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||<100% bgcolor="#FFFF99">'''Using a field-map to undistort EPIs'''[[BR]][wiki:FmBackground Background][[BR]][wiki:FmPower Improvement in power!][[BR]][wiki:FmFieldmaps Acquiring fieldmaps][[BR]][wiki:FmDownload Download][[BR]][wiki:FmRequirements What you'll need to undistort an EPI data series][[BR]][wiki:FmReference Guide and reference][[BR]][wiki:FmExample Step-by-step example][[BR]][wiki:FmBatch Batch mode]||
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== Siemens step-by-step example ==
First, get the [http://imaging.mrc-cbu.cam.ac.uk/downloads/fmu/fmu_siemens_exampledataset.tar Siemens example dataset (2MB)] (thanks to Michael Benharrosh and Marlene Richter at Princeton University for this).
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||<tablewidth="648px">First, get the [http://www.mrc-cbu.cam.ac.uk/Imaging/Common/download_files/fmu_siemens_exampledataset.tar Siemens example dataset (2MB)] (thanks to Michael Benharrosh and Marlene Richter at Princeton University for this). Unzip it and you should have three images in analyze format: an EPI, and the phase and magnitude from a gre_fieldmapping sequence. When you've installed the tool, at the matlab prompt type >> fieldmap_undistort_v3 Then, in the SPM window, choose the following options The EPI before and after undistortion should look like this: There's nothing that can be done about the dropout, but even the large distortion produced by this mis-shimming is mostly corrected. If you are going to collect your own data on a Siemens machine and your system doesn't allow you to reconstruct both mag and phase simultaneously, you'll need to change one line in your pulse sequence. Contact Stefan Thesen at Siemens [his surname] @siemens.com who'll probably be able to help.) First, get the [http://www.mrc-cbu.cam.ac.uk/Imaging/Common/download_files/fmu_exampledataset.tar Bruker example dataset (34MB)] Run by typing fieldmap_undistort at the SPM prompt, and choose the following options. Where requested, choose the directories and files from your copy of the data. The undistorted EPIs will be in the same directory as the raw EPIs, with the added suffix ‘u’. ||
|| ||
----
[http://imaging.mrc-cbu.cam.ac.uk/pdfs/ ]
Unzip it and you should have three images in analyze format: an EPI, and the phase and magnitude from a gre_fieldmapping sequence.
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CBU Imaging Website.
© Copyright MRC Cognition and Brain Sciences Unit 2006.
Page maintained by: daniel.bor@mrc-cbu.cam.ac.uk
When you've installed the tool, at the matlab prompt type
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>> fieldmap_undistort_v3

Then, in the SPM window, choose the following options

||<tablewidth="90%">Accept all defaults||No||
||Start at which stage||Reco ''(default)''||
||Which option?||Siemens gre_fieldmapping||
||Realign fieldmaps to com||Yes ''(default)''||
||Shift EPI forward by||0 ''(default)''||
||Evolution time||2.46 ''(default)''||
||Slice angle of EPIs relative to fieldmaps||0 ''(default)''||
||Bandwidth||2604||
||Axis of phase encoding (undistortion)||y ''(default)''||
||Constrain coregistration||Translations only ''(default)''||
||Type of interpolation||sinc ''(default)''||
||Maximum shift allowed||9999 ''(default)''||
||Adjust mean displacement?||Force mean to zero ''(default)''||
||Directory for fieldmap files||Choose a blank directory (e.g., fieldmaps)||
||Choose GRE phase map||PHANTOM_FIELDMAP_PHASE.img||
||Choose GRE magnitude map||PHANTOM_FIELDMAP_MAG.img||
||Choose EPI to coregister to||PHANTOM_EPI.img||
||Choose EPIs to undistort||PHANTOM_EPI.img||
The EPI before and after undistortion should look like this:

||<tablewidth="90%"> http://imaging.mrc-cbu.cam.ac.uk/images/fm_phantom_before_undist.jpg || http://imaging.mrc-cbu.cam.ac.uk/images/fm_phantom_after_undist.jpg ||
There's nothing that can be done about the dropout, but even the large distortion produced by this mis-shimming is mostly corrected.

If you are going to collect your own data on a Siemens machine and your system doesn't allow you to reconstruct both mag and phase simultaneously, you'll need to change one line in your pulse sequence. Contact Stefan Thesen at Siemens [his surname] @siemens.com who'll probably be able to help.)

== Bruker step-by-step example ==
First, get the [http://imaging.mrc-cbu.cam.ac.uk/downloads/fmu/fmu_exampledataset.tar Bruker example dataset (34MB)]

Run by typing fieldmap_undistort at the SPM prompt, and choose the following options. Where requested, choose the directories and files from your copy of the data.

||<tablewidth="638px"^ 38%>Accept all defaults: ||<^ 62%>Yes ||
||<^ 38%>Choose Directory of Phase Map: ||<^ 62%>example_dataset/phasemaps ||
||<^ 38%>Choose Directory of Phase 1a: ||<^ 62%>example_dataset/rawprereco/10 ||
||<^ 38%>Choose Directory of Phase 1b: ||<^ 62%>example_dataset/rawprereco/11 ||
||<^ 38%>Choose Directory of Phase 1c: ||<^ 62%>example_dataset/rawprereco/12 ||
||<^ 38%>Choose EPI header file (IMND or brkhdr): ||<^ 62%>example_dataset/epis/000484 m03_04_EPI.brkhdr ||
||<^ 38%>Choose EPI to register to: ||<^ 62%>example_dataset/epis/meany000484-m03_04_EPI_0002.img ||
||<^ 38%>Choose EPI to undistort: ||<^ 62%>example_dataset/epis/meany000484-m03_04_EPI_0002.img ||
The undistorted EPIs will be in the same directory as the raw EPIs, with the added suffix ‘u’.

Using a field-map to undistort EPIsBR[wiki:FmBackground Background]BR[wiki:FmPower Improvement in power!]BR[wiki:FmFieldmaps Acquiring fieldmaps]BR[wiki:FmDownload Download]BR[wiki:FmRequirements What you'll need to undistort an EPI data series]BR[wiki:FmReference Guide and reference]BR[wiki:FmExample Step-by-step example]BR[wiki:FmBatch Batch mode]

Siemens step-by-step example

First, get the [http://imaging.mrc-cbu.cam.ac.uk/downloads/fmu/fmu_siemens_exampledataset.tar Siemens example dataset (2MB)] (thanks to Michael Benharrosh and Marlene Richter at Princeton University for this).

Unzip it and you should have three images in analyze format: an EPI, and the phase and magnitude from a gre_fieldmapping sequence.

When you've installed the tool, at the matlab prompt type

>> fieldmap_undistort_v3

Then, in the SPM window, choose the following options

Accept all defaults

No

Start at which stage

Reco (default)

Which option?

Siemens gre_fieldmapping

Realign fieldmaps to com

Yes (default)

Shift EPI forward by

0 (default)

Evolution time

2.46 (default)

Slice angle of EPIs relative to fieldmaps

0 (default)

Bandwidth

2604

Axis of phase encoding (undistortion)

y (default)

Constrain coregistration

Translations only (default)

Type of interpolation

sinc (default)

Maximum shift allowed

9999 (default)

Adjust mean displacement?

Force mean to zero (default)

Directory for fieldmap files

Choose a blank directory (e.g., fieldmaps)

Choose GRE phase map

PHANTOM_FIELDMAP_PHASE.img

Choose GRE magnitude map

PHANTOM_FIELDMAP_MAG.img

Choose EPI to coregister to

PHANTOM_EPI.img

Choose EPIs to undistort

PHANTOM_EPI.img

The EPI before and after undistortion should look like this:

http://imaging.mrc-cbu.cam.ac.uk/images/fm_phantom_before_undist.jpg

http://imaging.mrc-cbu.cam.ac.uk/images/fm_phantom_after_undist.jpg

There's nothing that can be done about the dropout, but even the large distortion produced by this mis-shimming is mostly corrected.

If you are going to collect your own data on a Siemens machine and your system doesn't allow you to reconstruct both mag and phase simultaneously, you'll need to change one line in your pulse sequence. Contact Stefan Thesen at Siemens [his surname] @siemens.com who'll probably be able to help.)

Bruker step-by-step example

First, get the [http://imaging.mrc-cbu.cam.ac.uk/downloads/fmu/fmu_exampledataset.tar Bruker example dataset (34MB)]

Run by typing fieldmap_undistort at the SPM prompt, and choose the following options. Where requested, choose the directories and files from your copy of the data.

Accept all defaults:

Yes

Choose Directory of Phase Map:

example_dataset/phasemaps

Choose Directory of Phase 1a:

example_dataset/rawprereco/10

Choose Directory of Phase 1b:

example_dataset/rawprereco/11

Choose Directory of Phase 1c:

example_dataset/rawprereco/12

Choose EPI header file (IMND or brkhdr):

example_dataset/epis/000484 m03_04_EPI.brkhdr

Choose EPI to register to:

example_dataset/epis/meany000484-m03_04_EPI_0002.img

Choose EPI to undistort:

example_dataset/epis/meany000484-m03_04_EPI_0002.img

The undistorted EPIs will be in the same directory as the raw EPIs, with the added suffix ‘u’.

CbuImaging: FmExample (last edited 2013-03-07 21:24:05 by localhost)