Quality Resource Guide l Digital Radiography 7th Edition 5 www.metdental.com intended use and to follow the manufacturer’s recommendations. It is always preferable to transfer images digitally when possible. Image Archival and Backup The use of digital imaging in dentistry requires an image archiving and management system that is very different from conventional radiography. Storage of diagnostic images on magnetic or optical media raises a number of new issues that need to be considered. The file size of dental digital radiographs varies considerably, ranging from approximately 200 kB for intraoral images to up to 6 MB for extraoral images. Storage and retrieval of these images in an average size dental practice is not a trivial issue. Fortunately, the development of new storage media and the continuing decrease in the price of a unit of storage has alleviated the capacity issue in dental radiography. Hard drive capacities of modern computers already exceed the storage needs of most dental practices. The use of online practice management systems using cloud- type technologies has gained popularity in recent years. Online systems provide location-independent access. The technology has matured to the point that data security and integrity are acceptable for day-to-day clinical operations. The simplicity with which digital images can be modified through image processing poses a potential risk with respect to ensuring the integrity of the diagnostic information. Once in a digital format, critical image data can be deleted or modified. It is important that the software prevents the user from permanently deleting or modifying original image data, whether intentional or unintentional. Not all software programs provide such a safeguard. As the use of digital imaging in dentistry continues to expand, the implementation of standards for preserving original image data becomes urgent. The use of computers for storing critical patient information mandates the design and use of a backup protocol. The backup hardware, software and protocol need to be considered while setting up a digital system, not some time later. Table 2 shows some issues that need to be considered when designing a backup protocol. A number of media options are available for external storage of digital radiographs including backup servers, external hard drives, DVDs and web-based services. When clinical operations depend on access to digital data, it is imperative that backup data are generated continuously and that an off- site copy is available when needed. Catastrophes such as fires and floods are fortunately relatively rare, but malfunctioning of computer hardware is quite common. Thus, a secure and user-friendly backup system needs to be part of every practice that relies on digital data for its clinical and administrative operations. Image Compression The purpose of image compression is to reduce the size of digital image files for archiving or transmission. Especially the storage of extraoral images in a busy clinic may pose a challenge to storage capacity and speed of image access. The purpose of file compression is to significantly reduce the file size while preserving critical image information. Compression methods are generally classified as lossless or lossy. Lossless methods do not discard any image data and an exact copy of the image is reproduced after decompression. The maximum compression rate for lossless compression is usually less than 3:1. Lossy compression methods achieve higher levels of compression by discarding image data. Empirical evidence suggests that this does not necessarily affect the diagnostic quality of an image. Compression rates of 12:1 and 14:1 were shown to have no appreciable effect on caries diagnosis. Version 3.0 of the DICOM standard adopted JPEG (Joint Photographic Experts Group) as the compression method, which provides a range of compression levels. Although the use of low and medium levels of lossy compression appear to have little effect on the diagnostic value of dental images, the application of lossy compression should be used with caution and only after evaluating its effect for specific diagnostic tasks. With the continuing increase in the capacity of storage media and the widespread use of high- speed data communication, lossy compression of dental radiographs is not urgent. At the same time, new digital image receptors are generating images with more and more pixels and more bits per pixel, thus increasing storage needs. Image compression negates to some extent the gain from such high-end detectors. Whether or not we need high resolution detectors and whether or not we can use image compression should be dictated by diagnostic criteria. Current evidence suggests that detector quality and moderate image compression have a very limited impact on diagnostic outcomes. Imaging Processing The use of digital imaging in dental radiography involves a variety of image processing operations. Some of these operations are integrated in the image acquisition and image management software and are hidden from the user. Others are controlled by the user with the intention to improve the quality of the image or to analyze its contents. Any operation that acts to improve, restore, analyze or in some way change a digital image is a form of image processing. The term image enhancement is often used to describe adjustments to the image that make the image visually more appealing (subjective Table 2 - Digital Image Backup Considerations • Type of Media DVD, server, hard disk, cloud? • Method Selective, full, compressed, uncompressed? • Timing Continuous, daily, weekly? • Storage Location On-site and off-site! • Recovery Time Minutes, hours, days? • Recovery Reliability Test! • Future Compatibility Requires regular upgrading • Security Safeguarding protected health information