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Hi Greg,
Ultimately, getting all the signs right is a complicated combination of (1) how the manufacturer implements its PE gradient blips, (2) the DICOM to NIFTI converter that you use (and whether you 'reorient' the data, e.g., using 'fslreorient2std'), (3) your
settings for "Phase enc. dir." and "Invert RO/PE Polarity and (4) the plane/oriention that the EPI is acquired in. It is very dangerous for us to provide you a "rule", as it is very difficult to anticipate all usage cases. That's why I stressed the importance
of confirming that you have all the conventions correct in your own data (by explicitly inverting the value of the "PhaseEncodeList" parameter in the pipeline, and seeing if the result indeed gets worse).
That said, as a sanity check for you, on a Siemen's scanner, acquiring transverse slices, using 'dcm2nii' as your NIFTI converter, with transverse slices, I would expect that you find the following:
If phase encoding direction=COL, and directionPositive=1, then PEdir="-y"
If phase encoding direction=COL, and directionPositive=0, then PEdir="+y"
As Matt noted, those "PEdir" (i.e., PhaseEncodeList values)
themselves are dependent on a certain convention for the SpinEchoFieldMaps, which I believe is outlined in the comments of the HCP pipeline scripts.
cheers,
-MH
--
Michael Harms, Ph.D.
-----------------------------------------------------------
Conte Center for the Neuroscience of Mental Disorders
Washington University School of Medicine
Department of Psychiatry, Box 8134
660 South Euclid Ave.
Tel: 314-747-6173
St. Louis, MO 63110
Email: mha...@wustl.edu
From: <Book>, Gregory <gregory.b...@hhchealth.org>
Date: Monday, December 15, 2014 4:17 PM To: "Harms, Michael" <mha...@wustl.edu>, Matt Glasser <glass...@wusm.wustl.edu>, "hcp-users@humanconnectome.org" <hcp-users@humanconnectome.org> Subject: Re: [HCP-Users] spin echo phase encoding direction Ok, good to know what that means as to how the data is collected relative to the label.
-G
From: Harms, Michael [mha...@wustl.edu]
Sent: Monday, December 15, 2014 4:10 PM To: Book, Gregory; Glasser, Matthew; Harms, Michael; hcp-users@humanconnectome.org Subject: Re: [HCP-Users] spin echo phase encoding direction Hi,
If you had "A>>P" with "Invert RO/PE Polarity" checked, then that would be the same as if you had set "P>>A" and "Invert RO/PE Polarity" was left unchecked.
The *dInPlaneRot field does NOT include the impact of the "Invert RO/PE Polarity" flag. Sorry, I directed you to the wrong shadow field previously. "PhaseEncodingDirectionPositive" is (according to my notes) subfield #20 of (0029, 1010). If it doesn't
have a value, that means it value was 0 for that scan. (Its value is either 0 or 1).
cheers,
-MH
--
Michael Harms, Ph.D.
-----------------------------------------------------------
Conte Center for the Neuroscience of Mental Disorders
Washington University School of Medicine
Department of Psychiatry, Box 8134
660 South Euclid Ave.
Tel: 314-747-6173
St. Louis, MO 63110
Email: mha...@wustl.edu
From: <Book>, Gregory <gregory.b...@hhchealth.org>
Date: Monday, December 15, 2014 2:59 PM To: Matt Glasser <glass...@wusm.wustl.edu>, "Harms, Michael" <mha...@wustl.edu>, "hcp-users@humanconnectome.org" <hcp-users@humanconnectome.org> Subject: Re: [HCP-Users] spin echo phase encoding direction I’m slightly more confused now. So, using the CMRR sequences, if I set the phase encoding direction on my spin echo to A>>P, and “Invert RO/PE Polarity” option is checked… a) what is the actual phase direction of the data b) what is recorded in the DICOM header in the *.dInPlaneRot field?
From: Glasser, Matthew [mailto:glass...@wusm.wustl.edu]
If your phase encoding directions are inverted, I would recommend swapping the SpinEchoPositive and NegativeImage values. This would make the computed field map have the same sign as a typical field map and then the PhaseEncodeList would not have to change.
Peace,
Matt.
From: <Book>, Gregory <gregory.b...@hhchealth.org>
Would that be the *.dInPlaneRot value for each slice in the CSA header?
From: Harms, Michael [mailto:mha...@wustl.edu]
The value of "PhaseEncodingDirectionPositive" in the shadow field (0029,1020) reflects the combination of both "Phase enc. dir." on the Routine tab (e.g., "A>>P" vs. "P>>A") AND the setting of "Invert RO/PE Polarity" on the Sequence/Special tab.
As long as you have one of each polarity, you can use the spin echo field map correction. I highly recommend that you purposely try both possible assignments, and visually confirm which one is giving the correct results. That's because the correct setting for PhaseEncodeList (e.g., "y-" vs. "y+") can in theory even be dependent on which DICOM to NIFTI converter you use. (e.g., if one converter returns a +LAS orientation, while another returns a +LPS orientation, then the proper settings for PhaseEncodeList may be swapped).
cheers, -MH
-- Michael Harms, Ph.D. ----------------------------------------------------------- Conte Center for the Neuroscience of Mental Disorders Washington University School of Medicine Department of Psychiatry, Box 8134 660 South Euclid Ave. Tel: 314-747-6173 St. Louis, MO 63110 Email: mha...@wustl.edu
From: <Book>, Gregory <gregory.b...@hhchealth.org>
I have another question about the spin echo images, hopefully this will be my last question!
It turns out that we’ve been collecting our spin echo images with the “Invert RO/PE Polarity” option selected, which apparently inverts the phase encoding direction 180deg, but does not record this to the DICOM header. We’ve been collecting the EPI images without this inversion. So, for our data: EPI is A>>P “A>>P” SE is actually P>>A “P>>A” SE is actually A>>P
Would we be able to use the spin echo correction if we simply switched the positive and negative images? So, would this work for our data? TaskList=”task1” PhaseEncodeList=”y-“ … SpinEchoPositiveImage=”the P>>A labeled image (actually acquired A>>P)” SpinEchoNegativeImage=”the A>>P labeled image (actually acquired P>>A)”
-G
_________________________________________________ Gregory Book Senior Technology Manager Olin Neuropsychiatry Research Center, Institute of Living, Hartford Hospital 200 Retreat Avenue Hartford, CT 06106 Tel: 860-545-7267 Fax: 860-545-7797
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The materials in this message are private and may contain Protected Healthcare Information or other information of a sensitive nature. If you are not the intended recipient, be advised that any unauthorized use, disclosure, copying or the taking of any action in reliance on the contents of this information is strictly prohibited. If you have received this email in error, please immediately notify the sender via telephone or return mail. _______________________________________________ The materials in this message are private and may contain Protected Healthcare Information or other information of a sensitive nature. If you are not the intended recipient, be advised that any unauthorized use, disclosure, copying or the taking of any action in reliance on the contents of this information is strictly prohibited. If you have received this email in error, please immediately notify the sender via telephone or return mail. _______________________________________________ |
- [HCP-Users] spin echo phase encoding direction Book, Gregory
- Re: [HCP-Users] spin echo phase encoding direction Harms, Michael
- Re: [HCP-Users] spin echo phase encoding directi... Book, Gregory
- Re: [HCP-Users] spin echo phase encoding dir... Glasser, Matthew
- Re: [HCP-Users] spin echo phase encoding... Book, Gregory
- Re: [HCP-Users] spin echo phase enc... Glasser, Matthew
- Re: [HCP-Users] spin echo phase enc... Harms, Michael
- Re: [HCP-Users] spin echo phase... Book, Gregory
- Re: [HCP-Users] spin echo p... Harms, Michael
- Re: [HCP-Users] spin echo p... Book, Gregory
- Re: [HCP-Users] spin echo p... Harms, Michael
