MATLAB: How to convert four points to 24 equally spaced point forming a circle

circleimage processingimage segmentation

hello

please help me..

i'm working on DICOM images for the heart and i wanna extract the LV (left ventricle) wall…and my professor told me to define four points interactively and then by doing interpolation convert these four points to 24 point equally spaced with keeping the insertion point…these 24 points will make a circle around the LV outer wall and i will repeat this for the inner wall in order to remove the blood pool thus keeping only the LV wall…

thank you and please help me.. if you wanna more explanation just tell me…

Best Answer

This is tricky. 4 hand-placed points usually do not all lie on a circle. 3 points define a circle.

Naively, in the absence of a sample image (hint, hint), it sounds to me as if thresholding would be more effective than hand-placement.

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MATLAB: Left ventricle segmentation

Looking at your original image, I don't know if it was necessary or useful to go through all those steps. I get the impression from the image that if you were to threshold at a sufficiently high grey level, and then imlabel() and regionprops(), that the target area would be the one with the lowest eccentricity.

MATLAB: Dividing a circle into six equal parts

You could write a custom function to do this:

function P = plot_arc(a,b,h,k,r)
% Plot a circular arc as a pie wedge.
% a is start of arc in radians, 
% b is end of arc in radians, 
% (h,k) is the center of the circle.
% r is the radius.
% Try this:   plot_arc(pi/4,3*pi/4,9,-4,3)
% Author:  Matt Fig
t = linspace(a,b);
x = r*cos(t) + h;
y = r*sin(t) + k;
x = [x h x(1)];
y = [y k y(1)];
P = fill(x,y,'r');
axis([h-r-1 h+r+1 k-r-1 k+r+1]) 
axis square;
if ~nargout
    clear P
end

Now from the command line:

hold on
for ii = 1:6
   P(ii) = plot_arc(pi/3*(ii-1),pi/3*(ii),9,-4,3); 
end

If this doesn't do it, consider using the LINE function. For example, replace this line:

P = fill(x,y,'r');

with this:

P = line(x,y);

and possibly delete the calls to the AXIS function.

Best Answer

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MATLAB: Left ventricle segmentation

MATLAB: Dividing a circle into six equal parts

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