http://www.k-wave.org/forum/topic/large-number-of-sensor-points-distort-pa-waveform-in-3d-time-reversal Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 13:01:34 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/large-number-of-sensor-points-distort-pa-waveform-in-3d-time-reversal#post-5782 Thu, 08 Dec 2016 15:03:56 +0000 ivalus@uwo.ca 5782@http://www.k-wave.org/forum/ <p>Thanks so much Brad! That paper explains the source of these artefacts quite nicely.</p> <p>Ivan </p> http://www.k-wave.org/forum/topic/large-number-of-sensor-points-distort-pa-waveform-in-3d-time-reversal#post-5759 Tue, 22 Nov 2016 16:39:32 +0000 Bradley Treeby 5759@http://www.k-wave.org/forum/ <p>Hi Ivan,</p> <p>When running a forward simulation, the sensors are passive. However, when running time reversal image reconstruction, the signals are enforced as a Dirichlet boundary condition. When you use zeros at the input data, this is equivalent to creating a pressure-release boundary, which will reflect the waves 180 degrees out of phase. The two approaches you mention are equivalent to setting the flag <code>source.p_mode</code> to <code>&#39;additive&#39;</code> or <code>&#39;dirichlet&#39;</code>. </p> <p>You might also find <a href="http://www.k-wave.org/papers/2010-Cox-IEEETMI.pdf">this paper</a> helpful.</p> <p>Brad. </p> http://www.k-wave.org/forum/topic/large-number-of-sensor-points-distort-pa-waveform-in-3d-time-reversal#post-5739 Fri, 11 Nov 2016 10:54:22 +0000 ivalus@uwo.ca 5739@http://www.k-wave.org/forum/ <p>Hi All,</p> <p>Thanks for the great package!</p> <p>I am running time reversal using kspaceFirstOrder3d using a sensor mask with 24000 sensors and experimental time series. The grid size is 384x384x180 with 1mm spacing, so max supported f=750kHz. I am using the default PML but changing it makes little difference. I run it on the GeForce GTX 1080 card and an 8 core PC.</p> <p>The strange thing is that when I run the full recon with all 24000 sensors, it produces distorted images but when I split it up into 100 sets of 240 and then sum/stitch the sub-images, the results are clear, similar to results from standard back-projection. In fact, I determined that using a single sensor which gets a non-zero time series, along with many (&gt;1000) sensors whose time series are all zeros, produces distorted results compared to using the same sensor/time-series but without other sensors present. </p> <p>So it seems that even though the other sensors have all zeros as input data, they significantly affect the pressure calculations. I thought that the sensors are supposed to be passive....is that an approximation? i.e. Does a large amount &gt;1000 of sensors affect the calculation even tough they have zero time-series amplitude as input?</p> <p>Thanks,<br /> Ivan Kosik </p>