Medical scientists today are applying light and sound technologies in innovative ways in order to study our bodies in more detail than ever before. In XLab this week, Stalo introduces us to a scientist who creates 3D laser images which allow the detection of disease; another who uses ultrasound techniques to monitor embryos' health in the womb and a third scientist who uses microbubbles to detect the way blood flows through a diseased area. In the studio Stelio helps the students write invisible messages!