Hi Martin,

I am just curious to know, why trace weighted images ? why not others ?

I just looked SNR using ROIs, and I found SNR b0=  128.19 and on diffusion image 16.5, and Trace image is not so good to draw the outer ROI, it almost shows 0 mean/ 0 SD, so when I come bit at the border of brain, than it shows SNR 9.3.

Is there any desciption that, how much should be SNR on trace weighted images ?

Best, Vin



On Sat, Sep 6, 2008 at 8:24 AM, Martin Kavec <[log in to unmask]> wrote:

Hi,

I would do ROI, as Vin says, but on a calculated trace-weighted images. By this you would avoid a problem of orientation dependent contrast in individual DTI images, which could compromise your SNR values.

Best,

Martin


On Sat, Sep 6, 2008 at 1:03 AM, vin <[log in to unmask]> wrote:

If you are in so much hurry to check SNR over the weekend, than you can use following tip. may be some experienced user will write name of any tool regarding this soon. otherwise you can write one.

So, if you have siemens scanner, than in the syngo program under tools you will find possibility to draw a ROI and see the mean / SD of image.  Now what you need to do is, to draw two ROIs, one in the center of image and other one outside from the image, but not out side from the image space.

now SNR= mean (center)/ sd (outside)..  

there are several other things in respect to SNR that also matters, but in short I check with this way.  

comments from other users are welcome on this procedure.

vin



On Fri, Sep 5, 2008 at 5:25 PM, Kochunov, Peter <[log in to unmask]> wrote:

In my experience FA values are quite sensitive to SNR levels. From my observations, higher SNR, produced by my directions or by a better coil, result in a uniform increases in FA. This sort of make sense since FA is basically a standard deviation-like measurement and is supposed to change with SNR.
pk

________________________________

From: FSL - FMRIB's Software Library on behalf of Jiansong Xu User
Sent: Fri 9/5/2008 10:19 AM
To: [log in to unmask]
Subject: [FSL] DTI signal noise ratio



Dear All:

I'm wondering if any one has tools for assessing the signal/noise ratio of
DTI raw images.

A recent publication " Diffusion tensor imaging at low SNR: nonmonotonic
behaviors of tensor contrasts. Landman et al. Magnetic Resonance Imaging 26
(2008) 790­800" reported that the FA value was affected by signal/noise
ratio. So, if I want to compare the FA between patients and control
subjects, I need to assess if the signal/noise ratio of two groups were
match.

Any help is appreciated.


Best

--
Jiansong Xu, M.D., Ph.D.
Associate Research Scientist
Dept. of Psychiatry
Yale Medical College
34 Park St., Room S-100
New Haven, CT 06519