Open tashrifbillah opened 3 years ago
I haven't worked with DWI in BIDS much yet, but at first glance I think summing dir
entities is grounds for confusion and should be avoided.
I think what would be most beneficial here is a sense of run
. Looking at the diffusion specification, it could look like:
sub-2001_ses-1_acq-99_dir-AP_run-1_desc-XcUn_dwi.nii.gz
sub-2001_ses-1_acq-99_dir-PA_run-2_desc-XcUn_dwi.nii.gz
then, if you correct 1 volume, you can keep the run
entity, and when you are merging volumes, drop it altogether. Besides naming, JSON sidecars would be most beneficial.
I think summing dir entities is grounds for confusion
Can you explain why?
It is unclear whether the file is a processed derivative of sub-2001_ses-1_dir-198_dwi.nii.gz
or 2 (or more) separate files.
Also, it seems you have the acq
/dir
entities switched:
The OPTIONAL acq-
The OPTIONAL dir-
Edit: Removed bit because I didn't realize @mgxd had posted the original spec link, and also answered your question already.
Just as a note, the next relevant section is Derivatives - File naming conventions.
Each Derivatives filename MUST be of the form:
<source_entities>[_keyword-<value>]_<suffix>.<ext>
(where<value>
could either be an<index>
or a<label>
depending on the keyword; see Definitions).
I'm trying to find the text1, but there should be a rule that says you can drop source entities when they no longer apply to a file.
Re the original filenames, what does XcUn
mean? Are these already derivatives?
sub-2001_ses-1_acq-AP_dir-99_desc-XcUn_dwi.nii.gz sub-2001_ses-1_acq-PA_dir-99_desc-XcUn_dwi.nii.gz
1 Here is the text:
One exception to this rule is filename entities that are no longer relevant.
Re the original filenames, what does XcUn mean?
Xc
: axis alignment
Un
: Gibbs unringing
Are these already derivatives?
Yes. After each process, we have appended a string to _desc-*
to indicate the process that was done.
The above is consistent with the following of the linked source:
When necessary to distinguish two files that do not otherwise have a distinguishing entity, the _desc-
Got it. I think I agree with @mgxd's assessment, overall. Use dir-
for PE direction. I'm not sure if acq-
is buying you much unless you have different acq-
s. Editing acq-
downstream breaks the visual connection with the source images.
As I'm also not very familiar with diffusion techniques, if there are remaining questions, it might be a good idea to ping the BIDS-DWI community (I'd probably ask on https://neurostars.org) who may have seen similar sequences and have good suggestions.
Also:
Just for our mental peace--is the acq
and dir
specification new? We have been naming as above for more than a year and I am not sure how we switched them!
Hi all, I would like to know your opinion about BIDS convention naming of topup+eddy corrected data of the following two:
when one set of volume is corrected, we name the output:
(
_dir-99
is preserved)when both volumes are corrected, we name the output:
(
_dir-99
is doubled hence_dir-198
)The other candidate could be to drop
_dir-*
completely because the reader already knows about topup+eddy correction step from_desc-XcUnEdEp
.1 The rationale for dropping
_acq-*
is that acquisition direction-specific distortion has been corrected by topup. 2 Addition ofEdEp
string after_desc-XcUn
signals that topup+eddy correction has been done.@effigies @mgxd @sbouix @yrathi