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Physics A level OCR > Medical Imaging (C27) > Flashcards

Medical Imaging (C27) Flashcards

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1
Q

How do you produce x-rays

A

thermionic emission of electron
electron is accelerated
hit target metal and emit photons

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2
Q

max energy of x-ray photon =

A

max KE of electron

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3
Q

define attenuation

A

decrease in intensity as EM radiation passes through matter

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4
Q

4 possibilities when an x-ray collides with an atom

A

simple scatter
Photoelectric effect
Compton scattering
Pair production

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5
Q

What is Compton scattering

A

Incident X-ray collides with electron and removes it and a lower energy EM photon is also emitted

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6
Q

Why is simple scatter bad for hospitals

A

Creates blurriness

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7
Q

What is a CAT scan in simple terms

A

3D X-ray

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8
Q

Describe a cat scan

A

360 rotation
X-ray
Computer stitches together images

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9
Q

Advantage of a CAT scan

A

allows you to determine foreground and background

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10
Q

What does PET stand for

A

Positron emission Tomography

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11
Q

How does PET work

A

Uses a beta plus source
emitted positron annihilates with electron giving off antiparallel gamma rays
these are recorded and time delay can be used to find location.

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12
Q

How does the scanner work in PET

A

Incident photon hits scintillator (which amplifies signal) and then photomultiplier produces a voltage

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13
Q

Advantages of PET scanning

A

Non-invasive

Can see where respiration is occurring

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14
Q

disadvantages of PET scanning

A

very expensive

high radiation dose

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15
Q

What device is used in PET

A

radiopharmaceutical or medical tracer

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16
Q

what method of medical imaging is non-invasive and non-ionising

A

ultrasound

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17
Q

What is the name of the device that makes and receives ultrasound

A

transducer

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18
Q

What is the piezoelectric effect

A

Crystals that change shape under voltage (or the reverse)

19
Q

How does a transducer make ultrasound

A

alternating p.d. causing crystal to vibrate via the piezoelectric effect

20
Q

What is an A-scan

A

records ultrasound reflections in a line

21
Q

What is a B-scan

A

Creates 2d images by plotting intensity as brightness

22
Q

what is Z

A

acoustic impedance

23
Q

what is acoustic impedence

A

a material propety that affects how much sound is reflected and refracted

24
Q

what must be true to get a small proportion reflected

A

z1 ~ z2

25
Q

What is used in ultrasound

A

coupling gel

26
Q

why is a coupling gel used

A

ensures acoustic matching which reduces reflection

27
Q

What can be said between the air skin boundary compared to the skin gel boundary

A

there is impedance matching in the skin gel, whereas almost all the sound would be reflected at the air skin

28
Q

What is the intensity reflection coeffecient

A

ratio of the reflected to the initial intensities

29
Q

what effect is used to measure blood flow

A

doppler effect

30
Q

what happens to the frequency if the blood is moving towards the transducer

A

the frequency is high, the wavelength is lower

31
Q

what happens to the ultrasound if the blood is moving away

A

the frequency lowers the wavelength is larger

32
Q

what does a blood flow scan look like

A

different colours for different directions

33
Q

What medical tracer is used in PET

A

Fluorine 18 attached to fluorodeoxyglucose (FDG)

34
Q

what tracer is used in the gamma camera

A

Technetium-99m (Tc-99m)

35
Q

half life of Tc-99m

A

6 hours

36
Q

What does tc-99m emit

A

gamma radiation

37
Q

What is a key advantage of Tc-99m as a tracer

A

decays into a stable isotope

38
Q

Five key parts of a gamma camera

A 
Source in organ
collimator
scintillator 
photomultiplier
computer
39
Q

What is a collimator

A

long thin lead tubes

40
Q

what does a scintillator do

A

turns gamma photon into many visible photons

41
Q

What does a photomultiplier do

A

turns photon into an electric pulse

42
Q

Why does a gamma camera use a collimator

A

means only radiation travelling along axis of lead tubes is recorded, giving a clear image

43
Q

What is a gamma camera used for

A

Used to measure the function of organs like the kidney

Physics A level OCR (23 decks)

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