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37 Cards in this Set
- Front
- Back
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A T1 weighted image has a ___ TR and a ___ TE.
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short TR and short TE
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A T2 weighted image has a ___ TR and a ___ TE
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Long TR and Long TE
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A density weighted image has a ___ TR and a ___ TE
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Long TR and short TE
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The signal immediately after the RF pulse is always proportional to:
a. M0 b. the flip angle c. the T1 value of the tissue d. the T2 value of the tissue |
a. M0
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Mz represents ___
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longitudinal magnetization (the NMV)
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Most of the signal lost caused by T2* decay can be regained by using:
a. a long TR b. a SE sequence c. a short TR d. an IR sequence e. a high flip angle |
b. a SE sequence
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In a T1 weighted image, the brightest signal usually comes from:
a. fat b. muscle c. white matter d. grey matter e. CSF |
a. fat
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In a T2 weighted image, the brightest signal usually comes from:
a. fat b. muscle c. white matter d. grey matter e. CSF |
e. CSF
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What determines the pixel value in an MRI image?
a. T2 contrast b. bandwith c. signal strength d. signal difference |
c. the signal difference determines pixel value in an MRI image
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What determines contrast in an MRI image?
a. T2 decay b. T1 relaxation c. signal strength d. signal difference |
d. signal difference
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Spin Echo
___ controls the contrast between tissues due to T1 relaxation |
TR
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Spin Echo
TR controls the contrast between tissues due to ___ relaxation |
T1
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Spin Echo
The longer the TR, the _____ (better/worse) the SNR. Why? What is compromised? |
As TR is increased, SNR increases due to longitudinal magnetization, but this happens at an expense to T1 contrast.
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Spin Echo: echo time
Echo Time (TE) controls what? |
TE controls the contrast in the tissues due to T2 decay.
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Spin Echo: echo time
The shorter the TE, the ____ (better/worse) the SNR. Why? What is compromised? |
A short TE results in better SNR because there's more transverse magnetization at time of echo. BUT a shorter TE means less contrast.
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Spin Echo
What kind of image would the following parameters create? TR = 500 TE = 20 |
T1 weighted
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Spin Echo
What kind of image would the following parameters create? TR = 2500 TE = 20 |
PD
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Spin Echo
What kind of image would the following parameters create? TR = 2500 TE = 80 |
T2
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Inversion Recovery sequences are used for _____.
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Nulling signal
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What is a typical inversion recovery time?
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150ms
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STIR stands for ___-
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Short Time Inversion Recovery
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FLAIR stands for ___
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Fluid Attenuated Inversion Recovery
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Which sequence nulls tissue with a pre pulse of 180 degrees, followed by an excitation pulse of 90?
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FLAIR
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T2 is a first-order exponential time constant so that ___% of the initial transverse magnetization or signal is lost during one TR period.
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63%
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True/False
T2* effects are reversible |
True
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Spin Echo recaptures all the effects that were lost; it recaptures what is lost during t2*
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from recording feb19 @ 48:00
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Spin Echo
Most of the contrast in T1/T2/PD weighted images comes from variations in relaxation times T1, T2, and PD |
feb 19 class
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___ controls the contrast in tissues in an image due to T1 relaxation
a. TR b. TE |
Tr
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____ controls the contrast between tissues in an image due to T2 decay
a. TR b. TE |
TE
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True or False - T1 is longer in pure water than in proteinaceous solutions or tissues.
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True
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True or False - The presence of paramagnetic contrast agents within the body lengthens T1 relaxation times.
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False
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True or False - T1 relaxation reflects the molecular tumbling rate of protons.
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True
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True or False - T2 is longer in pure water than in proteinaceous solutions.
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True
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Signal intensity of any given pixel in a T1 map image corresponds to ____.
a. T1 relaxation time b. T2 decay |
a. T1 relaxation time
the same is true for T2 images |
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___ is a first-order exponential time constant that reflects the molecular tumbling rate of protons and the strength of local magnetic fields they experience.
A. T1 B. T2 |
A. T1
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___ is shorter when protons exchange between different chemical environments or diffuse between regions of different susceptibility.
A. T1 B. T2 |
B. T2
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True/False:
Most of the contrast in MR images comes from variations in relaxation times T1 and T2 and PD. |
True
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