Multipart combined DWI scheme with different acquisition parameters

[kabilar]

Hi BIDS team, we have a situation that is different than the Multipart (split) DWI scheme, whereby we have acquired a single concatenated DWI run but parts of the DWI run have different acquisition parameters (i.e. TE, time between diffusion gradients [uppercase delta], duration of each diffusion gradient [lowercase delta]). It is ideal for us to keep this data as a single volume since downstream analysis is performed on the entire DWI run.

Right now we are thinking of saving sidecar files similar to the .bvals and .bvecs with the TE values, time between diffusion gradients, and duration for each diffusion gradient as .techo, .tdelta, .tsmalldelta, respectively. What do you think? Happy to submit a pull request to the spec if this approach is agreed upon. Thanks.

cc @satra @Tinggong @ayendiki

[kabilar]

One alternative option would be to break the DWI run into separate volumes using the acq-<label> entity and create a sidecar json file for each volume with the different parameters.

[kabilar]

I just noticed that the EchoTime can be an array of numbers.

@Tinggong Perhaps the time between diffusion gradients and duration for each diffusion gradient can be represented by the RepetitionTime and FrameAcquisitionDuration, respectively?

We would just need to modify the BIDS spec so that the RepetitionTime and FrameAcquisitionDuration can also be an array of numbers.