BIDS tag RepetitionTimeExcitation

[neurolabusc]

For EPI-based DWI and fMRI scans the DICOM RepetitionTime (0018, 0080) is identical to the sampling rate. However, this is not the case for all sequences. Upcoming versions of dcm2niix measure the time between volumes (based on AcquisitionTime of the first slice in the first and last volume). If this differs between the DICOM RepetitionTime (0018, 0080), the BIDS tag RepetitionTime will be used for time between volumes and the tag RepetitionTimePreparation will store the value of (0018, 0080).

[neurolabusc]

dcm2niix will follow the advice of Paul S. Morgan (below) for BEP001 tags. Perhaps @mr-jaemin and @drmclem can provide any advice from a manufacturer perspective or advocate for more details in DICOMS with future software releases.

Regarding non-EPI scans, the TR in 0018,0080 appears to be manufacturer specific. Unfortunately, the is no known mechanism to infer both RepetitionTimeExcitation and RepetitionTimeInversion from DICOM.

• Siemens: this has traditionally been RepetitionTimeInversion (when 0018,9009 Inversion Recovery is YES), else it’s RepetitionTimeExcitation. FYI, I don’t see 0018,0082 set for a Siemens MPRAGE exported from XA20 as enhanced DICOM. But the inversion time is now in 0018,9079.
• Philips: 0018,0080 TR always appears to be RepetitionTimeExcitation. I don’t think RepetitionTimeInversion is stored directly. 0018,9009 Inversion Recovery isn’t set for MPRAGE (but 2001,101c is set to INV and the TI is stored in 2001,101b) however 0018,9009 is YES for 3D FLAIR.
• GE: Appears similar to Siemens, i.e., the TR in 0018,0080 is RepetitionTimeInversion (when 0018,0020 Scanning Sequence contains IR), else it’s RepetitionTimeExcitation. The inversion time is in 0018,0082.
  The BRAVO sequence is interesting – it has an inversion pulse (with TI stored in 0018,0082), but no IR in 0018,0020 and the TR in 0018,0080 is in the range of a few ms, so this is RepetitionTimeExcitation and so follows the above “rule”. As do other GE sequences (including FLAIR with an IR; FIESTA, CUBE, spin echo – all without IR)