Calculate effective echo spacing and total read-out time for GE machine


#1

Hello:
I have a question for calculating the effective echo spacing and total read-out time for different machine(Siemens, GE, Philips), and I made it with Siemens and Philips, but can not find the formula to calculate with GE machine. Here is the link for the Siemens and Philips:

  1. Siemens: https://lcni.uoregon.edu/kb-articles/kb-0003

  2. Philipq: http://support.brainvoyager.com/functional-analysis-preparation/27-pre-processing/459-epi-distortion-correction-echo-spacing.html

  3. GE, I tried with FSL fugue, but did not understand it well, also a link to the GE: https://cni.stanford.edu/wiki/GE_Processing#Fieldmaps

Any suggestion will be appreciated, I searched google but not get more information.

Thanks in advance

Hao


#2

Hi @Junhao_Wen, did you finally find out an answer?

The only thing I can add here is that Siemens’ “EPI factor” in GE nomenclature is “ETL” - (echo train length). If you had access to read the PE bandwidth, you could calculate the total read-out time as 1/PE bandwidth and the Effective echo spacing as 1 / (PE bandwidth * (ETL - 1) * acc factor)


#3

Hi Hao,

We are looking for the Philips solution. Do you happen to have the formula? The link does not work anymore.

Thank you

Eduardo


#4

Nevermind, I found the new link:

https://support.brainvoyager.com/brainvoyager/functional-analysis-preparation/29-pre-processing/78-epi-distortion-correction-echo-spacing-and-bandwidth

Thanks

Eduardo


#5

dcm2niix (and I believe dicm2nii) will automatically insert echo spacing parameters into the BIDS file. Michael Harms provided a validation dataset that demonstrated accuracy of the algorithms for computing these parameters from Siemens headers. I suspect this method works for all Siemens scanners from B11-E11. Unfortunately, the new Siemens DICOM XA format is relatively impoverished, and I do not think total readout time can be computed from the DICOMs.

To the best of my knowledge, contemporary DICOM data from GE and Philips do not contain all the parameters required to compute these values. The links above are useful, but require a user to know several sequence settings that can be viewed from the MRI console but are not stored in the DICOMs. If anyone identifies a way to detect there parameters from the scanner, I would like to know.