Error in TI tutorial

[bryn]

Are you using the latest Sim4Life, v8.2.2.18061?

[abbytang]

Yes, I'm currently using the latest Sim4Life version (v8.2.2.18061). I will also install version 8.2.0.16876 and test it again for comparison.

[abbytang]

When I copy the file tutorial_TI_|X|025_head_model.ipynb into the CAD files folder of Sim4Life version 8.2.0.16876 and run it in this older version, most sections execute correctly, including the "Auto Label Tissues and Extract Surfaces" part. However, the script fails at the "Computing the Maximum Modulation Using the Masked Electric Fields" section with the following error:
AttributeError: module 's4l_v1.analysis.core' has no attribute 'MaxModAmpEvaluator'.
Could you please advise on how to resolve this issue? Thank you for your assistance.

[bryn]

the MaxModAmpEvaluator was exposed in s4l_v1 6 months ago, so after 8.2.0.16876. You could probably use it though via the 'raw api': XPostProcessor.MaxModAmpEvaluator.

[lucky_lin]

@bryn Hello, I am using a script to run TI simulations. I noticed that when I change the maximum grid step size for the electrodes and tissues from [2.0, 2.0, 2.0] to [3.125, 3.125, 3.125] in each simulation, the peak value of the calculated electric field (E-field) changes from 205 V/m to 445 V/m. Why does the grid step size affect the final calculated E-field value? Additionally, I found that changing the step size also significantly alters the Scale Factor used to normalize the results in each simulation. Here is the relevant code :
manual_grid_settings.MaxStep = numpy.array([3.125, 3.125, 3.125]), units.MilliMeters
manual_grid_settings.Resolution = numpy.array([1.0, 1.0, 1.0]), units.MilliMeter

[bryn]

@lucky_lin Please post your question as a separate thread. This is unrelated to the topic of this thread. Thanks

[bryn]

@abbytang I can reproduce your issue in v8.2.2.18061. Investigating what is causing it and what workaround i can offer (except for reverting to the previous version). Sorry for the inconvenience.

[abbytang]

Thank you for your help. I will run it in a previous version.

[halder]

Hi, @abbytang this is happening because in Sim4Life 8.2.2, due to internal environment changes the matplotlib default backend is set to: matplotlib_inline. The fix is to override the backend manually to a compatible one (Agg) early in the script. The fixed tutorial will be included in the v9 which will release soon. However, for now you can add this to the beginning of the script
"import os
os.environ["MPLBACKEND"] = "Agg"

import matplotlib
matplotlib.use("Agg")"

Please send an email to s4l-support@zmt.swiss and I can send you the updated jupyter notebook.

[abbytang]

Thank you. It can work right now.

[bryn]

BTW. this is a temporary fix, which breaks inline plotting with matplotlib. We have fixed it in the release branch. A slightly improved workaround may be to temporarily unset the MPLBACKEND environment variable before the call to HeadModelGeneration, e.g. something like this

import os

original_backend = os.environ.pop("MPLBACKEND", None)
labelfield = HeadModelGeneration(
    images=image_list,
    add_dura=True,
    close_skin=True,
    close_csf=True,
    close_skull=True,
    version=ImageML.eHeadModel.head16,
)
if original_backend is not None:
    os.environ["MPLBACKEND"] = original_backend