isotropic expansion for a mask with anisotropic voxels

Question

Farah 2024-9-23，12:43

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回答： Farah 2024-9-25，10:09

Hello,

I'm trying to expand my mask by 2 mm in all direction ( isotropic expansion) but my voxels are anisotropic ( x and y are the same but the z is higher [0.9,0.9,4] ). how I do this 2 mm expansion wihtout changing the volume of my mask?

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Answer 1

Image Analyst 2024-9-25，3:29

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I'm not sure how many voxels per mm you have. Is 0.9 mm the voxel width? You can use imdilate but be aware that you'll probably have quantization effects if 2 mm is not an integer number of voxels.

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Answer 2

Farah 2024-9-25，10:09

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i did used imdilate. I created an isotrpic space with 1x1x1

vox_a = voxelSize; % Original voxel size (anisotropic)

vox_b = [1, 1, 1]; % Set isotropic voxel size to [1, 1, 1] in mm

then I created the original and isotropic grids using meshgrid then I resampled the original mask to isotropic grid using interp3 then I wanted to expand in this new isotropic space and I used imdilate; stepSize_mm = 2;

stepSize_pixels = round(stepSize_mm / vox_b(1))

D_isotropic = imdilate(D_isotropic, strel('sphere', stepSize_pixels)); but yet when I calculate the radius of the expansion is not 2 mm