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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

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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
what are the 2 forces that result from the static mag field
translational and rotational forces
26
what does the translational force generated by the static mag field affect
projectiles
27
what does the rotation force generated by the static mag field affect
implants
28
what is the difference between passive and active implants
Passive implants hold things in place/together but active implants are things like neurostimulator/pacemaker
29
what are bioeffects generated by static mag field and what do they depend on
depend on scanner strength and include headaches/nausea/blinking lights etc
30
are bioeffects generated by static mag field serious
normally transient and not long term
31
what are the 2 safety considerations/effects that the radiofrequency field can have on patients and devices
tissue heating and burns medical device heating
32
what does the gradient magnetic field do
localise the MR signals
33
what does cryogens do
maintains superconducting magnetic field
34
what are the 2 safety considerations/effects that the gradient magnetic field can have on patients
acoustic noise peripheral nerve stimulation
35
what are the 2 safety considerations/effects that cryogens can have on patients
quench can lead to asphyxiation or bodily harm
36
what are the 2 safety considerations of GBCA
nephrogenic systemic fibrosis Gd brain deposition
37
what are the 5 components of the MRI machine that should be safety considerations
RF field static magnetic field gradient magnetic field cryogens GBCAs
38
why can gradient mag field cause loud noises and peripheral nerve stimulation
Switches quickly generates loud noises and can cause peripheral nerve stimulation not dangerous but uncomfortable on certain pulses sequences that are very fast
39
what magnetic field is responsible for the most significant injuries and fatalities
static magnetic field
40
how strong is the magnetic field in the MRi 2 strengths
1.5T or 3T
41
what is 1 tesla equivalent to in terms of gauss
10,000 Gauss
42
when is the magnet on in MRI
the magnet is always on
43
is the magnetic field confined to within the scanner
no
44
what is the fringe field
the magnetic field extending beyond the physical covers of the scanner
45
where does the fringe magnetic field get stronger
as you approach the magnet the fringe magnetic field quickly gets stronger
46
what does the 5 Gauss line indicate
the point in the fringe field beyond which it is considered unsafe for an unscreened person to pass
47
where is the magnetic field strongest in the MRI
strongest at the centre in the bore
48
is the 5Gauss line limited to the floor of the room
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
what are the 3 methods of site access restriction
4 zone concept levels of MR personnel screening procedures
50
what is the controlled access 4 zone prinicples
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
what is considered zone 1
region includes all areas that are freely accessible to the general public typically the first access to the MR dept
52
what is considered zone 2
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
what is considered zone 3
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
what is access like to zone 3
strictly physically restricted and all access must be controlled by and entirely under the supervision of MRI personnel
55
what is considered zone 4
the MR scanner room
56
how can zone 4 be accessed
only by zone 3
57
what are the requirements for non MR personnel access in zone 4 and 3
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
what are the 2 levels of MR personnel
level 1 and 2
59
what are level 1 MR personnel
those who have passed minimal safety educational efforts to ensure their own safety as they work within zone 3
60
what are some examples of level 1 MR personnel
MRI dept office staff or patient aides
61
what are level 2 MR personnel
individuals who have been more extensively trained and educated in the broader aspects of MR safety issues
62
what are some examples of level 2 MR personnel
MRI technologist, radiologist, radiology dept nurses
63
what are the 3 classifications of implant and device labelling
MR safe MR conditional MR unsafe
64
what is a MR safe equipment label
item that poses no known hazards in all MRI environments
65
what is a MR conditional equipment label
item that has been demonstrated to pose no known hazards in a specified MRI environment with specific conditions of use
66
what is a MR unsafe equipment label
an item that is known to pose hazards in all MRI environments
67
what are some examples of MR safe equipment/materials
non conducting, non metallic, non magnetic objects plastic petri dish
68
what are some examples of MR unsafe equipment/materials
pair of ferromagnetic scissors
69
what are 5 access control methods
warning signs barriers swipe access appropriate supervision in restricted zones (zones 3 and 4) ferromagnetic detectors
70
who has to complete the MRI screening questionnaire
everyone entering the MRI scanner room
71
how often do patients or their family have to complete the MRI screening questionnaire
every time
72
how often do staff have to complete the MRI screening questionnaire
first time and then verbal follow ups each time after
73
what are the 3 stages where safety screening should be administered for patients
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
why do we need know the patients height and weight in the MRI screening process
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
what is patient preparation for MRI in terms of what it involves
change into plain cotton gown or scrubs - remove underwear if there is metal in it
76
what are 4 other considerations apart from getting the patient changed into a gown for patient preparation
patient mobility anxiety/claustrophobia looks for hairclips/watches/piercings cultural considerations such as turbans, kirpans, hijab and burkas etc
77
how thick do patient positioning pads need to be
>1cm thick
78
what are the 3 functions of patient positioning pads
burn prevention - RF field immobilization patient comfort
79
what are 3 things/equipment that should be considered when positioning the patient
leads/cables earplugs and headphones for the acoustic noise call bell

306 MEDIMAGE (2 decks)

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