ZMT zurich med tech

Thank you for the detailed answer!

These error messages can be safely ignored, but I will pass them along to see if such overzealous and misleading error messages can be suppressed in the future.

Would like to know too in 2024 🙂

@brown
Thank you, I will check these things. Additionally, there are some warning messages which may help:
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Is the mesh division not precise enough？

Thank you so much you are a godsend 🙏 You saved me a couple days worth of work!

You definitely have enough memory here. It's likely that the solver could not use the device for some other reason. Can you try updating your graphics drivers?

In terms of the material settings in the thermal simulation:
The heat transfer rate defines whether heat removal by perfusion should be considered. In the absence of this term, heat is only removed by thermal conduction (diffusion) and boundary conditions. The options provided for heat transfer rate affect whether perfusion is constant or affected by local thermoregulation (temperature (T) dependent perfusion, e.g., to account for vasodilation). As for the heat transfer rate, the heat generation rate term can be constant or affected by local thermoregulation (T dependent, reflecting increased metabolic activity with increasing temperature). It is also possible to introduce time-dependent heat generation, e.g., to model a heating battery.
Baseline perfusion values (incl. variability information) are available in the IT'IS database and can be automatically assigned from sim4life: (http://www.itis.ethz.ch/virtual-population/tissue-properties/database/database-summary/).
If non-constant perfusion should be applied or not depends on the tissue and temperature increase magnitude (e.g., muscle above 39 starts to have a strong perfusion increase). The conservativeness of a perfusion model choice is application-dependent.

To simulate the heating effect of tissues over time, blood perfusion and heat generation rate (metabolic heat generation) of the tissue would also need to be considered. The perfusion is covered in the option "Heat Transfer Rate". All options that you can enter here are related to heat-transfer based removal of energy from the system. Perfusion can be adjusted by changing the type of hear transfer (None, Constant, Linear (T), Piecewise Linear (T).

The constant term assumes constant perfusion, independent of tissue temperature. It is the default assigned when using the IT'IS tissue database in Sim4Life. Linear (T) or Piecewise Linear (T) assume temperature dependent perfusion. You can add your your transition temperatures using the little "+" icon. Please note that the linear coefficients represent the slope of the linear perfusion. Each transition temperature indicates the change of the perfusion rate.
For example, if you wish to enter constant perfusion up to 37 degrees, linear perfusion of 10 times the "standard" perfusion rate between 37 and 43 degrees, and constant perfusion above 43 degrees, then you would enter:
transition temperatures: [37,44], linear coefficients: [10,0].

Wow I can't believe I missed that. Thank you so much! The warning definitely threw me off

Thanks for your reply

I think you can change how the steps change between gridlines with the grading option. If you have some entities that should not influence the grid set priority to zero (for those entities). Then choose the largest grid step you want for the global settings and and the smallest (0.5mm) for the arrays_grid. You should manage to control how the grid changes away from the arrays_grid.

When using a long line as "normal" edge source, the discretization will result in one edge being the actual source and rest of the line being discretized as PEC filament. This can lead (depending on the excitation frequency, the length of the source line and the setup) to inaccuracies due to the additional capacitance introduced be the PEC filaments. An alternative that is, in most cases, a more accurate source representation is using the "Distribute Along Line" option, the source is equally distributed over all the discretized edges of a line element (see image, right). That prevents any PEC filaments and therefore makes the injection of the signal more realistic.

Time delay = distance between the transmitter and receiver*sin(theta)/c where theta is the angle of antenna. I would suggest looking into antenna array literature for theoretical background on calculating this quantity.

You must be referring to this: This is windows configuartion related issue. You might not have access to log counter data, try logging in as an administrator. Later you can add user to the Performance Logs User Group. Look at this page for more details: https://learn.microsoft.com/en-us/windows/win32/perfctrs/limited-user-access-support

This is windows configuartion related issue. You might not have access to log counter data, try logging in as an administrator. Later you can add user to the Performance Logs User Group. Look at this page for more details: https://learn.microsoft.com/en-us/windows/win32/perfctrs/limited-user-access-support

Note that the above is only true in the case of a harmonic signal, which is why Sim4Life does not provide the RMS by default. It is up to the user to calculate the RMS based on their knowledge of the signal.

If you are interested in B1+/B1-, the rotational components of B1 are by definition constant in time and so their RMS magnitudes are equal to their absolute magnitudes.

If you click on Network Analysis in your Analysis tree, what is your Reference Impedance?

It is set to 50 ohms by default, but you have change it based on the Input Impedance for the coil before plotting the S11 curve.

Plot the complex Input Impedance. At resonance, the imaginary part will be zero (the circuit is purely resistive). So at the desired resonant mode / frequency, you should find the corresponding real value, and set this value as the reference impedance to plot |S11|.
image.png
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When you used the Mask Filter, did you check the option 'Invalidate Masked Values'? This will set the Background to NaN, which should hide it. Otherwise, the Background value will be changed to a user-defined replacement value, which would still show up during visualization.

The first method might not be working if your spline doesn't have a parametrization. If you click on the spline in the Model tree and don't see a list of points in the Controller window, then the information is no longer available and you'll have to stick to the second method.

To perform such a study, define your region or quantity of interest, then parametrize it. After a quantity has been parametrized, you can run multiple simulations using the built in Sweeper feature or using the Sim4Life Python API.

There is an example in the Sim4Life manual titled 'Parametrized Patch Antenna' that shows how to use the Sweeper feature.

If using the Python API, the easiest way would be to create a baseline simulation by hand, then right-click on the simulation name and select To Python. Then you would find the quantity of interest in the auto-generated script and assign it to a variable instead of the hardcoded value. Using a simple loop in Python, you can create multiple simulation that have identical setup except for parameters of interest.

In your example, multiple simulations would be run with identical setup except for the grid resolution within a region of interest (e.g., a wire block surrounding a region of interest is placed in a manual grid settings folder, then Maximum Step is changed from 0.3 to 1.0 mm).

Then in Analysis you extract a quantity of interest and compare how this value changes as a function of grid resolution.

If the change in the value is small as you increase resolution, you can proceed in future simulations with a coarser resolution to save on run time. The exact convergence of the value needed depends on your application.

Thank you very much. This fixed the issue. This was related to Ares also.

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