Systems and Safety: MR Hardware and Fields Flashcards
What is the frequency of the radiofrequency wave required to move a proton from the spin-up to the spin-down state called?
the Lamor or Resonance Frequency
What is the range of amplitudes for clinical MR static magnetic fields?
0.2 - 7 T
What is the range of amplitudes for the static spatial field gradient in clinical MRI?
0 - 25 T/m
What are the amplitude, duration, and frequency ranges for the imaging gradients?
0 - 80 mT/m, 0 - 10kHz, 0 - 10 ms
What are the amplitude, duration, and frequency ranges for the rf transmit field, B1?
0 - 50 ut, 8 - 300 MHz, 0 - 10 ms
What is the unit of magnetic flux density?
Tesla
What is the unit of magnetic field strength?
Amperes per metre
How are magnetic flux density and magnetic field strength related?
B = u0 x H
Where are the magnetic field lines most dense and uniform?
Inside the bore
What is the fringe field spatial gradient?
The amount the fringe field decreases as a function of distance.
What hazard is the fringe filed spatial gradient reposinable for?
The projectile hazard
How does shielding affect the spatial gradient fringe field?
Compresses it, stronger spatial gradient, closer to the bore
How is the flip angle related to the area under the curve of the the waveform that produces it?
They are equal
Is the peak B1 amplitude alone enough to determine the flip angle?
No, it depends on the pulse shape and duration
How does B0 affect the flip angle from the same B1 pulse?
B0 has no effect on the flip angle of the B1 pulse.
What does the + stand for in B1+rms?
The + refers to the rotational component of B1 responsible for excitation of the magnetisation. An efficient coil should not produce B1-
What 4 factors does B1+rms depend on?
Flip Angle
Number of RF pulses (echoes, slices etc)
RF Pulse Shape
TR
What is the definition of the Normal Mode of Scanning?
Outputs have a value that may cause physiological stress to patients?
What is the definition of the First-Level Mode of Scanning?
One or more outputs reach a value that may cause physiological stress to patients that needs to be controlled by medical supervision.
What is the minimum restriction required for entering first-level controlled mode?
Software must require specific acknowledgement from the operator to enter.
What is the definition of the First-Level Mode of Scanning?
One or more outputs reach a value that may cause significant risks to patients that needs explicit ethical approval.
What is the definition of MR Safe?
The device poses no known risks in the MR environment. It must be non-metallic, non-magnetic, and non-conductive.
What is the definition of MR Conditional?
The device poses no additional rusks when introduced to the MR Environment as long as stated conditions are followed.
What is the definition of MR Unsafe?
The device cannot be introduced into the MR Environment as it poses significant risk to patients and/or staff.
What is the definition of MR Unlabelled?
A device without and MR Safety Label.
