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December 2019

ROMEO Unwrapping

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Please cite ROMEO if you use it!

Getting Started

This repository contains ROMEO 3D/4D unwrapping on arrays.
For MR data in the NIfTI format, a compiled command line tool is available under ROMEO (windows and linux executables; does not require a Julia installation) and otherwise, for opening NIfTI files in Julia NIfTI.jl or MriResearchTools.jl can be helpful.

Usage

using ROMEO
unwrapped = unwrap(phasedata3D; mag=magdata3D)

or via MriResearchTools:

using MriResearchTools
phase4D = readphase("Phase.nii") # 4D phase in NIfTI format
unwrapped = unwrap(phase4D; TEs=[4,8,12])

Function Reference

https://korbinian90.github.io/ROMEO.jl/dev

Different Use Cases

Multi-Echo

If multi-echo data is available, supplying ROMEO with multi-echo information should improve the unwrapping accuracy. The same is true for magnitude information.

Phase Offsets

If the multi-echo data contains large phase offsets (phase at echo time zero), default template unwrapping might fail. Setting the individual-unwrapping flag is a solution, as it performs spatial unwrapping for each echo instead. The computed B0 map is not corrected for remaining phase offsets.

For proper handling, the phase offsest can be removed using mcpc3ds from MriResearchTools. This works for monopolar and bipolar data, already combined or uncombined channels. However, if the phase is already "corrupted" by other coil combination algorithms, it might not be possible to estimate and remove the phase offsets.

Repeated Measurements (EPI)

4D data with an equal echo time for all volumes should be unwrapped as 4D for best accuracy and temporal stability. The echo times can be set to TEs=ones(size(phase,4))

Setting the Template Echo

In certain cases, the phase of the first echo/time-point looks differently than the rest of the acquisition, which can occur due to flow compensation of only the first echo or not having reached the steady state in fMRI. This might cause template unwrapping to fail, as the first echo is chosen as the template by default.
With the optional argument template=2, this can be changed to the second (or any other) echo/time-point.

License

This project is licensed under the MIT License - see the LICENSE for details

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