Hello,
I am running a 3D simulation with a 500kHz transducer which has two elements. I calibrated phase and amplitude so that in free water I receive a max. Isppa of 20W and a distance of 35mm. I imported a mask for the skull and also for the brain.
I used the values for the medium according to this paper: „Benchmark problems for transcranial ultrasoundsimulation: Intercomparison of compressional wavemodels“ (Table 1). More specifically, I define the media in the following way, starting with specifying water values and then adding skull and brain values:
medium.sound_speed = 1500* ones(Nx,Ny,Nz)
medium.sound_speed(brain_mask) = 1560;
medium.sound_speed(skull_mask) = 2800;
medium.density = 1000* ones(Nx,Ny,Nz);
medium.density(brain_mask) = 1040;
medium.density(skull_mask) = 1850;
alpha_coeff_true = 0* ones(Nx,Ny,Nz);
alpha_coeff_true(brain_mask) = 0.3;
alpha_coeff_true(skull_mask) = 4;
alpha_power_true = ones(Nx, Ny, Nz);
medium.alpha_coeff = fitPowerLawParamsMulti(alpha_coeff_true, alpha_power_true, medium.sound_speed, freq, 2);
medium.alpha_power = 2;My outcome looks very different than expected.In free water the max Isppa was around 35mm where we expected it and we had a small far-field with low intensities. However, in the simulation where we included the skull and brain acoustic properties, our maximum intensity map shows a much higher intensity in the far field and a lower intensity at our intended focus (ie 35mm away from the transducer). We never experienced this issue when using different acoustic properties for the skull and brain. Do you perhaps have any idea what might be causing this far-field to become so pronounced when including the acoustic properties of the skull and brain? Is it possible that the fitPowerLawParamsMulti function is being used incorrectly?
I would appreciate any guidance here!