Biomedical Imiaging MRI L5

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What are the desirable properties of a magnet
- Strong field strength(tesla
- Uniform field (ppm)
- stable field (ppm/hr)
- Good patient access and comfort
- Low operating cost (eg cryogenic consumption/hr)
- Small scanner footprint
What are the magnet types
- Superconducting
- Most common
- 1.5T most common
- Very stable
- cryogenic running costs-liquid helium
- Permanent
- No running costs
- always on
- But limited to 02-0.3T
- Resistive
- Can turn on/off
- But limited to 0.2-0.3 T
- Field not so stable
- Costs of electricity/cooling
Why would you want a high field strength
- High spatial resolution: More signal from each pixel means each pixel can be smaller
- High temporal resolution: More signal per unit time means images can be acquired faster
What are the problems with High field strength
- Increased chemical shift and artefact susceptibility
- Increased purchasing and siting costs
- Increased Safety concerns
What be dem trade-offs for magnet design?
- clinically useful imaging volume with good image quality
- Magnet diameter
- Length
- Cost
What benefits does a high amplitude gradient give
- Better resolution
- Less distortion
What benefit does a high slew rate gradient give
- Faster sequences
- Shorter TEs (more signal)
What are gradient performances measured in
- Amplitude
- Slew rate ( how fast amplitude is reached)
- How linear gradient is over space
- How often the gradient on/off switching can be repeated.
What this

Gradient coil
What this

RF coil (transmiter)
What this

Receiver coil
What this

Receiver surface coil
How does phased array coil work

Surface coils are combined like
What are the main components of an MRI
- Magnet
- RF transmitter
- RF receiver
- Gradients
- Computer system
What are the main sources of hazards of an MRI
- Main field
- Gradient field
- RF field
- Acoustic noise
Give some Main field hazards
- Missile effect
- Torque effect
Gradient field hazards
- Can induce currents in body
- Can cause magnetophosphenes
Give some RF safety precautions
- Scanner calculates SAR (W/kg)(scanner absorption rate) as to not exceed it
- Insulate coils from patient
- Remove jewellery from patient
- No skin-skin contact loops
- Check coils are functioning properly
Hazrds from RF field
- Tissue heating
- Burns which go deep
Hazards from acoustic noise

Can cause temporary deafness

Author

keesukim

340166

Card Set

Biomedical Imiaging MRI L5

Description

MRI5 safety and stuff

Updated

2018-05-12T22:01:03Z

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