EffectiveEchoSpacing and TotalReadoutTime definitions

[hugofluhr]

Hi all,

I am trying to find out how to compute EffectiveEchoSpacing and TotalReadoutTime for my BOLD data. So far I have failed to find a reference that gives a formula for these, I have heard that different softwares have different definitions so I am especially looking for references that are compatible with fmriprep (/sdcflows) distortion correction.

Many thanks,
Hugo

[jsein]

Hi @hugofluhr

These are two references I like for these definitions:

• EPI distortion correction: echo spacing and bandwidth - Support BrainVoyager

• field maps – Lewis Center for Neuroimaging

This post seems to be very complete too:

Consolidating EPI echo spacing and readout time for Philips scanner

Dear All, I know that this has been previously discussed on various forums . However, I have noticed some discrepancy in the way EPI echo spacing and readout time are being calculated, specifically for Philips scanner. I will first attempt to summarize various methods that I have found and then through two cases show the discrepancies. I hope that this thread can be used for resolving these. The readout time is an important value that is required for “unwarping” using fieldmap; it is additional…

[effigies]

Here are the sdcflows docs on methods we can use to determine the TRT:

https://www.nipreps.org/sdcflows/master/api/sdcflows.utils.epimanip.html#sdcflows.utils.epimanip.get_trt

If you are using dcm2niix, you may have gotten EstimatedEchoSpacing. dcm2niix is conservative and will not claim a EchoSpacing when it is not directly in the DICOMs, but you can rename it to EchoSpacing if you want sdcflows to pick it up.

[hugofluhr]

Thank you both for these references, I will look at them in more details!

[mr-jaemin]

For GEHC dataset, EffectiveEchoSpacing and TotalReadoutTime documented here:
Also, dcm2niix reports these in BIDS JSON for GEHC

dcm2niix/GE at development · rordenlab/dcm2niix