Radiation detection equipment

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Chapter: Pharmaceutical Drugs and Dosage: Radiopharmaceuticals

The most common radiation detection equipment includes the following:


Radiation detection equipment

The most common radiation detection equipment includes the following:

1. Scintillation detector for the detection of gamma-radiation emitting probes. A scintillation probe can be suitably modified to detect the localization of isotopes in the organs of interest. For example, detec-tion of 131I uptake by the thyroid and the uptake of red blood cells labeled with 51Cr by the spleen require appropriately modified gamma scintigraphy equipment.

2. Scintillation counters are typical laboratory equipment used for the detection and measurement of ionizing radiation. These counters can be used to test samples of in vitro testing (such as drug release or dissolution) and in vivo samples after digestion into a homogeneous liquid (such as biodistribution studies). The operating principle of a scintillation counter is the excitation of a scintillating material, typically a transparent crystal, with the high-energy photons of the incident ionizing radiation. A scintillating material is a luminescent material that absorbs incoming high-energy radiation and reemits the absorbed energy in the form of light. The scintillating material could be, for example, cesium iodide, to detect protons and alpha particles, sodium iodide containing small amounts of thallium to detect gamma radiation, zinc sulfide to detect alpha particles, and lithium iodide to detect neutrons. This instrumentation also contains a sensitive photomultiplier tube that converts light energy to electri-cal signal and the needed electronics to quantitatively process and display this signal.

3. Positron emission tomography (PET) is a functional imaging technique applied in nuclear medicine to measure whole body metabolism. It detects gamma rays emitted by a positron-emitting radionuclide 18F flu-orodeoxyglucose that is administered to the patient as a tracer before the procedure. A computerized tomography (CT) X-ray scan is con-currently performed on the patient to construct a three-dimensional (3D) image of the patient, which is then utilized to construct a 3D location of the radioisotope in the body in what is known as the CT-PET scan. This scan can detect regional metabolic activity, as indicated by regional glucose uptake. This scan is commonly used to detect cancer metastases.

A similar nuclear medicine tomographic (providing 3D information in 2D cross-sectional slices) imaging technique is the single-photon emission computed tomography (SPECT or SPET). This technique is often applied in an organ-specific way, with the administration of a specific radionuclide or its conjugate with a targeting ligand.

4. Geiger counter, also known as the Geiger–Muller counter, is a typ-ical name for a handheld device for measuring ionizing radiation most commonly used by the laboratory safety personnel. It detects ionizing radiation, including alpha particles, beta particles, and gamma rays, using the ionization effect produced by the radiation in a Geiger–Muller tube. The Geiger–Muller tube is filled with an inert, unionized gas (He, Ne, or Ar) at low pressure and is equipped with an anode and a cathode under high voltage (400–600 V). However, there is no flow of current, since the gas in the chamber is unionized. Ionization of the inert gas with incident radiation leads to the flow of current in direct proportion to the amount of incident radiation, which is detected and reported.

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