X ray imaging goes digital
Authors: Kwan-Hoong Ng, Madan M Rehani
Journal: BMJ (2006)

Digital x ray imaging has brought obvious benefits to health care, but, as with all new technologies, it both requires and leads to changes in behaviour and processes, some obvious and some less so. The issues include cost and productivity, the need to acquire new skills, radiation doses, overuse, and image quality. Moreover, some of the ethical and legal issues surrounding teleradiology remain unclear.1

Physicians have long been accustomed to viewing and interpreting images on film. Film is now being replaced with digital images in the same way as film cameras are being replaced with digital cameras. Digital x ray imaging does away with film processing, and the images can be viewed just minutes after exposure via computer networks, to be seen by many people at once, in many different places. So what are the issues surrounding the transition to digital imaging?

The initial cost of buying digital systems has dropped substantially during the past two decades, but such systems are still more expensive than a conventional system. Conventional film images can be viewed anywhere, just by holding up the film to light, whereas monitors with network connections and software capabilities are needed to view digital images. The high cost of implementation has clearly impeded the adoption of digital systems, though some cost analyses have shown that the high cost can be justified in a high volume setting.2,3 The increase in the overall speed of service, from the request for an examination to reporting, may also justify the high cost. One comparison of the operating and investment costs of conventional and digital systems found that the average total cost of digital technology was 20% lower than that of a conventional system.3 Several studies have shown that the transition to filmless technologies offers potential for improved workflow and increased productivity.2 w1

New technology requires new skills. Physicians must become familiar with viewing images on a display screen. For many years, even radiologists found digital images not as acceptable as film for interpretation.4 Today, high resolution displays have greatly aided interpretation of digital images.

It was once thought that digital systems would reduce radiation doses. They can facilitate dose monitoring by recording factors that have direct bearing on radiation exposure to patients, such as x ray tube voltage and tube current. Any technical errors can be promptly rectified, thus further reducing risk to the patient. Although some studies have shown dose reductions,5 w2 there is a tendency towards increased doses.6 The reasons include the fact that overexposure can go undetected, unlike with film, where the image turns dark, but more important factors are a tendency to take more images than necessary and at a higher image quality (and hence radiation dose) than necessary.

One study showed that some centres with digital systems used an average of 68 exposures per examination in upper gastrointestinal fluoroscopic examinations, compared with 16 exposures in other centres with conventional systems.7 In several US hospitals the number of examinations per inpatient day increased by 82% after transition to digital systems and the number of examinations per outpatient visit increased by 21%, while the number of examinations per visit nationally decreased by 19%.8 It is easy to delete digital images, and repeat exposures normally go undetected.

Different imaging tasks require different levels of image quality. For example, the follow-up examination for a fracture does not require the same image quality as that required for its diagnosis.8 w3 A lower quality image may look slightly less clear but still be good enough for diagnosis. The image quality routinely used in digital imaging is often greater than that required for diagnosis, so how does a physician know if it is higher than necessary? This is a question of training. Studies using simulated images have shown that it is possible to reduce radiation doses by half or more by having slightly less clear images, without affecting the detection of simulated pathologies.9 w4 Organisations such as the International Commission on Radiological Protection and the International Atomic Energy Agency recommend that quality assurance programmes should be implemented,10 as do the UK regulations.11

One big advance of digital technology is, of course, that it enables the electronic transfer of images to any location. This timely production and transmission of images gives physicians greater access to them during consultations.12 The option of remote interpretation of images has the potential to ease the burden on hard pressed radiology departments. Images taken in short staffed departments at night can be reported by remote fully staffed departments in the day.1

Despite the obvious benefits of digital x ray imaging, there is lack of clarity about related ethicolegal issues. Whether the current law relates to telemedicine in the same way that it does to other medical specialties remains controversial.1 Telemedicine raises licensure questions, such as whether teleradiologists practising medicine in another country need a license for that place. This is complicated by individual hospitals having different standards for accreditation.

In the UK, practice guidelines on legal issues relating specifically to telemedicine or teleradiology are lacking. The next step is to develop and implement guidelines to safeguard both patients and professionals. Until such guidelines exist, practitioners should be mindful of their position regarding issues such as duty of care, liability, and confidentiality.