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W/Biophysics > 20.21. X-rays > Flashcards

20.21. X-rays Flashcards

1
Q

What is the voltage difference used in diagnostic X-rays?

A

100eV-120keV

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2
Q

Typical energy range of X-ray photon

A

100eV - 120keV

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3
Q

Typical wavelength range of X-ray

A

10 picometers to 10 nanometers

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4
Q

How is the electron beam generated?

A

thermionic emission

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5
Q

What is the energy of the emitted X-ray photon proportional to?

A

to the distance of electron with the nucleus : the closer it gets, the more it is deflected and the more of its energy goes to the photon

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6
Q

Which type of contrast generation is photoeffect a main contributor of?

A

for tissues with similar density but different atomic number

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7
Q

Duane-hunt law

A 
min wavelength = (hc/e) * (1/U)
h : plank's constant
c : speed of light in vacuum
e : charge of electron
U : accelerating voltage
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8
Q

What is the spectrum of Bremsstrahlung?

A

Power/lamda vs lamda

  • for different accelerating voltages
  • power is area under the curve
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9
Q

What does the minimum wavelength correspond to?

A

the process of converting the total energy of 1 electron into 1 photon with h*fmax energy

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10
Q

What is an Auger electron?

A

Energy of an electron transition to a lower level can be used to eject an outer shell electron: the auger electron

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11
Q

What is the characteristic X-ray spectrum?

A

line spectrum

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12
Q

What is the total power of the X-ray tube?

A 
Px = Cx * Uanode² * Ianode * Z
Cx : X-ray constant
Uanode : accelerating voltage
Ianode : anode current = number of electrons hitting the anode
Z : atomic number of anode atoms
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13
Q

What is the efficiency of the X-ray tube?

A

ratio of total power / power invested. Typically low because much of the energy is lost as heat

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14
Q

Energy range of rayleigh scattering in soft tissue

A

1-30keV

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15
Q

Energy range of photoeffect absorbtion in soft tissue

A

10-100keV the limit is higher when the atomic number is higher

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16
Q

Energy range of compton absorbtion in soft tissue

A

0.5 - 5 MeV

17
Q

Which substance are used for positive contrast?

A

High Z substance, for example Barium

18
Q

What can be used for negative contrast?

A

gases with low specific gravity : O2, CO2

19
Q

What is a summation image?

A

sum of all the elementary densities of all the layers the x-ray photon goes through

20
Q

What does the X-ray amplifier do?

A

Produces an amplified, digital image

21
Q

What are the advantages of using an X-ray amplifier?

A

can use lower E photons since it will be amplified + digital so no need for a light behind the scan etc (useful for surgery)

22
Q

How does the X-ray amplifier work?

A
  • Input phosphor : produces a large number of light photons (lower E)
  • Photocathode releases electrons (pptional to number of photons)
  • electrons are accelerated to anode
  • electromagnetic grids focus and minify electron distribution, which augments inensity
23
Q

What is DSA?

A

digital substraction angiography

24
Q

What is a CT scan?

A

combines a series of X-ray images taken from different angles around the body and uses computer processing to make cross-sections

25
Q

What is the voltage range in CT scan?

A

120kV-140kV

26
Q

What is windowing?

A

CT image greyscale component is manipulated via Ct numbers expressed in HU. Change the appearance of the picture to highlight certain structures

27
Q

What is a wide window width?

A

400-2000 HU, used in areas with already lots of different attenuation values

28
Q

What is a narrow window width?

A

50-350 HU, for areas of similar attenuation factors

29
Q

What is the method for producing high energy X-ray?

A

LINAC : accelerates charged particles (electrons) to the speed of light by tube electrodes. Diameter of electron beam is very small

30
Q

What is the advantage of using LINAC based radiation therapy?

A
  • can be turned on/off unlike normal radiating isotopes

- very precise

31
Q

Voltage difference in LINAC

A

4-20MeV

W/Biophysics (24 decks)

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