When visible light scanning is not successful we can turn to another part of the electromagnetic spectrum to produce our 3D models – we use an X-ray beam. Unlike light, X-rays can penetrate even thick opaque material. Some of the X-rays in the beam will be absorbed by the object and the amount of absorption varies with the thickness, density and materials of the object. By detecting the variations in the X-rays that have passed through an object we can build a picture of the internal features. This only gives us a 2D image but by taking lots of digital X-ray images from different directions it is possible to reconstruct a 3D X-ray image of an object. This is computed tomography, also known as CT scanning.
At the weekend we made an out-of-hours visit to Radiology at Pinderfields Hospital, West Yorkshire, with a range of weird and wonderful packages that certainly raised a few curious eyebrows as we traversed the hospital foyer. The largest of these was half of the lower jaw of a sperm whale. When the CT scan it made, the x-ray source and detector spin round the object as it slowly passes through the circular gantry.
From the CT data we can explore the internal structures of the jaw, recreating slices through the bone at any angle and reconstruct the surface of the object in 3D. This will only be a black and white 3D model until the texture photographs are applied to the surface.