k-Wave User Forum » Topic: Image Artefacts

k-Wave User Forum » Topic: Image Artefacts - Ultrasound Imaging http://www.k-wave.org/forum/topic/image-artefacts-ultrasound-imaging Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 02:33:51 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://www.k-wave.org/forum/search.php Mithun on "Image Artefacts - Ultrasound Imaging" http://www.k-wave.org/forum/topic/image-artefacts-ultrasound-imaging#post-4849 Fri, 21 Nov 2014 16:40:12 +0000 Mithun 4849@http://www.k-wave.org/forum/ Hi Brad, That was of great help. Thank you. Kind Regards, Mithun Bradley Treeby on "Image Artefacts - Ultrasound Imaging" http://www.k-wave.org/forum/topic/image-artefacts-ultrasound-imaging#post-4810 Sat, 01 Nov 2014 11:30:51 +0000 Bradley Treeby 4810@http://www.k-wave.org/forum/ Hi Mithun, If you plot the simulation, you'll see the wave from the edge of the aperture. It looks like a spherical wave (or cylindrical wave depending on your aperture shape), but varies in polarity on either side of planar wave front. I've created a very simple example to illustrate: <pre><code>clear all; % create the computational grid Nx = 64; % number of grid points in the x direction Ny = 32; % number of grid points in the y direction Nz = 96; % number of grid points in the z 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] dz = 0.1e-3; % grid point spacing in the z direction [m] kgrid = makeGrid(Nx, dx, Ny, dy, Nz, dz); % define the properties of the propagation medium medium.sound_speed = 1500; % create time array kgrid.t_array = makeTime(kgrid, medium.sound_speed, 0.5, 4e-6); % create initial pressure distribution source.p0 = zeros(Nx, Ny, Nz); source.p0(20, 14:19, 38:59) = 1; % define sensor mask sensor.mask = zeros(Nx, Ny, Nz); sensor.mask(Nx/2, Ny/2, Nz/4) = 1; sensor.mask(3*Nx/4, Ny/2, Nz/2) = 1; % input arguments input_args = {'PlotPML', false, 'DataCast', 'single'}; % run the simulation sensor_data = kspaceFirstOrder3D(kgrid, medium, source, sensor, input_args{:}); % plot the simulated sensor data figure; plot(sensor_data.') ylabel('Pressure'); xlabel('Time Step'); legend('Off Axis', 'On Axis');</code></pre> Hope that helps, Brad. Mithun on "Image Artefacts - Ultrasound Imaging" http://www.k-wave.org/forum/topic/image-artefacts-ultrasound-imaging#post-4789 Fri, 24 Oct 2014 10:33:07 +0000 Mithun 4789@http://www.k-wave.org/forum/ Hi Brad, Thank you for the valuable comments. Yes of-course, I can zero the first part of the signal. But I would like to understand whats happening actually. The high signal is coming not in the very beginning, but at around 100th sample for the middle element. It is a bipolar signal with negative cycle first and positive next. Then I thought it may be a reflection with phase shift of input signal with 1 cycle. How can I recognize an edge wave? Combining sensor data is really useful. Thank you. Regards, Mithun Bradley Treeby on "Image Artefacts - Ultrasound Imaging" http://www.k-wave.org/forum/topic/image-artefacts-ultrasound-imaging#post-4784 Tue, 21 Oct 2014 16:04:57 +0000 Bradley Treeby 4784@http://www.k-wave.org/forum/ Hi Mithun, This function was added as part of k-Wave V1.1 (released a couple of weeks ago). The signal at the beginning will be your input signal. Inside the code, the source and sensor act independently, so if they are in the same position, the sensor will also record the input signal. There's a couple of ways you could remove this: (1) You could zero the first part of the signal, e.g., following the "Simulating B-mode Ultrasound Images Example". (2) You could run a separate simulation in a homogeneous medium, and subtract the recorded signal from the signal you record when you have scatterers. Are you sure it's a reflection, and not an edge wave from the edge of the transducer? Brad. Mithun on "Image Artefacts - Ultrasound Imaging" http://www.k-wave.org/forum/topic/image-artefacts-ultrasound-imaging#post-4783 Tue, 21 Oct 2014 15:02:38 +0000 Mithun 4783@http://www.k-wave.org/forum/ Dear Brad, I fixed it by adding the code you provided in another post to KwaveTransducer class. Thats amazing, it saved lot of time. Thank you. My problem is that I am getting a huge initial signal in all elements. This is a phase inverted bipolar signal. Is it the input signal itself? How can I get rid of it? My transducer is below PML I guess. Even after this initial signal, I have another weak reflection also from unexpected depth. Any ideas on it looking at the code above? Thank You, Kind Regards, Mithun Mithun on "Image Artefacts - Ultrasound Imaging" http://www.k-wave.org/forum/topic/image-artefacts-ultrasound-imaging#post-4781 Tue, 21 Oct 2014 14:08:29 +0000 Mithun 4781@http://www.k-wave.org/forum/ Dear Brad, Thanks for the response. Great to know about apodization in c++ code. I am not able to use transducer.combine_sensor_data(sensor_data). Its throwing an error "No appropriate method, property, or field combine_sensor_data for class kWaveTransducer". Do I have to write the method explicitly? Please help me on this. I am not going to use scan_line method as I am interested in data from each elements separately. Thank You, Regards, Mithun Bradley Treeby on "Image Artefacts - Ultrasound Imaging" http://www.k-wave.org/forum/topic/image-artefacts-ultrasound-imaging#post-4771 Thu, 16 Oct 2014 11:40:56 +0000 Bradley Treeby 4771@http://www.k-wave.org/forum/ Hi Mithun, There is currently a difference in the way the C++ and MATLAB codes return the data when using an object of the <code>kWaveTransducer</code> class as a sensor. The MATLAB code returns one time series per active transducer element, while the C++ code returns one time series per grid point that forms part of the active transducer. If using the C++ code, before using the <code>scan_line</code> method, you should call: <code>sensor_data = transducer.combine_sensor_data(sensor_data);</code> This will combine the sensor data to give a single time series per active transducer element, analogous to the output from the MATLAB code. Note that transmit apodization is not currently implemented in the C++ code, i.e., the apodization is always the same as: <code>transducer.transmit_apodization = 'Rectangular';</code> (see the discussion <a href="http://www.k-wave.org/forum/topic/question-about-the-transducercombine_sensor_data-method">here</a>). Let me know if that doesn't solve the problem. Brad. Mithun on "Image Artefacts - Ultrasound Imaging" http://www.k-wave.org/forum/topic/image-artefacts-ultrasound-imaging#post-4767 Sun, 12 Oct 2014 09:34:55 +0000 Mithun 4767@http://www.k-wave.org/forum/ Dear All, I am trying to do a simple US image simulation using K-wave [Transducer as source and sensor]. Quite new to it. I created a medium and then a ball in the middle with different speed of sound and density. I expected only the reflection from the ball. Instead I am seeing a very high signal in the beginning of time trace (May be input signal?, How to get rid?) and different reverberations at almost all depths. What may be the reason for this? I put my transducer below PML. I am pasting my script below. Can anyone please throw your views on it? It would be of great help for me to move forward. clear all; clc % simulation settings DATA_CAST = 'single'; % ========================================================================= % DEFINE THE K-WAVE GRID % ========================================================================= % set the size of the perfectly matched layer (PML) PML_X_SIZE = 20; % [grid points] PML_Y_SIZE = 10; % [grid points] PML_Z_SIZE = 10; % [grid points] % set total number of grid points not including the PML Nx = 512 - 2*PML_X_SIZE; % [grid points] Ny = 512 - 2*PML_Y_SIZE; % [grid points] Nz = 128 - 2*PML_Z_SIZE; % [grid points] % set desired grid size in the x-direction not including the PML x = 30e-3; % [m] % calculate the spacing between the grid points dx = x/Nx; % [m] dy = dx; % [m] dz = dx; % [m] % create the k-space grid kgrid = makeGrid(Nx, dx, Ny, dy, Nz, dz); % Total time, 2 times for US t_end = (x/1500)*2; % [s] [kgrid.t_array,dt] = makeTime(kgrid, 1500, [], t_end); % ========================================================================= % DEFINE THE INPUT SIGNAL % ========================================================================= % define properties of the input signal source_strength = 5e6; % [Pa] tone_burst_freq = 1.5e6; % [Hz] tone_burst_cycles = 2; % create the input signal using toneBurst input_signal = toneBurst(1/kgrid.dt, tone_burst_freq, tone_burst_cycles); % scale the source magnitude by the source_strength divided by the % impedance (the source is assigned to the particle velocity) input_signal = (source_strength./(1500*1000)).*input_signal; medium.sound_speed =1500; % [m/s] medium.density = 1000; % [kg/m^3] % medium.alpha_coeff = 0.0022; % [dB/(MHz^y cm)] % medium.alpha_power = 2; % medium.BonA = 6; % define properties density_map = 1000*ones(Nx_tot, Ny_tot, Nz_tot); medium.density = density_map (:,:,:); ball_radius = round(.1e-3/dx); % [mm] p1 = 962*makeBall(Nx, Ny, Nz,PML_X_SIZE + round(16e-3/dx),PML_Y_SIZE + round(15e-3/dx), PML_Z_SIZE + Nz/2, ball_radius); medium.density = medium.density + p1; % DEFINE THE ULTRASOUND TRANSDUCER % ========================================================================= % physical properties of the transducer transducer.number_elements = 64; % total number of transducer elements transducer.element_width = 2; % width of each element [grid points/voxels] transducer.element_length = 24; % length of each element [grid points/voxels] transducer.element_spacing = 0; % spacing (kerf width) between the elements [grid points/voxels] transducer.radius = inf; % radius of curvature of the transducer [m] % calculate the width of the transducer in grid points transducer_width = transducer.number_elements*transducer.element_width ... + (transducer.number_elements - 1)*transducer.element_spacing; % use this to position the transducer in the middle of the computational grid transducer.position = round([PML_X_SIZE+1, Ny/2 - transducer_width/2, Nz/2 - transducer.element_length/2]); % properties used to derive the beamforming delays transducer.sound_speed = 1500; % sound speed [m/s] transducer.focus_distance = 15e-3; % focus distance [m] transducer.elevation_focus_distance = 16e-3 + PML_X_SIZE; % focus distance in the elevation plane [m] transducer.steering_angle = 0; % steering angle [degrees] % apodization transducer.transmit_apodization = 'Hanning'; transducer.receive_apodization = 'Rectangular'; % define the transducer elements that are currently active transducer.active_elements = zeros(transducer.number_elements, 1); transducer.active_elements(1:transducer.number_elements) = 1; transducer.input_signal = input_signal; % create the transducer using the defined settings transducer = makeTransducer(kgrid, transducer); % print out transducer properties transducer.properties; % ========================================================================= % RUN THE SIMULATION % ========================================================================= sensor.mask=transducer.all_elements_mask; % set the input settings input_args = {... 'PMLInside', false, 'PlotSim', false, 'PMLSize', [PML_X_SIZE, PML_Y_SIZE, PML_Z_SIZE], ... 'DataCast', DATA_CAST}; % run the simulation sensor_data = kspaceFirstOrder3DC(kgrid, medium, transducer, transducer, input_args{:}); % extract a single scan line from the sensor data using the current % beamforming settings scan_line = transducer.scan_line(sensor_data); % reshape sensor data to y, z, t sensor_data_rs = reshape(sensor_data, transducer.number_elements*transducer.element_width, transducer.element_length, length(kgrid.t_array)); Thank You Kind Regards, Mithun