By readout direction you mean phase encoding direction.
Peace,
Matt.
On 6/28/14, 10:46 AM, "Barbara Kreilkamp" <[log in to unmask]> wrote:
>Dear Shi,
>
>The b0 image acquired without any diffusion weighting gives higher
>signal-to-noise ratio than DW images, you might notice when looking at
>the images that the contrast is also way better in the b0 image.
>Also the b0 image will suffer from fewer artifacts than the DW images,
>this is why we use it as a reference volume during registration.
>The b0 image is not chosen as a mask, a mask can be generated from it
>easily because of the contrast as I said above. So that you can avoid
>doing unnecessary computations around the brain.
>
>However, b0 images can be distorted in readout-direction, these are
>called EPI distortions, you might correct these by acquiring a field map
>or a structural scan (preferably T2 image because of similar contrast
>and intensities) for non-linear coregistration.
>
>Hope it helps.
>All the best,
>Barbara
>
>
>
>On 28/06/2014 08:18, SUBSCRIBE FSL Xinfa_Shi wrote:
>> Hi ,
>>
>> I am running through the TBSS processing stream .When creating FA
>>images from your diffusion study data ,a step is to create a brain mask
>>by running bet on one of the B=0 (no diffusion weighting) images . I use
>>the command "fslroi data nodif 0 1 " to extract b=0 image .
>>
>> As far as I know , b=0 image is used as mask when extracting brain
>>.Could you explain it ? Why is b=0 image chose as mask ? How does it
>>works? What's is its function ?
>>
>> Regards .
>>
>> Shi Xin-Fa.
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