Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

A Level Physics Anix > M6, C5 Medical Imaging > Flashcards

M6, C5 Medical Imaging Flashcards

You may prefer our related Brainscape-certified flashcards:
Physics 101 flashcards AP® Physics flashcards
1
Q

state some basic facts about x-rays

-wavelength range, frequency, speed

A

form of EM radiation
wavelength range from 10^-8 - 10^-13 m
high frequency
travel through a vacuum at the speed of light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

how are x-rays produced in x-ray tubes

A

1) at the cathode, electrons are emitted by the hot filament. This filament is heated from passing current through it
2) the target metal (tungsten) acts as the anode. The high pd across the tube causes the electrons to accelerate towards it
3) When the electrons smash into the anode, they decelerate and some of their kinetic energy is converted in electromagnetic energy as X-ray photons
4) Whatever energy is lost by the electron is gained by the photon - there is a continuous spectrum of x-ray radiation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what are x-ray tubes

A

a glass tube containing an electric circuit
it has a cathode where electrons are emitted and an anode where the electrons are directed towards
surrounded by lead to keep x-rays contained
there is a small window where x-rays can pass

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

why is an x-ray tube evacuated

A

to prevent emitted electrons from colliding with gas particles while in the tube

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

in the x-ray tube, what does the maximum kinetic energy of the electrons equal?

A

the maximum energy of the x-ray photons

and (the pd of the x-ray tube X elementary charge)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

in the x-ray tube, what percentage of the electrons’ kinetic energy is converted to x-rays
what does the remaining energy transfer to

A

1% converted to x-rays

the rest is converted into heat

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

how is overheating avoided in the x-ray tube

A

the tungsten anode is rotated very quickly to spread the heat generated around the whole anode

the anode is also mounted on copper to conduct heat away

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

how else are x-rays formed, other than the conversion of kinetic energy in the x-ray tube

A

when beam electrons knock out electrons from the inner shells of the tungsten atoms
electrons in the atoms’ outer shells fall into the vacancies in the inner energy levels, and release energy in the form of X-ray photons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what are the components of an x-ray tube

A

heater (cathode)
anode
target metal
high voltage supply

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

how do x-rays used in hospitals produce an image

A

x-rays are absorbed by the bone
flesh and tissue are less absorbing
hence producing a white image of the bones against a black background

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what is attenuation of x-rays

A

the gradual decrease in x-ray beam intensity as it passes through matter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

name the 4 x-ray attenuation mechanisms

A

simple scatter
photoelectric effect
Compton scattering
pair production

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what happens to x-ray photons during the simple scatter x-ray attenuation mechanism

A

the x-ray photons interact with an electron but has less energy than is required to remove an electron so the x-ray photon is scattered without any change to its energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what happens to x-ray photons during the photoelectric effect x-ray attenuation mechanism

A

x-ray photon is absorbed by one electron, the electron uses this energy to escape from the atom

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what happens to x-ray photons during the Compton scattering x-ray attenuation mechanism

A

x-ray photon interacts with an electron in the atom, the electron is ejected but x-ray photon doesn’t disappear - it is scattered with reduced energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what happens to x-ray photons during the pair production x-ray attenuation mechanism

A

x-ray photon interacts with the nucleus, it disappears and the energy is used to decay into an electron and positron

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

which mechanisms of attenuation of x-rays leads to a less sharp image

A

simple scatter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

in the x-ray tube, how can you increase the intensity of the x-ray beam

A

increase the tube voltage - gives the electrons more kinetic energy meaning they have more energy available to be converted into photons on deceleration

increase current supplied to filament - stimulates more electrons per second from the cathode which produces more x-ray photons per second

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what does this equation mean?

I = I_0Xe^-µx

A

transmitted intensity = initial intensity X e^(linear attenuation coefficient for material X thickness of material)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

an x-ray beam of initial intensity 50Wm^-2 is incident on soft tissue of attenuation coefficient 1.2cm^-1. Calculate its intensity after it has passed through a 5cm thickness of tissue

A

don’t worry about the units of cm and m being different. as long as the µ and x have the same units its all good.

I = 50 X e^-1.2 X 5
= 0.12 Wm^-2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

if tissues in a region of interest have similar attenuation coefficients, what should you use to get a clearer image?

A

Artificial contrast media

Iodine and barium have high atomic numbers so show up clearly in x-ray images

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

how are iodine and barium used to give a clearer x-ray image

A

a barium meal can be swallowed and it’s path through the digestive system imaged

iodine is usually injected into blood vessels or tissues so they can be viewed more clearly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what is a CAT scan

A

they produce an image of a 2D slice through the body

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

how does a CAT scan work

A

1) Patient lies in ring of detectors and bed slides through
2) X-ray tube rotates around ring
3) Patient experiences a fan shaped beam of x-rays and traces out a spiral path around the patient
4) The x-rays are absorbed by dense, high Z materials such as bone
5) Detectors opposite the tube send signals to computer
6) Computer builds up a 3D image
7) Enables slices to be viewed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

how can CAT scans be better than regular x-rays

A

they produce a more detailed image especially for soft tissue
they can distinguish between tissues of similar density
the data can also be manipulated to generate a 3D image

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

what is a disadvantage of a CAT scan

A

high dose of radiation for patient

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

what types of waves are ultrasound

what is their frequency

A

longitudinal

above 20,000Hz

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

what happens when ultrasound meets a boundary

A

it is partially reflected and partially transmitted

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What frequency of ultrasound is used for medical purposes

A

1-15 MHz

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

what are the benefits of ultrasound

A
  • non-ionising
  • non-invasive (doesn’t require going inside someone)
  • quick
  • no known side effects
  • real time images can be obtained
  • relatively cheap and portable
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

what are the disadvantages of ultrasound

A
  • low resolution of images produced
  • doesn’t penetrate bone
  • can’t pass through spaces filled with air
  • identifies solid masses but can’t tell you much about the composition
32
Q

what does the piezoelectric effect mean

A

the ability of certain materials to produce a potential difference across them when they are deformed

33
Q

what happens when a piezoelectric crystal is deformed

A

In piezoelectric crystals, one end is more positively-charged and the other end is more negatively-charged.
When stress is applied to the crystal, it shifts the orientation of the electric charges.
Some particles move so that their charged ends line up in one direction - generating a pd across the crystal

34
Q

what happens when you apply a pd across a piezoelectric crystal
what happens if its an alternating pd

A

the crystal deforms to rebalance the charge across it

if the pd is alternating, then the crystal vibrates at the same frequency

35
Q

What are ultrasound transducers? How do they work?

A

Ultrasound transducers generate and detect ultasound waves.
They convert ultrasound into electric signals and vice versa.
They contain PZT crystals which use the piezoelectric effect.
Inside the transducer, an alternating pd is applied to the PZT crystals which vibrate creating an ultrasound wave.
When the wave is reflected and returns, it causes the crystals to vibrate, which in turn creates an alternating pd that is detected in an adjoining circuit.

36
Q

The ultrasound waves produced by an ultrasound transducer have a wavelength _______ the thickness of the PZT crystals inside.

A

DOUBLE

37
Q

what is the benefit of the ultrasound transducer only receiving large signals from waves of wavelength equal to twice the thickness of the crystals?

A

reduces unwanted interference from other sources

38
Q

What happens to the resolution of the ultrasound transducer as the length of each ultrasound pulse decreases?
Relate this to the damping material in an ultrasound transducer.

A

The resolution increases as the length of each ultrasound pulse decreases.
So the vibrations of the PZT crystal are reduced with damping material to produce shorts pulses.

39
Q

what is coupling media? why is it used for ultrasounds

A

Coupling media is placed in between an ultrasound transducer and the body. This is because ultrasound energy is reflected from the surface of the body if there is air between the transducer and the body.
The coupling media is an oil or gel which displaces the air and has an impedance much closer to the body tissue.

40
Q

What are A-scans used for? What are B-scans used for?

A

A-scans are mostly used for measuring distances/

B-scans are used to form images.

41
Q

How does the A-scan (amplitude scan) work?

A

It sends a short pulse of ultrasound into the body as an electron beam inside a cathode ray oscilloscope (CRO) starts to sweep across its screen.
The receiver detects reflected ultrasound pulses which are displayed as peaks on the CRO screen.

42
Q

How is the A-scan used to work out distances between structures in the body?

A

The horizontal positions of the reflected pulses indicate the time the ‘echo’ took to return.

43
Q

In an A-scan a process called time-gain compensation (TCG) is used. What does this mean?

A

Weaker pulses (that have travelled further in the body and arrive later) are amplified more than the stronger, earlier pulses to avoid the loss of valuable data.

44
Q

How does the B-scan (brightness scan) work?

A

The amplitude of the reflected pulses is displayed as the brightness of a spot on a screen representing tissue boundaries. You can use lots of transducers arranged in a line to produce a 2D image.

Eg. baby scan

45
Q

For a B-scan, what is the brightness of the dot proportional to?

A

intensity of reflected ultrasound

46
Q

In the equation Z = ρc

What do all the parts mean?

A

acoustic impedance = density of material X speed of SOUND within it

47
Q

What is acoustic impedance

A

The amount of reflection an ultrasound wave experiences at a boundary between different materials depends on the difference in acoustic impedance.

48
Q

For the equation
I_r / I_0 = (Z_2 – Z_1)^2 / (Z_2 + Z_1)^2
what do all the parts mean

A 
I_r = intensity of reflected wave
I_0 = intensity of incident wave
Z_1 = acoustic impedance of first material
Z_2 = acoustic impedance of second material
49
Q

what are the units for acoustic impedance?

A

kgm^-2s^-1

50
Q

A sound wave travels from bone (Z=8X10^6 kgm^-2s^-1) to water (Z=1.5X10^6kgm^-2s^-1).
What will the intensity of the reflected wave be as a percentage of the intensity of the incident wave?

A

using the equation I_r / I_0 = (Z_2 – Z_1)^2 / (Z_2 + Z_1)^2

I_r / I_0 = ((1.5X10^6 - 8X10^6)^2) / ((1.5X10^6 + 8X10^6)^2)
= 0.4681
so the percentage = 47%

51
Q

how is the doppler effect used in ultrasound

A

Ultrasound waves reflected at an angle off moving cells undergo a change of frequency or wavelength.
This change can allow doctors to find the speed at which those cells are moving.

52
Q

what does this equation mean

∆f / f = 2vcosθ / c

A 
∆f = change in frequency (doppler shift)
f = initial frequency of ultrasound
v = speed of moving cell
θ = angle between the ultrasound receiver and the line along which the cell is moving in
c = speed of SOUND in the medium
53
Q

can you ultrasound lungs?

A

no because air has a very low acoustic impedance and hence a high proportion of ultrasound waves will be reflected

54
Q

when doing an ultrasound of a blood vessel, what would happen to the waves when blood is moving towards the transducer?

A

frequency increases

55
Q

what are medical tracers

A

radioactive substances used to show the function and structure of tissues and organs

56
Q

Give 2 examples of medical tracers

A

technetium–99m

fluorine–18

57
Q

how do medical tracers work

A

Consist of a radioactive isotope bound to a substance that is used by the body (eg. glucose or water).
The tracer is injected into or swallowed by the patient and moves through the body.
The radiation emitted due to the isotope is detected and used to produce an image of inside the patient.

58
Q

How can medical tracers be used for the heart, cancer treatment and neurological conditions?

A

Medical tracers can show damaged tissue in the heart by indicating areas with decreased blood flow. Reveals coronary artery disease or conditions leading to heart attacks.
Can identify active cancer tumours. Cancer cells take up more tracer as they have a higher metabolism.
Can show blood flow and activity in the brain which helps research into Alzeihmer’s, Parkinson’s, epilepsy or depression.

59
Q

Why is technetium–99m widely used in medical tracers?

A

The gamma radiation it emits can easily pass out of the body to reach the detector.
It has a half life of 6 hours (long enough for data to be recorded but short enough to limit exposure of the radiation).
It also decays to a much more stable isotope.

60
Q

Why is fluorine–18 used in PET scans?

A

It undergoes beta-plus decay (which is necessary for a PET scan)
It has a short half life of 110 minutes meaning the patient’s exposure to dangerous radioactivity is kept as low as possible.

61
Q

what are the five main components in gamma cameras

A
  • lead shield - surrounds most of camera and stops radiation from other sources being detected
  • lead collimator
  • scintillator
  • photomultiplier tubes
  • electronic circuit - collects signals from photomultiplier tubes and sends to computer
62
Q

what does the lead collimator do in a gamma camera

A

it’s a piece of lead with thousands of vertical holes in it, which only gamma rays travelling parallel to the holes can pass through

63
Q

what is a scintillator
what is it made of
what does it do in a gamma camera

A

a sodium iodide crystal that emits a flash of light whenever a gamma ray hits it

64
Q

what do photomultiplier tubes do in gamma cameras

A

detect flashes of light from the scintillator and turn them into pulses of electricity

65
Q

how does the gamma camera work

A

The computer maps the spatial distribution and the frequency of gamma ray emissions detected by the gamma camera to make a 2D image, effectively forming a snapshot of regions where the medical tracer has been taken up.
The gamma camera is often rotated to take multiple images from different angles to provide different perspectives of the area.

66
Q

what are the benefits of gamma cameras

A

can diagnose patients without surgery

cheaper than PET scans

67
Q

what are the cons of gamma cameras

A

a patient needs to be exposed to ionising radiation

68
Q

What is the first stage of a PET scan (what’s injected?)

A

A patient if injected with a substance used by the body (eg. glucose) that is bound to a positron-emitting radiotracer with a short half-life (eg. F-18). The patient is left for some time to allow the radiotracer to move around the body.

69
Q

After the patient has been injected for the PET scan, what happens?

A

The positrons emitted by the radioisotope collide with electrons in the organs and annihilate.
This annihilation results in 2 high energy gamma rays being emitted in opposite directions.

70
Q

In a PET scan, what do the detectors detect? What do they do with the information?

A

the gamma rays that have been emitted due to positron-electron annihilation
they then send the information to a computer which builds up a map of the radioactivity in the part of the body

71
Q

How can a PET scan be used for cancer diagnosis

A

Glucose can be used as a radiotracer so the radioactivity will correspond to metabolic activity in different parts of the body. (Because cells with higher metabolism will take up more radioactive glucose).
Cancer cells have a higher level of activity than healthy cells meaning they can be detected this way.

72
Q

what are the advantages of PET scans

A

Brain activity can be investigated.
Non-invasive.
The radiotracers have a short half-life so patient is exposed to radiation for only a short amount of time.

73
Q

what are the cons of PET scans

A

The short half life of the radiotracer means there is only a limited amount of time when the patient can be scanned.
Incredibly expensive

74
Q

What are the risks of using ionising radiation for medical use?

A
  • can lead to cell mutations and cancerous tumours if cell’s DNA is damaged or altered
  • can lead to cell sterility meaning the cell can no longer reproduce
  • can lead to cell death
  • skin burns, sterility, radiation sickness, hair loss and death
75
Q

suggest why it is desirable to have ultrasound of short wavelength for a scan

A

small wavelength means finer detail can be seen/ greater resolution

76
Q

explain what is meant by a photon

state one of its main properties

A

quantum of energy

travels at 3X10^8 ms^1 (speed of light) IN A VACUUM

A Level Physics Anix (17 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions