k-Wave

1. Gabrielle
   

   Member
   Joined: Mar '15
   Posts: 8

   Hi,

   I am doing the simulation of hifu in skull with attenuation coefficient ranges from 22 dB/MHz^y cm to 33 dB/MHz^y with transducer frequency=0.7MHz. before running the simulation, I checked the accuracy of k-wave for modeling strong attenuation with the mfile 'example_na_modelling_absorption'. I increased the 'medium.alpha_coeff' to 10 and kept the 'medium.alpha_power=1.1'. It turned out that both dispersion and attenuation have large errors when compared with the theoretical curve, even when I reduced the cfl to 0.005.

   How can I reduce those errors if I want to get accurate results for simulating HIFU in skull with k-wave?

   Posted 6 years ago #

2. Bradley Treeby
   

   Developer
   Joined: Mar '10
   Posts: 1,640

   Hi Gabrielle,

   For large attenuation values, it's not actually the phase errors that are responsible for the mismatch, it comes an assumption of small attenuation in the derivation of the fractional absorption term used in k-Wave. To account for this, you can select a different set of alpha_coeff and alpha_power to give you the desired behaviour using the function fitPowerLawParams. There are some details of this towards the end of Sec. II.D of this paper.

   Brad.

   Posted 6 years ago #

3. Gabrielle
   

   Member
   Joined: Mar '15
   Posts: 8

   Hi, Brad.

   Thanks for your reply.
   now I have another question. The case I am simulating has attenuation coefficient heterogeneity. I assumed a constant power which was 1.1 before. Now if I use the functionfitPowerLawParams, I will get different fitted 'alpha_power' values. It seems that I cannot implement them to the code directly. Do I need to assume a constant 'alpha_coeff' before using the fitting function?

   Garielle

   Posted 6 years ago #

4. Bradley Treeby
   

   Developer
   Joined: Mar '10
   Posts: 1,640

   Hi Garielle,

   I would start with your actual values for the power law parameters, use the fitting function, and then afterwards, select a single value of alpha_power, and then adjust the remaining alpha_coeff values to give the correct absorption at a particular frequency of interest.

   Brad.

   Posted 6 years ago #

5. Gabrielle
   

   Member
   Joined: Mar '15
   Posts: 8

   Brad:

   thanks for the suggestion.
   finally, I have a question for the the function 'powerLawKramersKronig':
   c_kk = powerLawKramersKronig(w, w0, c0, a0, y).

   how do you define the reference angular frequency w0? a random frequency of interest? or central frequency of the TR?

   many thanks
   Gabrielle

   Posted 6 years ago #

6. Bradley Treeby
   

   Developer
   Joined: Mar '10
   Posts: 1,640

   Hi Gabrielle,

   It's the frequency for which c0 is defined (or measured). If you're using the function to compare with a simulation or experiment, then I normally chose a w0/c0 pair from the centre of the frequency range.

   Brad.

   Posted 6 years ago #

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