Scan Principles: Imaging Basics (MRQuiz) Flashcards
(113 cards)
1
Q
A ________________________ is a set of specifically timed instructions to the magnet telling it how images
should look with regards to the tissue being sampled
A
pulse sequence
2
Q
Is T1 or T2 relaxation quicker?
A
T2
3
Q
_______ relaxation occurs when nuclei give up their energy to the surrounding tissue, which is
known as spin lattice relaxation.
A
T1
4
Q
T1 relaxation is also known as ______________________ relaxation
A
spin lattice
5
Q
T1 is synonymous with the nuclei’ regrowth along longitudinal magnetization, and is also
referred to as _______ axis regrowth.
A
Z axis regrowth
6
Q
T1 relaxation time is the recovery of ________% longitudinal magnetization of a specific tissue’s
original magnetization.
A
63%
7
Q
_____ relaxation time is defined as the time it takes for 63% of the transverse magnetization to
decay, or the time it takes the spins to de-phase to 37% of their original value.
A
T2 relaxation time
8
Q
Fat has a __________(short or long?) T1 relaxation time and a ____________(short or long?) T2 relaxation time.
A
short, short
9
Q
Water has a ________________(short or long?) T1 relaxation time and a _____________________(short or long?) T2 relaxation time.
A
long, long
10
Q
The two extremes of contrast in MRI are __________ and __________
A
water and fat
11
Q
The Larmor frequency of hydrogen in water is higher or lower than hydrogen in fat?
A
Higher
12
Q
To obtain low signal, there must be a small or large component of magnetization in the transverse plane in the coil?
A
Small
13
Q
To obtain high signal, there must be a small or large component of magnetization in the transverse plane in the coil?
A
Large
14
Q
Is the T1 time of fat shorter or longer than water?
A
Shorter
15
Q
Does T1 have short or long TR?
A
Short
16
Q
Does T1 have a short or long TE?
A
Short
17
Q
On T1 imaging, which tissues/items appear bright (increased intensity)?
A
Fat or gadolinium enhancing tissues
18
Q
The T2 time of fat is shorter or longer than water?
A
Shorter
19
Q
On T2 imaging, is water bright or dark?
A
Bright
20
Q
On T2 imaging is fat bright or dark?
A
Dark
21
Q
In T1 imaging, is fat bright or dark?
A
Bright
22
Q
In T2 imaging, is TR long or short?
A
Long
23
Q
In T2 imaging is TE long or short?
A
24
Q
On T2 images, which structures/ tissues are bright (increased intensity)?
A
Edema or CSF
25
_______________ is the controlling factor of T1 weighting/ contrast in an image
TR (repetition time)
26
____________________ is the controlling factor of T2 weighting/contrast in an image
Echo Time (TE)
27
Increasing the TR will:
-**improve or decrease** SNR
-**increase or decrease** scan time
-**increase or reduce** T1 weighting
- **increase or decrease** the available # of slices
-improve SNR
-Increase scan time
-Reduce T1 weighting
-Increase the available # of slices
28
Decreasing the TR will:
-**improve or decrease** SNR
-**increase or decrease** scan time
-**increase or reduce** T1 weighting
- **increase or decrease** the available # of slices
-lower SNR
-reduce scan time
-increase T1 weighting
-reduce the available # of slices
29
Does shorter TE increase or decrease SNR?
Increase
30
What is the TR and TE range for T1 weighted images?
TR 350-700ms
TE 10-30ms
31
What is the TR and TE range for PD weighted images?
TR 1500-3000ms
TE 10-30ms
32
What is the TR and TE range for T2 weighted images?
TR 2000-6000ms
TE 70-120ms
33
If the TR is doubled, what will happen to the scan time?
Double
34
Is TR directly or indirectly proportional to scan time?
Directly
35
Does reducing TR **increase or decrease** scan time?
Decreases
36
Does reduction in NSA/NEX cause scan time to **increase or decrease**?
Decrease
37
To reduce scan time, the parallel imaging factor needs to be **increased or decreased**?
Increase
38
Does using RecFOV increase or decrease scan time?
Decrease
39
Does using Half-Fourier/Halfscan increase or decrease scan time?
Decrease
40
Does using a tighter matrix increase or decrease scan time?
Increase
41
True or false: the slice thickness directly affects the SNR ratio of the image
True
42
Thinner slice thickness gives you **better or worse** image resolution?
Better
43
A reduction in excitations (NEX/NSA) would **REDUCE OR INCREASE** SNR
Reduce
44
When increasing NEX/NSA, ______________ increases by the square root of the % increase
SNR
45
What does NEX stand for?
Number of excitations
46
As the NEX is increased, the scan time ____________, SNR _____________ and the resolution ___________
NEX Increases, SNR increases, resolution stays the same
47
Does NEX have an effect on pixel size?
No
48
Smaller pixel size = higher or lower phase matrix?
Higher
49
Larger pixel size = higher or lower phase matrix?
Lower phase matrix
50
Does a smaller pixel size increase or decrease resolution?
Increase
51
Does a smaller pixel size cause increased or decreased SNR?
Decreased SNR
52
The parameters that are used to make adjustments to voxel volume include:
FOV, slice thickness and matrix
53
NSA stands for __________
Number of signal averages
54
Doubling the NEX will increase the SNR by __________% and double the scan time
140%
55
Decreasing the slice thickness will increase or decrease SNR?
Decrease the SNR
56
Increasing NEX/NSA does what to SNR?
Increases it
57
Increasing FOV= _____SNR
Increased
58
Decreasing phase matrix= _________ SNR
Increased SNR
59
Increasing TR = _______ SNR
Increased
60
Increase slice thickness = ________ SNR
Increased
61
Reduced bandwidth = _________SNR
Increased
62
Reduce ETL (echo train length) = _______ SNR
Increased
63
True or false, the longer the echo train length (ETL) the increased chance of blurring in the image
True
64
Reducing the FOV yields a _________ to SNR, but a _________ in spatial resolution
Decrease SNR, increase spatial resolution
65
What formula is used to calculate the size of a pixel?
FOV divided by matrix
66
Reducing the FOV by a factor of 2 will reduce the voxel volume by a factor of _____
4
67
The _______ is measured in phase and frequency dimensions
FOV
68
___________ is an MRI option characterized by a shortening of the overall FOV in the phase encoding direction, reducing pulse sequence scan time while maintaining resolution
Rectangular FOV
69
Phase matrix is in which coding direction- A-P or L-R?
L-R
70
Frequency Matrix is in which coding direction- R-L or A-P?
A-P
71
With a ______% Rectangular FOV, the phase matrix must be exactly half the frequency matrix in order to yield square pixels
50%
72
What do you divide milliseconds by to get scan time into seconds?
1000
73
Scan time formula for spin echo is:
TR x Phase Matrix x NEX
74
What is the scan time for a spin echo sequence with parameters 450 TR, 20 TE, 224x224 matrix, 20cm FOV, and 3 NEX?
5 minutes and 2 seconds (how: 450 x 224 x 3 =302,400 milliseconds divided by 1000 = 5 min 2 sec)
75
Scan time formula for fast spin echo?
TR x Phase Matrix x NEX / ETL
76
Calculate scan time for Fast spin echo sequence using parameters 2300 TR, 120 TE, 320 x 272 matrix, 240mm FOV, 4 NSA and an Echo Train Length of 8
5 min 12 seconds— Scan time would be calculated as 2300 x 272 (phase matrix is always the smaller number) x 4, then divide by ETL of 8 = 312800 milliseconds. Divide by 1000 to get seconds = 312.8 seconds. Take this number divided by 60= 5.2133 (so 5 minutes, then take 60 times 0.21 to get the seconds which is 12 seconds)
77
In a matrix number, the __________ is always the smaller number
Smallest
78
Scan time formula for Gradient Echo (assuming 2D) is?
TR x Phase Matrix x NEX
79
Calculate the scan time for a 2D gradient echo sequence using parameters 400 TR, 25 TE, 256 x 192 matrix, 18cm FOV, Flip angle 15 degrees, and 2 NEX
2 min 34 seconds (scan time calculated by 400 x 192 x 2 =153,600 153600ms divided by 1000 to convert to 153.6 seconds or 2 min 34 seconds)
80
Scan time formula for 3D gradient Echo sequence?
TR x Phase Matrix x NEX x Number of slices
81
What is the scan time for 3D gradient echo sequence with TR 100, 10 TE, 224 x 160 matrix, 20cm FOV, flip angle 10 degrees, 1 NEX, 48 slices
12 min 48 seconds (scan time is calculated by taking 100 x 160 x 1 x 48 =768,000 ms, divided by 1000= 768 seconds = 12 min 48 seconds)
82
_____________ is defined as a picture element
Pixel
83
Is a pixel 2D or 3D?
2D
84
Pixel size= ___________ divided by _____________
Pixel size = Field of View divided by matrix
85
NSA = NEX ( means the same thing)
NSA = NEX
86
A _________ size calculation would include measurements in millimeters and both the phase and frequency directions
Pixel size calculation
87
________ is defined as a volume element and is 3D
Voxel
88
What is the equation to determine voxel size?
FOV divided by Matrix (phase and frequency — then multiply) x slice thickness measurement = voxel size
89
To produce a high-quality reformatted image, the acquisition voxel should be ___________
Isotropic
90
Calculate the pixel size for a FOV 220mm and a matrix of 256?
FOV divided by Matrix……….. 220 divided by 256 = 0.86mm
91
Calculate the frequency and phase dimensions for the following sequence: 500 TR, 20 TE, 18cm FOV, 272 x 256 matrix, 3 NEX.
1. Convert 18cm FOV into mm…. Take 18 x 10 =180 FOV
2. Pixel calculations are 180 divided by 272 for the frequency measurement (0.66)
3. Pixel calculations are 180 divided by 256 for the phase direction (0.70)
4. Frequency and phase dimensions for this sequence are **0.66mm x 0.70mm**
Remember: FOV divided by Matrix = pixel size
92
Calculate the voxel measurements for the following sequence: 2500 TR, 100 TE, 24cm FOV, 320 x 272 matrix, 5mm slice thickness, 1mm interslice gap, 6 ETL, and 4 NEX for a T2 Weighted axial sequence of the brain
1. Find out the pixel frequency and phase dimensions
240 divided by 272 = 0.88 in the phase direction
240 divided by 320= 0.75mm in the frequency direction
Voxel measurements are Phase x frequency x slice thickness…… 0.88 x 0.75 x 5mm
93
What is the equation for voxel measurements?
Phase x Frequency x Slice Thickness
94
Pixel area is calculated by multiplying what dimensions?
Phase dimensions x frequency dimension
95
Calculate the pixel area for a 0.75 phase direction pixel by 0.75mm frequency direction pixel
0.75 x 0.75 =0.5625 millimeter squared pixel area
96
To calculate voxel volume, multiply __________ x ______________
Pixel area x slice thickness
97
Calculate the pixel area for a sequence with FOV 25 cm and a matrix of 272.
1. Convert 25 cm to mm =250 mm
2. Divide 250 divided by 272 = 0.919 pixel size
3. Calculate pixel area by multiplying 0.919 x 0.919=0.845mm squared
REMEMBER: pixel area = phase dimensions x frequency dimension
98
Pixel area is measured in what measurement?
Mm squared
99
Voxel volume is measured in which measurement type?
Mm cubed
100
Calculate the voxel volume for the following pulse sequence: TR 500, TE 20, FOV 240mm, 224 x 224 matrix, NSA 2, Slice thickness 4mm
REMEMBER: voxel volume = pixel area x slice thickness
1) 240 divided by 224 = 1.07mm (this is the pixel size)
2) 1.07 x 1.07 =1.14mm squared (this is the pixel area)
3) 1.14 x 4= 4.56mm cubed (this is the voxel volume)
101
FOV divided by Matrix = __________________
Pixel size
102
______________ = phase x frequency
Pixel area
103
Pixel area X slice thickness = _______________
Voxel volume
104
Calculate the voxel volume for the following sequence: 2500 TR, 100 TE, 28cm FOV, 400 x 320 matrix, 5mm slice thickness, 1mm interslice gap, 6 ETL, 3 NSA.
1) FOV divided by matrix to get pixel size…. 280 / 400=0.7 mm pixel size (frequency dimension)
2) 280 / 320 = 0.88 mm pixel size (phase dimension)
3) 0.7 x 0.88= 0.616mm squared pixel area
4) Pixel area x slice thickness = voxel volume….. 0.616mm squared x 5mm= 3.08mm cubed
105
______ is defined as the storage location of MR signal data
K-space
106
Each line of k-space is defined by the _____________ gradient
Phase encoding gradient
107
Referring to k-space, the data containing signal and contrast information are located along the _________________.
Central lines
108
Referring to k-space, the data containing high resolution are located along the ______________
Outer lines
109
Reducing the number of lines filled in kspace will produce an image with a ______________ in spatial resolution
Decrease
110
The center of ________________ is where signal and contrast are found
K-space
111
In a fast spin echo sequence the number of rows filled per
TR period is the same as ___________
ETL
112
Center of k-space = _________ (max or min) signal
Maximum
113
