What Is A Picture Archiving And Communication System (PACS)

AbstractA PACS is a digital system for acquiring, storing, moving and displaying picture orimage information. It is an alternative to film jackets that has been made possible by re-cent breakthroughs in computer technology: telecommunications, local area nets and optical disks. The fundamental concept of the digital representation of image information is in-troduced. It is shown that freeing images from a material representation on film or paperleads to a dramatic increase in flexibility in our use of the images. The ultimate goal ofa medical PACS system is a radiology department without film jackets. The inherent natureof digital images and the power of the computer allow instant free "copies" of images to bemade and thrown away. These copies can be transmitted to distant sites in seconds, withoutthe "original" ever leaving the archives of the radiology department. The result is a ra-diology department with much freer access to patient images and greater protection againstlost or misplaced image information. Finally, images in digital form can be treated asdata for the computer in image processing, which includes enhancement, reconstruction andeven computer -aided analysis.IntroductionA single technical concept, the digital image, has made possible the creation of PictureArchiving and Communication Systems (PACS). This paper defines the digital image and ex-plores the far -reaching consequences that it has for the way in which radiologists andothers do their work.The digital imageA picture is a visual representation drawn, photographed or otherwise rendered on a flatsurface. In this paper the term image will refer to the representation of a picture interms of the l's and 0's upon which digital computing is based. Digital images in thissense are familiar to the radiologist, because the pictures of modalities such as CT scan-ning ultrasound and nuclear medicine originate as digital data which is turned into pic-tures to make it accessible to human senses. In the world of computing, the digital imagehas been a concept since the mid- 1950's, especially in intelligence and space applications.In these fields pictures began as photographs and were converted to digital images in orderto make them accessible to the computer. A need was felt to harness the power of the com-puter to cope with the large quantities of picture information acquired by planes, satel-lites and space craft. Only recently, however, has the cost of the large memories neededfor digital image data decreased to the point where it is practical to consider their appli-cation in medicine, banking, office work and other fields.Let us briefly review the way in which a digital image represents a picture, and how itis stored in a digital computer, before considering how images will affect radiology andother fields.Consider a monochrome picture. The basic idea of creating a digital image is to imposea fine grid over the entire picture, thus dividing it up into many very small squares,called pixels (from picture elements). We then assign to each pixel a numerical valuerepresenting a shade of gray For example, zero represents white and the highest numberrepresents black. A pixel may be a uniform shade, so that assigning a number to it is