add B0 harmonics to gradient harmonics

[bwheelz36]

• the B0 field does not change between acquisition, but it's effect on marker position does
• this is described in equation 5 of this work
• we need to figure out how to represent the effects of these sequence specific distortion in the harmonics.
• it might be as simple as scaling the B0 harmonics by gradient strength and adding them in...?

[bwheelz36]

I think we do this by adding a function in utilities called "combine gradient and B0" or something:

def combine_gradient_and_B0_harmonics(Gx, Gy, Gz, B0, dicom_data):

then we figure out the frequency encode direction, scale B0 by gradient strength, and add the harmonics together...will it be that simple?

• note: what we can explicitly calculate is the impact that B0 has on marker position {x} - have to check if this directly corresponds to just adding harmonics or not...

[bwheelz36]

• need to figure out whether to add or subtract - otherwise this might be working already...

[bwheelz36]

• [x] test with every orientation
• [ ] add documentation