Support siemens phase map images

[bwheelz36]

Started work on this on the PhaseMap branch

• Data here

This site seems useful:

"if you used the stock double-echo gradient echo field map sequence (method 1), you'll have two series. The first will contain two magnitude images, one for each echo. The second series will contain a single phase difference image, a subtraction of the two phase images from each echo."

This is indeed what we get from the SIemens sequence; one folder containing two echo time images, and one folder containing some type of phase-map-looking image.

Here's another useful resource

and

https://github.com/fithisux/FSL/blob/fsl-5.0.9/src/fugue/fsl_prepare_fieldmap