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MRI Physics > Chapter 1 > Flashcards

Chapter 1 Flashcards

1
Q

What are the two main ways to explain MRI principles?

A

Classical Theory (Newtonian): Uses mass, spin, and angular momentum.
Quantum Theory (Planck, Einstein, Dirac): Explains MRI at the subatomic level, focusing on energy levels of protons, neutrons, and electrons.

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2
Q

Why is classical theory used more often in MRI explanations?

A

Because it is easier to understand than quantum mechanics for describing large-scale MRI concepts.

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3
Q

What are the two ways to characterize an atom?

A

Atomic number = Number of protons in the nucleus (defines chemical identity).
Mass number (atomic weight) = Sum of protons + neutrons in the nucleus.

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4
Q

What are isotopes?

A

Atoms with the same number of protons but a different number of neutrons.

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5
Q

What are the charges of atomic particles?

A

Protons = Positive charge (+1).
Neutrons = No charge (neutral).
Electrons = Negative charge (-1).

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6
Q

What are ions?

A

Atoms that have lost or gained electrons, becoming electrically unstable.

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7
Q

What are the three types of atomic motion?

A
  1. Electrons spinning on their own axis.
  2. Electrons orbiting the nucleus.
  3. Nucleus spinning about its own axis.
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8
Q

What determines whether an atomic nucleus has spin?

A

Even atomic and mass number → No net spin (e.g., Carbon-12).
Odd atomic/mass number → Has spin (e.g., Hydrogen-1, Oxygen-17).

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9
Q

What are MR-active nuclei?

A

Nuclei that have angular momentum (spin) and a net electrical charge, allowing them to interact with a magnetic field.

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10
Q

What law explains how MR-active nuclei acquire a magnetic field?

A

Faraday’s Law of Electromagnetic Induction – A moving electric charge creates a magnetic field.

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11
Q

What are examples of MR-active nuclei?

A

¹H (Hydrogen), ¹³C (Carbon), ¹⁵N (Nitrogen), ¹⁷O (Oxygen), ¹⁹F (Fluorine), ²³Na (Sodium).

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12
Q

Why is hydrogen used in MRI?

A

Most abundant element in the human body.
Single proton gives it a large magnetic moment.

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13
Q

What is Faraday’s Law of Electromagnetic Induction?

A

A moving electric charge (like a spinning hydrogen proton) creates a magnetic field.

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14
Q

How is the hydrogen nucleus represented in MRI diagrams?

A

As an arrow called the magnetic moment:
Length = Magnitude of magnetic field.
Direction = Alignment with the external magnetic field (B₀).

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15
Q

What happens to hydrogen nuclei when placed in a strong external magnetic field (B₀)?

A

Their magnetic moments align with the field, a process called alignment.

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16
Q

What are the two types of alignment?

A

Parallel alignment (spin-up) → Low-energy state (aligned with B₀).
Antiparallel alignment (spin-down) → High-energy state (opposed to B₀).

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17
Q

What determines the number of energy states a nucleus can have?

A

Equation: Number of energy states = 2S + 1 (S = Spin quantum number).
For hydrogen (S = ½): 2(½) + 1 = 2 energy states (parallel and antiparallel).

The spin quantum number can only be two numbers:

  1. +½ → This means the electron is spinning up (↿).
  2. -½ → This means the electron is spinning down (⇂).
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18
Q

What is Zeeman Interaction?

A

The process where protons couple with the external magnetic field (B₀), resulting in two distinct energy states.

spin up or spin down

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19
Q

What is the net magnetic vector (NMV)?

A

The sum of all magnetic moments in the body, representing the small excess of spin-up nuclei in alignment with B₀.

there are always more magnetic moments parellel than anti parallel

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20
Q

Why does the NMV align with B₀?

A

Because there are always more spin-up nuclei than spin-down nuclei, creating a measurable net magnetization in the longitudinal (z-axis) direction.

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21
Q

What is the most abundant element in the body?

A

Hydrogen.

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22
Q

Which nuclei are used in MRI?

A

Nuclei with a net spin.

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23
Q

Why do spinning nuclei create a magnetic field?

A

Due to Faraday’s Law (a moving charge induces a magnetic field).

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24
Q

How is a nucleus’s magnetic field represented?

A

By a magnetic moment (arrow).

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25
Q

According to Avogadro’s law, how many molecules are present per gram of tissue?

A

6 × 10²³ molecules per gram of tissue

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26
Q

How many excess spins are present per gram of tissue?

A

6 × 10¹⁷ excess spins per gram of tissue

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27
Q

How does increasing B₀ affect the number of spin-up (low-energy) and spin-down (high-energy) nuclei?

A

Increasing B₀ increases the number of spin-up (low-energy) nuclei and decreases the number of spin-down (high-energy) nuclei

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28
Q

What is the equation for the ratio of spin-up (N⁺) to spin-down (N⁻) populations?

A

N⁺ / N⁻ = e^(-ΔE / kT)

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29
Q

What does the variable ΔE represent in the Boltzmann equation?

A

The energy difference between high- and low-energy populations (in Joules)

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30
Q

What is the value of Boltzmann’s constant (k)?

A

1.381 × 10⁻²³ J/K

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31
Q

Why does SNR increase at higher B₀ values?

A

Higher B₀ increases the NMV, leading to a greater signal-to-noise ratio (SNR)

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32
Q

What is precession?

A

The wobbling motion of magnetic moments around B₀ due to its influence

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33
Q

What is the Larmor frequency (ω₀)?

A

The rate at which magnetic moments precess around B₀

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34
Q

What is the equation for Larmor frequency?

A

ω₀ = γB₀

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35
Q

What does the gyromagnetic ratio (γ) represent?

A

The relationship between angular momentum and the magnetic moment of MR-active nuclei

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36
Q

What are the units of Larmor frequency?

A

Megahertz (MHz)

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37
Q

What is the gyromagnetic ratio of hydrogen?

A

42.58 MHz/T

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38
Q

What is the precessional frequency of hydrogen at 1.5T?

A

63.87 MHz (42.58 × 1.5)

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39
Q

What is the precessional frequency of hydrogen at 1.0T?

A

42.58 MHz (42.58 × 1.0)

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40
Q

What is the precessional frequency of hydrogen at 0.5T?

A

21.29 MHz (42.58 × 0.5)

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41
Q

What is the precessional frequency of hydrogen at 3.0T?

A

127.74 MHz (42.58 × 3.0)

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42
Q

What is the gyromagnetic ratio of ¹³C (carbon-13)?

A

10.71 MHz/T

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43
Q

What is the precessional frequency of carbon at 1.5T?

A

16.06 MHz (10.71 × 1.5)

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44
Q

What is the gyromagnetic ratio of ¹⁵N (nitrogen-15)?

A

4.32 MHz/T

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45
Q

What is the precessional frequency of nitrogen at 1.5T?

A

6.48 MHz (4.32 × 1.5)

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46
Q

Why is hydrogen (¹H) primarily used in MRI instead of other MR-active nuclei?

A

It has the highest abundance in the body and a large magnetic moment

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47
Q

What does phase refer to in MRI?

A

The position of magnetic moments on their precessional path at any moment in time

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48
Q

What does out of phase (incoherent) mean?

A

Magnetic moments of hydrogen are at different places on the precessional path

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49
Q

What does in phase (coherent) mean?

A

Magnetic moments of hydrogen are at the same place on the precessional path

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50
Q

What happens to precessional frequency when B₀ is increased?

A

Larmor frequency increases proportionally

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51
Q

How does the Larmor equation explain the specificity of MRI?

A

Different MR-active nuclei have unique gyromagnetic ratios, allowing MRI to selectively image hydrogen while ignoring other nuclei

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52
Q

What is the equation for calculating the ratio of spin-up to spin-down nuclei?

A

N⁺ / N⁻ = e^(-ΔE / kT)

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53
Q

What happens to the NMV when the external magnetic field (B₀) increases?

A

Increases

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54
Q

What is the gyromagnetic ratio of nitrogen-15?

A

4.32 MHz/T

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55
Q

Which of the following is NOT a correct description of precession?

A

It occurs due to thermal energy transfer

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56
Q

What is the precessional frequency of hydrogen at 1.5T?

A

63.87 MHz

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57
Q

What is resonance in MRI?

A

A phenomenon where a nucleus absorbs energy when exposed to an RF pulse at its Larmor frequency.

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58
Q

What happens if the applied RF pulse is not at the Larmor frequency of hydrogen?

A

Resonance does not occur, and the nucleus does not absorb energy.

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59
Q

Why do other MR-active nuclei not resonate with the RF pulse used for hydrogen imaging?

A

Their gyromagnetic ratios are different, leading to different precessional frequencies.

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60
Q

What is B₁ in MRI?

A

The weak oscillating magnetic field created by the RF excitation pulse, applied perpendicular to B₀.

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61
Q

How is B₁ different from B₀?

A

B₀ is a strong, static magnetic field, while B₁ is a weak, oscillating magnetic field applied at 90° to B₀.

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62
Q

According to classical theory, what happens when an RF excitation pulse is applied?

A

The NMV spirals from the longitudinal plane to the transverse plane (nutation).

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63
Q

What is nutation?

A

A spiral motion caused by the NMV transitioning from the longitudinal to the transverse plane.

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64
Q

According to quantum theory, what does RF excitation do?

A

It increases the number of high-energy (spin-down) hydrogen nuclei.

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65
Q

Why does the net effect of RF excitation result in energy absorption?

A

Because there are initially more low-energy spins, causing an overall shift toward high-energy states.

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66
Q

What happens to the phase of magnetic moments after RF excitation?

A

They become in-phase (coherent), leading to a detectable MRI signal.

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67
Q

What is Planck’s equation for energy absorption?

A

E = hω₀

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68
Q

What does the variable h represent in Planck’s equation?

A

Planck’s constant (6.626 × 10⁻³⁴ J/s).

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69
Q

How does increasing B₀ affect the energy required for resonance?

A

A stronger B₀ increases the energy difference (ΔE) between spin-up and spin-down states.

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70
Q

What happens to ω₀ (Larmor frequency) as B₀ increases?

A

ω₀ increases proportionally.

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71
Q

What is the relationship between B₀ and resonance frequency?

A

Higher B₀ leads to a higher resonance frequency, requiring a higher RF pulse frequency for excitation.

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72
Q

What is the typical flip angle for a 90° RF pulse?

A

π/2 radians.

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73
Q

What is the typical flip angle for a 180° RF pulse?

A

π radians.

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74
Q

How is flip angle calculated?

A

θ = γB₁τ

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75
Q

What happens to magnetization at a 90° flip angle?

A

The NMV is completely transferred into the transverse plane.

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76
Q

What happens at a 180° flip angle?

A

The NMV is completely inverted, saturating the system.

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77
Q

What is the principle behind MR signal generation?

A

Faraday’s Law of Electromagnetic Induction.

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78
Q

What does Faraday’s Law state?

A

A changing magnetic field induces an electromotive force (emf) in a closed circuit.

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79
Q

What equation describes electromagnetic induction?

A

ε = -N (dΦ/dt)

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80
Q

In the equation ε = -N (dΦ/dt), what does Φ represent?

A

Magnetic flux.

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81
Q

How is MR signal detected?

A

By placing a receiver coil in the path of precessing transverse magnetization.

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82
Q

What happens when the RF excitation pulse is turned off?

A

The NMV begins to realign with B₀, causing relaxation.

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83
Q

What is the Free Induction Decay (FID) signal?

A

A decaying MR signal induced in the receiver coil due to dephasing of spins.

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84
Q

What causes the loss of transverse magnetization after RF excitation?

A

Dephasing due to inhomogeneities in B₀ and spin-spin interactions.

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85
Q

Why does MR signal fade over time after excitation?

A

Due to transverse relaxation and spin dephasing.

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86
Q

What happens to the NMV as relaxation occurs?

A

It gradually returns to the longitudinal axis.

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87
Q

What must be true for resonance to occur in MRI?

A

The RF excitation pulse must match the Larmor frequency.

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88
Q

What is the role of B₁ in MRI?

A

It provides the oscillating field needed for resonance.

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89
Q

According to quantum theory, what happens during RF excitation?

A

The number of low-energy spins decreases.

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90
Q

What equation describes the energy difference between spin-up and spin-down states?

A

ΔE = hγB₀.

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91
Q

What happens to magnetization at a 180° flip angle?

A

The NMV is inverted, fully saturating the system.

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92
Q

What is the equation for calculating the flip angle?

A

θ = γB₁τ.

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93
Q

What happens when an RF pulse is applied at the Larmor frequency?

A

Resonance occurs, and hydrogen nuclei absorb energy, moving into a high-energy state.

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94
Q

What is excitation in MRI?

A

The net absorption of RF energy, causing a shift in spin populations and creating transverse magnetization.

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95
Q

What does the orientation of the Net Magnetic Vector (NMV) depend on?

A

The balance between spin-up (low-energy) and spin-down (high-energy) nuclei.

96
Q

What happens to the NMV when there are equal numbers of spin-up and spin-down nuclei?

A

It moves completely into the transverse plane (90° to B₀).

97
Q

Why do hydrogen nuclei need to be in-phase after excitation?

A

Coherent transverse magnetization is required to generate an MRI signal.

98
Q

How is an MR signal detected?

A

By placing a receiver coil in the transverse plane, where the rotating transverse magnetization induces a voltage.

99
Q

What happens to transverse magnetization when the RF pulse is turned off?

A

The spins begin to dephase, leading to Free Induction Decay (FID).

100
Q

What is Free Induction Decay (FID)?

A

The signal decay that occurs when transverse magnetization dephases after the RF pulse is turned off.

101
Q

What two factors contribute to FID?

A

B₀ inhomogeneities and spin-spin interactions (T₂ decay).

102
Q

Why does the MR signal fade over time after the RF pulse is removed?

A

Because of dephasing of spins, leading to a loss of coherent transverse magnetization.

103
Q

What does the rate of FID decay depend on?

A

T₂ relaxation time and magnetic field homogeneity.

104
Q

Why is FID not used directly for image formation?

A

It decays too quickly, making it unsuitable for capturing stable signals.

105
Q

What is a pulse sequence in MRI?

A

A series of RF pulses, signal acquisitions, and relaxation periods that generate an image.

106
Q

What does TR stand for in MRI?

A

Repetition Time – the time between successive RF excitation pulses for a slice.

107
Q

What does TR control?

A

The amount of T₁ relaxation that occurs before the next RF pulse is applied.

108
Q

What does TE stand for in MRI?

A

Echo Time – the time from the RF excitation pulse to the peak of the detected signal.

109
Q

What does TE control?

A

The amount of T₂ relaxation that has occurred when the signal is read.

110
Q

What unit are TR and TE measured in?

A

Milliseconds (ms).

111
Q

If TR is too short, what happens to T₁ contrast?

A

T₁ contrast increases because tissues do not fully recover before the next RF pulse.

112
Q

If TE is long, what kind of contrast is emphasized?

A

T₂-weighted contrast, highlighting tissues with long T₂ relaxation times.

113
Q

What is the purpose of an RF excitation pulse in MRI?

A

c) To induce resonance and create transverse magnetization.

114
Q

How is MR signal detected?

A

b) By the movement of transverse magnetization cutting through a receiver coil.

115
Q

Which of the following factors contributes to Free Induction Decay (FID)?

A

a) Inhomogeneities in B₀.

116
Q

What does repetition time (TR) determine?

A

b) The amount of longitudinal relaxation before the next RF pulse.

117
Q

If TE is long, what type of image contrast will be emphasized?

A

c) T₂-weighted contrast.

118
Q

What does TE control?

A

a) The amount of T₂ relaxation occurring before the signal is read.

119
Q

What is required for resonance to occur in MRI?

A

b) The applied RF pulse must match the Larmor frequency of hydrogen.

120
Q

What happens to the NMV when a 90° RF pulse is applied?

A

b) It shifts completely into the transverse plane.

121
Q

What happens when the RF pulse is turned off?

A

b) Spins gradually return to thermal equilibrium.

122
Q

Why is Free Induction Decay (FID) not used for image formation?

A

b) It decays too quickly.

123
Q

In what year did MRI receive FDA approval?

A

1985

124
Q

When did Felix Bloch and Edward Purcell receive the Nobel Prize for Physics for developing nuclear induction?

A

1952

125
Q

What was Raymond Damadian’s first human-sized MRI machine called?

A

Indomitable

126
Q

Who is credited with the first human body image in 1977?

A

Raymond Damadian

127
Q

One of the original names for MRI technology was NMR. What does NMR stand for?

A

Nuclear Magnetic Resonance

128
Q

Which two physicists first won a Nobel Prize in Physics for their development of nuclear induction?

A

Bloch and Purcell

129
Q

Define relaxation in MRI.

A

The process by which spins lose energy.

130
Q

The longitudinal plane is in which axis?

A

z-axis

131
Q

What is NMV?

A

Net Magnetic Vector

132
Q

Precessional frequency in MRI is measured in what unit?

A

MHz

133
Q

What is the Larmor equation used for?

A

To calculate precessional frequency

134
Q

What is the Larmor equation?

A

ω₀ = γB₀

135
Q

What is the gyromagnetic ratio of hydrogen at 3T?

A

127.74 MHz

136
Q

What does the NMV do as the main magnetic field strength increases?

A

It gets larger.

137
Q

According to Avogadro’s law, how many molecules exist per gram of tissue?

A

6 × 10²³ molecules per gram

138
Q

In MR imaging, the term “spin” refers specifically to the spinning of what?

A

Nuclei

139
Q

What is the small magnetic field created by the hydrogen proton called?

A

Magnetic moment

140
Q

Parallel alignment occurs when:

A

Protons are introduced into a magnetic field.

141
Q

What happens during the ‘excitation’ phase in an MRI scan?

A

The RF excitation pulse gives energy to nuclei and causes a net increase in high-energy, spin-down spins.

142
Q

What happens if there is a moving magnetic field?

A

Electricity is created.

143
Q

If there is a moving electrical field, what is created?

A

Magnetism

144
Q

The potential signal-to-noise ratio (SNR) does what as field strength increases?

A

Increases

145
Q

When is Free Induction Decay (FID) created?

A

After any RF excitation pulse.

146
Q

Describe Free Induction Decay (FID).

A

Induction of rapidly decreasing signal.

147
Q

What is thermal equilibrium in MRI?

A

When all protons that are going to align with the field have done so in the low and high-energy states.

148
Q

The application of an RF pulse that causes resonance to occur is called:

A

Excitation

149
Q

Which state of alignment is more abundant in MRI?

A

Parallel

150
Q

What controls the amount of T1 contrast in an image?

A

TR (Repetition Time)

151
Q

What controls the amount of T2 contrast in an image?

A

TE (Echo Time)

152
Q

What is the time from the RF pulse to the peak of the signal called?

A

Echo Time (TE)

153
Q

What is TR?

A

Repetition Time – the time from one RF excitation pulse to the next.

154
Q

What is TE?

A

Echo Time – the time from the RF pulse to the peak of the signal detected.

155
Q

What does TR control?

A

The amount of T1 relaxation that occurs before the next RF pulse is applied.

156
Q

What does TE control?

A

The amount of T2 dephasing that occurs when the signal is read.

157
Q

Which particle of an atom has a negative charge?

A

Electron

158
Q

Which particle of an atom has a positive charge?

A

Proton

159
Q

What happens to NMV when field strength increases?

A

It gets larger.

160
Q

What does frequency represent in MRI?

A

Speed of precession, in MHz

161
Q

The time constant of the precessional frequency of a specific MR active nucleus at 1 Tesla is called:

A

Gyromagnetic ratio

162
Q

The hydrogen proton induces a strong magnetic field because it is:

A

Charged and spinning

163
Q

In what year did MRI receive its FDA approval?

A

1985

164
Q

Define relaxation.

A

Process by which spins lose energy

165
Q

The longitudinal plane is in the _____________ axis.

A

z-axis

166
Q

What is the gyromagnetic ratio of hydrogen at 3T?

A

127.74 MHz

167
Q

In MR imaging, the term “spin” refers specifically to the spinning:

A

Nuclei

168
Q

What is the Larmor equation used for?

A

To calculate precessional frequency

169
Q

The principles of MRI rely on -

A

Spinning motion of specific nuclei present in biological tissues

170
Q

What is NMV?

A

Net Magnetic Vector (NMV)

171
Q

Precessional frequency in MRI is measured in:

A

MHz

172
Q

If there is a moving magnetic field, what could be created?

A

Electricity

173
Q

In what year did Felix Bloch and Edward Purcell receive the Nobel Prize for physics for developing nuclear induction?

A

1952

174
Q

Raymond Damadian’s first human-sized machine, now in the Smithsonian, is named:

A

Indomitable

175
Q

When is FID created?

A

After any RF excitation pulse

176
Q

What type of motion is letter A?

A

Precession

177
Q

What is the Larmor equation used to calculate?

A

Precessional frequency

178
Q

Which particle of an atom has a negative charge?

A

Electron

179
Q

Which particle of an atom has a positive charge?

A

Proton

180
Q

The tiny magnetic field of the hydrogen proton that is induced by spin and charge and has a north and south pole is called:

A

Magnetic moment

181
Q

Parallel alignment is created when -

A

The protons are introduced into a magnetic field

182
Q

What controls the amount of T1 that will be in an image?

A

TR

183
Q

Frequency is -

A

Speed of precession, in MHz

184
Q

One of the original names for the technology, NMR, stood for what?

A

Nuclear Magnetic Resonance

185
Q

The time constant of the precessional frequency of a specific MR-active nucleus at 1 Tesla in MHz/T is called:

A

Gyromagnetic ratio

186
Q

What happens to NMV as the main magnetic field strength is increased?

A

It gets larger

187
Q

What is thermal equilibrium?

A

When all the protons that are going to line up with the field have done so in the low and high-energy states.

188
Q

Describe the free induction decay.

A

Induction of rapidly decreasing signal

189
Q

The hydrogen proton induces a strong magnetic field because it is:

A

Charged and spinning

190
Q

What happens during the ‘excitation’ phase in an MRI scan?

A

RF excitation pulse gives energy to nuclei and causes a net increase in the number of high-energy, spin-down spins.

191
Q

If there is a moving electrical field, what is created?

A

Magnetism

192
Q

What controls the amount of T1 relaxation that occurs when the signal is read?

A

TR

193
Q

What equation is represented by ‘omega 0 = gamma B0’?

A

Larmor equation

194
Q

The time from the application of the RF pulse to the peak of the signal induced in the coil is termed the:

A

Echo time (TE)

195
Q

What controls the amount of T2 that will be in an image?

A

TE

196
Q

Which two physicists first won a Nobel Prize in Physics for their development of nuclear induction?

A

Bloch and Purcell

197
Q

The application of an RF pulse that causes resonance to occur is termed:

A

Excitation

198
Q

Which state of alignment is more abundant?

A

Parallel

199
Q

The potential signal-to-noise ratio (SNR) -

A

Increases as the field strength increases

200
Q

Who is credited with the first human body image in 1977?

A

Raymond Damadian

201
Q

According to Avogadro’s law -

A

There are about 6 × 10^23 molecules per gram of tissue.

202
Q

What controls the amount of T2 dephasing that occurs when the signal is read?

A

TE

203
Q

What is letter B?

A

Net magnetic spin

204
Q

Why is the hydrogen atom used in clinical MRI?

A

Due to its abundance in the body and its solitary proton giving a large magnetic moment.

205
Q

The symbol for the primary static field is:

A

Bₒ

206
Q

MR-active nuclei are:

A

Nuclei that possess an odd mass number.

207
Q

Out of phase means:

A

Magnetic moments of H are at different places on the precessional path at a moment in time.

208
Q

One reason the hydrogen atom is used in clinical MR imaging is its abundance in the body and:

A

Its solitary proton creates a large magnetic moment.

209
Q

How many electrons does the hydrogen atom have?

A

1

210
Q

What is the gyromagnetic ratio of hydrogen at 1.2T?

A

51.09 MHz

211
Q

What are the two branches of physics used to describe the basic principles of MRI?

A

Classical and quantum theories.

212
Q

The relative balance between spin-up and spin-down nuclei is called:

A

Net magnetic vector.

213
Q

What happens to the hydrogen protons when they are placed in a magnetic field?

A

They align parallel or anti-parallel.

214
Q

What prompted the name change from NMR to MRI prior to FDA approval?

A

To prevent patients from thinking it was radiation.

215
Q

What determines the relative quantities of spin-up and spin-down nuclei?

A

The strength of the main magnetic field.

216
Q

Which of the following is the most abundant atom in the human body?

A

Hydrogen.

217
Q

The nucleus of a hydrogen atom contains:

A

One proton.

218
Q

Phase is:

A

A position at a given time.

219
Q

Spin of MR active nuclei, which depends on the balance between number of protons and neutrons in the nucleus, is defined as:

A

Angular momentum.

220
Q

TE determines how much decay of _______________ magnetization is allowed to occur.

A

Transverse.

221
Q

What is the most common excitation ‘flip angle’?

A

90°.

222
Q

What were the early NMR machines used to study, and what was the name of this technique?

A

Chemicals, spectroscopy.

223
Q

Who was the first person to demonstrate a radio signal from the nucleus of an atom?

A

Isidor Rabi.

224
Q

What is termed B1?

A

RF field.

225
Q

What conditions are necessary for resonance?

A

Energy applied at the precise frequency and at a right angle.

226
Q

Energy is most effectively transferred from one system to another when the systems are at:

A

Resonance.

227
Q

Whose law states that ‘a moving magnetic field induces a voltage in a conductor coil’?

A

Faraday’s Law.

228
Q

Antiparallel is the:

A

High-energy state.

229
Q

The number of protons in a nucleus is termed:

A

Atomic number.

230
Q

What are the two most common molecules in the human body, where hydrogen is found?

A

Lipids and water.

231
Q

Amplitude and duration of an RF pulse will determine:

A

The flip angle.

232
Q

How many protons does the hydrogen atom have?

A

1.

233
Q

With regard to energy, protons in parallel alignment are in the _________ state, whereas protons in anti-parallel alignment are in the __________ state.

A

Low-energy, high-energy.

234
Q

What is ‘TR’?

A

Time to repeat RF excitation.

235
Q

TR determines the amount of ____________ relaxation that occurs between the end of one RF pulse and the application of the next.

A

Longitudinal.

236
Q

How is the MR signal produced?

A

Signal is produced when in-phase transverse magnetization cuts across a receive coil.

237
Q

The Larmor precessional frequency of hydrogen in a 1.5T magnet is:

A

63.86 MHz.

MRI Physics (6 decks)

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