Medical physics

  • Created by: emy105
  • Created on: 11-06-18 15:36
What is the frequency of an x-ray?
3X10^16 Hz - 3X10^19 Hz
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What is the wavelength of an x-ray?
1X10^-8 - 1X10^-11
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How does an X-ray tube work?
A heater excites the electrons to move out from the atom. A Tungsten anode will accelerate these. (The electrons accelerate towards it).The electrons are then emitted as x-ray photons.
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Why does the Tungsten anode have a special shape?
It enables the photons to be emitted in the required direction.
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Why is the tube incased in lead?
For safety as the x-rays cannot pass through.
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What is pair production?
A procces where an X-ray photon produces a an electron-positron pair
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Describe the photoelectric effect
In the photoelectric effect, a single photon interacts with a single electron at the surface of a metal. In this, energy is conserved. In Einstein equation, hf is the energy of the photon and 1/2mv^2 is the max Ke of the electron.
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What is the Compton effect?
scattering An interaction between an x-ray photon and an electron in which the photon is scattered with a longer wavelength.
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Using logarithms solve: 8^(4-x)=33
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Using logarithms solve: e^(7-x) +7=1009
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What is meant by the attenuation of x-rays?
Attenuation is the reduction of the intensity of an x-ray beam as it traverses matter. The reduction may be caused by absorption or by deflection (scatter) of photons from the beam
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For medical x-rays would it be more beneficial to use x-rays with a high or low energy?
Lower- biggest difference between attenuation of materials
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How do CAT Scans work?
X-ray tube and detectors are rotated around the body. It is a thin fan shaped beam of x-ray photons. The detectors send the intensities detected to a computer which forms an image of a slice. It is then moved down the body for another slice.
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What are the advantages of CAT Scans over normal x-rays?
3D images are produced in CAT scans. Also, CAT scans can see soft tissues.
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What is human hearing range?
20Hz - 20KHz
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What is ultrasound?
Ultrasound is sound too high for a human to hear so is greater than 20KHz.
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How does the wavelength effect the image produced?
A smaller wavelength will produce a clearer image with more detail. Ultrasounds hove a small wavelength.
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What is a B-scan?
Is a brightness scan. Produces brightness levels based on echo strengths.
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What is an A-scan?
Boundary echos are detected.
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What will be the result of a greater difference in acoustic impedance be to the rays?
More rays will be reflected
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What is the Piezoelectric effect?
Piezoelectric crystals produce ultrasound. This is done using an alternating current to create fast vibrations are made. This is called a Piezoelectric transducer- creates patterns of echos.
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What is Doppler imaging?
The Doppler effect states that when a wave is reflected off a moving medium the frequency of the wave changes.By measuring the change in frequency of reflected waves Doppler scans can be used to scan blood vessels & flow of blood.
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Other cards in this set

Card 2


What is the wavelength of an x-ray?


1X10^-8 - 1X10^-11

Card 3


How does an X-ray tube work?


Preview of the front of card 3

Card 4


Why does the Tungsten anode have a special shape?


Preview of the front of card 4

Card 5


Why is the tube incased in lead?


Preview of the front of card 5
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