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| Result: Searchterm 'signal'
found in 52 messages |
| Result Pages: 1 2 3 4 5 6 7 [8] 9 10 11 |
More Results:  Database (369) News Service (50) Resources (8) |
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andre jefferson
Wed. 23 Jul.08,
04:38
[Start of:
'information needed'
2 Replies]
 Category:
Protocols
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| information needed |
I am trying to get better at reading knee MRI's. I would like to know which protocols are best for evaluating meniscii, collaterals,cartilage, cruciates, bone marrow signals. Please advise.
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Reader Mail
Wed. 12 Dec.07,
10:07
[Reply (1 of 2) to:
'double ir physic'
started by: 'soontorn siriserussa'
on Sun. 2 Dec.07]
Category:
Sequences and Imaging Parameters
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| double ir physic |
Different types of double inversion recovery (DIR, 2IR) sequences are used to improve the suppression of blood signal (black blood technique) or to null the signals from two different tissue types (e.g. white matter and cerebrospinal fluid).
The black blood technique (used in cardiovascular MRI) works with two inversion pulses, where the first pulse is nonselective and the second pulse is slice-selective. TI is set to a value at which the signal of the recovering inverted blood is zero (http://www.mr-tip.com/serv1.php?type=db1&dbs=Double%20Inversion).
The second technique (also named gray matter only) is used in brain imaging to improve the detection of lesions, for example in the diagnostic of multiple sclerosis. Two 180° pulses with different TI are used to suppress two different types of tissue simultaneously.
Hope this helps
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Paul Tesla
Fri. 9 Nov.07,
15:31
[Start of:
'How do you measure SNR?'
0 Reply]
Category:
Basics and Physics
|
| How do you measure SNR? |
I know this is a basic question but how do you measure SNR?
This page:
http://dnl.ucsf.edu/users/dweber/dweber_docs/mri_quality.html
tells me to measure an as small as possible ROI for the signal mean and as large as possible ROI for the standard deviation.
But I have a book called "MRI from picture to proton": This says that the standard deviation of the noise (Sn) can be measured using the mean or standard deviation (sd) of a background region. Then you can use the relationship:
Mean = 1.25 Sn
sd = 0.66 Sn
to find Sn. But where do the values 1.25 and 0.66 come from?
It also says that the measured mean of the signal ROI is related to the MR signal instensity (S) using:
Mean = sqrt(S^2 + Sn^2)
But why do they add up quadratically?
Thankyou for your help. Please leave a message or email me,
Paul
-------------
mri.tesla@gmail.com
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Bear DuDu
Thu. 18 Oct.07,
07:28
[Reply (1 of 2) to:
'DWI'
started by: 'Reader Mail'
on Wed. 17 Oct.07]
Category:
Applications and Examinations
|
| DWI |
DWI reflects the degree of water molecule movement. If the degree of water molecule movement in the tumor is the same as the normal tissue, the signal of DWI will have no difference between the tumor and the normal tissue.
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Reader Mail
Wed. 17 Oct.07,
19:34
[Start of:
'DWI'
1 Reply]
Category:
Applications and Examinations
|
| DWI |
What does normal signal in the diffusion-weighted images mean?
Would a large brain tumor show normal signal in diffusion-weighted images?
Thanks
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