Dear Ashley,
just to add to Matthew's reply.
From the perspective of how well the eddy current and motion correction works all three options would be good. 2 gives you lower overall angular sampling, though all three options give you more than enough for FA.
Of options 1 and 3
1 Would give you _slightly_ better alignment between scans, which would potentially result in _slightly_ sharper looking FA image.
3. Would give you _slightly_ higher anatomic fidelity, in that the inevitable small residual susceptibility distortions would average out across the two PE directions.
On the whole I would say that both are good options, and I don't have a strong option in favour of either.
Jesper
> On 9 Dec 2020, at 05:37, Ashley <[log in to unmask]> wrote:
>
> Hi there,
>
> We are planning to acquire diffusion data on a 3T Siemens Prisma. We want to follow the HCP Lifespan diffusion protocol as closely as possible however we have limited acquisition time and can therefore only collect 2 DWI scans instead of the 4 DWI scans HCP collects (AP & PA in 98 directions and AP & PA in 99 directions). What's the best way to adapt the HCP dMRI protocol?
>
> For 1.5mm isotropic voxels with multi-shells (b=1000 & b=3000) would it be better to:
>
> 1. collect more directions in a single phase encoding direction
> - ie. AP dir 98, AP dir 99, PA b0s
> 2. fewer directions acquired in both phase encoding directions
> - ie. AP dir 98, PA dir 98
> 3. a different number of directions acquired for each phase encoding direction
> - ie. AP dir 98, PA dir 99
>
> I want to make sure that there are sufficient directions for each shell. Because of the interspersed b0s #2 only has 46 unique directions for b=1500 and b=3000 vs. #1 which would have 93 directions for b=1500 and 92 directions for b=3000. Could #3 provide a solution to increase the angular resolution? Do you recommend one of these options over the other or a different approach? At the moment we are interested in FA and don't plan to use this data for tractography but may in the future. For Eddy correction what's more important the number of gradients or having the reverse phase encoding acquisition?
>
> Many thanks!
> Ashley
>
> ########################################################################
>
> To unsubscribe from the FSL list, click the following link:
> https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=FSL&A=1
>
> This message was issued to members of www.jiscmail.ac.uk/FSL, a mailing list hosted by www.jiscmail.ac.uk, terms & conditions are available at https://www.jiscmail.ac.uk/policyandsecurity/
########################################################################
To unsubscribe from the FSL list, click the following link:
https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=FSL&A=1
This message was issued to members of www.jiscmail.ac.uk/FSL, a mailing list hosted by www.jiscmail.ac.uk, terms & conditions are available at https://www.jiscmail.ac.uk/policyandsecurity/
|