DWI grouping for sub-01
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Output "sub-01" (MultipartID auto+concat+0 [inferred]): 2 series
  Distortion group sub-01_dir-LR (PE i-, TRT 0.05s):
    - sub-01_dir-LR_dwi.nii.gz
    corrected by: auto+pepolar+ij [inferred]
  Distortion group sub-01_dir-PA (PE j, TRT 0.05s):
    - sub-01_dir-PA_dwi.nii.gz
    corrected by: auto+pepolar+ij [inferred]

Fieldmap estimations:
  auto+pepolar+ij [inferred]: PEPOLAR (reverse phase-encoding)
    - sub-01_dir-LR_dwi.nii.gz
    - sub-01_dir-PA_dwi.nii.gz
    phase encoding axes: i (one direction only), j (one direction only)

Processing preview: eddy + TOPUP (--hmc-method eddy --sdc-method topup)
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Output "sub-01" (2 series):
  1. Each series is denoised on its own, then all 2 series are concatenated. (--denoise-after-combining reverses this order.)
  2. TOPUP estimates the susceptibility field from b=0 images spanning 2 distortion groups (2 rows in the acquisition-parameters file).
  3. eddy corrects head motion, eddy currents, and susceptibility distortion in one model, using the TOPUP field. Every volume is assigned to its distortion group in the eddy index file.
  4. The corrected series is written as one output file.

Processing preview: TORTOISE + DRBUDDI (--hmc-method tortoise --sdc-method drbuddi)
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Output "sub-01" (2 series):
  1. Each series is denoised on its own, then all 2 series are concatenated. (--denoise-after-combining reverses this order.)
  2. TORTOISE DIFFPREP corrects head motion and eddy currents separately for each distortion group (sub-01_dir-LR, sub-01_dir-PA).
  3. DRBUDDI has no opposing blip for axis i, TRT 0.05s; axis j, TRT 0.05s, so they are left uncorrected (no T2w for a T2Wreg fallback).
  4. The corrected series is written as one output file.
  !! WARNING [drbuddi-no-opposing-pair]: Estimation 'auto+pepolar+ij' has blip group(s) with no opposing (blip-up/blip-down) pair: axis i, TRT 0.05s; axis j, TRT 0.05s. DRBUDDI needs a matched pair, so on the TORTOISE path those series are left uncorrected (no T2w for a T2Wreg fallback). Add the missing reverse blip(s) to use DRBUDDI for 'sub-01'.

Processing preview: eddy + TOPUP→DRBUDDI (--hmc-method eddy --sdc-method topup+drbuddi)
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Output "sub-01" (2 series):
  1. Each series is denoised on its own, then all 2 series are concatenated. (--denoise-after-combining reverses this order.)
  2. TOPUP estimates an initial susceptibility field from the b=0 images (as in the FSL path).
  3. eddy corrects head motion and eddy currents using the TOPUP field.
  4. There is no reverse phase-encoded dMRI series for DRBUDDI to refine with, and no T2w or synthetic b=0 for a T2Wreg stage: correction is single-stage (TOPUP + eddy).
  5. The corrected series is written as one output file.
  !! WARNING [drbuddi-refinement-not-useful]: Estimation 'auto+pepolar+ij' has no reverse phase-encoded dMRI series: a DRBUDDI second stage would reuse the same b=0 images TOPUP already consumed and is probably not useful. No T2w or SyNb0 synthetic b=0 is available for a T2Wreg second stage either, so 'sub-01' gets single-stage (TOPUP+eddy) correction.

Processing preview: SHORELine + DRBUDDI (--hmc-method shoreline --sdc-method drbuddi)
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Output "sub-01" (2 series):
  1. Each series is denoised on its own, then all 2 series are concatenated. (--denoise-after-combining reverses this order.)
  2. SHORELine iteratively corrects head motion by registering each volume to a 3dSHORE signal-model prediction (eddy currents are not corrected).
  3. DRBUDDI has no opposing blip for axis i, TRT 0.05s; axis j, TRT 0.05s, so those series are left uncorrected (SHORELine has no T2Wreg fallback).
  4. The corrected series is written as one output file.
  !! WARNING [drbuddi-no-opposing-pair]: Estimation 'auto+pepolar+ij' has blip group(s) with no opposing (blip-up/blip-down) pair: axis i, TRT 0.05s; axis j, TRT 0.05s. DRBUDDI needs a matched pair, so on the SHORELine path those series are left uncorrected (SHORELine has no T2Wreg fallback). Add the missing reverse blip(s) to use DRBUDDI for 'sub-01'.
