The Madonna of the Yarnwinder (The Lansdowne Madonna) was the first painting to be examined using a CAT scan. With the help of Siemens and their newest Somotom model, the painting was put through the machine, just like a human, in order to capture images of the inside of the painting.
http://www.universalleonardo.org/scientificAnalysis.php?tool=545&id=313
