Using a mask with a Different matrix size as target image to obtain image

I have a known Mask as a 240x240 Double. I usually use this mask against the same matrix size image but I need a way to convert this to use it against an image with a matrix size 448x448 uint16.

The code i usually use is

        T2FS=dicomread(T2FSa{1});
        T2FS(~mask)=NaN;
        imagesc(T2FS); %shows the mask
        avgSig=mean(T2FS(mask));

but the mask and the image T2FS aren't the same image matrix size. Any help would be greatly appreciated.

[Image Analyst]

So where in the larger image do you want to place your mask? Or do you want to scale it with imresize() so that it's the same size as your image?