TWI Frequently asked questions
by Bruce Blakeley
A digital radiograph is stored and displayed on a PC, rather than a radiographic film. The advantage of this is that the image can be processed, enhanced and communicated much faster than a conventional film. There are three mainways of capturing a digital radiograph: the first is to scan a conventional film radiograph in a specialist scanner, similar to a document scanner. The second is to use a 'flat-panel' similar to a digital camera, which converts the X-ray quanta directly in to charge. The flat panel is positioned in the same place as the film and is connected directly to a PC. The third method is known as Computed Radiography (CR).
CR uses a flexible imaging plate in the place of film. A chemical process in the imaging plate captures the radiograph. The imaging plate is then attached to a drum and placed in a scanner. This scanner reads the latent image off the plate. Exposing it to bright light erases the plate.
Digital radiography typically requires lower values of kV and smaller exposure times. The disadvantage is poorer resolution compared with fine-grain film. However, the technology is improving with time. Digital radiography isnormally used to inspect castings and pipe-welds.
