MRI in Practice: Ch. 1 Basic Principle

Question 1

MR active nuclei have:

a. angular momentum
b. forward momentum
c. angular proportion
d. forward proportion

Answer 1

a. Angular momentum.

Question 2

The law of electromagnetic induction refers to three individual forces. What are they?

Answer 2

Motion, magnetism and charge.

If two of these are present, the third is induced.

Question 3

What is the isotope of the hydrogen nucleus?

a. protium
b. potassium
c. palium
d. protalia

Answer 3

a. protium

The isotope of the hydrogen nucleus is protium. This is the MR active nucleus used in MRI.

Question 4

True or false? The magnetic moment has vector properties?

Answer 4

True. It has size and direction and is denoted by an arrow.

Question 5

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

Answer 5

c. Parallel, spin up.

Question 6

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

Answer 6

d. Anti- parallel, spin down

Question 7

In thermal equilibrium there are always fewer ___ energy nuclei than ____ energy nuclei.

a. high, low
b. low, high

Answer 7

a. high, low

The excess of low energy produces a NMV

Question 8

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

Answer 8

The magnitude of NMV is larger at high field strengths than low field strengths resulting in improved signal

Question 9

What is the NMV?

Answer 9

The net magnetic vector. This reflects the relative balance of spin-up and spin-down nuclei

Question 10

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

Answer 10

a. The spin or wobble of the magnetic moments of hydrogen around B0

This spin is precession

Question 11

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

Answer 11

b. The circular path that the magnetic moments of hydrogen wobble around B0.

Question 12

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

Answer 12

c. The speed at which magnetic moments of hydrogen wobble around B0

Question 13

What unit is precessional frequency measured in?

a. Megahertz (MHz)
b. Megahertz/ Tesla (MHz/T)
c. Tesla (T)
d. Tesla/ Megahertz (T/MHz)

Answer 13

a. Megahertz (MHz)

Question 14

What is the Larmor equation?

Answer 14

ω0 = B0 x λ

ω0 = precessional frequency
B0 = magnetic field strength
λ = gyromagnetic ratio

Question 15

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

Answer 15

a. 68.86

ω0 = B0 x λ
ω0 = 1.5T x 42.57 MHz/T
ω0 = 68.86

Question 16

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

Answer 16

d. RF pulse of energy at larmor frequency is applied

Question 17

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

Answer 17

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

Question 18

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

Answer 18

b. transverse

Question 19

When resonance occurs the magnetic moments of hydrogen move

a. into phase with each other
b. out of phase with each other

Answer 19

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.

Question 20

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.

Answer 20

True

Question 21

The process by which hydrogen nuclei lose energy is called _______.

a. relaxation
b. excitation
c. resonance
d. charge

Answer 21

Relaxation

T1 relaxation = recovery of longitudinal

T2 relaxation results = loss of coherent transverse magnetization

Question 22

Which recovery is the recovery of longitudinal magnetization?

a. T2 recovery
b. T1 recovery

Answer 22

b. T1 recovery

Also called spin- lattice relaxation

T1 relaxation time = time it takes 63% of the longitudinal magnetization to recover

Question 23

Which decay is the decay of transverse magnetization?

a. T2 decay
b. T1 decay

Answer 23

a. T2 decay

Also called spin-spin relaxation

T2 relaxation time= time it takes 63% of the transverse magnetization to be lost (37% remains)

Question 24

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

Answer 24

TR = Repetition Time

b. The time between the applied RF pulse to the application of the next RF pulse