A knotty problem

THE saw, the bradawl and the drill are among the many tools that carpentry has bequeathed to surgery. Now medicine is about to return the favour. Although operating theatres no longer much resemble sawmills, they are both still places where success depends on cutting organic matter with great precision. To guide their incisions, doctors have developed a range of techniques for peering inside their patients. InVision, a firm based just across the San Francisco Bay from Silicon Valley, aims to adapt a medical imaging technique, computerised axial tomography (CAT), to help sawyers see inside logs before slicing them up.