MATLAB runs under X11 on Macs. This means that it is running in UNIX, rather than the Mac OS, and therefore the file hierarchy looks different.

Your files may be found through a path that may look like Macintosh HD/Users/Username. For example Macintosh HD//Users/Beth/Desktop/Beth & Steve Barebones.

For convenience, set the Current Directory in MATLAB to your folder (see image below).
The little box with the ... to the right of the path window is the browse files button.

Use File/Set Path to select and save the path to your XrayProject folder. If this path is saved, then MATLAB can always find the XrayProject scripts, and you can set your Current Directory to the folder containing your data.