k-Wave User Forum » Topic: photoacoustic presumptions in simulation

k-Wave User Forum » Topic: photoacoustic presumptions in simulation http://www.k-wave.org/forum/topic/photoacoustic-presumptions-in-simulation Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 01:52:33 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://www.k-wave.org/forum/search.php Bradley Treeby on "photoacoustic presumptions in simulation" http://www.k-wave.org/forum/topic/photoacoustic-presumptions-in-simulation#post-5527 Wed, 08 Jun 2016 21:08:38 +0000 Bradley Treeby 5527@http://www.k-wave.org/forum/ Hi Moein0114, When using k-Wave, there are two frequencies to consider. The first is the maximum frequency supported by the spatial grid, given by f_max_x = c / (2*dx). The second is the maximum frequency supported by the temporal sampling, given by f_max_t = 1 / (2*dt). These are related by the CFL number, where CFL = c*dt/dx. The default value in k-Wave is CFL = 0.3. If you want to set a sampling rate of 40 MHz, you can do this by setting the appropriate dt (see the k-Wave manual for how to define the time array). However, you should keep in mind the effect that changing dt will have on the CFL number and/or the spatial sampling. The assumption made when using <code>source.p0</code> is that the duration of the laser pulse is much shorter than the characteristic acoustic travel time across the heated region (this is known as stress confinement). You can read some more details <a href="http://www.k-wave.org/papers/2005-Cox-JASA.pdf">here</a>. Brad. Moein0114 on "photoacoustic presumptions in simulation" http://www.k-wave.org/forum/topic/photoacoustic-presumptions-in-simulation#post-5521 Tue, 31 May 2016 05:13:38 +0000 Moein0114 5521@http://www.k-wave.org/forum/ Dear Cox and Treeby, I am trying to set properties of my own simulation which is : 1-Eight 100 μm radius spherical absorbers were positioned along the vertical axis every 10 mm with the first two point targets located 1 mm away from the transducer surface. Two absorbers at each depth were laterally 1 mm away from the center of each absorber. Imaging region was 40 mm laterally and 50 mm axially. 2- Point targets were visualized by modeled 128 element linear array of transducers operating at 5 MHz center frequency and having 77% fractional bandwidth. 3- speed of sound was assumed to be 1540. 4- radiofrequency signals were digitized using 40MHz sampling frequency. for these properties i wrote these codes : %% create the computational grid Nx = 501; % number of grid points in the x (row) direction Ny = 400; % number of grid points in the y (column) direction dx = 0.1e-3; % grid point spacing in the x direction [m] dy = 0.1e-3; % grid point spacing in the y direction [m] kgrid = makeGrid(Nx, dx, Ny, dy); %% define the properties of the propagation medium medium.sound_speed = 1540; % [m/s] medium.alpha_coeff = 0.75; % [dB/(MHz^y cm)] medium.alpha_power = 1.5; %% create initial pressure distribution using makeDisc (phantom definition) %1 disc_magnitude = 1e4; % [Pa] disc_x_pos = 101; % [grid points] disc_y_pos = 206; % [grid points] disc_radius = 1; % [grid points] disc_1 = disc_magnitude*makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius); %1c disc_x_pos = 101; % [grid points] disc_y_pos = 194; % [grid points] disc_radius = 1; % [grid points] disc_1c = disc_magnitude*makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius); %2 disc_x_pos = 201; % [grid points] disc_y_pos = 206; % [grid points] disc_radius = 1; % [grid points] disc_2 = disc_magnitude*makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius); %2c disc_x_pos = 201; % [grid points] disc_y_pos = 194; % [grid points] disc_radius = 1; % [grid points] disc_2c = disc_magnitude*makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius); %3 disc_x_pos = 301; % [grid points] disc_y_pos = 206; % [grid points] disc_radius = 1; % [grid points] disc_3 = disc_magnitude*makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius); %3c disc_x_pos = 301; % [grid points] disc_y_pos = 194; % [grid points] disc_radius = 1; % [grid points] disc_3c = disc_magnitude*makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius); %4 disc_x_pos = 401; % [grid points] disc_y_pos = 206; % [grid points] disc_radius = 1; % [grid points] disc_4 = disc_magnitude*makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius); %4c disc_x_pos = 401; % [grid points] disc_y_pos = 194; % [grid points] disc_radius = 1; % [grid points] disc_4c = disc_magnitude*makeDisc(Nx, Ny, disc_x_pos, disc_y_pos, disc_radius); %sume of point absorber source.p0 = (disc_4 + disc_3 + disc_2 + disc_1) + (disc_1c + disc_2c + disc_3c + disc_4c); %% define a linear array sensor sensor.mask = zeros(Nx, Ny); nomber_of_transducer=128; sensor.mask(1,(Ny/2)-(nomber_of_transducer/2)+1:(Ny/2)+(nomber_of_transducer/2)) = 1; %% create the time array [kgrid.t_array, dt] = makeTime(kgrid, medium.sound_speed); %% define the frequency response of the sensor elements center_freq = 5e6; % [Hz] bandwidth = 77; % [%] sensor.frequency_response = [center_freq, bandwidth]; %% run the simulation sensor_data = kspaceFirstOrder2D(kgrid, medium, source, sensor); %% % plot the initial pressure and sensor distribution figure; imagesc(kgrid.y_vec*1e3, kgrid.x_vec*1e3, source.p0 + sensor.mask*disc_magnitude, [-disc_magnitude disc_magnitude]); colormap(getColorMap); ylabel('x-position [mm]'); xlabel('y-position [mm]'); axis image; colorbar; here are my questions : 1- I do not know how to set the 40MHz sampling frequency, because in this code sampling frequency -that is declared by kgrid is 5.1333e+07 2- we set initial pressure to propagate as source of acoustic waves, what is the idea and assumption about excitation laser source? i mean if someone ask me, how did the initial pressure emerged, what should i say ?