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Lecture 12

ENGINEER 1C03 Lecture Notes - Lecture 12: Magnetic Resonance Imaging, Atomic Number, Angular Velocity


Department
Engineering (General)
Course Code
ENGINEER 1C03
Professor
Philip Britz- Mc Kibbin
Lecture
12

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4. discuss the interaction of electrons and positrons resulting in the production of gamma rays
When a positron meets an electron they ‘annihilate’ each other, converting their combined energy
and mass into two gamma rays (γ rays). The energy of each of these gamma rays is 0.51 MeV (million
electron volts) and they travel in opposite directions momentum and electrical charge must be
conserved in the interaction in accordance with the respective laws. This process is sometimes called pair
annihilation.
5. describe how the positron emission tomography (PET) technique is used for diagnosis
Using particular radio-pharmaceuticals, a cross-sectional image through an organ can be obtained or a
region of the body can be imaged, allowing the function of an area to be determined.
The radiopharmaceutical is usually injected into the patient but sometimes the chemical is
inhaled. After a short period of time the radiopharmaceutical has accumulated in
particular areas of the body and begun to decay by the emission of positrons. The positrons
will almost instantaneously come into contact with electrons in the target organ and undergo
pair annihilation resulting in the production of two gamma rays which travel in opposite
directions.
Modified gamma cameras detect these gamma emissions and transmit the
information to a computer for translation.
By knowing attenuation coefficients for the absorption of gamma rays in the target tissue, an
close approximate can be made for the accumulating radioisotope. The measurement from any
angles and intensities aids the computer's response to the accurate targeting of the accumulated
radioactive isotope.
Because the specific radioisotope is chosen to attach to a 'metabolite' in the body, then doctors are able to
determine what part of the body this radioisotope will best detect abnormalities in. The diagnosis of
disease and unknown deformities are displayed in coloured regions on a computer.
Often used in the brain.
1. perform an investigation to compare an image of a bone scan with an X-ray image
CAT Bone Sc an
X -ray of broken bone
The CAT scan/bone scan is a far more comprehensive method of
taking an image for medical diagnosis of disease or fractures.
Slices of the bone are compiled to form a three-dimensional
image.
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