Change the matrix dimensions of a analyze file to match the other?

My general question is how do you change the matrix dimensions of a analyze file to match the other?

Specifics: I am taking a spherical ROI and placing it on the FA map of a brain. Both images are binarized so I can overlay the ROI and from that overlay extract the data specific to that ROI on the FA map. Both of these files are analyze format (hdr/img) and this is the code and error I am using: -------------------------------------------

roi = analyze75read('2mmsphere_-20_6_5_roi.hdr'); fa = analyze75read('FA_analyze.hdr');

ROI = im2single(roi); result(i,j)= mean(nonzeros(ROI)*nonzeros(fa));

xlswrite(results);

I changed the roi file from a uint8 to single and tried to use the mean function and got this error: ??? Error using ==> mtimes Inner matrix dimensions must agree.

Error in ==> faanalysis at 10 result(i,j)= mean(nonzeros(ROI)*nonzeros(fa));

Can anyone help or propose a better solution???

Thanks!

Answer 1

[Image Analyst]

If ROI has 1000 non-zero numbers in it, and fa has 5000 non-zero numbers in it, then how can you matrix multiply a 1x1000 by a 1x5000 matrix? Even if it were an element-by-element multiplication instead of a matrix multiplication, they don't have the same number of elements, so exactly what are you trying to accomplish??? If you do want an element-by-element multiplication, you can do this:

nonzeros(ROI).* nonzeros(fa)

Note that I used a dot before the asterisk.

[Elle]

I can't believe I didn't think of that.

So I do want a matrix multiplication which would mean I would need to have one matrix have the same dimensions as the other. How would I go about adding/removing zeros to 1 matrix in order to get it to match the other?

i.e. ROI = 109X91X91 and fa = 128x128x50 so I would want the ROI to match the fa matrix