Hi,
you sould be able to tell by the direction of the geometric distortions.
For A>P, these should run from anterior to posterior.
Cheers,
Andreas
Am 11.02.15 10:27 schrieb "M Barendse" unter <[log in to unmask]>:
>Dear FSL users,
>We have acquired DWI data with a Philips 3T scanner. I would like to run
>topup and eddy on these and for that you need to create a file with
>acquisition parameters. However it©ös unclear to me what to put in this
>file.
>Philips scanners do not give you the phase encoding direction. Instead, it
>gives a Œfold-over direction©ö and Œfat shift direction©ö. Our scans are all
>in Œfold-over direction = ©øAP©÷©ö, and we have 1 b0 and 30 dwi©ös with Œfat
>shift direction = ©øA©÷ as well as 1 b0 and 30 dwi©ös with Œfat shift
>direction
>= ©øP©÷©ö.
>The question is: does Œfat shift direction = ©øA©÷ mean A -> P and ©øP©÷ P ->
>A
>or vice versa?
>A similar question was asked previously (see
>https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind1308&L=FSL&P=R26762&1=FS
>L&
>9=A&I=-3&J=on&d=No+Match%3BMatch%3BMatches&z=4 ). It was suggested that
>you
>can find out the answer to this question by running the correction both
>ways
>(i.e. with different acquisition parameters) and see which possibility
>leads
>to a good correction.
>I have tried this by running topup and applytopup with both of the
>following
>acquisition parameters.
>0 -1 0 0.19
>0 1 0 0.19
>and
>0 1 0 0.19
>0 -1 0 0.19
>Both options however lead to the exact same corrected images. Does anyone
>have an explanation for this?
>Kind regards, Marjolein
>
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