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| Result: Searchterm 'Matter'
found in 13 messages |
| Result Pages: [1] 2 3 |
More Results:  Database (10) News Service (28) Resources (3) |
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Rahul Manay
Mon. 27 Jun.16,
20:35
[Start of:
'Fractional Anisotropy'
0 Reply]
 Category:
General
|
| Fractional Anisotropy |
Hi,
I have been trying to mathematically derive the formula to find FRACTIONAL ANISOTROPYrn(Fractional anisotropy is a method that is used to emphasize and evaluate white matter fiber tracts)
The formula that is given in many textbooks and published paper
FA= Squareroot(3/2) * (Sqaureroot[ (lambda1-lambda)^2 + (lambda2-lambda)^2 + (lambda3-lambda)^2]/ Sqaureroot( Lambda1^2+Lambda2^2+Lambda3^2))
I understand the purpose of Lambda but unable to understand the need for SQUAREROOT (3/2)rnrnPlease do kindly explain the reason behind having SQUAREROOT(3/2) for the Fractional Anisotropy formula
-Rahul Manay
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adam wootton
Fri. 13 Apr.12,
17:31
[Start of:
'intracranial cavity volume'
2 Replies]
Category:
Applications and Examinations
|
| intracranial cavity volume |
Hello,
As part of a clinical trial, I have been asked to calculate Intracanial cavity volumes as well as whole brain, total gray matter, and total white matter volume.
I am on a GE Signa 3.0T running 15x software.
Can anyone give me a clue on how to do this?
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Artemiy Artemiy
Fri. 16 Mar.12,
19:54
[Start of:
'How to estimate areas of lesion on MRI in multiple sclerosis'
3 Replies]
Category:
Applications and Examinations
|
| How to estimate areas of lesion on MRI in multiple sclerosis |
Hello
I'm a neurologist from the Military medical academy at St-Petersburg in Russia. In Internet I found some articles about MS from you. I study correlation: cognitive impairments and areas of lesion by using MRI in multiple sclerosis. What the program would be better to estimate areas of lesion (total volume, topical spreading in white matter)? I'll be very glad to receive any answer. I didn't find answer to this question in Radiology department at the M-Med Academy. I tried to use SPM8, but understand, that its impossible to research volume of areal in MS. (I spent a lot of time for nothing)
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Steven Ford
Tue. 31 Jan.12,
08:19
[Reply (1 of 2) to:
'RF shimming'
started by: 'Reader Mail'
on Thu. 1 Oct.09]
Category:
Basics and Physics
|
| RF shimming |
For Magnetic fields, the overall field is adjusted to push it up a little bit in one spot and push it down a little bit in another area. The goal is to create a field that's perfectly homogenous.
The RF field created by the transmit coil likewise must be as homogenous as possible, so that the flip angle is constant throughout the imaging volume. In the past, designers have solved this problem by building coils such as the 'birdcage' style that would create a very even amount of energy inside. This is one reason why the transmit coils tend to be large.
With the advent of 3 Tesla and stronger magnets, the RF resonant frequency also rises. RF energy absorbed in the patient rises with the higher frequencies also, and another problem raises its head: it's a lot harder to make a very homogenous RF field. Even if you are scanning phantoms, the inside tends to be subject to different energy than the edges.
But in the human body, there are all sorts of irregular lumps and bumps that absorb RF differently, further complicating matters.
Now, on modern scanners it's possible to perform a magnetic field shim with the patient actually in the magnet in order to compensate for minute changes in the magnet from one exam to another. For super-high field magnets, an RF shim is also a handy thing to do.
If you have a Multi element RF transmit coil (regular phased array coils are just for receiving) you can run a program which selectively turns up the power in some elements so that the overall signal received is maximized. That's an RF shim.
Steven Ford
Professional Imaging Services, Inc.
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Anna Lena Golay
Wed. 25 Jan.12,
20:59
[Reply (3 of 7) to:
'Imaging optic neuritis'
started by: 'Karen Lesley'
on Wed. 18 Jan.12]
Category:
General
|
| Imaging optic neuritis |
A 2-3 mm STIR sequence through the optic nerves may show the characteristic high-signal intensity of optic neuritis. Gadolinium enhanced T1-weighted fat-saturated (to suppress the bright signal of the orbital fat tissue) images of the orbits show the inflammation of the optic nerve. White matter lesions, which denote a higher risk of developing MS, are typical imaged with FLAIR and T2-weighted images (hyperintense lesions), or show enhancement of T1-weighted images postcontrast.
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