 Two reasons medical tracers can be placed in a body:  Diagnose disease or Treat Disease  In both cases, several factors must be accounted for:  Gamma ray sources must be used! Alpha and Beta would be absorbed and damage the body.  Gamma-ray sources will expose patients to some radiation.  Half-Life of the source must be long enough to carry out the investigation, but no longer.  Source must not be chemically poisonous!  Tracer must be possible to monitor.  Must be possible to get the material to the part of the body where it is needed.

 These are radioactive substances that are used to show tissue/organ function.  Benefit over X-rays: Shows both structure and function.  Tracers (Technetium-99) are bound to a substance that is used by the body.  Tracer is injected/swallowed and moves through the body to the region of interest.  Once the substance is used up, the radiation emitted is recorded (Gamma Camera/PET scanner)

 Emits gamma radiation  Has a half life of 6 hours  Long enough to be recorded, short enough as not to cause any damage to the body.  Decays to a stable isotope.

 Areas of damaged tissue in the heart by detecting areas of decreased blood flow. This can reveal coronary artery disease and damaged or dead heart muscle caused by heart attacks.  They can identify active cancer tumours by showing metabolic activity; cancers will take up more tracer.  Can show blood flow in the brain. Helps research and treat neurological conditions such as Parkinson’s, Alzheimer’s, epilepsy, depression etc.

 The gamma camera is basically a detector of gamma photons emitted by a source inside a patient.  A block of lead with tens of thousands of vertical holes is located near the body.  These collimate the beams so only vertically travelling photons are detected: Ensures accuracy!  They then enter a large crystal of Sodium Iodide.  This scintillates when it absorbs a gamma photon.  This means gives off light!  Behind this is a layer of photomultiplier tubes.  These multiply the effect of the tiny flash,and gives an electrical pulse output.

Advantage of Gamma Camera! - No radiation from parts of the body where there are no radioactive material. - Doctor can look at a specific part of the body!

 Used to diagnose  Thyroid  Liver  Brain  Kidneys  Lungs  Spleen  Heart  Circulatory System

 Radioactive nuclide technetium-99 is used.  Nucleus decays from its excited state to its ground state with the emission of 140 keV photon, with a half-life of 6 hours.  This can be incorporated into many different kinds of molecules.  Example: Iodine compound containing this can be administered to test the function of the thyroid gland.

 Some cameras have more than one scintillating crystal; two at right angles to each other.  These are around the patient, and allows 3D images to be found.

 Methods are being developed for administering radioactive material with a longer half-life to people with certain cancers.  These will be attached to cancerous cells, thereby destroying them without giving dangerous doses of radiation to healthy tissue.

 Extension of gamma-ray photography.  Detects abnormal chemical/metabolic activity  Radiolabelled glucose is injected into the patients bloodstream, from which it is absorbed into the tissues, which need glucose for respiration.  Positron Emission = annihilation of positron and electron and keV gamma photons are released in opposite directions simultaneously.  If these two are detected simultaneously, the position can be detected.

1. Patient is injected with a substance used by the body. 2. This has a positron-emitting radiotracer with a short half-life. 3. Patient is left for a time so that the radiotracer can move through the body. 4. Positrons ( β + ) emitted from the radioisotope collide with electrons in the organs; results in annihilation which gives off high energy gamma rays. 5. Detectors record these emissions and map a slice. 6. Distribution of radioactivity matches up with metabolic activity because the substance is being used by the body.