This thread is from before the introduction of this function, so that might help you find a solution for older releases. I took the liberty of copying one of the answers below. It uses functions that aren't in the Matlab base, so you'll need the image processing toolbox (I'm assuming that isn't a problem, as imresize3 is as well, unlike imresize).
T = maketform('affine',[x_scale 0 0; 0 y_scale 0; 0 0 z_scale; 0 0 0;]);
R = makeresampler({'cubic','cubic','cubic'},'fill');
ImageScaled = tformarray(Image,T,R,[1 2 3],[1 2 3], round(size(Image)*x),[],0);
