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Medical Flashcards

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1
Q

What is used to create ultrasound impulses

A

Piezoelectric crystals

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2
Q

How are pulses of ultrasound produced by a transducer

A

Apply an alternating potential difference of high frequency to electrodes which are attached to piezoelectric crystals which causes the crystals to contract and expand repeatedly at the same frequency as the potential difference. This causes mechanical vibrations which produces sound waves over 20000hz

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3
Q

How are ultrasound signals detected

A

The piezoelectric crystals are forced to compress and extend repeatedly so they vibrate due to waves which causes an alternating potential difference at the same frequency as the sound waves and this pd can be measured

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4
Q

What metal is used in a X-ray tube

A

Tungsten

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5
Q

What happens in an X-ray tube

A
  • electrons are emitted from a heated filament
  • they are accelerated over a high potential difference
  • they hit the tungsten anode and decelerate, converting there kinetic energy into an X-ray photon
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6
Q

What’s bremmstrahlung

A

When the X-ray tube emits a continuous spectrum of X-ray radiation

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7
Q

What is the maximum kinetic energy of an X-ray

A

The production of the potential difference of the tube and the charge of an electron

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8
Q

What’s the maximum energy of a pd 50kv

A

50keV

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9
Q

How do you measure the intensity of the beam

A

The power per unit area

The energy per se one per unit area

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10
Q

What are two ways of increasing the intensity of the X-rays

A

1) increase the potential difference in the tube

2) increase the current supplied to the filament

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11
Q

How does increasing potential difference effect the electrons

A

The electrons have a greater kinetic energy, so higher energy electrons can knock off deeper electrons producting more characteristic spikes

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12
Q

What is the difference in the energy of e photons if you increase the potential difference

A

They have a higher maximum kinetic energy

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13
Q

How is intensity and voltage related

A

Intensity is proportional to the square of p.d

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14
Q

What does increasing the current do

A

This means the filament will emit more electrons per second and therefore produce more photons per second

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15
Q

What happens to the energy of the photons if you increase the current

A

The energy will stay the same

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16
Q

What is the relationship between current and intensity

A

They are proportional

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17
Q

What does the blood flow into first in the heart

A

The atrium

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18
Q

What do valves do in the heart

A

Prevent back flow of the blood

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19
Q

How does the heart work

A

Blood enters the atria, via veins and the atria contract, squeezing blood into the ventricles, which then contract pushing blood out via the arteries

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20
Q

How are electrical signals passed in the heart

A

Cells in the wall of the right atria send electrical impulses, these are passed to the atrioventricular node which delays the signal for about 0.1 before passing it to the ventricles

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21
Q

How many electrical signals occur per min

A

Around 70

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22
Q

What is an electrocardiograph used for

A

To find out about the condition of the heart

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23
Q

How does a cardiogram work

A

Electrodes are attached to the chest and a computer plots the potential difference between them against time

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24
Q

Why do we place electrodes on the chest

A

It’s close to the heart and the limbs at a point where arteries are close to the surface

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25
Q

Where on the body shouldn’t we connect electrodes to

A

The right leg as its too far away from the heart

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26
Q

How should the patient be during the exam and why

A

They should be relaxed and still to reduce any unwanted signals

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27
Q

How should the leads be treated

A

They should be shielded in order to reduce the interference from any nearby a.c sources

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28
Q

What happens to the signals at the electrodes and what is done to reduce this

A

The signals are attenuated through the body so they must be amplified by a high impedance amplifier

29
Q

How should you reduce electrical resistance between the contact points

A

Remove hair and dead skin cells, use a conductive gel and make sure electrodes are securely attached

30
Q

What are the 3 different waves on a electrocardiograph

A
  • P
  • QRS
  • T
31
Q

What do the p wave relate to

A

The signal generate which causes the contraction of the atria

32
Q

What causes the QRS wave

A

The signal which causes the ventricles to contract

33
Q

How long after the P wave does the QRS wave occur

A

0.2s

34
Q

What causes the T wave

A

The ventricles relaxing

35
Q

How long after the QRS wave does the T wave occur

A

0.2s

36
Q

What’s fluoroscopy used for

A

Create moving images

37
Q

What 3’screens are used in fluoroscopy

A

Fluorescent screen, photocathode and fluorescent viewing screen

38
Q

What do fluorescent screens do

A

Thy absorb X-ray photons and emit light

39
Q

What does the photocathode do

A

It absorbs light and emits electrons

40
Q

What changes the path of electrons in fluoroscopy

A

Electrodes help to focus electrons to produce and image

41
Q

What’s a flat panel detector

A

An digital way to record X-ray images

42
Q

How do flat panel detectors work

A

1) X-rays excite the scintillator material which produces light of intensity proportional to the energy of the incident photons
2) photodiode pixels create a voltage proportion to the intensity of light which hits them
3) thin film transistors are used to create a digital signal

43
Q

What are advantages of FTP

A
  • lightweight and compact, convenient to move around
  • higher resolution
  • less distortion of the image
  • easily copied, shared and stored
  • need less exposure to produce a clear image
44
Q

What are advantages of X-rays

A
  • they have good resolution
  • produce clear images of bones
  • CT scans are much quicker than MR scans
  • CT scan is quicker than MR scans
45
Q

What is an MR machine

A

A huge super magnet

46
Q

How does an MR scan need to be maintained and why is this a disadvantage

A

It needs to be cooled by liquid helium and this is expensive

47
Q

What is the magnetic field like during an MR scan

A

The super magnet creates a uniform magnetic field, and smaller electromagnets create small fields which interfere, creating a gradient of magnetic field strengths

48
Q

What does the magnetic field do to our bodies

A

If affects the protons (hydrogen nuclei), it makes them align and process around the field

49
Q

What affects the precession frequency

A

The magnetic field strength

50
Q

What is the precession frequency

A

The angular speed the protons precess at

51
Q

What happens to the protons after they have a gradiated magnetic field

A

They have different precession frequencies and hence absorb different frequencies of radiation

52
Q

How are radio waves used in MR scans

A

Radio frequency coils emit short pulses of radio waves the same frequency as the precession frequency which excites the protons and causes the to change alignment, the protons deexcite and emit the photons

53
Q

How can we change what part of the body were looking at

A

Change the frequency of the radio waves emitted

54
Q

What image is created from an MR scan

A

A 2D cross section image

55
Q

How can we enhance the response of different tissue types

A

Alter the time between impulses

56
Q

What type of molecules should have rapid impulses

A

Fat molecules

57
Q

What are rapid impulses used to image

A

The internal structure of the body

58
Q

What molecules should you allow more time for

A

Watery molecules

59
Q

What are slow Impulses used to look at

A

Diseased areas

60
Q

What are advantages of MR scans

A
  • no known side effects
  • an image can be made for any slice in any orientation from a single scan
  • high quality images of soft tissue including the brain
  • can change contrast to investigate different situations
  • it gives real time images
61
Q

What are disadvantages of MR scans

A
  • the imagine of bones is poor
  • people feel claustrophobic
  • scans can be noisy and take a long time
  • can’t be used on people with pace makes or metal impacts
  • scanners are very expensive
62
Q

Which is the safest scan to use

A

Ultrasound or Mr

63
Q

What scan is best for bones

A

X-rays

64
Q

What two scans can be used to look at soft tissue and which is better

A

MR Is best but X-rays work as well

65
Q

Which is cheapest and most portable

A

Ultrasound then X-rays

66
Q

What do medial tracers do?

A

They are used to show tissue or organ structure and function

67
Q

What three things to eh use for tracers

A

Technetium-99m
Iodine-131
Indium-111

68
Q

How are the tracers put into the body

A

They’re bound to substances the body uses and then injected or swallowed

Physics (14 decks)

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