types of radiation on cells.

  

Answer 1

b) A radioisotope used for diagnosis must emit gamma rays of sufficient energy to escape from the body and it must have a half-life short enough for it to decay away soon after imaging is completed. The radioisotope most widely used in medicine is Tc-99, employed in some 80% of all nuclear medicine procedures. It is an isotope of the artificially-produced element technetium. It has a half-life of six hours which is long enough to examine metabolic processes.  It decays by an 'isomeric' process, which involves the emitting of gamma rays and low energy electrons. Since there is no high-energy beta emission the radiation dose to the patient is low. The low-energy gamma rays it emits easily escape the human body and are accurately detected by a gamma camera.

Gallium-67 (Ga-67) [Gallium (Ga-67) Chloride Half-Life: 3.26 (days)]

Gallium chloride is usually complexed with sodium citrate to produce gallium citrate. It is useful for imaging various inflammatory conditions and tumors such as Hodgkin's disease, lymphoma (with the exception of lymphocytic), hepatoma and bronchogenic carcinoma.

c) The health effect from exposure to alpha particles depends greatly on how a person is exposed. Alpha particles lack the energy to penetrate even the outer layer of skin, so exposure to the outside of the body is not a major concern. Inside the body, however, they can be very harmful. If alpha-emitters are inhaled, swallowed, or get into the body through a cut, the alpha particles can damage sensitive living tissue. The way these large, heavy particles cause damage makes them more dangerous than other types of radiation. The ionizations they cause are very close together - they can release all their energy in a few cells. This results in more severe damage to cells and DNA.

Beta particles are more penetrating than alpha particles, but are less damaging to living tissue and DNA because the ionizations they produce are more widely spaced. They travel farther in air than alpha particles, but can be stopped by a layer of clothing or by a thin layer of a substance such as aluminum. Some beta particles are capable of penetrating the skin and causing damage such as skin burns. However, as with alpha-emitters, beta-emitters are most hazardous when they are inhaled or swallowed.

Gamma rays are a radiation hazard for the entire body. They can easily penetrate barriers that can stop alpha and beta particles, such as skin and clothing. Gamma rays have so much penetrating power that several inches of a dense material like lead, or even a few feet of concrete may be required to stop them. Gamma rays can pass completely through the human body; as they pass through, they can cause ionizations that damage tissue and DNA.