Nuclear medicine

Published on 12/06/2015 by admin

Last modified 12/06/2015

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16 Nuclear medicine

The introduction of a specific pharmaceutical (depending on which part of the body is to be targeted), which has been labelled with a radioisotope, into a patient. The gamma rays emitted by the radioisotope are scanned by a detector and the diagnostic image is produced showing the concentrations of the radiopharmaceutical (e.g. a bone scan) or an indication of function (e.g. the glomerular filtration rate of the kidneys)

Terminology

Charge Collection	The pooling of electrons across a crystal
Gamma Camera	A large, stationary, scintillation counter, which records the activity over the whole field at the same time. Used to detect pathologies where the physiology of the structure is changed
Gantry	A structure or support, in which the X-ray tube, detectors and associated electronics are housed
Half-life	The amount of time taken for the radioactivity of a radioactive substance to decay by half the initial value. The half-life is a constant for each radioactive isotope
Image Fusion	When a PET (or SPECT) image and a CT image are viewed together by one being superimposed on the other
Pharmaceutical	A drug used in medicine
Photodiode	A semiconductor used to detect light and then generate electricity in proportion to the quantity of light detected
Photomultiplier	Equipment that produces an amplified current when exposed to electromagnetic radiation (light). Photons hitting the cathode produce electrons which in turn hit other surfaces thus producing more electrons, forming a pulse of electricity which forms the subsequent image
Planar	A two dimensional image
Pulse Height Analyser	Receives the signal from the photomultiplier and only produces an electrical signal if the input pulse lies in a predetermined range
Radioisotope	Any isotope that is radioactive. Forms of an element which have the same atomic number but different mass numbers, exhibiting the property of spontaneous nuclear disintegration
Radiopharmaceutical	A drug consisting of a radioactive compound
Scintillation Counter	A number of scintillator crystals in containers, one surface of the crystal is attached to a transparent glass window and the other surfaces are coated with magnesium oxide to reflect light back into the crystal; the back of the crystal is attached to a photomultiplier tube. If a gamma ray hits the crystal, light is produced and some reaches the photocathode of the photomultiplier
Scintillator	A sodium iodide (or caesium iodide) crystal with a thallium activator
Segmented	Divided into sections
Solid State Detector Material	Semi conductor – Cadmium zinc telluride (CdZnTe)
Spatial Resolution	The smallest distance between two objects that can be visually seen on an imaging system

Equipment

Pharmaceutical	A drug which is absorbed by a specific (targeted) area of the body
Radioisotope	Technetium 99m (⁹⁹Tc^m) most commonly used • Is a gamma emitter • Has a half-life of 6.02 hours • Is readily available • Is readily combined with pharmaceuticals • Has lower emissions than other types of radiation It is combined with a specific pharmaceutical so that a specific area of the body will take up the radioisotope
Detector – Gamma Camera	Radiation from the patient passes through: A multichannel collimator • Parallel lead columns • Absorb extraneous radiation • Only allows gamma rays that are at 90° to the crystal face to reach the crystal A scintillation counter • Gamma rays from the patient hit the glass window • Light is produced by the crystal Photodiodes or photomultipliers • Detects the light from the crystal • Converts the light to an electrical pulse Pulse height analyser • Filters the electrical pulses • Only allows pulses of a predetermined strength to be measured over time • The signal then goes to the computer monitor Fig. 16.1 The main parts of a gamma camera.
Operator Console	Where the operator can determine the settings for the scan
Display Station	For the viewing, analysis, networking and storage of the final image