G485 Medical Physics

These are the main points that you will be awarded marks for for the medical essay style questions.

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  • Created on: 14-06-13 10:58
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Alice Smart
G485 long essay question mark points
Medical questions
Protons have spin
Precess about the magnetic field produced by a strong electromagnet at a larmor
Transmitting coil produces a radio frequency equal to the larmor frequency
Protons resonate and flip to a higher energy state
When they relax to a lower energy state they emit radio waves
Relaxation time depends on surrounding tissue
Radio waves picked up by receiving coils
Gradient coils alter magnetic flux density through the body
Larmor frequency and radio waves given of during relaxation times varies through the
body so the position of tissues can be identified
Computer processes the signals and generates an image
A positron emitting source is used
A positron annihilates with an electron in the patient
This produces two gamma photons
The gamma photons travel in opposite directions
The patient is surrounded by a ring of gamma detectors
The difference in direction times of photons indicates where they were emitted
from inside the body
A 3D image is created by a computer
Ultra sound
An EMF pulse is put across a piezoelectric crystal which turns the pulse into
Ultrasound waves are reflected at boundaries
Intensity of reflected signal depends on acoustic independences of the materials at
the boundary
Time from pulse to detection is used to determine depth of boundary in the body
A-scan is one dimensional
B-scan involves different directions and angles producing a 3D scan
CAT scan
Electrons are accelerated through a high voltage and then decelerated rapidly some
of the kinetic energy is transferred to X-rays
A thin fan shaped beam of X-rays is rotated around the patient and the X-rays
detected by a ring of detectors
An image of a cross sectional `slice' of the body is made from the detected X-rays by
a computer these slices can be put together to form a 3D image with better tissue
contrast than normal X-rays.
Gamma camera

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Alice Smart
Collimator ­ vertical tubes in lead that allow only parallel gamma photos to travel up
them, gamma photos not emitted at the desired point are absorbed by the lead this
makes the image sharper
Scintillator ­ contains fluorescent material that emits light photon when struck by a
gamma photon
Photomultiplier tubes- give out an electrical pulse for every flash of light from the
Computer- Generated an image from the electrical pulses…read more


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