MRI Flashcards
MRI – what are the two different types of relaxation curves image contrast?
Transverse – T2 - Decreases the time
Longitudinal – T1 - increases the time
What are the different types of image contrast used in MRI?
And what are their TE and TR
T1 weighted - short TR, short TE
T2 weighted - long TR, long TE
Proton density weighted - short TE, long TE
How does T1 versus T2 weighting show up on images?
How does proton density image appear as well?
T1 – fluid is dark
T2 – fluid is bright
PD fat sat - Proton density image – little tissue contrast
What does HCAI stand for – infection control MRI?
Healthcare associated infections
How does HCAI develop and how severe is the risks?
Direct – result of healthcare interventions such as medical or surgical treatment
Contact – healthcare setting

Poses a serious risk to the patient staff and visitors
HCAI – MRI infection control – why is infection prevention and control a key priority for NHS?
Incur significant cost for the NHS
cause significant morbidity to those infected
MRI infection control – NICE guidelines
Standardise care
Produced a wealth of information on the topic of healthcare associated infections which includes:
guidelines
Nice pathways
Quality standards and advice
What is the aseptic non-touch technique – ANTT?
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
What is the benefits of using the antiseptic non-touch technique – MRI infection control?
Provides a framework – standardises and raise clinical standards – consistent and reliable approach – best practice
What is the principle/ main principles of the anti-septic then touch technique – MRI infection control?
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
What are the two levels of antiseptic non-touch technique – MRI infection control?
Surgical – ANTT – more complicated procedure is E.G.central venous access
Standard – ANTT – procedures which are not significantly versive E.G.IV cannulation
What is the ANTT procedure – MRI infection control?
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
What are the different types of clinical magnets? – MRI
Permanent
Resistive
Superconductive
Description of positives and negatives of the permanent magnet?
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
Description of positives and negatives of the resistive magnet?
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
Description of positives and negatives of the Superconducting magnet?
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
Permenant:
Field Strength
Homogeneity
Stability
Fringe Field
Weight
Emergency Shutdown
Power Consumption
Cooling
Manufacturing Costs
Permanent
>0.5T
Moderate
Temperature dependent
Negligible
High
Not Possible
None
None
Medium
resistive:
Field Strength
Homogeneity
Stability
Fringe Field
Weight
Emergency Shutdown
Power Consumption
Cooling
Manufacturing Costs
0.02T – 0.6T
Moderate
Moderate
Small
Low
Switch Off
High
Chilled Water
Low
Superconducting:
Field Strength
Homogeneity
Stability
Fringe Field
Weight
Emergency Shutdown
Power Consumption
Cooling
Manufacturing Costs
Superconducting
0.15T – 14T
Good
Good
Large (without shielding)
Moderate (with no shielding)
Quench (expensive)
Moderate
Cryogen liquids
High
Cryogren -superconducting magnet
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

What does NMV stand for
Net magnetisation vector
What is the NMV in the superconducting magnet
The LMB is high which leads to faster scanning and higher resolution
What are the negatives of a superconducting magnet and risks
Is expensive to buy and maintain
Most significant risk come from the use of cryogens
What is the risk of a cryogen?
Helium weeks which would lead to asphyxiation - boil off

What is in place to make aware that helium has leaked?
The monitor will alarm if O2 is below 19%
Sensor and filter need to be replaced - if not alarm may go off
What should you do if the alarm goes off/helium is leaked into the MRI Room?
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
What is a quench?
And what may be the result of this on the machine
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

What is the risk of the quench pipe failing?
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
What is the risks of the magnetic field in clinical practice
Projectiles
Implants
Magnetohydrodynamic effect
International guidelines:
World health organisation
International condition or not ionising radiation protection – ICNIRP
International electoraltechnical commission
UK guidelines:
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
Local policies – NHS level
Radiation safety committee
MR safety committee
Local rules
- implementation of policy
- delegation of responsibilities
- authorisation of personnel
-Standard operating procedures
Projectiles:
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
Control of projectile risk:
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
Implants:
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
Implants control the risk:
MRI safety questionnaire
Authorised personnel
Controlled Areas
The MRI safety questionnaire:
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
Authorised person:
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
The MRI responsible person:
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
The MR safety expert:
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
Magnetohydrodynamic effect:
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

Gradient safety:
Tissue or nerve stimulation
Acoustic noise
Tissue or nerve stimulation:
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
Acoustic noise:
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
Radio-frequency safety:
Specific absorbing rate - SAR
Induced loops and RF Burns
Specific absorbs rate – SAR:
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
Induced loops and RF burns:
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
MRI safety – Fire:
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
MRI safety – clinical emergency in MRI
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
MRI safety key points:
Superconducting magnets are always on
Controlled areas are there for the safety of all users of the department
If you doubt - No entry
Controlled area door:
Always locked
Staff ID badge or keypad to unlock
Emergency exit
Patient prep area:
What are the steps before entering the controlled area
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
Magnet room preparation:
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
Patient preparation:
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
Control room:
Check the patient can hear over intercom
Would the patient like to listen to music
Warn of noises before commencing the scan
Blinds - privacy
What is spin wrap:
Radio-frequency – hydrogen – signal back
Gs – slice direction
Gr - readout direction
Gp - phase direction
Pulse - readout (signal)
2DFT image data collection:
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
Wraparound/aliasing artefact
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

Image artefacts in MRI
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
What can Radiographers operating and MR system use to reduce certain artefacts such as:
blood flow
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.
What can Radiographers operating and MR system use to reduce certain artefacts such as:
Peristalsis
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.
What can Radiographers operating and MR system use to reduce certain artefacts such as:
respiratory movement
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.
navigator trigger:
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.
What can Radiographers operating and MR system use to reduce certain artefacts such as:
cardiac motion
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)
