Physics Chapter 1 Flashcards
1
Q
Atoms are organized into…
A
Molecules
2
Q
Most abundant molecule
A
Hydrogen
3
Q
_____ orbit Atoms / spin around nucleus
A
Electrons
4
Q
_____ within atoms contain all of atoms mass
A
Nucleus
5
Q
Nucleons are subdivided into
A
Protons and neutrons
6
Q
Positive nucleons
A
Protons
7
Q
No charge nucleons
A
Neutrons
8
Q
Negative nucleons
A
Electrons
9
Q
Sum of protons in the nucleus
A
Atomic number
10
Q
Sum of protons and neutrons in nucleus
A
Atomic weight/mass number
11
Q
Atoms with same number of protons but different number of neutrons
A
Isotopes
12
Q
Electron position not predictable and depends on the energy of an individual electron at any given time
A
Heisenberg‘s uncertainty principle
13
Q
Equal amount of negative charged electrons and positive charged protons are…
A
Stable atoms
14
Q
Applying energy to knock out electrons and alter balance causes…
A
Electrical instability
15
Q
Atoms knocked out by electrical instability are called
A
Ions
16
Q
Process of knocking out electrons
A
Ionization
17
Q
What are the three motions within atoms
A
Electrons spin on own axis,
Electrons orbit nucleus,
Nucleus spins on own axis
18
Q
MRI relies on…
A
Spinning of specific nuclei in body tissues
19
Q
Atomic mass and numbers affect amount of…
A
Spin values
20
Q
Nucleus has no spin if…
A
It has even atomic and mass numbers
(6 protons + 6 neutrons = mass of 12)
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
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
23
Q
If a nucleus has a net spin this is called…
A
Angular momentum
24
Q
Nuclei with an odd mass number or atomic weight are…
A
MR – active nuclei
25
Align their axis of rotation to an applied field
MR active nuclei
26
Refers to connection of electric and magnetic fields and motion. Determines a moving electric field produces a magnetic field and vice versa
Faradays law
27
_____ Have an electrical charge and are spinning therefore acquire a magnetic field
MR active nuclei
28
_______ Of each nucleus has size and direction
Magnetic moment/ Magnetic field
29
__________ Of the nucleus is the vector sum of all the magnetic moments of protons in the nucleus
Total magnetic moment
30
Isotope of hydrogen is…
Protium
31
Most common MR active nucleus used is…
Protium
32
Protium has a mass and atomic number of…
1 (nucleus has a single proton and no neutron)
33
A solitary proton has a _______ magnetic moment
Large
34
The spinning of the one positively charged proton in protium induces a magnetic field around it acting as
A small magnet
35
The magnet of each hydrogen nucleus has…
Equal strength north and south poles
36
In the absence of applied magnetic fields, orientation of hydrogen nuclei is…
Randomly aligned producing no magnetic field
37
When placed in a strong static magnetic field (B0) the magnetic moment…
Align with the magnetic field
38
Alignment of magnetic moments in the same direction as the main B0 field
Parallel Alignment/ Spin-Up (low energy)
39
Alignment of magnetic moments in the opposite direction to B0 field
Anti-parallel Alignment/ Spin-down (high energy)
40
Protons of hydrogen nuclei couple with external magnetic field B0
Zeeman interaction
41
The 2 energy states for hydrogen are…
Low energy nuclei and High energy nuclei
42
Not enough energy to oppose B0 field. Spin up or parallel alignment
Low energy nuclei
43
Do you have enough energy to oppose B0 field. Spin down or anti-parallel alignment
High energy nuclei
44
Predicts the number of spins in each energy level
Boltzman equation
45
A patient’s temperature determines whether a spin is…
In the high or low energy population
46
A patient’s temperature is usually similar inside and out of B0. This is called…
Thermal equilibrium
47
In _______ there are more magnetic moments in spin up then in spin down
Thermal equilibrium
48
As more spins are aligned to B0, there is a small excess that produces a ________
Net magnetic moment (NMV)
49
_________ reflects the balance between spin up and spin down nuclei
NMV
50
The sum of all magnetic moments of excess spin up nuclei and is measurable
NMV
51
Aligns parallel to main magnetic field in the longitudinal plane (Z axis)
NMV
52
Number of spins depends on…
The number of molecules per gram of tissue and the strength of B0
53
As B0 increases more magnetic moments are…
Parallel
54
As field strength increases fewer spins have…
Enough energy to align in opposition to B0
55
When low energy population increases in size and high energy population decreases in size…
The NMV increases
56
For every million protons at 1.5 T the NMV is about…
4.5 million
57
For every million protons at 3 T the NMV is about…
10 million
58
SNR increases at higher field strengths because of…
Increased NMV
59
______ produces an additional spin to hydrogens nucleus spin
B0
60
Additional spin produced by B0 is called
Precession
61
________ causes magnetic moments to spin around B0
Precession
62
The course that hydrogen nucleus spins around B0 is called a
Precessional path
63
The speed which hydrogen nuclei spin is called
Precessional frequency
64
Precessional frequency is known as…
Larmour equation
65
_______ Is one cycle of rotation per second
1 Hz
66
______ is 1 million cycles per second
1 MHz
67
Larmour equation is represented by
W0=y*B0
68
W0 represents
Precessional frequency in MHz
69
Y represents
Gyromagnetic ratio (MHz/T)
70
B0 represents
Strength of external field (T)
71
Relationship between angular momentum and the magnetic moment of each MR active nucleus
Gyromagnetic Ratio
72
The Gyromagnetic ratio of hydrogen expresses at 1 T is…
42.58 MHz/T
73
Gyro magnetic ratio of hydrogen at 1.5 T is
63.87 MHz
74
Gyro magnetic ratio of hydrogen at 0.5 T is…
21.29 MHz
75
Gyro magnetic ratio of hydrogen at 3 T is…
127.74 MHz
76
The equation for a Gyro magnetic ratio is…
42.58 MHz * _______ T
77
_____________ fall into the radiofrequency band of the electromagnetic spectrum
Precessional frequencies
78
The position of magnetic moments on their professional path
Phase
79
The unit of phase is…
Radian
80
A magnetic moment travels through 360 rad or 360° during…
One rotation
81
Frequency being the rate of change of phase of magnetic moments is defined as
How quick the phase position of a magnetic moment changes over time
82
Magnetic moments are at different places on the precessional path
Out of phase/ Incoherent
83
Magnetic moments are at the same place on precessional path
In phase/ Coherent
84
When B0 is the only influence, nuclei are________
Out of phase with each other
85
When nuclei are out of phase the NMV…
Does not precess
86
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)
Resonance
87
When a nucleus is exposed to an external force with similar oscillation to the natural frequency of its magnetic moment, the nucleus…
Gains energy from the external source
88
If energy is delivered at a different frequency, resonance…
Does not occur and the nucleus does not gain energy
89
For resonance to occur, ________is applied at the Larmour frequency of hydrogen
An RF pulse
90
Resonance is achieved by transmitting a….
RF pulse/RF excitation pulse
91
An RF excitation pulse is produced by a….
Transmit coil (ex: body, head, extremity coils)
92
Consists of electric and magnetic fields that spread in waves at 90° to each other
RF excitation pulse
93
The RF excitation is only from the component (coil) and produces an oscillating magnetic field called
B1
94
The B1 field is applied at ____ to B0 at a narrow range or bandwidth of frequencies centered around a central frequency (transmit bandwidth)
90°
95
Magnetic field of____ is very weak compared to_____
B1; B0
96
Represented in the transverse plane/ x-y axis
B1 field
97
Application of B1 in the 90° plane to B0 causes magnetic moments of the spins to…
Precess around transverse/ x-y axis rather than at the longitudinal or Z axis
98
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 spiral downward motion of the NMV from longitudinal to transverse plane
99
Downward spiral of NMV is called
Nutation
100
_________ Is caused by 2 precessional motions that happen simultaneously (precession around B0 and a slower precession around B1)
Nutation
101
RF excitation moves magnetic moments of spin up and spin down…
Into phase with each other
102
RF pulse application is called…
Excitation
103
Excitation means…
Energy giving
104
RF excitation gives energy to hydrogen, increasing the…
Number of high energy, spin down nuclei
105
__________________ absorb energy from RF excitation pulse and move into high energy
Low energy, spin up nuclei
106
At the same time of the RF excitation, spin down, high energy nuclei are stimulated to…
Release energy and return to the low energy state
107
Because there are more low energy spins, the net affect is of…
Energy absorption
108
If the right amount of energy is absorbed, the NMV lies in the…
Transverse plane at 90° to B0
109
When the right amount of energy is absorbed and the NMV lies in the transverse plane it has moved through a…
Flip angle or tip angle of 90°
110
The frequency required to cause resonance is related to the difference in…
Energy between high energy and low energy populations and the strength of B0
111
As B0 increases, the energy difference between the two populations_______
Increases
112
__________ depends on amplitude and magnitude of RF excitation
Flip angle
113
The flip angle is usually______
90°
114
When a flip angle less than 90° is used….
Only a portion of NMV is transferred to the transverse plane
115
A flip angle of 180° is caused by…
RF excitation of twice the magnitude
116
____________ produces an inversion of spin populations called saturation
Flip angle of 180°
117
__________ is caused when spins are unable to absorb more energy or to be stimulated and release more energy
Saturation
118
Because of resonance, in phase (coherent) magnetization processes in the…
Transverse plane
119
The change of magnetic flux through a closed circuit induces a
Electromotive force (EMF) in the circuit
120
______ Is the energy available from a unit of charge traveling once around the loop of wire
EMF
121
 The movement of electrons caused by a changing magnetic field is called a
Current
122
If a receiver coil is placed in a moving magnetic field, a _________ generated by current is induced in the receiver coil
Voltage
123
Voltage generated in a receiver coil is called
Signal
124
_________ is produced when coherent (in- phase) magnetization cuts across the coil
Signal
125
When RF excitation is switched off…
NMV is only influenced by B0 and tries to realign with it
126
When hydrogen nuclei lose energy from RF
Relaxation
127
During relaxation, the NMV…
Realigns with B0
128
Simultaneously and independently during relaxation, hydrogen magnetic moments lose coherency due to
Dephasing
129
_________ is due to inhomogeneities in the B0 field and due to interactions between the spins in the patient’s tissue
Dephasing
130
The induction of decaying voltage is called the
FID signal
131
FID signal is named FID because
Spins FREELY precess influenced only by B0
Signal DECAYS with time
Magnetic moments INDUCE a current in the receiver coil
132
The magnitude and timing of the RF pulses formed part of_____________which are the basis of contrast generation in MRI
Pulse sequences
133
A simple pulse sequence combines…
RF pulses, signals, and interleaving periods of relaxation
134
A pulse sequence consists of several time periods. The two main periods are
TR & TE
135
TR is also known as
Repetition time
136
TE is also known as
Echo time
137
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
TR
138
TR determines the amount of______ relaxation that occurs when signal is read
T1
139
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.
TE
140
TE controls the amount of_______relaxation that has occurred when signal is read
T2
