Physics Final Flashcards
(163 cards)
1
Q
The principal flow phenomenon is also known as:
A
-Time of flight
-Entry slice phenomenon
-Intra-voxel dephasing
2
Q
How many types of principal flow are there?
A
4
3
Q
When flow occurs at different velocities and fluctuates randomly, it is known as:
A
Turbulent flow
4
Q
Flow that is initially laminar, but then experiences a stricture or stenosis in a vessel is known as:
A
Vortex flow
5
Q
Flow in a vessel that has different velocities, but remains constant is known as:
A
Laminar flow
6
Q
Flowing nuclei that have excitation, but not rephasing have experienced the phenomenon known as Time of Flight.
A
True
7
Q
Time of Flight phenomenon causes vessels to appear bright.
A
False
8
Q
High velocity signal loss reflects an increase of Time of Flight effect.
A
True
9
Q
Time of Flight effects depend on:
A
-Velocity of flow
-TE
-Slice thickness
10
Q
Flowing nuclei are more likely to receive both the 90° and 180° pulses in a thin slice.
A
False
11
Q
Gradient Echo pulse sequences are said to be flow sensitive.
A
True
12
Q
Nuclei that have not received repeated RF pulses are called fresh.
A
True
13
Q
Nuclei flowing parallel to the slice enter the slice fresh.
A
False
14
Q
The slices in the middle of a stack exhibit less entry slice phenomenon.
A
True
15
Q
Flow that is in the same direction of the slice is known as co-current flow.
A
True
16
Q
Intra-voxel results in an increase of signal amplitude from a voxel.
A
False
17
Q
The methods for reducing flow are:
A
-Even echo rephasing
-Gradient moment nulling
-Spatial pre-saturation
18
Q
Even echo rephasing is useful in reducing the effects of:
A
Intra-voxel dephasing
19
Q
Gradient moment rephasing predominately reduces the effects of:
A
Intra-voxel dephasing
20
Q
Gradient moment rephasing is more effective on turbulent flow than laminar flow.
A
False
21
Q
Spatial pre-saturation minimizes the effects of entry slice phenomenon and time of flight phenomenon.
A
True
22
Q
In sagittal and axial images, pre-saturation pulses are usually placed to the left and the right of the FOV.
A
False
23
Q
Pre-saturation bands cannot be brought into the FOV itself.
A
False
24
Q
Pre-saturation is usually used in T1 and PD images where fluid is dark anyways.
A
True
25
The frequency difference between fat and water is called chemical shift.
True
26
Fat or water saturation is most effectively achieved on low field systems.
False
27
The frequency difference between fat and water at 1.0 Tesla is:
147
28
The interval between saturation pulses is known as the SAT TR.
True
29
SPIR technique combines fat saturation with inversion recovery mechanisms.
True
30
TR determines the amount of:
-T1 weighting
-PD weighting
31
The flip angle used determines the amount of:
-T1 weighting
-PD weighting
32
TE determines the amount of:
T2 weighting
33
The voltage induced by the NMV in the transverse plane (in the receiver coil) results in signal.
True
34
As magnetic field strength increases, the SNR _________________.
Increases
35
As the proton density of an area being examined increases, the SNR _________________.
Increases
36
The building unit of a digital image is the voxel.
False
37
The voxel represents a volume of tissue within the patient.
True
38
The size of the voxel is not influenced by the slice thickness.
False
39
The size of the voxel can be altered by:
-Changing the slice thickness
-Changing the image matrix
-Changing the FOV
40
Gradient echo pulse sequences generally have more signal than spin echo pulse sequences.
False
41
The maximum signal amplitude is created with flip angles of 90°
True
42
TR has no influence on scan time.
False
43
Generally, a sequence with a long TE will have a lower SNR than sequences with a short TE.
True
44
Increasing the NEX is the only way to increase SNR.
False
45
To double the SNR, we need to increase the NEX and scan time by a factor of 9.
False
46
The type of coil does not influence the SNR.
False
47
The contrast to noise ratio (CNR) is defined as the difference in SNR between two adjacent areas.
True
48
Spatial resolution is the ability to distinguish two points as separate and distinct and is controlled by voxel size.
True
49
Reducing the slice thickness increases the spatial resolution.
True
50
Rectangular pixels provide better spatial resolution than square pixels.
False
51
Any movement of the patient will probably degrade the image quality, so shorter scan times are optimal.
True
52
All manufacturers use the same acronyms to distinguish between individual pulse sequences.
False
53
An inversion recovery pulse sequence is an example of a spin echo pulse sequence.
True
54
Examples of a gradient echo sequence are:
-Coherent gradient echo
-Steady state free precession
-Echo planar imaging
55
To achieve a T1 weighted sequence, utilize:
A short TR, a short TE
56
To achieve a T2 weighted sequence, utilize:
A long TR, a long TE
57
A spin echo pulse sequence utilizes:
A 90° excitation pulse, followed by one or more 180° rephasing pulses
58
T1 weighted sequences are useful for visualizing normal anatomy.
True
59
Pathology is well visualized on a T2 weighted sequence because of edematous and vascularized pathology.
True
60
The TR of a T1 weighted sequence is typically in the range of:
300-700 ms
61
The TE of a T1 weighted sequence is typically in the range of:
10-30 ms
62
The TR of a T2 weighted sequence is typically in the range of:
2000+ ms
63
The TE of a T2 weighted sequence is typically in the range of:
80+ ms
64
One of the advantages of spin echo sequences is their relatively short scan times.
False
65
Fast or Turbo spin echo sequences have scan times that are shorter than traditional spin echo sequences.
True
66
The higher the turbo factor or echo train length, the shorter the scan time.
True
67
In a fast spin echo, data with the effective TE fill the outer lines of K space.
False
68
Fast spin echo has largely replaced spin echo, especially in T2 weighted sequences.
True
69
Fat remains bright in T2 fast spin sequences.
True
70
Muscle appears brighter in T2 fast spin echo sequences than it does in traditional spin echo sequences.
False
71
Fast spin echo sequences reduce magnetic susceptibility artifact.
True
72
A single shot fast spin echo sequence takes longer than a fast spin echo sequence.
False
73
A reverse flip angle excitation pulse is applied at the end of the echo train in a driven equilibrium Fourier transform.
True
74
Inversion recovery pulse sequences begin with a 180° inverting pulse.
True
75
Fast inversion recovery often utilizes weighting that produces high signal in water and pathology.
True
76
It is beneficial to use contrast enhancement in conjunction with STIR sequences.
False
77
Lesions, bone bruising, and tumors are well visualized in STIR sequences.
True
78
Gradient echo sequences can allow for a reduction in scan times because the TR is greatly reduced.
True
79
Coherent gradient echo usually produce rapid images that are T1 weighted.
False
80
RF spoiled sequences demonstrate good T1 anatomy and pathology after gadolinium.
True
81
Keyhole filling of K space is used mainly for contrast enhanced angiography.
True
82
Once a slice is selected, the signal is located or encoded along both axes of the image.
True
83
Gradients alter the external magnetic field in a nonlinear fashion.
False
84
Spatial encoding is achieved by utilizing:
Gradients
85
The position of a nucleus along a gradient can be identified according to its precessional frequency.
True
86
If the gradient field adds to the external magnetic field, the precessional frequency of nuclei slow down.
False
87
In a typical super conducting machine, which gradient affects the long axis of the magnet?
Z gradient
88
Permanent magnets have different axes than superconducting magnets.
True
89
Steep gradient slopes alter the precessional frequency of nuclei between two points, more than shallow gradient slopes.
True
90
Locating a slice within the scan plane is termed:
Slice selection
91
Spatially locating signal along the short axis of anatomy is called:
Phase encoding
92
Spatially locating signal along the long axis of anatomy is called:
Frequency encoding
93
Typically, which gradient selects axial slices?
Z gradient
94
Typically, which gradient selects sagittal slices?
X gradient
95
Typically, which gradient selects coronal slices?
Y gradient
96
To achieve thin slices, a shallow slice select slope and/or broad transmit bandwidth is applied.
False
97
In coronal and sagittal images, the long axis of the anatomy lies along the
Z axis of the magnet and therefore, the Z gradient performs frequency encoding.
True
98
The size of the anatomy covered during a scan is referred to as the:
Field of View (FOV)
99
Two or more molecules arranged together are known as an atom.
False
100
The abundance of hydrogen in the human body is found in molecules of water and fat.
True
101
The mass of an atom comes mostly from:
Nucleons
102
The mass number is the sum of the protons in the nucleus.
False
103
Atoms of elements with the same number of protons but a different number of neutrons are called:
Isotopes
104
_____________________ spin around the nucleus.
Electrons
105
The nucleus itself spinning about its axis, in nuclei with an ________________
mass number.
Odd
106
In nuclei with odd mass numbers, spin directions are equal and opposite.
False
107
MR active nuclei have ______________________ mass numbers.
Odd
108
The mass number of Hydrogen is:
1
109
The isotope of the hydrogen nucleus that is the MR active nucleus used in clinical MRI is called:
Protium
110
The magnet of each hydrogen nucleus has a North and a South pole of equal strength.
True
111
The direction of a vector designates the size of the magnetic moment, and the length of the vector designates the direction of the magnetic moment.
False
112
In the absence of an applied magnetic field, the magnetic moments of the hydrogen nuclei are randomly orientated.
True
113
When placed in a strong static external magnetic field, the magnetic moments of the hydrogen nuclei align with this magnetic field, both parallel and anti-parallel.
True
114
Low energy nuclei align their magnetic moments parallel to the external field and are termed spin-down nuclei.
False
115
It is the strength of the external magnetic field that determines the relative quantities of spin-up to spin-down nuclei.
True
116
The secondary spin caused by the influence of an external magnetic field is called precession.
True
117
1 MHz is equal to:
One million cycles per second
118
At 1.0T the precessional frequency of hydrogen is:
42.57 MHz
119
_____________________ is a phenomenon that occurs when an object is exposed to an oscillating perturbation that has a frequency close to its own natural frequency of oscillation.
Resonance
120
For resonance of hydrogen to occur, an RF pulse of energy at exactly the Larmor frequency of hydrogen must be applied.
True
121
The application of an RF pulse that causes resonance to occur is termed:
Excitation
122
The angle to which the NMV moves out of alignment is called the:
Flip angle
123
B₀ is termed the transverse plane and the plane at 90° to B₀ is termed the longitudinal plane.
False
124
Frequency is the position of each magnetic moment on the precessional path around B₀
False
125
The MR signal is produced when coherent (in phase) magnetization cuts across the coil.
True
126
The process by which hydrogen loses this energy is called excitation.
False
127
The induction of reduced signal in the receiver coil is called the free induction decay (FID) signal.
True
128
The recovery of longitudinal magnetization is caused by a process termed
T1 recovery and the decay of transverse magnetization is caused by a process termed T2 decay.
True
129
T1 recovery is caused by the nuclei giving up their energy to the surrounding environment or lattice, and is termed spin lattice relaxation.
True
130
131
T2 relaxation time is the time it takes 63% of the transverse magnetization to be lost.
True
132
TR is the time from the application of the RF pulse to the peak of the signal induced in the coil and is also measured in milliseconds.
False
133
TE controls the amount of T2 relaxation that has occurred when the signal is read.
True
134
Extrinsic contrast parameters are those that cannot be changed because they are inherent to the body’s tissues.
False
135
T1 recovery time, T2 decay time, proton density, flow, and apparent diffusion coefficient (ADC) are examples of intrinsic contrast parameters.
True
136
TR, TE, flip angle, T1, turbo factor/echo train length, and b value are examples of extrinsic contrast parameters.
True
137
A tissue with high signal appears dark on an image.
False
138
The lower the proton density of a tissue, the more signal available from that tissue.
False
139
Hydrogen in fat recovers more rapidly along the longitudinal axis than water and loses transverse magnetization faster than in water.
True
140
The NMV of fat aligns rapidly with B₀ so the T1 time of fat is long.
False
141
T2 decay in water is less efficient than in fat.
True
142
On T1 weighted images, fat is bright and water is dark.
True
143
On T2 weighted images, fat is dark and water is bright.
True
144
PD weighted images are characterized by areas with high proton density (dark) and areas with low proton density (bright).
False
145
To achieve T1 weighting, the TR must be short enough so that neither fat nor water has sufficient time to fully return to B₀
True
146
The TE controls the amount of T2 decay that is allowed to occur before the signal is received.
True
147
For T2 weighting, the TE must be long.
True
148
To achieve PD weighting, the effects of T1 and T2 contrast must be diminished so that PD weighting can dominate.
True
149
Inhomogeneities are areas within the magnetic field that do not exactly match the external magnetic field strength.
True
150
T2* decay happens in part because of dephasing due to magnetic field Inhomogeneities.
True
151
Sequences that use a 180° pulse to regenerate signal are called gradient echo pulse sequences, those that use a gradient are called spin echo pulse sequences.
False
152
The spin echo pulse sequence commonly uses a 90° excitation pulse to flip the NMV into transverse plane.
True
153
In a spin echo sequence, TR is the time between each 90° excitation pulse for each slice and TE is the time between the 90° excitation pulse and the peak of the spin echo.
True
154
A spin echo sequence flips the NMV through any angle.
False
155
Magnetic field gradients are generated by coils of wire situated within the bore of the magnet.
True
156
The middle of the axis of the gradients, remains at the field strength of the main magnetic field, which is known as isocenter.
True
157
Since gradients rephase slower than 180° RF pulses, the minimum TE is much shorter than in spin echo pulse sequences and so the TR must be increased.
False
158
Gradients that rephase are called rewinders.
True
159
Gradient echo pulse sequences are very susceptible to magnetic field inhomogeneities.
True
160
In gradient echo sequences, the flip angle is an extrinsic contrast parameter that is changed to affect image contrast.
True
161
Gradients that dephase are called ___________________.
Spoilers
162
At 2.0T the precessional frequency of hydrogen is __________________.
85.14 MHz
163
