Looking Through Your Skin

To be asked to diagnose a fault inside such a complex system as the human body without being able to look inside it would appear to make the task very difficult, yet this is a problem doctors had to face until the advent of X-rays at the turn of the century. Tissue and bone, except in very thin layers, are opaque to visible light; we cannot therefore look through or into the body in the ordinary sense at all. Other forms of electromagnetic radiation can penetrate tissue and bone to varying degrees, and with their aid avisible image can be reconstructed.