Teleradiology is unique among telemedicine applications in that it grew out of the evolution of the specialty itself. Radiology by its nature is probably the most technology-dependent clinical specialty in existence and thus had an advantage over nearly all other specialties by having technology, technical support, practice procedures and knowledge, and research programs in place even before the “tele” option arose. Yet even with this infrastructure, radiology faced (and still faces) challenges when it came to convincing users that it was at least as good as traditional film-based radiology in terms of quality, diagnostic accuracy, cost, and utility.
Teleradiology has its origins in the development of digital radiography. For over 80 years patient care depended on film-based radiology, but these images had to be physically transported throughout a hospital, between hospitals, and between cities. This was very labor intensive and often involved radiologists doing “windshield” duty, driving from small town to small town to interpret batches of cases that had been acquired over the previous week or even month, delaying interpretation and thus treatment. Film-based radiology was also subject to lost or misplaced images. 12,13
In the 1970s, the idea of an electronic-based imaging system replacing all X-ray film took root. Research with video-based and other digital detector systems primarily being conducted at the University of Arizona and the University of Wisconsin 14,15 led to the first digital subtraction angiogram being successfully performed and reported in 1977 followed by other digital imaging applications. 16–18 All of these early efforts led to digital radiology as we know it today and made direct transmission of digitally acquired images possible for teleradiology. 19
From an integration point of view, it is very difficult to distinguish teleradiology from radiology today, as from the perspective of the radiologist, the majority of the workflow is very much the same. Before digital radiography, images were acquired and viewed on pieces of film that were put on a lightbox for viewing and interpretation. Digital imaging changed this dramatically. Although printed to film in the early days, it soon became obvious that digital images are most effectively displayed on digital/electronic computer monitors. This led to increased interacting between image and viewer as radiologists could now use window/level techniques to adjust the contrast of images, use zoom/pan (instead of a magnifying glass and hot light) to view fine image details at high resolution, and use image processing and image analysis tools to extract more information from the images and render more accurate decisions. Once digital images were introduced, computer-aided detection and diagnosis tools were rapidly developed and are becoming commonplace in many radiology applications such as breast and lung screening. 20
In this transition from film to the digital world, however, issues arose that affected integration and acceptance of the new technologies—very much in the same ways that new technologies for other telemedical applications face integration challenges. In the transition, film images were the gold standard against which digital was judged due to its higher resolution and rendition of fine details required for interpretation (in fact, film is still technically better than digital in this respect). Complicating the transition to digital display was the fact that electronic displays in the 1980s and early to mid-1990s were basically inadequate in terms of resolution and contrast. As a result of the mismatch between high-quality, high-resolution digital images and low-quality, low-resolution displays, significant developments in medical-grade display technology were started in the late 1980s and actually continue to today as new display technologies are developed.
The first displays used for digital radiographs were cathode ray tubes (CRTs), 21–23 and issues such as luminance and even the type of phosphor in the display faceplate were variable and less than ideal. Today liquid crystal displays (LCDs) and variants (organic light-emitting diodes, or OLEDs) are the norm in most radiology reading rooms. 24,25 As with telemedicine in general, the quality of images is the deciding factor on whether users (radiologists) are satisfied with the information presented to them clinically. 26,27
Some of the key display parameters that have guided the development of these displays are directly related to the perceptual requirements of the radiologists and the digital nature of the images, and the complex nature of the anatomic structures and lesions in those images. 28 All of these factors are also important in telemedicine displays, including luminance (or brightness) and contrast, 29,30 viewing angle, 31,32 calibration methods, 33,34 and, more recently, the use of color and commercial off-the-shelf displays instead of more expensive medical-grade monochrome and color displays. 35–37 It is important to note that much of this foundational research on display optimization has been incorporated into the major practice guidelines for the practice of digital radiology and teleradiology. 38–40 Today even laptops, iPads, and smart phones are being considered for use, especially in teleradiology for viewing images 41–44 and capturing images. 45–47 Many of the recommendations in these guidelines are directly applicable to telemedicine applications and should be referenced as feasible when designing a telemedicine work area.
Another key aspect of integration that helped advance teleradiology was the development and use of the DICOM (Digital Imaging and Communications in Medicine) standard. 48,49 In fact, the DICOM standard is used today in many telemedicine applications as a tool for formatting, transmitting, and archiving visible light and other images (eg, ophthalmology, pathology, dermatology). The development of technical standards to optimize interoperability across platforms and institutions was fundamental to teleradiology, and the lessons learned in radiology are readily transferable to telemedicine in general.
Through joint efforts of the American College of Radiology (ACR) and the National Electrical Manufacturers Association (NEMA), DICOM was developed in 1993. DICOM is an internationally accepted standard for medical images and metadata (now extending beyond radiology to visible light and other images used in telemedicine) with respect to handling, storing, printing, and transmitting image and other medical record information. It includes standards for file format and network communications. For example, the communication protocol uses Transmission Control Protocol/Internet Protocol (TCP/IP) for system communications enabling system interoperability or the exchange of image and patient data in a standard format so that images acquired on a device from one vendor can be viewed on any workstation.
The display used in teleradiology is obviously critical for efficient and accurate diagnoses, and the same is true in any telemedicine application. Two DICOM standards are important when considering displays: the Grayscale Presentation State Standard (GSPS) and the Grayscale Standard Display Function (GSDF). These are not only important for teleradiology but also for any other tele-application in which radiographic images would be viewed—for example, telestroke, teleorthopedics, telesurgery, and telecardiology, to name a few. GSPS is a data object associated with an image specifying how it should be presented on any DICOM-compliant viewer. It includes features such as customized look-up tables (LUTs), text overlay, and zoom/pan. The GSDF addresses the issue of having multiple displays from multiple vendors, each with different luminance ranges, white points, and minimum and maximum luminance settings. Standardization was required because the same image would look very different depending on the display it was viewed on. The GSDF maximizes the perceptibility of information and promotes consistency of presentation across different displays. As a calibration tool, it is based on the concept of perceptual linearity across grayscale values, so changes in image pixel values across a grayscale range are perceived as having similar contrast.
A similar display standard does not exist for telemedicine or for color medical images in general, whether for telemedicine or standard clinical uses. This has been the topic of a number of papers, with a recent consensus report 50 being the most relevant to telemedicine. It is noted in this consensus report that areas that would benefit the most from consistency and standardization of color would be digital microscopy, telemedicine, medical photography (eg, ophthalmic, dental photography), and display calibration. It provides overviews of some of the most critical color applications (including telemedicine) and then notes that a variety of important organizations are addressing this issue, including DICOM, American Association of Physicists in Medicine (AAPM), International Color Consortium (ICC), International Commission on Illumination (CIE), International Engineering Consortium (IEC), Video Electronics Standards Association (VESA), International Committee for Display Metrology (ICDM), and the American College of Radiology (ACR). It does provide reference to some methods available for calibrating color displays.
At the heart of any radiology or teleradiology enterprise is its Picture Archiving and Communications System, or PACS. A PACS is usually composed of various digital acquisition imaging systems (eg, computed radiography/digital radiography [CR/DR], magnetic resonance imaging [MRI], computed tomography [CT]), a secure network for transmitting images from those devices to workstations (onsite or offsite as with teleradiology), archives (onsite, offsite, or cloud based) to store and retrieve images and related data, and viewing terminals (eg, workstations, mobile devices). Increasingly, PACS systems that were traditionally limited to radiology departments and their images are becoming enterprise-wide transmission and archiving systems that many departments use not only for routine images but also for those used in telemedicine practices. 51 Images from devices such as digital cameras, endoscopes, digital slit cameras (ophthalmology), digital otoscopes, and many other devices are being stored in and retrieved from PACS systems (often using a DICOM wrapper).
As with telemedicine in general, the main drivers for teleradiology were the need for after-hours (∼5:00 P.M. to 8:00 A.M., weekends and holidays) coverage for urgent and emergent radiologic studies 19,52 and the need for subspecialist or expert reads. Even in its more advanced stage of acceptance and integration, however, there is still considerable debate in the radiology community regarding its use, regulation, and commoditization, 53–63 with many of the same concerns being raised in many other clinical specialties using telemedicine. It is clear and evidence supports its role, and with appropriate care 63 and consideration, one can select an appropriate teleradiology or any other telemedicine provider.
On the regulatory side, telemedicine may someday soon follow the path of teleradiology in some aspects. For example, how well teleradiology has been integrated into general radiology practice is demonstrated by the ACR Teleradiology Guidelines and its history. The ACR Standard for Teleradiology was first issued in 1994 and was revised in 1996, 1998, and 2002. In 2007 the ACR sunset it, as everyday digital practice could not be differentiated from teleradiology. Recently released white papers on teleradiology practice from the ACR and the European Society of Radiology summarize the pros and cons of teleradiology and comment on best practices. 64–66 With respect to licensing, the ACR position is that physicians who interpret images originating from another state must be licensed and credentialed at the site of origin of the images and in the state they are doing the interpretation. 67,68 Telemedicine has a number of practice guidelines as well (many from the ATA), and some of them have been updated over the years much like the ACR guidelines—and in many cases deal with similar issues: quality, process and procedures, legal and regulatory, safety, and privacy and security. It will be interesting to track these guidelines to see when and if they, too, sunset at some point in time!