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[kev-m]

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[szj7398]

Dear Author,
Thank you for providing the open-source code. I would like to customize a shimming coil using your code based on the data I collected from the DSV surface. I am inputting the coordinates I uniformly sampled on the DSV surface into the target_field. After generating the shimming coil using your code, I want to calculate the magnetic field produced by the coil at those sampling points on the DSV and combine it with the original magnetic field to compute a new homogeneity. Is there a way to achieve this?

[kev-m]

Hello! Thank you for your support.

I am not 100% sure that I fully understand your question.
As described in the documentation, section 5.3 CoilSolution, the computed magnetic field is present in the target_field of the CoilSolution class.
You can get a hint on how to access the data in the S2 Shim Coil code fragment.

Does this help?

[szj7398]

Thank you for your answer. The issue I'm encountering is that the magnetic field data I input was collected on the surface of a sphere, with around 1500 sample points. However, after running the program, the number of coordinates stored in the coilsolution does not correspond to my input coordinates, which makes it impossible for me to calculate the homogeneity after shimming. Could it be that the method I’m using is problematic? Thank you again for your help.

[kev-m]

Can you create and share a project that shows what you are doing? I'd like to see your inputs, e.g. how you define the target field, and how you are reading the CoilSolution afterwards, to extract the calculated field.

[susanna-m-weber]

Hello,

I had a question about the way that the current strength for a coil is calculated by pyCoilGen and CoilGen. I am trying to simulate a coil that can generate a 100 mT homogenous field by setting the 'field_shape_function' parameter to 100. While generating the coil itself has worked well, the current strength determined by the program, which is generally on the scale of of 10^6 or 10^7 for the cylindrical coils I am simulating. Double checking with the paper, I can see that the current strengths reported for the shim coils are on the scale of 10^4, but other results, namely the brain shimming coil, show a current strength of less than 1 amp in the figures. The very large current values seem unreasonable to me, and I am also a bit confused by how the current strength is different from the 'opt_current_layout' variable, the ideal current strength for the connected layout to match the target field.

Could you clarify why there is such a large range of current strengths shown in the paper figures, and what user errors could result in the program outputting such massive currents?

Thank you very much for your help!

[kev-m]

Hello,
A quick observation: The top of the configuration section notes that all units must be in standard SI.

Note: All values are specified in SI units, i.e. metre, Ampere, Tesla.

I infer that by setting the 'field_shape_function' value to 100, you are requesting a 100T field.
This would probably justify the 10^6 A current that you are seeing.
Could this explain what you are experiencing?

[susanna-m-weber]

Hi,

Thank you very much for your reply!

I assumed that the field strength was set in mT rather than in T because of the figure labeling produced by the “plot_errors” function - when I enter a value of 0.1, it shows the target Bz as being 0.1 mT on the figure produced.

Using this lower field strength, CoilGen outputs a current strength on the scale of 10^4 A, which still seems too large for a 100 mT field. How does this value differ from the "opt_current_layout" variable that both CoilGen and pyCoilGen output?

Thank you again for your help!

[kev-m]

Hello!

I assumed that the field strength was set in mT rather than in T because of the figure labeling produced by the “plot_errors” function - when I enter a value of 0.1, it shows the target Bz as being 0.1 mT on the figure produced.

That does sound like a bug in the figure label. The value should only be mT if the value is divided.

Using this lower field strength, CoilGen outputs a current strength on the scale of 10^4 A, which still seems too large for a 100 mT field.

This is best checked with another, independent, application. Are you aware of any other tool that can be used to cross-check this result?

How does this value differ from the "opt_current_layout" variable that both CoilGen and pyCoilGen output?

Good question. All I know is the line of code that computes this value:
opt_current_layout = np.abs(np.mean(target_field.b[2, :] / combined_field_layout[2, :]))

If I examine the the TargetField data-structure, I believe that the 2 index means that it is sampling only the z-coordinate.