IMPOLGRID Polar-type grid for ultrasound images
IMPOLGRID returns a polar-type (fan-type) grid expressed in Cartesian coordinates. This is the "natural" grid (before scan-conversion) used when beamforming signals obtained with a cardiac phased array or a convex array.
Contents
Syntax
[X,Z] = IMPOLGRID(SIZ,ZMAX,WIDTH,PARAM) returns the X,Z coordinates of the fan-type grid of size SIZ and angular width WIDTH (in rad) for a phased array described by PARAM. The maximal Z (maximal depth) is ZMAX.
[X,Z] = IMPOLGRID(SIZ,ZMAX,PARAM) returns the X,Z coordinates of the fan-type grid of size SIZ and angular width WIDTH (in rad) for a convex array described by PARAM. For a convex array, PARAM.radius is not Inf. The maximal Z (maximal depth) is ZMAX.
[X,Z,Z0] = IMPOLGRID(...) also returns the z-coordinate of the grid origin. Note that X0 = 0.
Units: X,Z,Z0 are in m. WIDTH must be in rad.
PARAM is a structure which must contain the following fields:
- PARAM.pitch: pitch of the linear array (in m, required)
- PARAM.Nelements: number of elements in the transducer array, (required)
- PARAM.radius: radius of curvature (in m, default = Inf, linear array)
Example #1: Low-resolution grids (for clarity purpose)
This example shows how polar-type grid look like for a phased array or convex array.
Choose a 2.7-MHz 64-element cardiac phased array with GETPARAM.
param = getparam('P4-2v');
Create a 60-degrees wide polar-type 20-by-20 grid.
[x,z] = impolgrid([20 20],10e-2,pi/3,param);
Display the grid.
plot(x*1e2,z*1e2,'ko','MarkerFaceColor','k') xlabel('[cm]') ylabel('[cm]') axis equal ij tight title('A polar-type grid for a cardiac phased-array')
Now choose a 3.6-MHz 128-element curved linear array.
param = getparam('C5-2v');
Create a polar-type 20-by-20 grid.
[x,z] = impolgrid([20 20],10e-2,param);
Display the grid.
plot(x*1e2,z*1e2,'ko','MarkerFaceColor','k') xlabel('[cm]') ylabel('[cm]') axis equal ij tight title('A polar-type grid for a curved array')
Example #2: A focused pressure field with a phased-array
This example shows how to simulate a pressure field on a polar-type grid.
Choose a 2.7-MHz 64-element cardiac phased array with GETPARAM.
param = getparam('P4-2v');
Define a focus position.
xf = 2e-2; zf = 5e-2;
Calculate the transmit delays with TXDELAY.
txdel = txdelay(xf,zf,param);
Create a 80-degrees wide 10-cm deep 100-by-50 grid with IMPOLGRID.
[x,z] = impolgrid([100 50],10e-2,80/180*pi,param);
Simulate the RMS pressure field with PFIELD.
y = zeros(size(x)); P = pfield(x,y,z,txdel,param);
Display a scatter plot of the pressure field.
scatter(x(:)*1e2,z(:)*1e2,5,20*log10(P(:)/max(P(:))),'filled') colormap jet caxis([-20 0]) c = colorbar; c.YTickLabel{end} = '0 dB'; axis equal ij tight xlabel('[cm]') ylabel('[cm]')
Display the pressure field.
pcolor(x*1e2,z*1e2,20*log10(P/max(P(:)))) shading interp colormap hot axis equal ij tight xlabel('[cm]') ylabel('[cm]') caxis([-20 0]) c = colorbar; c.YTickLabel{end} = '0 dB';
See also
About the author
Damien Garcia, Eng., Ph.D. INSERM researcher Creatis, University of Lyon, France
websites: BioméCardio, MUST
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