MR safety Flashcards
What are the criteria for an object to be labelled as MR Safe?
Poses no hazard in MR Environment
electrically non-conductive, non-magnetic and non-metallic
How can I reduce SAR?
Use 1.5 T over 3 T
Reduce flip angle
Use low SAR pulses
Increase repetition time
Use GRE over SE
Reduce # slices
Increase parallel imaging factor
Reduce turbo factor for TSE
What are the time varying magnetic field criteria for normal mode?
dB/dt < 80% of median threshold for PNS
PNS may be experienced
What are the time varying magnetic field criteria for controlled mode?
dB/dt 80-100% of median threshold for PNS
PNS may be painful
What are the risks and associated risk factors associated with Gadolinium -based contrast agents?
Adverse effects are generally mild, but allergic reactions can occur. Nephronic Systemic Fibrosis risk factors include high dose, choice of agent, and poor kidney function.
What is a stent used for?
keep arteries open
How is a stent delivered?
catheter with balloon
How does magnetic torque relate to static field strength?
tau = mu X B
tau \propto B0^2
How does magnetic force relate to spatial field gradient and static field strength?
F \propto dB/dz * B
What is a Vagus Nerve Stimulator (VNS) used for?
Generator in chest, leads to vagus nerve in neck.
Treats epilepsy, depression, hypertension and heart failure.
Which Regs place requirements on implant manufacturers?
MDR
How is magnetic force on implant tested in ASTM F2052?
suspend from string
measure angular displacement
How is magnetic torque on implant tested in ASTM F2213?
stick in bore on surface with known friction coeff
watch for rotation
What does ASTM F2503 contain?
implant labelling reqs
What does ASTM F2119 say about implant artefact characterisation?
SE with and without implant.
artefact = 30% change in intensity
Measure from implant edge to artefact fringe.
