ZMT zurich med tech

Hi Bryn, I would like to ask a question regarding posing. My aim is to detect the variation in bone position from the skin in different poses (hypothesis being: as the soft tissues deform, the bone wont always be at the same position wrt the skin). I currently have 8 antennas placed around the skin which are supposed to mimic wearable antennas and I would like to move these antennas along with the pose. But if I link these antennas to the bone using "link-parent tool", the bone is always at the same location wrt to the bone irrespective of the pose. But I cannot link the antennas wrt to the skin as the antennas dont move with the pose. How can I do this? I would like the antennas which are placed around the skin to similar to the skin rather than the bone? Based on the first video in this chain, triangular meshes can be posed similar to the body. If I convert the antennas to meshes and then pose it, will I be getting the same issue i.e the bone is always at the same location wrt to the antennas? Thanks

@bryn Is the 6.8 displayed on the color bar the actual maximum field strength value? I exported the values and found that the maximum is around 5.9 instead. [image: 1735124755536-42fb974e-d830-42c2-8373-84c85ee63339-image.png]

Yes I did mean wavelength, not period .. That's the drawback of running high frequency simulations in FDTD, they require a lot of voxels ... If appropriate, try running it at 500 kHz and then update the automatic grid settings ... The auto grid settings is based on the material in your domain that has the lowest speed of sound, please remove air from the simulation domain if appropriate ... One of my previous comments tells you how to calculate the wavelength, the units and magnitude seem wrong in yours, remember that you're not using the speed of light to calculate the wavelength, you use the speed of sound in the medium (around 1500m/s)

Thanks for your help.

@montanaro Thanks for your clarification.

@halder When I performed TI simulation using the spherical model, I found that if I changed the current direction of one pair of electrodes, the maximum value of the TI Max (x, y, z) slice remained unchanged. Changing the current of one pair of electrodes should have shifted from the original same-direction superposition to a reverse weakening, so why does it remain unchanged? Is it because Max Modulation only uses EM for calculations?

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

THank you very much for the hints.

@Sylvain Hi Sylvain! Thanks for sharing the method. I tried it in this very simple structure but get unexpected result for current density. Also available at my post here https://forum.zmt.swiss/post/2071. I use the following very simple structure to test whether I am using the LF Ohmic Quasi-Static Solver correctly. The voltage comes out as expected but the current (density) is incorrect. I have these three electrodes of the same radius (1mm) stacking together (touching each other) in an electrode-cylinder-electrode configuration. I want to apply to a 2V (+1V top, -1V bottom) to the two silver electrodes and achieve a 1 kA current through. So I chose the cylinder material (copper) and length such that the resistance is 2 mOhm. After running the simulation, where I place a line as voltage sensor (it runs from 2mm offset from the top electrode to 2mm offset from the bottom electrode, in the centre), it gives a value of -1.9786V as expected. When I combine the J(x,y,z,f0) from the overall field and a plane I created and use flux evaluator to measure total current density as described here, unexpected resutls occur. I tried two different planes and they gave different results:: A block with 0mm thickness and 1m x 1m in area in the middle of the cylinder parallel to the electrodes, result: 1 A/m^2, multiply by the area gives 1A A cylinder with 0mm thickness and 1mm in radius in the middle of the cylinder parallel to the elctrodes, resutls: 49.7369 A/m^2, multiply by the area gives 0.156mA (P.S. why the current density has a unit of [A/m^2 m^2]?) Model, Simulation and Analysis details are summaried in the screenshots attached. [image: 1736740622839-img_5162.jpg] [image: 1736740622913-img_5163.jpg] [image: 1736740622953-img_5164.jpg] [image: 1736740634276-screenshot-2025-01-12-at-21.26.50-resized.jpg] [image: 1736740634609-screenshot-2025-01-12-at-21.27.16-resized.jpg] [image: 1736740634957-screenshot-2025-01-12-at-21.27.32-resized.jpg] [image: 1736740635384-screenshot-2025-01-12-at-21.31.17-resized.jpg] [image: 1736740635771-screenshot-2025-01-12-at-21.34.49-resized.jpg] [image: 1736740636120-screenshot-2025-01-12-at-21.35.28-resized.jpg]

Right. Thank you very much for your explanation and comments.

@bryn @gc00 @halder Thank you so much, You've been very helpful !

Hello, Sorry I am facing an issue with moving antennas to different locations based on the steps above. I used three points on the skin and calculated the transformation between static and posed states. I used this transformation to transform the antenna position to the new position (using RigidTransform and ApplyTransform functions). However I get errors that the antenna source edge is within a solid. I have changed priorities during voxelling providing antennas higher priority but the errors still exist. What can I do? I would like to move antennas in a similar fashion to how soft tissues deform. Thanks Vignesh

@mkn how about you post your code. maybe somebody will show you where the bug is

Yeay. It worked. Great. Thank you so much for your patience :)

Thanks @Bryn!

@christos1996 when I reach into the "Sensors" setting at Simulation Settings (Neuron)], the option "Point "Sensor Tool" is not available to click into. I am sure I have load the model. So have you solved this problem? how to solve ? hope you can reply me .

@pastis Hello, Have you solved this question? can we compare the amount of electric field that reach the targeted region to evaluate the TI simulation ?

Hmm I am not sure I understand. Is it possible to share more of your code and explain exactly what is not working? I use the lines of code you posted regularly and it works just fine.

After a call with S4L support, here is the solution for future reference: My machine had two GPUs connected, one of them old and deactivated. However, the script ExtractCudaInfo.py detected both of these in the line 'num_gpus = int(xml_root.find("attached_gpus").text)' and then got stuck trying to find information on the deactivated GPU. A quick fix for the issue is therefore to manually set the correct number, in my case 'num_gpus=1', in the script.

Dear Sim4Life developers, I have came across the same problem and cannot update materials database due to the Russian words within a pathway. Is it possible to solve this problem by directing Sim4Life to search for materials in another pathway? Thank you a lot in advance, Valeriia