A clinician's guide to digital X-ray systems.

Computers are invading all areas of our lives. Over the next few years there will be major changes in radiology departments around the UK. The invading system is known as PACS (picture archive computer/communication systems). These PACS allow X-rays and other diagnostic images to be captured, distributed and stored in a digital format viewable on computer screens around the hospital. This paper offers a simple explanation of what PACS is and how it works, a discussion of the advantages and pitfalls, and lessons for clinicians learnt from the procurement of our own system. The X-ray-taking process starts with the normal X-ray source and the patient and X-ray cassette arranged in the usual positions. The difference is that the cassette contains a reusable phosphor plate which is sensitive to X-rays but not light. Once the plate has been exposed it is fed into a laser computer reader which captures the image in a digital format. The reader then resets the plate ready for reuse. The phosphor plates are expensive but can be reused several thousand times; they are also more X-ray-sensitive than ®lm, allowing a slightly lower radiation dose to be used. The advantages of this process over silver-®lm developing are the elimination of the expensive ®lm, the absence of toxic developing chemicals and the speed. Within 30 seconds the image is visible, so if the image needs to be repeated for technical reasons this can be done immediately. If the image is satisfactory then the patient can be released thus improving the throughput of the X-ray rooms. The radiographer then orientates the image on the screen according to hospital protocols and can also alter the contrast and grey scale (a process known as windowing). When the image has been optimized the ®le is archived and additional copies are sent to any computer on the network. Typically the image would be sent directly to the requesting doctor so that it can be seen and acted upon immediately. A copy would also be sent to the radiologists for reporting. Figure 1 shows the imaging journey. Hard copies of any images can be made on ®lm printers or paper if required. Large amounts of printing should be avoided since this is expensive and unnecessary once most areas in a hospital have the computer viewing screens. Once the computer image has been seen in the clinical area it can be deleted from that workstation …