Read in the 9 images with imread.
image1 = imread('image1.tif');
image2 = imread('image2.tif');
image3 = imread('image3.tif');
image4 = imread('image4.tif');
image5 = imread('image5.tif');
image6 = imread('image6.tif');
image7 = imread('image7.tif');
image8 = imread('image8.tif');
image9 = imread('image9.tif');
Then concatenate:
image3D = cat(3, image1, image2, image3, image4, image5, image6, image7, image8, image9);
