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Apply a mask to 4D medical images in a vectorized way

Asked by AP on 11 Feb 2013

Dear All,

I have a 4D array V, with the size [144 144 12 25]. In fact, it is a 4D medical image with 12 stacked slices in 25 different time. I want to apply a mask, named M, to each image in the array in a vectorized way. M is a 144x144 array containing logical values. Could someone help me how to do it?



1 Comment

José-Luis on 11 Feb 2013

I notice that you don't seem accept many answers after asking questions. Some of the answers seemed valid to me. Please remember to accept answers if they help you, since it is the only "payment" the volunteers in this forum receive.



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2 Answers

Answer by José-Luis on 11 Feb 2013
Edited by José-Luis on 12 Feb 2013
Accepted answer
 data = rand(144,144,12,25);
 your_mask = rand(144,144) > 0.5;

Assuming you want to multiply by the mask:

 your_result = bsxfun(@times,data,mask);

Note that you can do operations other than multiplication. Please have a look at

 doc bsxfun


Sean de Wolski on 11 Feb 2013

Isn't that what you want?


AP on 11 Feb 2013

I want the operation on each image. I thought bsxfun is only for each pixel and can't be applied to each image in a 4D array. Please correct me if I am wrong: so when we call bsxfun(@times,data,mask), bsxfun applies the mask to each 144x144. Is that right?

José-Luis on 12 Feb 2013

Yes. That's what the "singleton expansion" in the documentation means.

Answer by Conrad on 11 Feb 2013

Something like this:

fV = V.*M(:,:,ones(1,size(V,3)),ones(1,size(V,4)));



AP on 11 Feb 2013

How can I convert M, with size [144 144] to M with [144 144 12 25]?

AP on 11 Feb 2013

I think, I have to use

repmat(M, [1 1 size(V,3) size(V,4)])

to duplicate M in other dimensions and make it [144 144 12 25].


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