Week 6 Flashcards
Types of MR safety rooms are __
safe, conditional, hazard
what does magnet do
Patient placed within static magnetic field to align H+
what does RF coils do
- RF energy direct to patients to produce a signal
- Antennas of the MRI to transmit & receive signal
what does gradient coils do
- Creates own magnetic field via current
- Rapidly switching polarity allows for spatial localisation
SSG, FEG, PEG
- Single slice gradient
- Frequency encoding gradient
- Phase encoding gradient
what is K-spaces
- Data info collected during scan
- Does not represent specific pixel in final image
- Each data point represents signal coming from entire slice selected
static magnetic field causes __
translational & torque force
Force of attraction between magnet & ferromagnetic object is determined by
- Magnetic field strength
- Magnetic susceptibility of object
- Mass
- Distance from magnet
- Field orientation
biological forces of static magnetic field
- Magnetophosphenes = light flashes
- Dizziness & nausea = induction of current in nerve
- Magnetohydrodynamic effects = elevated voltage & T-wave
conditions when quenching is allowed
- Someone in life-threatening situation
- Fire & SCDF needs access to room
- Equipment stuck to magnet and unable to be removed manually
- Patient collapsed and needs resuscitation
how is RF measured
Energy deposited to body as heat which is measured as SAR which is dependent on patient height & weight
Thermal load depends on __
- Type of RF pulse
- scan room temperature
- room ventilation
- humidity
Patient with compromised thermal regulatory ability are __
- Diabetes
- impaired heart function
- hypertension
- implants
- tattoos
- fever
gradient magnet causes __
- PNS
- Rapidly switching magnetic field
- Muscular twitching
- Nerve are good conductors
why is hearing protection is needed
Gradient magnet creates acoustic noise (100 – 120dB) due to vibrations
patient preparation for MRI
- Safety screening
- Declare implants / ferromagnetic objects
- Previous operations
- FB
- allergies
- serum creatinine
what is the property of MRI contrast agent
paramagnetic
MRI contrast agent enhances __
T1 relaxation = good for imaging vessels
MRI contrast agent is __ based
gadolinium
patient positioning during the scan
- Hearing protection given
- Warned of warm sensation
- Keep hands and legs separated during scan
- Do not cross hands and/or legs during scan
- Spacer pad placed between thighs to separate legs
- Call bell given to them and to squeeze if any discomfort occurs
what is the purpose of a localiser
3D plane localiser done to plan sequences and usually less than 25s
how to increase signal intensity
- Increases B0
- Larger voxel sizes
- Higher averages
- Narrower receiver bandwidth
SNR is ___ proportional to pixel size
directly
extending TR beyond a limit will result in __
T1 effect
what are the effects of MRI on fetus
inconclusive but must evaluate risks vs benefits
macrocyclic MRI contrast agents are favoured due to
- Less likely to cause adverse reactions
- More stable by reducing gadolinium retention
- Provides better image contrast
STIR
short term inversion recovery
what happens if the resolution is too high or low
too high = graininess
too low = blurriness
how does increasing TR increase SNR
allows longitudinal magnetization to recover and generate higher signal intensities
