Hi Ajna,
As far as I understand you should be able to correct spin echo data by the
same method (theoretically 1=yes but i haven't tried it myself). Spin echo
EPI will contain distortion due to background magnetic field gradients via
the same mechanism as gradient echo EPI.
You cannot get a field map from spin echo data at 2 TEs because it does not
contain signal evolution due to background magnetic fields. Gradient echo
data is T2* weighted and so is contains signal decay (from T2 and background
fields) and phase evolution from the background magnetic field gradients
that you use to calculate the local field. So the answer to 2 is that you
need to calculate the field maps in the normal way from gradient echo data.
Best regards
David
______________________________________
David Carmichael PhD MInstP
Senior Research Fellow in MR Physics
Department of Clinical and Experimental Epilepsy
Institute of Neurology, University College London
Correspondence to:
Wellcome High Field MR Research Laboratory
University College London
12 Queen Square
London WC1N 3AR
Tel +44 (0)20 76762006
Fax +44 (0)20 76762005
email [log in to unmask]
-----Original Message-----
From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] On
Behalf Of Haakon G. Engen
Sent: 20 January 2009 20:41
To: [log in to unmask]
Subject: [SPM] SV: [SPM] field map for spin echo epi
Hi Ajna,
While I can't address your first question, I can affirm that using the phase
and magnitude images from a 3.0 T Achieva can be used for unwarping in the
Fieldmap toolbox as I've recently implemented that step on data from our own
Achieva scanner. The one caveat is that the SPM Fieldmap toolbox requires
that they are acquired with either AP or PA fold-over direction.
Kind regards,
Haakon Engen
University of Oslo
----- Opprinnelig melding -----
Fra: Ajna <[log in to unmask]>
Sendt: 20. januar 2009 20:04
Til: [log in to unmask]
Emne: [SPM] field map for spin echo epi
Dear SPMers,
I would like to use the SPM5 unwarping tool to correct any distortions
on my spin-echo EPIs acquired at 3T.
Few questions:
1.) Are field map generation tool and unwarping algorithm usable on
spin-echo epi data (as SPM had been developed primarily for use with
BOLD acquisition)?
2.) Our scanner (3T Philips Achieva) acquires magnitude and phase images
based on gradient-echo non-EPI sequence. Can I use these images for
making the field map to correct spin-echo epi data, or would I have to
acquire se-epi data at 2 TEs?
All hints and advice will be extremely appreciated.
-Ajna Borogovac, Columbia University
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