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PHYSICS > Chapter 27 - Medical imaging > Flashcards

Chapter 27 - Medical imaging Flashcards

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1
Q

how are x-rays produced

A

by rapidly accelerating or decelerating charged particles, their kinetic energy transfers to high-energy photons

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2
Q

why are x-rays referred to as soft

A

because they have energies lower than that of gamma rays

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3
Q

structure of an x-ray tube

A

heated filament (cathode) and tungsten anode with p.d. between them up to 200kV, and sealed in a vacuum tube

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4
Q

how does an x-ray tube work

A

electrons emitted from cathode and drawn towards anode. they collide with the anode and some KE is released as x-rays in all directions

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5
Q

why do x-ray tubes need a vacuum

A

to prevent electrons from colliding with molecules of air before enough energy is gained to release x-rays

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6
Q

how is the anode prevented from overheating

A

water is used as a coolant, circulating through the anode

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7
Q

importance of x-rays being focused at one point

A
  • minimise patients exposure
  • can be directed at specific areas (broken bone)
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8
Q

what is x-ray attenuation

A

when a material absorbs x-rays, exponentially decreasing the intensity

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9
Q

what does a greater attenuation coefficient mean

A

material will absorb more incident x-rays

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10
Q

what happens to the kinetic energy of electrons during the x-ray process

A
  • less than 1% is emitted as x-rays
  • the rest is transferred to thermal energy in the anode
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11
Q

photoelectric effect (x-rays)

A
  • less than 100 keV
  • x-rays absorbed by electrons, photoelectron is released when absorbed, and another electron is moved down an energy level
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12
Q

Compton effect (x-rays)

A
  • 0.5 to 5 MeV
  • inelastic collision between photon and electron
  • x-rays lose a fraction of their energy to electrons in the absorbing material
  • scattered x-ray photon has less energy than before
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13
Q

Pair production (x-rays)

A
  • energy greater than 1.02 MeV
  • x-ray passes through the electric field of an atom
  • produces an electron-positron pair
  • positron collides with another electron and annihilate produced photons
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14
Q

CAT

A

computerised axial tomography

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15
Q

ultrasound frequency

A

greater than 20kHz

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16
Q

two invasive processes

A

x-rays
surgery

17
Q

3 non-invasive processes

A

MRI
ultrasound
endoscopy

18
Q

benefits of PET

A

non-invasive
versatile diagnoses

19
Q

downsides of PET

A

expensive
complex diagnoses only
not all hospitals have access to them

20
Q

pros of ultrasound

A

no ionising radiation
quick and affordable
can distinguish between tissues

21
Q

cons of ultrasound

A

high intensity US can cause potential tissue damage

22
Q

acoustic impedance

A

the resistance to sound travelling through a substance

23
Q

pulse repetition frequency

A

time taken for pulse to travel to and from a direction

24
Q

a-scans

A

no image produced
measurements can be taken
shows reflected intensities over time

25
Q

b-scans

A

images produced
many echoes collected and collated

26
Q

what is a transducer

A

electronic device which converts energy from one form to another

27
Q

why is gel used during ultrasound

A

the gel has similar acoustic impedance to the skin, meaning hardly any ultrasound is reflected, so that the transducer can only target the desired area

28
Q

two main properties of ultrasound

A

-cant travel through a vacuum
-vibrate at a frequency greater than the human hearing range - more than 20kHz

29
Q

difference between a-scans and b-scans

A

a-scans don’t produce an image but b-scans do

30
Q

two factors effecting the value of acoustic impedance

A

-density of tissue
-velocity of sound wave transmitted through boundary

31
Q

two properties of x-rays

A

-can travel in a vacuum
-produce images of human bones

32
Q

what does I0 stand for in intensity equation

A

intensity of incident beam

33
Q

difference between MRI scans and PET scans

A

PET scans use a radioactive tracer to display areas, MRI scans use radio waves and magnetism to display areas

34
Q

advantages of CAT scans compared to an x-ray image

A

CAT scans show internal organs as well as bones whereas x-rays only display bones

35
Q

why is a contrast medium used in x-ray imaging

A

helps radiologists identify between normal and abnormal conditions

PHYSICS (24 decks)

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