Brainscape's Knowledge GenomeTM

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


See full index

A2 Physics > G485 - Medical Imaging > Flashcards

G485 - Medical Imaging Flashcards

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

How are x-rays produced?

A
  1. high voltage applied between anode and cathode
  2. electrons are pushed on to the cathode by the negative terminal of the battery
  3. p.d accelerates electrons across the gap between the cathode and the anode
  4. when the electron collides with the anode it loses a lot of kinetic energy which cannot be easily dissipated through the anode
  5. some energy heats the anode and some is released as an x-ray photon
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why are x-rays produced in a vacuum?

A

so that air particles don’t deflect the electrons and disrupt the current

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

What is the maximum energy of a produced x-ray photon equal to?

A

the kinetic energy of one electron = WQ

Emax = hfmax = hc/λmin

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

What material is the anode made from and why?

A

tungsten

  • high melting point
  • durable
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How is the anode kept cool?

A

The anode rotates so that the same area isn’t constantly heated
each section has time to cool while it rotates outside of the electron beam

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

Gamma Wavelength

A

0.0001nm

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

X-Ray Wavelength

A

0.1nm

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

Visible Wavelength

A

600nm

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

Radio Wavelength

A

1m

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

Intensity Definition

A

energy incident per unit area per unit time

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

X-ray Spectra - Characteristic Peaks

A
  • specific to anode metal
  • electrons are stripped out of shells in the anode atoms by incident electrons
  • atoms from higher energy levels drop down to replace them
  • difference in energy when they drop down is released as a photon
  • so some specific wavelengths are produced in greater numbers
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Work Function Definition

A

minimum energy required to release a photoelectron from the surface of a metal

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

X-ray Photon Energy Equation

A

Work Function + KEmax

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

Attenuation Definition

A

decrease in intensity

decrease in the number of photons in the x-ray beam

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

Attenuation - Absorption

A
  • all energy from the photon is transferred to the atom
  • some of that energy is used to liberate an electron
  • a special case is pair production
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Attenuation - Pair Production

A
  • all energy from photon transferred to atom
  • electron and positron emitted
  • for this to happen the energy of the incident photon has to be greater than or equal to mc², where m is the mass of the electron and the positron
  • this can only occur at an atom as linear momentum has to be conserved (the atom is deflected to balance the movement of the electron and the positron away from the atom)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Attenuation - Scattering

A

photon from the beam continues but changes direction so that is no longer part of the beam i.e. the intensity if the beam is decreased
in elastic scattering the energy of the photon is conserved

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

Attenuation - The Compton Effect

A

the photon transfer some of its energy to an electron ionising it
the remaining energy continues moving as a photon but in a different direction

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

What happens as an object approaches the speed of light?

A

mass decreases

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

What is the function of a collimator?

A

a series of parallel tubes

incident radiation can only travel through the collimator if it is parallel to the tubes

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

How can sharpness be increased using a collimator?

A

longer tubes

thinner tubes

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

How can the radiation absorbed by a patient during an x-ray be minimised?

A
  • collimator
  • aluminium sheet
  • shielding surrounding tissue
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the purpose of an aluminium sheet in x-ray production?

A
  • the aluminium sheet absorbs low energy photons after they have passed through the collimator
  • the low energy photons would not have enough energy to pass through the patient and produce an image but are still ionising
  • this has little to no effect on useful high energy photons
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

How can the intensity of the produced x-rays be increased?

A
  • increased p.d.

- increased current

25
Q

How is an image produced using an x-ray?

A
  • x-ray radiation is passed through the patient
  • different materials absorb more or fewer photons
  • photons that do pass through hit a photographic film where they trigger a chemical reaction causing it to change colour
26
Q

Image Enhancement - Fluorescent Plate

A
  • absorbs x-ray photons and emits visible light photons
  • one x-ray photon causes lots of visible light photons to be emitted as x-ray photons are much higher energy than visible light photons
  • the emitted visible light photons hit the photographic film
27
Q

Image Enhancement - Barium Meal

A
  • a liquid suspension of barium sulphate is ingested
  • barium sulphate is a relatively large molecule and insoluble so it doesn’t enter the blood
  • it has a high attenuation coefficient
  • greater contrast between different soft tissues
28
Q

Angiogram

A
  1. a normal x ray is taken of the organ
  2. a contrast medium is injected into the blood stream
  3. same x ray is taken again
  4. the two images are subtracted from each other
  5. differences stand out and similarities fade
  6. blood vessels stand out as they only contained the contrast medium in the second image
29
Q

What does CAT stand for?

A

Computerised Axial Tomography

30
Q

How is a CAT scan taken?

A
  1. an x-ray emitter rotates on a ring around the patient
  2. radiation is detected by a detector which rotates opposite the emitter or by a stationary ring of detectors
  3. data is processed by a computer
  4. a series of cross sectional images are produced which can be compiled to produce a 3D image
31
Q

What tracer is used for a gamma camera?

A

technetium-99m

32
Q

What is the half life of technetium-99m?

A

6 hours

33
Q

Why is technetium-99m used as a tracer?

A

it is a metastable isomer - a high energy arrangement which can decay to a lower energy arrangement releasing a gamma photon
it can be attached to many different molecules e.g. glucose to detect a tumour

34
Q

How does a gamma camera work?

A
  1. tracer injected / ingested
  2. patient is put under a gamma camera
  3. photons are emmited from the body and travel along the axis of the lead tubes in a collimator to ensure that the detected radiation corresponds to the part of the body directly below
  4. a layer of sodium iodide crystal absorbs the gamma photons and remits visible light photons
  5. for every gamma photon that is aabsorbed, thousands of visible light photons are emmited
  6. photomultiplier tubes detect the visible light photons and emit an electrical impulse relative in magnitude to the intensity of the light
  7. the data is processed by a computer and an image is produced
35
Q

What does PET stand for?

A

Positron Emission Tomography

36
Q

How does a PET scan work?

A
  1. glucose is labelled with a radioactive isotope which undergoes beta decay to emit positrons
  2. the glucose is injected into the blood stream
  3. once inside the body, when a positron is emitted it collides with an electron already in the body and annihilates
  4. two gamma photons are released in opposite directions
  5. the photons are detected by a ring of detectors around the patient, as they are moving at the same speed, the time between detection of opposite sides of the ring allows the position they were emitted from to be determined
  6. this information is processed by a computer to produce a 3D image
37
Q

What does MRI stand for?

A

Magnetic Resonance Imaging

38
Q

Nuclear Precession

A
  • nuclei spin on an axis
  • when they are placed in a magnetic field the spin axis lines up with the field and the axis of spin precesses
  • the position of one end of the axis is fixed and the other end draws out a circular path
  • single protons (hydrogen nuclei) precess more easily than those that are in a nucleus with other nucleons
39
Q

Larmor Frequency Definition

A

frequency of precession
the number of circles drawn out by the spin axis per second
dependent on the flux density of the magnetic field

40
Q

How does an MRI machine work?

A
  1. patient is placed in a strong magnetic field
  2. half of the protons in the body line up with the field half line up against
  3. however a few protons in every million are unpaired and also line up with the field but are free to switch alignment
  4. gradient coils are used to make small adjustments to the field at specific point which also makes small changes to the larmor frequency of the protons in those areas
  5. radio transmitting coils emit pulses of radio waves at a a specific frequency, they will only be absorbed by protons with a matching larmor frequency
  6. absorption of radio waves causes protons to flip on their vertical spin axis to a high energy state where they are lined up against the field
  7. after a specific relaxation time the protons flip back to their original state and reemit the radio photon they absorbed
  8. this photon is detected and the data is processed to locate the position in the body it was emitted from an produce an image
41
Q

What are ultrasound waves?

A

high frequency sound waves

42
Q

How are ultrasound waves produced?

A
  1. a high frequency alternating p.d. is applied across a piezoelectric crystal
  2. this causes it to oscillate at the same frequency as the alternating p.d.
  3. this high frequency vibration produces ultrasound waves
43
Q

How are ultrasound waves used to produce an image?

A
  1. ultrasound waves are emitted in pulses by an ultrasound transducer
  2. the waves enter the body
  3. at every tissue boundary a proportion of the wave is reflected back towards the transducer
  4. the waves are emitted in pulses so that the transducer can be used as a detector inbetween pulses
  5. when the ultrasound wave reaches the piezoelectric crystal it causes it to oscillate which induces a measurable alternating p.d.
44
Q

What is the purpose of the backing block in an ultrasound transducer?

A

it stops the piezoelectric crystal from vibrating as soon as the p.d. is switched off
this means that the reflected ultrasound waves can be detected
if the crystal is already oscilating then the echos can’t be detected

45
Q

Why is gel required to do an ultrasound scan?

A

the gel acts as a coupling medium to allow the ultrasound waves to enter the body
there is a much smaller difference in acoustic impedence between the gel and the skin than there is between the air and the skin
this allows almost 100% of the ultrasound waves to enter the body

46
Q

What is a type A ultrasound scan?

A
  • produces a graph
  • the time between emission and detection and the speed of the ultrasound waves in the tissue is used to calculate the distance between tissue boundaries (s=d/t/)
  • the magnitude of the induced p.d. corresponds to the height of the peaks on the graph
47
Q

What is a type B ultrasound scan?

A
  • produces a sonogram, a 2D image

- each returning signal is plotted as a shaded pixel where the darkness is relative to the induced p.d.

48
Q

The Doppler Effect

A

If a source is moving towards the detector, the frequency increases
If a source is moving away from the detector the frequency decreases

49
Q

Acoustic Impedence Equation

A

Z = pc

Acoustic Impedence = density x speed

50
Q

Fraction of Reflected intensity Equation

A

Ir/Io = (Z2-Z1)² / (Z2+Z1)²

51
Q

The Doppler Effect Equation

A

f’ = cf / (c-v)

f = initial frequency
c = wave speed
v = speed of source
f' = new frequency
52
Q

Frequency of a wave reflected off a moving object

Equation

A

f’ = cf / (c-2v)

f = initial frequency
c = wave speed
v = speed of object
f' = new frequency
53
Q

Advantages of MRI

A
  • detailed soft tissue images
  • 3D image
  • no ionising radiation
54
Q

Disadvantages of MRI

A
  • very expensive
  • takes a long time
  • dense tissue (bones) not as detailed
  • requires a lot of energy
  • magnetic metals can’t be taken near the machine
55
Q

Advantages of CAT

A
  • 3D image
  • can be taken in a few minutes
  • cheaper than MRI
  • good for imaging bones
  • most hospitals have one
56
Q

Disadvantages of CAT

A
  • increased exposure to high frequency x-rays

- ionising radiation

57
Q

X Rays

Properties

A

Can travel in a vacuum
Travels at 3x10^8 m/s in a vacuum
Highly Ionising
No charge / rest mass

58
Q

Ultrasound

Properties

A

High frequency, higher than 20Hz

Longitudinal Wave

A2 Physics (8 decks)

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