MRI in Practice: Ch. 1 Basic Principle Flashcards
MR active nuclei have:
a. angular momentum
b. forward momentum
c. angular proportion
d. forward proportion
a. Angular momentum.
The law of electromagnetic induction refers to three individual forces. What are they?
Motion, magnetism and charge.
If two of these are present, the third is induced.
What is the isotope of the hydrogen nucleus?
a. protium
b. potassium
c. palium
d. protalia
a. protium
The isotope of the hydrogen nucleus is protium. This is the MR active nucleus used in MRI.
True or false? The magnetic moment has vector properties?
True. It has size and direction and is denoted by an arrow.
Low-energy nuclei align their magnetic moments _____ to the external magnetic field and are known as _______.
a. anti-parallel, spin up
b. parallel, spin down
c. parallel, spin up
d. anti-parallel, spin down
c. Parallel, spin up.
High- energy nuclei align their magnetic moments _____ to the external magnetic field and are known as _____.
a. anti-parallel, spin up
b. parallel, spin down
c. parallel, spin up
d. anti-parallel, spin down
d. Anti- parallel, spin down
In thermal equilibrium there are always fewer ___ energy nuclei than ____ energy nuclei.
a. high, low
b. low, high
a. high, low
The excess of low energy produces a NMV
Is the magnitude of NMV larger at high field strengths or low field strengths?
a. Low field strengths
b. High field strengths
c. Not impacted by field strength
d. NMV does not have magnitude
The magnitude of NMV is larger at high field strengths than low field strengths resulting in improved signal
What is the NMV?
The net magnetic vector. This reflects the relative balance of spin-up and spin-down nuclei
What is precession?
a. The spin or wobble of the magnetic moments of hydrogen around B0
b. The circular path that the magnetic moments travel
c. The speed at which the magnetic moments travel around B0
a. The spin or wobble of the magnetic moments of hydrogen around B0
This spin is precession
What is the processional path?
a. The spin or wobble of the magnetic moments of hydrogen around B0
b. The circular path that the magnetic moments travel
c. The speed at which the magnetic moments travel around B0
b. The circular path that the magnetic moments of hydrogen wobble around B0.
What is the processional frequency?
a. The spin or wobble of the magnetic moments of hydrogen around B0
b. The circular path that the magnetic moments travel
c. The speed at which the magnetic moments travel around B0
c. The speed at which magnetic moments of hydrogen wobble around B0
What unit is precessional frequency measured in?
a. Megahertz (MHz)
b. Megahertz/ Tesla (MHz/T)
c. Tesla (T)
d. Tesla/ Megahertz (T/MHz)
a. Megahertz (MHz)
What is the Larmor equation?
ω0 = B0 x λ
ω0 = precessional frequency
B0 = magnetic field strength
λ = gyromagnetic ratio
The gyromagnetic ratio of hydrogen is 42.57 MHz/T. At 1.5 T what is the precessional frequency?
a. 68.86 MHz
b. 42.57 MHz
c. 21.28 MHz
d. 127.71 MHz
a. 68.86
ω0 = B0 x λ
ω0 = 1.5T x 42.57 MHz/T
ω0 = 68.86
How does excitation of hydrogen occur?
a. Nucleus exposed to magnetic field > 1.5 T
b. nucleus is exposed to external magnetic field
c. RF pulse of energy at any frequency is applied
d. RF pulse of energy at larmor frequency is applied
d. RF pulse of energy at larmor frequency is applied
One of the results of resonance is that the NMV moves
a. Out of alignment away from B0
b. Into alignment with B0
c. parallel to B0
a. Out of alignment with B0
As the NMV reflects the balance between the low and high - energy populations, resonance causes the NMV to no longer lie parallel to B0 but at an angle to it. The angle to which the NMV moves out of alignment is called the flip angle
With a flip angle of 90 ° the nuclei are given sufficient energy so that the longitudinal NMV is completely transferred into a _____ NMV.
a. longitudinal
b. transverse
b. transverse
When resonance occurs the magnetic moments of hydrogen move
a. into phase with each other
b. out of phase with each other
When resonance occurs the magnetic moments of hydrogen nuclei move into phase with each other.
Magnetic moments that are in phase (or coherent ) are in the same place on the precessional path around B 0 at any given time.
True or false:
Magnetic moments that are in phase (or coherent ) are in the same place on the precessional path around B0 at any given time.
True
The process by which hydrogen nuclei lose energy is called _______.
a. relaxation
b. excitation
c. resonance
d. charge
Relaxation
T1 relaxation = recovery of longitudinal
T2 relaxation results = loss of coherent transverse magnetization
Which recovery is the recovery of longitudinal magnetization?
a. T2 recovery
b. T1 recovery
b. T1 recovery
Also called spin- lattice relaxation
T1 relaxation time = time it takes 63% of the longitudinal magnetization to recover
Which decay is the decay of transverse magnetization?
a. T2 decay
b. T1 decay
a. T2 decay
Also called spin-spin relaxation
T2 relaxation time= time it takes 63% of the transverse magnetization to be lost (37% remains)
What is TR?
a. The time between an applied RF pulse to the peak of the signal induced in the coil
b. The time between the applied RF pulse to the application of the next RF pulse
c. The amount of echo trains between applied RF pulses
d. The number of excitations
TR = Repetition Time
b. The time between the applied RF pulse to the application of the next RF pulse
