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MRSO - RADIO FREQUENCY - MODULE 4 questions and answers rated A+ 2024/2025
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MRSO - RADIO FREQUENCY - MODULE 4 questions and answers rated A+ 2024/2025
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MRSO - RADIO FREQUENCY - MODULE4
Purpose of RF (B1) field - ANSexcite hydrogen protons
RF energy is absorbed by tissues - ANSwithin the volume of the RF transmit coil. This is a
thermogenic process.
Thermogenic process - ANSResults in production of heat. Ex: RF energy absorption
MRI local and whole-body tissue heating is due to - ANSmagnetic induction
Types of RF coil designs - ANS-linearly polarized
-circularly polarized (quadrature)
Function of coils - ANS-transmit only
-receive only
-transmit/receive
Most common type of coil used - ANSreceive only
Integrated body coils are capable of functioning - ANS-as transmit/receive coil
-as transmit only coil
When receive only coil is used, RF energy is transmitted by - ANSthe integrated body coil
Modern integrated body coils are - ANScircularly polarized
Quadrature mode - ANS-some 3T systems have option
-Advantage: dielectric shading reduction
-safety considerations with implants/devices
RF Power Distribution Maps - ANS-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 - ANSdetermine 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 - ANSless
Radiofrequency definition - ANSelectromagnetic 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 - ANS43 mHz at 1T to 298 mHz at 7T
Radio frequency is applied in - ANSshort bursts (pulses)
Only the _________ rotating component of the magnetic (B) field is used to excite the protons -
ANSpositive
When determining RF energy, strength of magnetic field is measured in - ANSmT
Main biological effect of exposing tissue to electromagnetic radiation in that frequency range -
ANStissue heating
Cause of tissue heating - ANSMagnetic induction results in eddy currents of conductive tissue
Tissue heating is mostly ______________ with very little _______________ - ANSperipheral ,
deep body heating
How patient dissipates RF power - ANScooling.
If the input is greater than the output, heating occurs.
SAR (specific absorption rate) - ANSRF power absorbed per unit mass of tissue
SAR is SPECIFIC to: - ANSbody part and tissue
SAR represents - ANSABSORPTION of RF into the body/tissues
SAR is the - ANSRATE of RF exposure and absorption
SAR is measured in - ANSwatts/kg
SAR is proportional to: - ANS-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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