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306 MEDIMAGE > Lecture 1: MRI suite zones, controlled access, contraindications, labelling terminology, patient care, screening questionnaires > Flashcards

Lecture 1: MRI suite zones, controlled access, contraindications, labelling terminology, patient care, screening questionnaires Flashcards

1
Q

what are 2 reasons that MRI is considered safe

A

no harmful ionising radiation

no clearly demonstrated biological effects

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2
Q

what is the most common injury from MRI and which 2 injuries closely follows it in commonality

A

most common = burn

followed by projectiles and hearing damage

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3
Q

what are the 4 components of MRI hardware

A

magnet
radiofrequency coils
gradient coils
cryostat

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4
Q

what does the magnet do in terms of MRI hardware

A

it aligns protons in the body

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5
Q

what is the magnet in MRI hardware

A

large magnetic field that is homogenous over a large area

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6
Q

what does the radiofrequency coil do in terms of MRI hardware

A

transmit and receive RF energy into and from the body

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7
Q

what does the gradient coils do in terms of MRI hardware

A

induce linear change in magnetic field to enable spatial coding

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8
Q

what is the cryostat in terms of MRI hardware

A

large chamber of liquid helium in which the magnet coils are immersed

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9
Q

what do the H protons in the body do when there is no magnetic field vs when there is a mag field

A

H protons in body are spinning randomly but in MRI H protons align with magnetic field

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10
Q

what do the H protons do when RF energy is transmitted

A

RF energy transmitted, transmitted pulse in so protons moves away from alignment with magnet, away from parallel

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11
Q

what happens to the H protons when the RF pulse is turned on and off

how often does this happen in an examination

A

Turn pulse off and protons lose energy to realign with magnetic field

Happens very quickly and multiple times in an examination

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12
Q

what component of the MRI hardware is closest to the patient

A

RF coil

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13
Q

what does the RF coil transmit and receive

A

transmits RF pulse

receive signal when protons are realigning to mag field and release energy which is detected by RF receiver coils

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14
Q

where are the gradient coils located - what are they between

A

between the main magnetic coil and the RF coil

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15
Q

what does the gradient coil do

A

Gradient coil applies 3 very small mag field across patient in orthogonal planes so enables the localisation/coding of signals to determine where signal is coming from in the patient

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16
Q

what happens if you dont have a gradient coil

A

Without Gradient coils the signals would be coming back and wouldn’t know what signal was coming from where

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17
Q

what are the 3 electromagnetic fields in a MRI machine

A

main static magnetic field

RF field

gradient field

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18
Q

what is the gradient field in terms of time and why is that

A

Gradient field is time varying as they turn on and off v quickly in the scan

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19
Q

what temperature does the cryostat keep the MRI magnet to

A

-273 *C

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20
Q

what is the cryostat in terms of conductivity

A

a superconductor

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21
Q

what is the main magnet/magnetic field in a MRI machine

A

static magnetic field

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22
Q

what does the static magnetic field do

A

aligns Hydrogen protons to produce net magnetization

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23
Q

what does the radiofrequency field do

A

excites protons by transmitting radiofrequency pulses

RF coils also used to receive signals

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24
Q

what are the 4 safety considerations/effects that the static magnetic field can have on forces and patients

A

translational forces - projectiles

rotational forces - implants

medical device disruption

bio-effects

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25
Q

what are the 2 forces that result from the static mag field

A

translational and rotational forces

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26
Q

what does the translational force generated by the static mag field affect

A

projectiles

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27
Q

what does the rotation force generated by the static mag field affect

A

implants

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28
Q

what is the difference between passive and active implants

A

Passive implants hold things in place/together but active implants are things like neurostimulator/pacemaker

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29
Q

what are bioeffects generated by static mag field and what do they depend on

A

depend on scanner strength and include headaches/nausea/blinking lights etc

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30
Q

are bioeffects generated by static mag field serious

A

normally transient and not long term

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31
Q

what are the 2 safety considerations/effects that the radiofrequency field can have on patients and devices

A

tissue heating and burns

medical device heating

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32
Q

what does the gradient magnetic field do

A

localise the MR signals

33
Q

what does cryogens do

A

maintains superconducting magnetic field

34
Q

what are the 2 safety considerations/effects that the gradient magnetic field can have on patients

A

acoustic noise

peripheral nerve stimulation

35
Q

what are the 2 safety considerations/effects that cryogens can have on patients

A

quench can lead to asphyxiation or bodily harm

36
Q

what are the 2 safety considerations of GBCA

A

nephrogenic systemic fibrosis

Gd brain deposition

37
Q

what are the 5 components of the MRI machine that should be safety considerations

A

RF field

static magnetic field

gradient magnetic field

cryogens

GBCAs

38
Q

why can gradient mag field cause loud noises and peripheral nerve stimulation

A

Switches quickly generates loud noises and can cause peripheral nerve stimulation not dangerous but uncomfortable on certain pulses sequences that are very fast

39
Q

what magnetic field is responsible for the most significant injuries and fatalities

A

static magnetic field

40
Q

how strong is the magnetic field in the MRi

2 strengths

A

1.5T or 3T

41
Q

what is 1 tesla equivalent to in terms of gauss

A

10,000 Gauss

42
Q

when is the magnet on in MRI

A

the magnet is always on

43
Q

is the magnetic field confined to within the scanner

A

no

44
Q

what is the fringe field

A

the magnetic field extending beyond the physical covers of the scanner

45
Q

where does the fringe magnetic field get stronger

A

as you approach the magnet the fringe magnetic field quickly gets stronger

46
Q

what does the 5 Gauss line indicate

A

the point in the fringe field beyond which it is considered unsafe for an unscreened person to pass

47
Q

where is the magnetic field strongest in the MRI

A

strongest at the centre in the bore

48
Q

is the 5Gauss line limited to the floor of the room

A

no it can extend outside the scanner room such as the control area and as its 3D it can also extend up into the roof

49
Q

what are the 3 methods of site access restriction

A

4 zone concept

levels of MR personnel

screening procedures

50
Q

what is the controlled access 4 zone prinicples

A

as you progress towards the magnet room you undergo increasing levels of screening and observation to prevent incidents that could threaten the safety of the patients and staff

51
Q

what is considered zone 1

A

region includes all areas that are freely accessible to the general public

typically the first access to the MR dept

52
Q

what is considered zone 2

A

interface between the publicly accessible uncontrolled zone 1 and the strictly controlled zone 3

patients are greeted in zone 2 and are not free to move throughout the region at will - usually patient screening occurs in this zone

53
Q

what is considered zone 3

A

free access by unscreened non MRI personnel or ferromagnetic objects could result in serious injury or death

includes all areas with fringe field >5Gauss line

54
Q

what is access like to zone 3

A

strictly physically restricted and all access must be controlled by and entirely under the supervision of MRI personnel

55
Q

what is considered zone 4

A

the MR scanner room

56
Q

how can zone 4 be accessed

A

only by zone 3

57
Q

what are the requirements for non MR personnel access in zone 4 and 3

A

non MR personnel must be accompanied by or under the immediate supervision of a specifically identified level 2 MR person for the entirety of their duration within zone 3 or 4

58
Q

what are the 2 levels of MR personnel

A

level 1 and 2

59
Q

what are level 1 MR personnel

A

those who have passed minimal safety educational efforts to ensure their own safety as they work within zone 3

60
Q

what are some examples of level 1 MR personnel

A

MRI dept office staff or patient aides

61
Q

what are level 2 MR personnel

A

individuals who have been more extensively trained and educated in the broader aspects of MR safety issues

62
Q

what are some examples of level 2 MR personnel

A

MRI technologist, radiologist, radiology dept nurses

63
Q

what are the 3 classifications of implant and device labelling

A

MR safe
MR conditional
MR unsafe

64
Q

what is a MR safe equipment label

A

item that poses no known hazards in all MRI environments

65
Q

what is a MR conditional equipment label

A

item that has been demonstrated to pose no known hazards in a specified MRI environment with specific conditions of use

66
Q

what is a MR unsafe equipment label

A

an item that is known to pose hazards in all MRI environments

67
Q

what are some examples of MR safe equipment/materials

A

non conducting, non metallic, non magnetic objects

plastic petri dish

68
Q

what are some examples of MR unsafe equipment/materials

A

pair of ferromagnetic scissors

69
Q

what are 5 access control methods

A

warning signs

barriers

swipe access

appropriate supervision in restricted zones (zones 3 and 4)

ferromagnetic detectors

70
Q

who has to complete the MRI screening questionnaire

A

everyone entering the MRI scanner room

71
Q

how often do patients or their family have to complete the MRI screening questionnaire

A

every time

72
Q

how often do staff have to complete the MRI screening questionnaire

A

first time and then verbal follow ups each time after

73
Q

what are the 3 stages where safety screening should be administered for patients

A

on acceptance of booking - booking clerk

on arrival of the patient - written questionnaire checked by MRI personnel

immediately prior to entering zone 4 - verbal questioning by MRI personnel

74
Q

why do we need know the patients height and weight in the MRI screening process

A

so scanner can accurately calculate limits for RF deposition

specific absorption rate measured watts per kilo and height and weight are entered to calculate how much RF is allowed to be put into that patient safely

75
Q

what is patient preparation for MRI in terms of what it involves

A

change into plain cotton gown or scrubs - remove underwear if there is metal in it

76
Q

what are 4 other considerations apart from getting the patient changed into a gown for patient preparation

A

patient mobility

anxiety/claustrophobia

looks for hairclips/watches/piercings

cultural considerations such as turbans, kirpans, hijab and burkas etc

77
Q

how thick do patient positioning pads need to be

A

> 1cm thick

78
Q

what are the 3 functions of patient positioning pads

A

burn prevention - RF field

immobilization

patient comfort

79
Q

what are 3 things/equipment that should be considered when positioning the patient

A

leads/cables

earplugs and headphones for the acoustic noise

call bell

306 MEDIMAGE (2 decks)

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