Hi Andreas,
I thought that Dustin was referring to b=0's, so no eddy currents ;)
Obviously registration won't be perfect due to EPI distortions, but it is
safer to try 6 dofs rather than 12, if such a global within-subject
transformation is attempted.
Cheers
Stam
----- Original Message -----
From: "Andreas Bartsch" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, April 20, 2012 9:51 PM
Subject: Re: [FSL] b=0 averaging
>6 dof maybe be good but it assumes that there are no eddy currents
> involved and that the B0 volumes can be registered by a rigid body
> transformation.
> cheers,
> andreas
>
> Am 20.04.12 17:20 schrieb "Stamatios Sotiropoulos" unter
> <[log in to unmask]>:
>
>>Hi Dustin,
>>
>>correct, apart from the SNR gain. It is sqrt(N), so in your case sqrt(6).
>>
>>Cheers
>>Stam
>>
>>
>>----- Original Message -----
>>From: "Cunningham, Dustin" <[log in to unmask]>
>>To: <[log in to unmask]>
>>Sent: Friday, April 20, 2012 4:07 PM
>>Subject: [FSL] b=0 averaging
>>
>>
>>If I have say 6 b=0 images and I want to average them I would simply
>>coregister them (6 dof) then add and divide by 6, correct?
>>
>>...and this will give me a 6*sqrt(2) increase in SNR?
>>
>>Just want to make sure Im not missing anything.
>>
>>Dustin
>>
>>
>>________________________________________
>>From: FSL - FMRIB's Software Library [[log in to unmask]] On Behalf Of
>>Andreas Bartsch [[log in to unmask]]
>>Sent: Thursday, April 19, 2012 5:47 PM
>>To: [log in to unmask]
>>Subject: Re: [FSL] DTI: Order of Eddy_correction vs. Unwarping
>>
>>Hi Pete,
>>
>>this is good!
>>Cheers,
>>Andreas
>>
>>PS: You don't really need 2.c, do you?
>>
>>Am 19.04.12 15:38 schrieb "Peter Fried" unter <[log in to unmask]>:
>>
>>>Hi FSL Community,
>>>
>>>Can someone confirm the appropriate order of pre-processing steps for DTI
>>>data?
>>>
>>>Specifically, does it matter whether the unwrapping (using the pre-stats
>>>option in FEAT) occurs before or after the eddy_correction?
>>>
>>>Here is what I have been doing and I just want to make sure it's correct:
>>>
>>>#1. Eddy Correction
>>>#2. Feat Pre-stats
>>> a. Unwarp
>>> b. bet
>>> c. Registration
>>>#3. dtifit
>>>#4. bedpostx
>>>
>>>Thanks!
>>>
>>>Cheers,
>>>Pete Fried
>>>
>>>Department of Anatomy & Neurobiology
>>>Boston University School of Medicine
>
>
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