MRI Physics Questions And Answers 2025
In general terms, how does MRI work? - Correct Answer-the active nuclei (that DO NOT contain
an equal number of protons/neutrons) "spin" in the magnetic field
- they are slapped down with an RF pulse and then watched for how fast they get back up
- difference between how fast different protons bounce up is the "contrast" used to tell things
apart
MRI uses a _________ ________ to describe which direction the protons are pointing - Correct
Answer-Coordinate system
Protons aligned in the direction of the external magnet field is called ______
- what axis? - Correct Answer-longitudinal magnetiziation
- aka "Z axis"
- default setting when someone is in the magnet
Protons aligned perpendicular to the direction of the external magnet field is called ______
- what axis? - Correct Answer-transverse magnetiziation
- X-Y axis
___ = radiowave used to knock protons down - Correct Answer-RF pulse (90 degrees)
- this pulse is a radio wave
RF pulse establishes (longitudinal/transverse) magnetization. - Correct Answer-transverse
,Radio waves are (low/high) energy and have a (shorter/longer) wavelength than x-rays. - Correct
Answer-- low energy (low frequency)
- longer wavelength
Are radio waves ionizing? - Correct Answer-NO!
how do you know how fast protons are spinning? - Correct Answer-Larmour frequency
equation for larmour frequency - Correct Answer-w = yB
w = precession frequency (how fast protons are spinning)
y - gyromagnetic ratio (constant)
B - external magnetic field strength (Tesla)
____ describes the precession frequency of a nuclear magnetic moment and resonant
frequency of a nucleus and relates these to the magnetic field strength - Correct Answer-
larmour equation
how does field strength affect precession frequency - Correct Answer-Increase field strength -->
increase precession frequency
two things that RF pulse does - Correct Answer-1. decreases longitudinal magnetization (z axis)
2. causes protons to sync up and precess in phase (thus establishing a transverse magnetization
- xy axis)
when can signal be measured - Correct Answer-NOT in lognitduinal direction
- not in the default magnetization field
, two names for T1 - Correct Answer-Longitudinal relaxation
- time it takes for protons to re-orient in the longitudinal (default) orientation of the magnetic
field
Spin-lattice relaxation
- energy from the RF pulse is handed over to the surrounding lattice
T1 relaxation involves the exchange of _______ energy. - Correct Answer-thermal
spin-lattice relaxation is T1 or T2? - Correct Answer-T1
T1 is defined as the time at which longitudinal magnetization is ___% of its final value - Correct
Answer-63%
Short T1 = (bright/dark)?
Long T1 = (bright/dark)? - Correct Answer-Short T1 = bright
Long T1 = dark
"intrinsic T1 shortening" is something that is (bright/dark) on T1 - Correct Answer-bright
how does field strength affect T1 - Correct Answer-Stronger field strength (stronger magnet) -->
longer T1
- higher field strength means more energy for protons which precess faster and take longer to
recover
two other names for T2 - Correct Answer-spin-spin relaxation
In general terms, how does MRI work? - Correct Answer-the active nuclei (that DO NOT contain
an equal number of protons/neutrons) "spin" in the magnetic field
- they are slapped down with an RF pulse and then watched for how fast they get back up
- difference between how fast different protons bounce up is the "contrast" used to tell things
apart
MRI uses a _________ ________ to describe which direction the protons are pointing - Correct
Answer-Coordinate system
Protons aligned in the direction of the external magnet field is called ______
- what axis? - Correct Answer-longitudinal magnetiziation
- aka "Z axis"
- default setting when someone is in the magnet
Protons aligned perpendicular to the direction of the external magnet field is called ______
- what axis? - Correct Answer-transverse magnetiziation
- X-Y axis
___ = radiowave used to knock protons down - Correct Answer-RF pulse (90 degrees)
- this pulse is a radio wave
RF pulse establishes (longitudinal/transverse) magnetization. - Correct Answer-transverse
,Radio waves are (low/high) energy and have a (shorter/longer) wavelength than x-rays. - Correct
Answer-- low energy (low frequency)
- longer wavelength
Are radio waves ionizing? - Correct Answer-NO!
how do you know how fast protons are spinning? - Correct Answer-Larmour frequency
equation for larmour frequency - Correct Answer-w = yB
w = precession frequency (how fast protons are spinning)
y - gyromagnetic ratio (constant)
B - external magnetic field strength (Tesla)
____ describes the precession frequency of a nuclear magnetic moment and resonant
frequency of a nucleus and relates these to the magnetic field strength - Correct Answer-
larmour equation
how does field strength affect precession frequency - Correct Answer-Increase field strength -->
increase precession frequency
two things that RF pulse does - Correct Answer-1. decreases longitudinal magnetization (z axis)
2. causes protons to sync up and precess in phase (thus establishing a transverse magnetization
- xy axis)
when can signal be measured - Correct Answer-NOT in lognitduinal direction
- not in the default magnetization field
, two names for T1 - Correct Answer-Longitudinal relaxation
- time it takes for protons to re-orient in the longitudinal (default) orientation of the magnetic
field
Spin-lattice relaxation
- energy from the RF pulse is handed over to the surrounding lattice
T1 relaxation involves the exchange of _______ energy. - Correct Answer-thermal
spin-lattice relaxation is T1 or T2? - Correct Answer-T1
T1 is defined as the time at which longitudinal magnetization is ___% of its final value - Correct
Answer-63%
Short T1 = (bright/dark)?
Long T1 = (bright/dark)? - Correct Answer-Short T1 = bright
Long T1 = dark
"intrinsic T1 shortening" is something that is (bright/dark) on T1 - Correct Answer-bright
how does field strength affect T1 - Correct Answer-Stronger field strength (stronger magnet) -->
longer T1
- higher field strength means more energy for protons which precess faster and take longer to
recover
two other names for T2 - Correct Answer-spin-spin relaxation
