I would think that the opposite would generally occur, as noise would
increase the variability of signal intensity across the directions. Thus,
if you took the mean FA of a scan with low SNR, it would be higher than the
mean FA of a scan with high SNR. In fact the referenced paper below makes
this point. In localized regions with very high FA, this might be less
true, however.
Peace,
Matt.
-----Original Message-----
From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf
Of Kochunov, Peter
Sent: Friday, September 05, 2008 10:25 AM
To: [log in to unmask]
Subject: Re: [FSL] DTI signal noise ratio
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) 790-800" 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
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