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MRI Flashcards

1
Q

MRI – what are the two different types of relaxation curves image contrast?

A

Transverse – T2 - Decreases the time

Longitudinal – T1 - increases the time

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2
Q

What are the different types of image contrast used in MRI?

And what are their TE and TR

A

T1 weighted - short TR, short TE

T2 weighted - long TR, long TE

Proton density weighted - short TE, long TE

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3
Q

How does T1 versus T2 weighting show up on images?

How does proton density image appear as well?

A

T1 – fluid is dark

T2 – fluid is bright

PD fat sat - Proton density image – little tissue contrast

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4
Q

What does HCAI stand for – infection control MRI?

A

Healthcare associated infections

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5
Q

How does HCAI develop and how severe is the risks?

A

Direct – result of healthcare interventions such as medical or surgical treatment

Contact – healthcare setting

Poses a serious risk to the patient staff and visitors

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6
Q

HCAI – MRI infection control – why is infection prevention and control a key priority for NHS?

A

Incur significant cost for the NHS

cause significant morbidity to those infected

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7
Q

MRI infection control – NICE guidelines

A

Standardise care

Produced a wealth of information on the topic of healthcare associated infections which includes:

guidelines

Nice pathways

Quality standards and advice

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8
Q

What is the aseptic non-touch technique – ANTT?

A

It’s adopted widely by NHS organisations to reduce HCAI - standardised approach

Used to reduce the risk of microbial contamination in a vulnerable body site

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9
Q

What is the benefits of using the antiseptic non-touch technique – MRI infection control?

A

Provides a framework – standardises and raise clinical standards – consistent and reliable approach – best practice

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10
Q

What is the principle/ main principles of the anti-septic then touch technique – MRI infection control?

A

Principle – only uncontaminated equipment (key part) or sterile fluids come into contact with susceptible or sterile sites during clinical procedures

Always clean hands affectively
Never contaminate- key parts
Touch key parts with confidence 
Take appropriate infection prevention precautions

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11
Q

What are the two levels of antiseptic non-touch technique – MRI infection control?

A

Surgical – ANTT – more complicated procedure is E.G.central venous access

Standard – ANTT – procedures which are not significantly versive E.G.IV cannulation

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12
Q

What is the ANTT procedure – MRI infection control?

A

Wash/dry hands for delete
set up trolley/gather equipment
Disposal Tronic it/look for appropriate site
Clean hands
Apply non-sterile gloves
Clean injection set an alarm to dry
Disposal tourniquet/access vein/secure veflon
Dispose of sharps
Clean trolley
Move gloves
Clean hands

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13
Q

What are the different types of clinical magnets? – MRI

A

Permanent

Resistive

Superconductive

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14
Q

Description of positives and negatives of the permanent magnet?

A

Positives
- Small static field – so can often be cited close to public areas
- Open MRI – systems have been praised by patients as they are less confined running close Magnet design
- Lack of need for liquid helium into screwing or power for the magnet itself
- for your direction from south to north meaning that there are virtually no fringe fields

Negatives
-Often quite heavy compared to Superconducting systems
-There are also some superconducting MR systems on the market with an “open” configuration

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15
Q

Description of positives and negatives of the resistive magnet?

A

Positive
- Magnet can be switched on or off
“Open MRI” systems have been praised by patients as they are less confined than an enclosed magnet design
- Lack of need for liquid helium induced cooling or power for the magnet itself
- Field direction can run either vertically or horizontally on these systems. Both minimise the risk from fringe fields

Negative
- More expensive to run versus a permanent magnet due to electricity consumption.
- Field strengths still relatively low

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16
Q

Description of positives and negatives of the Superconducting magnet?

A

Positive
-Significantly higher field strengths allow for:
- Higher signal recover
- Higher resolution images
- Faster image acquisition
- The most common type of magnet design by far
- A few “open” systems now available

Negatives
- Expensive to buy and maintain
- Closed bore systems can increase patient anxiety or trigger feelings of claustrophobia
- Higher field strengths with larger fringe fields (field runs horizontally along the bore or the magnet) make these more difficult to house in established buildings

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17
Q

Permenant:
Field Strength
Homogeneity
Stability
Fringe Field
Weight
Emergency Shutdown
Power Consumption
Cooling
Manufacturing Costs

A

Permanent
>0.5T
Moderate
Temperature dependent
Negligible
High
Not Possible
None
None
Medium

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18
Q

resistive:
Field Strength
Homogeneity
Stability
Fringe Field
Weight
Emergency Shutdown
Power Consumption
Cooling
Manufacturing Costs

A

0.02T – 0.6T
Moderate
Moderate
Small
Low
Switch Off
High
Chilled Water
Low

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19
Q

Superconducting:
Field Strength
Homogeneity
Stability
Fringe Field
Weight
Emergency Shutdown
Power Consumption
Cooling
Manufacturing Costs

A

Superconducting
0.15T – 14T
Good
Good
Large (without shielding)
Moderate (with no shielding)
Quench (expensive)
Moderate
Cryogen liquids
High

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20
Q

Cryogren -superconducting magnet

A

Liquid helium is used to kill the wire windings to create zero desistance

The liquid helium being pumped around the superconducting system makes a chirpy noise



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21
Q

What does NMV stand for

A

Net magnetisation vector

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22
Q

What is the NMV in the superconducting magnet

A

The LMB is high which leads to faster scanning and higher resolution

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23
Q

What are the negatives of a superconducting magnet and risks

A

Is expensive to buy and maintain

Most significant risk come from the use of cryogens

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24
Q

What is the risk of a cryogen?

A

Helium weeks which would lead to asphyxiation - boil off



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25
Q

What is in place to make aware that helium has leaked?

A

The monitor will alarm if O2 is below 19%

Sensor and filter need to be replaced - if not alarm may go off

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26
Q

What should you do if the alarm goes off/helium is leaked into the MRI Room?

A

Get out oxygen
and turn off magnets

This is because of risk of combustion in the environment and fire services need to get in so the magnet needs to be turned off because of their equipment

27
Q

What is a quench?
And what may be the result of this on the machine

A

Liquid helium rapidly boils off through quench pipe – slowly eliminating magnetic field

Can be spontaneous or deliberate

Severe damage to the magnet or gradient coils may occur

Cost is 30,000+

Magnet downtime is five days plus


28
Q

What is the risk of the quench pipe failing?

A

Explosion and asphyxiation
- this is why the quench pipe is serviced regularly

Liquid helenium boiling off can also cause the volume of helium to increase up to 700 times 
- Some of the quench pipe feels this may create a huge pressure buildup in magnet room
- Should this happen doors that open inwards will not open due to the pressure
- that’s why doors in the MR environment should open outwards either fully or partially

29
Q

What is the risks of the magnetic field in clinical practice

A

Projectiles

Implants

Magnetohydrodynamic effect

30
Q

International guidelines:

A

World health organisation

International condition or not ionising radiation protection – ICNIRP

International electoraltechnical commission

31
Q

UK guidelines:

A

UK medicines and healthcare regularity authority - MHRA

UK health protection agency – HPA

Institute of physics and engineering in medicine - IPEM

British Association of MR Radiographers - BAMRR

Society and college of radiographers -SCoR

32
Q

Local policies – NHS level

A

Radiation safety committee

MR safety committee

Local rules
- implementation of policy
- delegation of responsibilities
- authorisation of personnel
-Standard operating procedures

33
Q

Projectiles:

A

Clinical Emma I magnets are very strong and produce a powerful attractive force on ferrous metals

 The magnetic field extend well beyond the board of the magnet

Items such as: pens, keys, scissors, mobiles - missals
Metal plus magnet that quickly missals into magnet

Larger items such as o2 cylinders, wheelchairs … And will be strongly feel towards magnet

34
Q

Control of projectile risk:

A

Only items that come into the magnet room are tested and marked as MR safe – MR conditional – MR unsafe

Anything without with markings must be considered unsafe to take into the MRI environment

35
Q

Implants:

A

Anyone entering the MRI environment with an active implant device such as:
Peacemakers

Implantable cardiac defibrillator – ICD

Cardiac loop recorder

 Neurostimulator

Impossible drug infusion pump

Programmable hydrocephalus shunt

Middle ear implant

Anyone with an Aneurysm clip in the brain

Anyone with shrapnel in the globe of the eye

36
Q

Implants control the risk:

A

MRI safety questionnaire

Authorised personnel

Controlled Areas

37
Q

The MRI safety questionnaire:

A

Everyone active ever environment must be screened prior to entry – there are no exceptions to this

Groups include
patient
Staff including estates and external contractors

Screening questionnaires should be signed by the individual and countersigned by an authorised person when they have satisfied themselves that all information is verified

38
Q

Authorised person:

A

A suitable trained member of staff authorised to have the access to the MR controlled area

Authorised person – non-MR environment - May not enter without supervision

Authorised person – MR environment - May enter

Authorised person – supervisor - May enter and supervise

39
Q

The MRI responsible person:

A

Delegated the day-to-day responsibility of MRI safety by the chief executive or head of organisation in writing

What are the main duties is the train and approve MR authorised persons

Often a senior individual such as principal medical physicist or consultant radiologist

40
Q

The MR safety expert:

A

This is a separate role from responsible person

At the Emma safety expert will have a knowledge of Emma and I technique is an appropriate understanding of the clinical applications – ideally they will be a physicist with expertise in MRI

MR safety expert should be in a position to adequately advise on the necessary engineering scientific and administrative aspects of the safe clinical use of MR devices

41
Q

Magnetohydrodynamic effect:

A

When I electrically conductive fluid (blood) moves within a magnetic field and electrical current is produced

It can cause staff that work in the MR environment:
Vertical, nausea, phosphenes
Worse at High fields
Staff may experience dizziness when leaning into the board of the magnet


42
Q

Gradient safety:

A

Tissue or nerve stimulation

Acoustic noise

43
Q

Tissue or nerve stimulation:

A

Specially in called Ama signals also in generate an electric current within the body

May cause tingling/twitching sensation in fingers and toes - but the MR systems warn operators when this may occur

Most commonly occurs when using echoplanar imaging techniques:

Diffusion weighted imaging
diffusion tenser imaging
functional MRI

44
Q

Acoustic noise:

A

Gradient switching generates acoustic noise as a byproduct

Sound pressure levers can Reach 115 DB

Health and safety legislation requires hearing protection to be worn when exposed to side pressures level over 90 DB

This is managed by using earplugs and/or headphones

45
Q

Radio-frequency safety:

A

Specific absorbing rate - SAR

Induced loops and RF Burns

46
Q

Specific absorbs rate – SAR:

A

RF is used to excite hydrogen

Our F – deposit heat in body tissues the heat is then removed removed via blood flow – convection

Rate of  heat disposition – SAR – watts per kilo should not exceed 2W–KG -1

47
Q

Induced loops and RF burns:

A

Induced current may occur in conducting loops in cables, wires and even body parts

Where there is a thin area of contact that electrons skin on skin contact this generates heat

This is a risk of RF burns

48
Q

MRI safety – Fire:

A

Am I specific fireplug their house to control names of each department

Firefighters know that they cannot enter the Emma environment without the advice of a present authorised person

Isolate medical gases and quench magnet

Fire extinguisher must be done within controlled areas

49
Q

MRI safety – clinical emergency in MRI

A

In cardiac arrest situations the patient must be removed immediately bearing in mind that manual handling procedures should always be adhered to

MR safe evacuation trolley
On some the couch can be removed

Patient taken into the controlled area where resus/CPR can commence

Door locked

50
Q

MRI safety key points:

A

Superconducting magnets are always on

Controlled areas are there for the safety of all users of the department

If you doubt - No entry

51
Q

Controlled area door:

A

Always locked

Staff ID badge or keypad to unlock

Emergency exit

52
Q

Patient prep area:
What are the steps before entering the controlled area

A

Go through entire screening form and countersign

Patient weight and height to determine the power/Safe limit of radio frequency

Patient clothes/artefacts are removed

Get rid of loose metal – keys coins, phone, wallet, loose jewellery

Cannulation if required

53
Q

Magnet room preparation:

A

Clean

Course selection

Immobilisation equipment that sandbags cushion Velcro

Contrast pump injector – filled up and ready to go

Getting equipment for cardiac or respiratory - EKG Tracing

oxygen - tube in room

Monitoring– MR safe monitor

54
Q

Patient preparation:

A

All metal removed

Manual handling equipment required:
MR safe wheelchair
Turntable
Glide sheet
Bed ladder
Pat slide for lateral transfers

Position position of the magnet couch

Earplugs and headphones

Contact buzzer

Place coil over the part to be scanned making sure that cables are not stretched

Pads between cables and bear skin

Move patient into the magnet slowly dash to the juice dizziness

Communicate – are they still okay comfortable happy to proceed

55
Q

Control room:

A

Check the patient can hear over intercom

Would the patient like to listen to music

Warn of noises before commencing the scan

Blinds - privacy

56
Q

What is spin wrap:

A

Radio-frequency – hydrogen – signal back

Gs – slice direction
Gr - readout direction
Gp - phase direction

Pulse - readout (signal)

57
Q

2DFT image data collection:

A

Echo time (TE) - raw data - manipulate + record

Line of raw data per pulse - repeated multiple times - image
( empty spaces - k-space)

Middle - contrast - quick scan dynamic contrast
Outer - resolution

58
Q

Wraparound/aliasing artefact

A

Front end up at the back of the image – happens in face directional scan

To fix that you did a larger field of view or NPW

Oversampling – extra data – get rid of it



59
Q

Image artefacts in MRI

A

Some artefacts can mimic pathologies

Artefacts that are easily solved such as motion artefacts and phase wrap

Other require engineers to correct such as hardware, electrical or software defects

Cosmo magnetic susceptibility differences in tissue can create field inhomogeneities at the interface

Made much worse on sequences with long echo times – EPI, DTI, DWI, FMRI

Often naturally occurs at air-tissue interfaces such as in the sinuses

60
Q

What can Radiographers operating and MR system use to reduce certain artefacts such as:
blood flow

A

Saturation pulses are bursts of RF energy used to actively suppress signal from selected tissues.
Selective saturation can be used on the oesophagus to eliminate swallowing artefacts
Often placed above and below fields of view (fov) to suppress flowing blood entering the slice.
They can also be use to suppress venous flow in Time of Flight (ToF) angiography (MRA) sequences.

61
Q

What can Radiographers operating and MR system use to reduce certain artefacts such as:
Peristalsis

A

Involuntary wave-like motion used to transit food through the bowel.
There are 2 methods to restrict this, scanning the patient in a prone position and by using an inhibiting drug such as Hyoscine Butylbromide (Buscopan)
Buscopan is also regularly administered by Radiographers via a Patient Group Direction (PGD) for CT procedures and for fluroscopic bowel exams.

62
Q

What can Radiographers operating and MR system use to reduce certain artefacts such as:
respiratory movement

A

There are many ways to attempt to correct for this:
Increasing the number of Excitations (NEX)
Breath holding
Respiratory triggering using bellows (Long TR) – Hardware solution that synchronises the acquisition with the patient’s breath.

63
Q

navigator trigger:

A

This is a software based solution
The navigator is placed at the top of the liver to trigger the acquisition whilst the patient breathes freely.
This can sometimes take a while to do (up to 9ish minutes per sequence – best put the kettle on)
This technique is often used for scanning of the abdominal organs, the chest and mediastinum and whole body imaging.

64
Q

What can Radiographers operating and MR system use to reduce certain artefacts such as:
cardiac motion

A

Cardiac gating is essential for cardiac MR studies
3 or 4 lead ECG devices are attached to the patient’s chest and the sequences pulses are triggered from the r wave of the ECG trace.
Alternatively a Peripheral Pulse Unit (PPU) or pulse oximetry sensor can be attached to the patients fingers or toes though this is far less effective for cardiac imaging
Can be useful for Neurology applications such as Diffusion Tensor Imaging or CSF flow studies.
Cardiac Arrhythmias cause symptoms in Radiographers that include mild profanity up to loudly expressed expletives. (And images like these)

DIS (17 decks)

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