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REVIEW > Physics Chapter 1 > Flashcards

Physics Chapter 1 Flashcards

1
Q

Atoms are organized into…

A

Molecules

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2
Q

Most abundant molecule

A

Hydrogen

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3
Q

_____ orbit Atoms / spin around nucleus

A

Electrons

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4
Q

_____ within atoms contain all of atoms mass

A

Nucleus

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5
Q

Nucleons are subdivided into

A

Protons and neutrons

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6
Q

Positive nucleons

A

Protons

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7
Q

No charge nucleons

A

Neutrons

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8
Q

Negative nucleons

A

Electrons

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9
Q

Sum of protons in the nucleus

A

Atomic number

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10
Q

Sum of protons and neutrons in nucleus

A

Atomic weight/mass number

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11
Q

Atoms with same number of protons but different number of neutrons

A

Isotopes

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12
Q

Electron position not predictable and depends on the energy of an individual electron at any given time

A

Heisenberg‘s uncertainty principle

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13
Q

Equal amount of negative charged electrons and positive charged protons are…

A

Stable atoms

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14
Q

Applying energy to knock out electrons and alter balance causes…

A

Electrical instability

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15
Q

Atoms knocked out by electrical instability are called

A

Ions

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16
Q

Process of knocking out electrons

A

Ionization

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17
Q

What are the three motions within atoms

A

Electrons spin on own axis,
Electrons orbit nucleus,
Nucleus spins on own axis

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18
Q

MRI relies on…

A

Spinning of specific nuclei in body tissues

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19
Q

Atomic mass and numbers affect amount of…

A

Spin values

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20
Q

Nucleus has no spin if…

A

It has even atomic and mass numbers
(6 protons + 6 neutrons = mass of 12)

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21
Q

Why does a nucleus with an even atomic number and mass number have no net spin?

A

Half spin in one direction and half spin in the opposite direction thus canceling spins

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22
Q

If there is an odd number of protons and an odd number of neutrons or an odd number of both protons and neutrons the spin directions…

A

Are not equal and are opposite so the nucleus has a net spin

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23
Q

If a nucleus has a net spin this is called…

A

Angular momentum

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24
Q

Nuclei with an odd mass number or atomic weight are…

A

MR – active nuclei

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25
Q

Align their axis of rotation to an applied field

A

MR active nuclei

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26
Q

Refers to connection of electric and magnetic fields and motion. Determines a moving electric field produces a magnetic field and vice versa

A

Faradays law

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27
Q

_____ Have an electrical charge and are spinning therefore acquire a magnetic field

A

MR active nuclei

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28
Q

_______ Of each nucleus has size and direction

A

Magnetic moment/ Magnetic field

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29
Q

__________ Of the nucleus is the vector sum of all the magnetic moments of protons in the nucleus

A

Total magnetic moment

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30
Q

Isotope of hydrogen is…

A

Protium

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31
Q

Most common MR active nucleus used is…

A

Protium

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32
Q

Protium has a mass and atomic number of…

A

1 (nucleus has a single proton and no neutron)

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33
Q

A solitary proton has a _______ magnetic moment

A

Large

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34
Q

The spinning of the one positively charged proton in protium induces a magnetic field around it acting as

A

A small magnet

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35
Q

The magnet of each hydrogen nucleus has…

A

Equal strength north and south poles

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36
Q

In the absence of applied magnetic fields, orientation of hydrogen nuclei is…

A

Randomly aligned producing no magnetic field

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37
Q

When placed in a strong static magnetic field (B0) the magnetic moment…

A

Align with the magnetic field

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38
Q

Alignment of magnetic moments in the same direction as the main B0 field

A

Parallel Alignment/ Spin-Up (low energy)

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39
Q

Alignment of magnetic moments in the opposite direction to B0 field

A

Anti-parallel Alignment/ Spin-down (high energy)

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40
Q

Protons of hydrogen nuclei couple with external magnetic field B0

A

Zeeman interaction

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41
Q

The 2 energy states for hydrogen are…

A

Low energy nuclei and High energy nuclei

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42
Q

Not enough energy to oppose B0 field. Spin up or parallel alignment

A

Low energy nuclei

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43
Q

Do you have enough energy to oppose B0 field. Spin down or anti-parallel alignment

A

High energy nuclei

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44
Q

Predicts the number of spins in each energy level

A

Boltzman equation

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45
Q

A patient’s temperature determines whether a spin is…

A

In the high or low energy population

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46
Q

A patient’s temperature is usually similar inside and out of B0. This is called…

A

Thermal equilibrium

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47
Q

In _______ there are more magnetic moments in spin up then in spin down

A

Thermal equilibrium

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48
Q

As more spins are aligned to B0, there is a small excess that produces a ________

A

Net magnetic moment (NMV)

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49
Q

_________ reflects the balance between spin up and spin down nuclei

A

NMV

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50
Q

The sum of all magnetic moments of excess spin up nuclei and is measurable

A

NMV

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51
Q

Aligns parallel to main magnetic field in the longitudinal plane (Z axis)

A

NMV

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52
Q

Number of spins depends on…

A

The number of molecules per gram of tissue and the strength of B0

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53
Q

As B0 increases more magnetic moments are…

A

Parallel

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54
Q

As field strength increases fewer spins have…

A

Enough energy to align in opposition to B0

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55
Q

When low energy population increases in size and high energy population decreases in size…

A

The NMV increases

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56
Q

For every million protons at 1.5 T the NMV is about…

A

4.5 million

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57
Q

For every million protons at 3 T the NMV is about…

A

10 million

58
Q

SNR increases at higher field strengths because of…

A

Increased NMV

59
Q

______ produces an additional spin to hydrogens nucleus spin

A

B0

60
Q

Additional spin produced by B0 is called

A

Precession

61
Q

________ causes magnetic moments to spin around B0

A

Precession

62
Q

The course that hydrogen nucleus spins around B0 is called a

A

Precessional path

63
Q

The speed which hydrogen nuclei spin is called

A

Precessional frequency

64
Q

Precessional frequency is known as…

A

Larmour equation

65
Q

_______ Is one cycle of rotation per second

A

1 Hz

66
Q

______ is 1 million cycles per second

A

1 MHz

67
Q

Larmour equation is represented by

A

W0=y*B0

68
Q

W0 represents

A

Precessional frequency in MHz

69
Q

Y represents

A

Gyromagnetic ratio (MHz/T)

70
Q

B0 represents

A

Strength of external field (T)

71
Q

Relationship between angular momentum and the magnetic moment of each MR active nucleus

A

Gyromagnetic Ratio

72
Q

The Gyromagnetic ratio of hydrogen expresses at 1 T is…

A

42.58 MHz/T

73
Q

Gyro magnetic ratio of hydrogen at 1.5 T is

A

63.87 MHz

74
Q

Gyro magnetic ratio of hydrogen at 0.5 T is…

A

21.29 MHz

75
Q

Gyro magnetic ratio of hydrogen at 3 T is…

A

127.74 MHz

76
Q

The equation for a Gyro magnetic ratio is…

A

42.58 MHz * _______ T

77
Q

_____________ fall into the radiofrequency band of the electromagnetic spectrum

A

Precessional frequencies

78
Q

The position of magnetic moments on their professional path

A

Phase

79
Q

The unit of phase is…

A

Radian

80
Q

A magnetic moment travels through 360 rad or 360° during…

A

One rotation

81
Q

Frequency being the rate of change of phase of magnetic moments is defined as

A

How quick the phase position of a magnetic moment changes over time

82
Q

Magnetic moments are at different places on the precessional path

A

Out of phase/ Incoherent

83
Q

Magnetic moments are at the same place on precessional path

A

In phase/ Coherent

84
Q

When B0 is the only influence, nuclei are________

A

Out of phase with each other

85
Q

When nuclei are out of phase the NMV…

A

Does not precess

86
Q

Occurs when an object is exposed to an oscillating perturbation(a movement disturbance) that has a frequency close to its own natural frequency of oscillation(movement)

A

Resonance

87
Q

When a nucleus is exposed to an external force with similar oscillation to the natural frequency of its magnetic moment, the nucleus…

A

Gains energy from the external source

88
Q

If energy is delivered at a different frequency, resonance…

A

Does not occur and the nucleus does not gain energy

89
Q

For resonance to occur, ________is applied at the Larmour frequency of hydrogen

A

An RF pulse

90
Q

Resonance is achieved by transmitting a….

A

RF pulse/RF excitation pulse

91
Q

An RF excitation pulse is produced by a….

A

Transmit coil (ex: body, head, extremity coils)

92
Q

Consists of electric and magnetic fields that spread in waves at 90° to each other

A

RF excitation pulse

93
Q

The RF excitation is only from the component (coil) and produces an oscillating magnetic field called

A

B1

94
Q

The B1 field is applied at ____ to B0 at a narrow range or bandwidth of frequencies centered around a central frequency (transmit bandwidth)

A

90°

95
Q

Magnetic field of____ is very weak compared to_____

A

B1; B0

96
Q

Represented in the transverse plane/ x-y axis

A

B1 field

97
Q

Application of B1 in the 90° plane to B0 causes magnetic moments of the spins to…

A

Precess around transverse/ x-y axis rather than at the longitudinal or Z axis

98
Q

As the B1 field associated with RF excitation is weak, the magnetic moments of spins precess at a much lower frequency than when aligned with B0 resulting in…

A

A spiral downward motion of the NMV from longitudinal to transverse plane

99
Q

Downward spiral of NMV is called

A

Nutation

100
Q

_________ Is caused by 2 precessional motions that happen simultaneously (precession around B0 and a slower precession around B1)

A

Nutation

101
Q

RF excitation moves magnetic moments of spin up and spin down…

A

Into phase with each other

102
Q

RF pulse application is called…

A

Excitation

103
Q

Excitation means…

A

Energy giving

104
Q

RF excitation gives energy to hydrogen, increasing the…

A

Number of high energy, spin down nuclei

105
Q

__________________ absorb energy from RF excitation pulse and move into high energy

A

Low energy, spin up nuclei

106
Q

At the same time of the RF excitation, spin down, high energy nuclei are stimulated to…

A

Release energy and return to the low energy state

107
Q

Because there are more low energy spins, the net affect is of…

A

Energy absorption

108
Q

If the right amount of energy is absorbed, the NMV lies in the…

A

Transverse plane at 90° to B0

109
Q

When the right amount of energy is absorbed and the NMV lies in the transverse plane it has moved through a…

A

Flip angle or tip angle of 90°

110
Q

The frequency required to cause resonance is related to the difference in…

A

Energy between high energy and low energy populations and the strength of B0

111
Q

As B0 increases, the energy difference between the two populations_______

A

Increases

112
Q

__________ depends on amplitude and magnitude of RF excitation

A

Flip angle

113
Q

The flip angle is usually______

A

90°

114
Q

When a flip angle less than 90° is used….

A

Only a portion of NMV is transferred to the transverse plane

115
Q

A flip angle of 180° is caused by…

A

RF excitation of twice the magnitude

116
Q

____________ produces an inversion of spin populations called saturation

A

Flip angle of 180°

117
Q

__________ is caused when spins are unable to absorb more energy or to be stimulated and release more energy

A

Saturation

118
Q

Because of resonance, in phase (coherent) magnetization processes in the…

A

Transverse plane

119
Q

The change of magnetic flux through a closed circuit induces a

A

Electromotive force (EMF) in the circuit

120
Q

______ Is the energy available from a unit of charge traveling once around the loop of wire

A

EMF

121
Q

 The movement of electrons caused by a changing magnetic field is called a

A

Current

122
Q

If a receiver coil is placed in a moving magnetic field, a _________ generated by current is induced in the receiver coil

A

Voltage

123
Q

Voltage generated in a receiver coil is called

A

Signal

124
Q

_________ is produced when coherent (in- phase) magnetization cuts across the coil

A

Signal

125
Q

When RF excitation is switched off…

A

NMV is only influenced by B0 and tries to realign with it

126
Q

When hydrogen nuclei lose energy from RF

A

Relaxation

127
Q

During relaxation, the NMV…

A

Realigns with B0

128
Q

Simultaneously and independently during relaxation, hydrogen magnetic moments lose coherency due to

A

Dephasing

129
Q

_________ is due to inhomogeneities in the B0 field and due to interactions between the spins in the patient’s tissue

A

Dephasing

130
Q

The induction of decaying voltage is called the

A

FID signal

131
Q

FID signal is named FID because

A

Spins FREELY precess influenced only by B0

Signal DECAYS with time

Magnetic moments INDUCE a current in the receiver coil

132
Q

The magnitude and timing of the RF pulses formed part of_____________which are the basis of contrast generation in MRI

A

Pulse sequences

133
Q

A simple pulse sequence combines…

A

RF pulses, signals, and interleaving periods of relaxation

134
Q

A pulse sequence consists of several time periods. The two main periods are

A

TR & TE

135
Q

TR is also known as

A

Repetition time

136
Q

TE is also known as

A

Echo time

137
Q

Time from the application of one RF excitation pulse to the next for each slice.
Measured in milliseconds.
Determines the amount of longitudinal relaxation between the end of one RF pulse and start of the next

A

TR

138
Q

TR determines the amount of______ relaxation that occurs when signal is read

A

T1

139
Q

Time from the application of the RF excitation pulse to the peak of signal induced in the receiver coil.
Measured in milliseconds.
Determines how much decay of transverse magnetization occurs.

A

TE

140
Q

TE controls the amount of_______relaxation that has occurred when signal is read

A

T2

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