Plot 3d volume from 2d slice with voxel size

Hi! I have to build 3D volume from segmentation of 25 2D MRI slices (768x728x25). I've crated a 3D binary matrix 768x768x25,named 'mask' (1 inside of region of segmentation and 0 outside), a 3D matrix with hounsfield value of slices 768x768x25, named 'HU' and then I've found a matrix with 0 outside the region of segmentation and hounsfield value inside, named 'ROI'.

(ROI=HU.*mask)

How can i build volume from ROI and voxel size (0.2995x0.2995x3) and plot it? thanks.