http://www.k-wave.org/forum/topic/phase-errors-for-simulation-of-hifu-in-skull-with-large-attenuation-coefficient Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 15:04:38 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/phase-errors-for-simulation-of-hifu-in-skull-with-large-attenuation-coefficient#post-6231 Tue, 12 Dec 2017 22:33:27 +0000 Bradley Treeby 6231@http://www.k-wave.org/forum/ <p>Hi Gabrielle,</p> <p>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.</p> <p>Brad. </p> http://www.k-wave.org/forum/topic/phase-errors-for-simulation-of-hifu-in-skull-with-large-attenuation-coefficient#post-6216 Mon, 13 Nov 2017 17:01:41 +0000 Gabrielle 6216@http://www.k-wave.org/forum/ <p>Brad:</p> <p>thanks for the suggestion.<br /> finally, I have a question for the the function 'powerLawKramersKronig':<br /> c_kk = powerLawKramersKronig(w, w0, c0, a0, y).</p> <p>how do you define the reference angular frequency w0? a random frequency of interest? or central frequency of the TR?</p> <p>many thanks<br /> Gabrielle </p> http://www.k-wave.org/forum/topic/phase-errors-for-simulation-of-hifu-in-skull-with-large-attenuation-coefficient#post-6209 Fri, 10 Nov 2017 15:04:51 +0000 Bradley Treeby 6209@http://www.k-wave.org/forum/ <p>Hi Garielle,</p> <p>I would start with your actual values for the power law parameters, use the fitting function, and then afterwards, select a single value of <code>alpha_power</code>, and then adjust the remaining <code>alpha_coeff</code> values to give the correct absorption at a particular frequency of interest.</p> <p>Brad. </p> http://www.k-wave.org/forum/topic/phase-errors-for-simulation-of-hifu-in-skull-with-large-attenuation-coefficient#post-6203 Wed, 08 Nov 2017 23:30:54 +0000 Gabrielle 6203@http://www.k-wave.org/forum/ <p>Hi, Brad.</p> <p>Thanks for your reply.<br /> 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 function<code>fitPowerLawParams</code>, 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?</p> <p>Garielle </p> http://www.k-wave.org/forum/topic/phase-errors-for-simulation-of-hifu-in-skull-with-large-attenuation-coefficient#post-6195 Wed, 08 Nov 2017 09:16:04 +0000 Bradley Treeby 6195@http://www.k-wave.org/forum/ <p>Hi Gabrielle,</p> <p>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 <code>alpha_coeff</code> and <code>alpha_power</code> to give you the desired behaviour using the function <code>fitPowerLawParams</code>. There are some details of this towards the end of Sec. II.D of <a href="http://bug.medphys.ucl.ac.uk/papers/2014-Treeby-JASA.pdf">this paper</a>.</p> <p>Brad. </p> http://www.k-wave.org/forum/topic/phase-errors-for-simulation-of-hifu-in-skull-with-large-attenuation-coefficient#post-6194 Wed, 08 Nov 2017 04:54:37 +0000 Gabrielle 6194@http://www.k-wave.org/forum/ <p>Hi, </p> <p>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.</p> <p>How can I reduce those errors if I want to get accurate results for simulating HIFU in skull with k-wave? </p>