How can I count the number of voxels in a region

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Gina Carts 2020-3-2

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https://ww2.mathworks.cn/matlabcentral/answers/508495-how-can-i-count-the-number-of-voxels-in-a-region

评论： Gina Carts 2020-3-3

Hi,

I have a 3D mask with 0 background (NIfTI format). The mask has some regions marked with number 1,other egions with number 2, others with number 3 and others with number 4.

I was wondering how to count the number of voxels involved in each region. If I have 20 regions in my mask: let's say 10 regions have number 1, 5 regions have number 2, 4 regions have number 3 and 1 region have number 4.

I want to know how many voxels correspond to each of my 10 regions with number 1. I want the individual number of voxels in each region not the overall number.

Any help is highly appreciated.

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Gina Carts 2020-3-2

在 MATLAB Online 中打开

When I typed the last line of code, I got the following error:

numVoxels = = cellfun(@numel,CC.PixelIdxList);
            ↑
Error: The expression to the left of the equals sign is not a valid target for an assignment.

I changed it to

numVoxels = cellfun(@numel,CC.PixelIdxList);

I don't really understand the output though. It says that numVoxels is 1x66 double. Does it mean it has 66 regions with label 1?

I know that this mask has 57 regions each of which 49 have label 1.

How can I see the number of voxels for each region? I deleted the ; in the last line of code but I don't really understand what I see

Alex Mcaulley 2020-3-2

Hve you read the documentation of bwconncomp? There are some examples to see what this function does.

numVoxels is an array with the number of voxels for each region found

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Answer 1

Image Analyst 2020-3-2

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/508495-how-can-i-count-the-number-of-voxels-in-a-region#answer_418104

在 MATLAB Online 中打开

Gina, to find the blob count and volume for all the regions for a particular label number, you can do (untested)

% Get a mask of only this number and label each blobs that has this number.
[thisLabeledImage, numBlobs] = bwlabeln(mask3d == desiredNumber); 
% numBlobs is the number of distinct, separate blobs with this label.
% Now find the volume of all those blobs.
props = regionprops3(thisLabeledImage, 'Volume');
allVolumes = [props.Volume]; % List of volumes for all blobs with this particular number only.

Repeat for whatever desiredNumber you want to check. For example

desiredNumber = 4;

Or you can put into a loop over all the numbers you know exist.

mask3d is the "mask" array you mentioned with the labeled regions.