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MRSO - RADIO FREQUENCY - MODULE 4 Questions and Answers 100% Accurate
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MRSO - RADIO FREQUENCY - MODULE 4
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MRSO - RADIO FREQUENCY - MODULE4
Purpose of RF (B1) field - answer excite hydrogen protons
RF energy is absorbed by tissues - answer within the volume of the RF transmit coil.
This is a thermogenic process.
Thermogenic process - answer Results in production of heat. Ex: RF energy absorption
MRI local and whole-body tissue heating is due to - answer magnetic induction
Types of RF coil designs - answer-linearly polarized
-circularly polarized (quadrature)
Function of coils - answer-transmit only
-receive only
-transmit/receive
Most common type of coil used - answer receive only
Integrated body coils are capable of functioning - answer-as transmit/receive coil
-as transmit only coil
When receive only coil is used, RF energy is transmitted by - answer the integrated
body coil
Modern integrated body coils are - answer circularly polarized
Quadrature mode - answer-some 3T systems have option
-Advantage: dielectric shading reduction
-safety considerations with implants/devices
RF Power Distribution Maps - answer-specific to vendor and transmit coil
-graph: horizontal axis represents z
-100% power is at isocenter (distance from isocenter should be identical on each side)
-measured in cm
-used for vendor integrated transmit coil only, not transmit/receive head or knee coil
Purpose of RF Power Distribution Map - answer determine percentage of RF frequency
power at a given location within the volume of the radiofrequency transmit coil
, -if metal item can not be removed, this map would be useful.
The further from isocenter, the _______ the RF power exposure - answerless
Radiofrequency definition - answer electromagnetic radiation with oscillating electric and
magnetic fields that range from 3 kHz to 300 gHz
Clinically approved MRI systems imaging hydrogen utilize radio frequencies ranging
from approximately - answer43 mHz at 1T to 298 mHz at 7T
Radio frequency is applied in - answer short bursts (pulses)
Only the _________ rotating component of the magnetic (B) field is used to excite the
protons - answer positive
When determining RF energy, strength of magnetic field is measured in – answer MT
Main biological effect of exposing tissue to electromagnetic radiation in that frequency
range - answer tissue heating
Cause of tissue heating - answer Magnetic induction results in eddy currents of
conductive tissue
Tissue heating is mostly ______________ with very little _______________ - answer
peripheral , deep body heating
How patient dissipates RF power - answer cooling.
If the input is greater than the output, heating occurs.
SAR (specific absorption rate) – answer RF power absorbed per unit mass of tissue
SAR is SPECIFIC to: - answer body part and tissue
SAR represents – answer ABSORPTION of RF into the body/tissues
SAR is the – answer RATE of RF exposure and absorption
SAR is measured in - answer watts/kg
SAR is proportional to: - answer-the power of 2 for system's resonant frequency (factor
of 4)
-the power of 2 for B1 amplitude of RF field (doubling flip angle with increase SAR by
factor of 4)
-the power of 5 for the pt's circumference
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