Teleradiology and telepathology form an integral part of the telemedicine concept. ... telepathology and teleradiology in the global telemedicine context.
Journal of Medical Systems, Vol. 19. No. 2, 1995
Teleradiology/Telepathology Requirements and Implementation Seong K. Mun, AI M. Elsayed, Walid G. Tohme, and Y. Chris Wu
Teleradiology and telepathology form an integral part of the telemedicine concept. Teleradiology is becoming a mature technology because of advances in imaging technology, database design and communications infrastructure and capabilities. Telepathology has also made significant progress but more development is needed in the definition of required images, database design and standards. While the requirements of most clinical applications of teleradiology are well established, telemammography still presents some impediments. Technical difficulties in telemammography are presented in terms of the lack of a clinically accepted digital imaging system and large data volume required per image. Another important aspect in tele-imaging is the database question. Workstations constitute a window into database. Comprehensive database development is the most difficult and expensive technology for tele-imaging and operational features of such systems are discussed. Finally, we explore current examples of the use of telepathology and teleradiology in the global telemedicine context.
INTRODUCTION Medical applications are increasingly depending on the digital medium for image management and communication. While analog support is still used in many applications, digital images are being used routinely in clinical diagnosis and radiology departments are considering going filmless in the near future.l'2 Digital imaging has many advantages over analog) It provides the ability to improve image quality but also allows for better management of data for archiving, retrieval and storage: Large film libraries are now replaced by optical jukeboxes: This not only reduces the amount of space required and improves the management of images but also reduces the amount of lost or misplaced f'des. Digital imaging allows for better, faster and easier communication of images through communication channels. Digital imaging is now finding newer and wider applications. While radiology is one From the Department of Radiology, Georgetown University Medical Center, Washington, DC; Armed Forces Institute of Pathology, Washington, DC; Deparm~nt of Radiology, Georgetown University Medical Center, Washington, DC; Department of Radiology, Georgetown University Medical Center, Washington, DC. 153 0148-5598/95/0400-0153507.50/0 9 1995 Plenum Publishing Corporation
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of the applications that use digital images for image management and communications, other applications in the medical field are relying on the digital medium such as pathology. Both teleradiology and telepathology form an integral part of the telernedicine concept. Teleradiology applications have become very widespread and the technology is now mature due to advances in imaging technology, database design and communication capability. 6 Telepathology has also made significant progress but more development is necessary in aspects such as developments of image quality criteria, database design and standards. This paper discusses teleradiology requirements and applications with a special case made for new applications such as digital mammography. Telepathology will be discussed as a field that is embracing digital applications.
BASIC COMPONENTS
OF TELE-IMAGING
The term tele-imaging encompasses telemedicine applications but also other applications based on multimedia technology. Tele-imaging includes all applications of telemedicine such as teleradiology and telemammography as well as telepathology. The basic components of tele-imaging include: image acquisition, image management, image display and presentation, smart imaging and decision support and a communication system. Image
Acquisition
Images used for radiology can either be in digital or conventional analog format. Acquiring the image can be done in several ways depending on the clinical application and its requirements. We distinguish between images used for radiology and mamrnography images because digital mammography !s still experimental. There are different ways of acquiring radiological images in a digital format: digital interfaces, video frame grabbers, film digitizers, direct digital capture. Conventional or analog radiography is mostly used for bone and chest applications. Well Established Digital Methodologies. Some methods of acquiring images in a digital manner are well established. These include digital interfaces for MIni or CT scanners or video-frame grabbers for ultrasound applications. Many image generating devices already output their images in digital form such as CT, MRI and nuclear medicine. In this case, one can use a digital interface which is a direct connection between the image generating device and the digital network acquisition device. The digital interface provides the full resolution of the imaging modality. It also conveys gray scale depth of up to 12 bits or 4096 shades of gray as well as an artifact-free image (little or no noise). 3 Both text as well as images can be communicated across these interfaces to the digital network. The problem with digital interfaces is that there are no widely implemented standards. Although they provide a direct interface with the digital network they tend to be slower than A/D conversion with video frame grabbers. They are also more expensive. Video frame grabbers are basically high speed A/D converters used to digitize video signals such as output from video imaging systems like ultrasound. Video frame grabbers provide a variable resolution typically 512 x 480 to 2k • 2k. s Also, they support gray
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scale depth of 8 bits or 256 shades of gray. These inexpensive and high speed devices do however introduce noise and artifacts into images. Bone and Chest. Conventional radiography (i.e.: hard-copy format images) is still used for bone and chest images. These images can also be captured directly in digital format through the use of Computed Radiography (CR) as well as other detector systems. CR systems use a photostimulable reusable phosphor plate x-ray imaging system. 7 The image capture on the phosphor plate is digitized by laser scanning. Another technology used in CR is selenium plate although it seems mostly restricted to chest applications, s X-ray films can be translated into digital format by using film digitizers such as laser scanners which provide higher speed than other digitizers, a resolution of lk x lk to 4k • 6k and gray scale bit depth of 12 bits or 4096 shades of gray. Another cheaper but less reliable method of digitizing these images is using a video camera. Since the output from this vidicon tube camera is analog, a video frame grabber must be also be used. These systems are known as camera on a stick models but they require tedious image-by-image focusing and zooming. These low cost systems have a maximum of 1024 x 1280 pixels matrix size and pixel depth of 8 bits and today they are used less often. Mammography. There are still technical difficulties to be resolved before the digital presentation of mammography images becomes clinically acceptable. Mammography is mostly performed on conventional X-rays and digital mammography is still in its experimental phase. There are several ways of digitizing mammography images obtained on conventional screen-film systems using video cameras, charge coupled devices (CCD) cameras or laser scanners. 9"1~It is important to ensure that mammography images retain all clinical information during the conversion to digital format. The digitization requirements such as pixel size or pixel depth for mammographic imaging are still unknown, primarily because high-resolution digital systems with pixel sizes smaller than 0.1 mm x 0.1 mm are not commonly available. ~ However they range from 100 microns per pixel to 21 microns and it seems that for clinical applications, a 50 micron pixel size might be appropriate. Direct digital capture using computed radiography systems (CR) is a method of obtaining the mammograms directly in digital format without going through the digitization process of screen-film. 7 This method is coming out of its experimental phase. Pathology. Telepathology allows physicians to visualize pathologic specimens images on a video monitor from a remote location rather than directly through a microscope.12 The process first involves capturing pathologic specimens at the transmitting site through a high definition CCD camera mounted on a light microscope. The images are then transmitted to the receiving site where they are viewed on a color monitor. Telepathology can be dynamic in which case images of a specimen are viewed live and in real time; or static, in which case images are captured in a digital format on an image frame grabber board and transmitted individually. ~3 We can identify several issues of importance in telepathology images. Some can be determined, others are still being investigated. Requirements related to matrix size and color which are based on image resolution and dynamic range respectively have been determined. On the other hand, requirements related to x-y-z coordinates and magnification remain under investigation. Although the development of a fully dynamic system incorporating a robotic microscope has posed many technical challenges, such a system presents important advantages over a static
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system. 13 Most importantly, a dynamic system provides a means for controlling a robotic microscope at the transmitting site by the consulting pathologist at the receiving site.
Image Management Image management consists of image handling, storage, archiving and retrieval. This underscores the importance of an efficient database system. The basic operational features of such a database are discussed below. Also issues of interaction with communication technology become crucial especially when transmitting images over a wide area network for telemedicine applications. System compatibility and standards development are key to such technologies. Image management includes the ability to deal with multimedia data. The available images will be coming from different sources; MRI/CT images, ultrasound, mammography, pathology etc . . . . The image management capability of the system should provide the possibility to manage all types of images. Operational Features of the Database. The database should be able to identify and describe each image. While the requirements of this task might be well defined for radiology applications, pathology applications requirements are still not clearly identified. Operational features for the intelligent database are: 9 9 9 9 9
Relating one image to the other Deciding on the protocol for use Determining the protocol for access Relating to other data Interactivity capability
Database Storage lssues. The storage, archival and retrieval issues bring up the subject of data volume, levels of storage and data compression. Data volume issues are linked to the types of images being stored. The amount of storage required varies widely depending on what type of imaging modalities are available. The number of bytes required per study depends on the number of pixels per image array, the number of bits per pixel and the number of images per study. The image parameters vary from system to system and the number of images making up a study is a matter of local convention. Among the factors affecting the amount required for storage are spatial resolution, contrast resolution and number of images per study. In other words, an image with a large array size (e.g., 2.5k x 2k) and with great bit depth (12 bit or higher) will require more storage space than other smaller size matrix images. Nuclear medicine studies, for example, require less storage per study than do CT studies. The image arrays for radiography can be as large as 4k x 5k x 12/16 bits for mammography images while nuclear medicine studies, such as spot views in barium studies, require only a 512 x 512 pixel array. Today, storage is done mostly on two types of media: magnetic for short-term storage and optical for long-term storage. This issue of levels of storage is brought up because of cost considerations. Short-term storage is commonly used to refer to images that are stored for rapid access. This means different time period for different departments and the jury is still out on deciding how short is short-term. For short-term storage, magnetic disks are used because they offer speed, limited portability and a great deal of dependability that is not available in other storage media. The more commonly used
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magnetic disks are the larger parallel disks and also the Redundant Array of Inexpensive Disks (RAIDs) technology used in MDIS systems. 14 Storing images for long periods on fast magnetic disks cannot be cost-justified. Optical disk technology has become very popular and is based on the WORM or Write-Once-Read-Many-times technology and offers lower cost per byte storage than magnetic disk at very reasonable data transfer rates. Also optical disks (14" size) can be stored in jukeboxes shelving hundreds of optical disks for terabyte (1000 Gbyte) storage. 15 The large amount of information that must be stored for medical imaging purposes has called for investigations into data compression whereby the array representing the original image is transformed into an intermediate set of data having fewer bits than the original array. This reduces the amount of storage required. Image compression algorithms are divided into two categories: lossy and lossless. 16-Is Lossy algorithms are capable of up to 20:1 or 30:1 ratios. Most lossless algorithms can only compress images up to 3:1 ratios and much less with mammography images. Most primary diagnosis is made off of images reconstructed with lossless algorithms while lossy algorithms are only used for consultative purposes.
Display and Presentation: W o r k s t a t i o n s The workstation is in fact a window into database design. Important characteristics for workstations are image quality and performance features. Image Quality. An image has two important criteria of quality: The first is the amount of noise in it, measured by the signal-to-noise ratio (SNR) measured in decibels. The higher the SNR, the better quality the image is. The second is resolution. It is divided into contrast resolution and spatial resolution. ~9 Contrast resolution is directly related to the gray scale and the dynamic range of an image. It measures the ability of distinguishing two objects of different composition. One noticeable advantage with digital images over plain films is the improved dynamic range and therefore contrast resolution. Spatial resolution is related to the sharpness of the image. It is a measure of the ability to separate two closely placed objects. It is related to the pixel size as well as to the array size of the image. Digitizing images can potentially induce a loss in spatial resolution. Performance Features. The workstation is the window into the database and its performance will be measured by how well it accomplishes that task. Furthermore workstations must have the capability to handle multimedia applications as well as medical reports and data. The University of Washington at Seattle has developed a Multimedia workstations (MS 5000) 20 for Project Seahawk (Telemedicine in the Puget Sound area). Now with the collaboration of Georgetown, this multimedia platform is being expanded to include telemedicine applications. The testbed for this project will be between a small village clinic in Alaska and a hospital in Sitka communicating with University of Washington and Georgetown. Display Monitors. Workstations must have display monitors that can handle large image arrays. While CT or MRI generated images require monitors of only 256 • 256 or 512 x 512 capability, chest images with matrices of 2.5k • 2k will require much higher resolution monitors. This kind of monitors is today commercially available. The problem remains for displaying full mammography images since no commercial monitors can handle arrays as large as 4k x 5k on a single screen.
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Smart Imaging and Decision Support The role of artificial intelligence technology has become increasingly important in medical applications allowing physicians to take advantage of smart imaging techniques and decision support. This has lead to the development of artificial neural networks (ANN), or neural networks, that constitute a non-algorithmic approach to information processing. 2~-23 Neural networks address detection, classification and decision-making problems not by pre-specified "conventional" algorithms, but rather by "learning" from examples presented repeatedly. An ANN consists of a number of layered and interconnected processing units which are similar to neurons in the human brain. The popularity of neural networks is primarily due to their apparent ability to make decisions and draw conclusions when presented with complex, noisy, or partial information and to adapt their behavior to the properties of the training data. 24 Neural networks are capable of parallelprocessing a large amount of information simultaneously and have been shown to be a useful tool for pattern recognition in fields where conventional algorithmic approaches and rule-based expert systems may not be successful. In telemedicine, like many other areas of medical imaging, there are many potential applications of ANN. Image processing. Diagnostic images from different sources such as projection X-rays, CT, MRI, and Ultrasound can be processed using neural networks that have architecture specifically designed for image processing. The image processing will, among other things, enhance image contrast, smooth noise, and electronically magnify a particular area to allow radiologists to better visualize any abnormal lesions in the images .25 QualityAssurance. A telemedicine system involves many components ranging from image acquisition to image storage and display. All components have to function appropriately for the telemedicine system to perform well. A neural network can b e implemented to oversee the system operation, detect faulty and malfunctioning components, and recommend necessary procedures to return the system to normal operation. Database Management and Design. ANN can be employed to design and manage large databases of multiple information sources. The use of ANN will allow fast access and flexible manipulation of the very complex information in a radiology database. Computer-aided Diagnosis (CADx). Computer-aided diagnosis will be a very important component in future telemedicine systems. 26 This will allow the radiologist establishing the diagnosis to have a computer generated diagnosis displayed side by side with the images received alerting of any possible abnormalities in the images. The CADx can provide accurate and consistent diagnosis 27 despite environmental distractions and any other factors that might prevent human observers from making correct decisions. It is very much like having a second radiologist for double reading to improve diagnostic accuracy, as is commonly used in radiology practice; it is only a lot cheaper to do it with a computer. Neural networks have been and will continue to be one of the most powerful and successful techniques in many CADx algorithms in the recent years.
Communication Requirements Now that digital imaging over high speed communication links has been established, the natural extension is tele-imaging. The axiom that we will adopt is: Preserve maximum
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image quality and observe good practice of imaging service. An important factor in determining the communication requirements for tele-imaging is clinical and operational need. The requirements for tele-imaging will differ depending on the application for which they are designed. This will have a bearing on the imaging technology required as far as display capabilities, communication link used for bandwidth availability and database design for storage and archival of images. Sending fractured bone X-ray images require less resolution than chest X-ray for example. Chest X-ray images require a matrix as large as 2k x 2.5k x 12/16 bits representing approximately a 10 Mbyte dataset. 2s The larger the dataset the more bandwidth intensive the transmission of the image will be. Communication links such as T-I lines (1.5 Mbps) or higher (T-3, 45 Mbps) will perform more adequately than slower communications link such as regular telephone lines or fractional T-1 applications (56/64 Kbps). While most radiological images can be handled by available communication links, mammography images still pose a significant amount of problems. Digitized mammography images represent a matrix of4k x 5k x 12/16 bits of data amounting to a dataset around 40 Mbyte per image. Transmitting such a large amount of information over T-1 lines is very time consuming. Data compression is another issue to consider with image transmission. 29 While lossy algorithms can achieve compression ratios of 30:1 or more, they do not preserve all the original information. This is crucial when remotely treating patients in a primary diagnosis situation. Because of medical liability and responsibility issues, most practitioners will choose lossless algorithms when they can afford the extra time or sophistication in equipment that this requires. Cost considerations come into play when considering the transmission medium to be used. Trading bandwidth for cost savings becomes the issue but finding the fight balance depends also on the availability and ease of access to a particular medium in a given area. Fiber optic communication is not available in all geographical areas and access to satellite earth stations or even 19.2 Kbps telephone lines through modems might cause several problems. Finally, some applications within telemedicine require interactive communication between the sites involved, a~ This may involve applications such as telesurgery or multimedia applications. This type of applications requires large amounts of bandwidth and T-3 transmission rates or equivalent may not be sufficient. Today new technology platforms such as ATM (Asynchronous Transfer Mode) are being developed overwhich data, voice and video can be offered. ATM is not a service, it is a technology that will support many services and speeds up to 155 Mbps and more. 31
E X A M P L E S O F T E L E P A T H O L O G Y AND TELERADIOLOGY PROJECTS T h e T e l e p a t h o l o g y P r o j e c t at A F I P Telepathology has been implemented through a project at AFIP (Armed Forces Institute of Pathology). Since October 1992, the AFIP started and has been providing Telepathology services in the form of diagnostic consultations to remotely located Army, Navy and Air Force pathology laboratories. In January 1994, the AFIP extended the same
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service to civilian laboratories and conducted its first electronic slide seminar through telepathology. The minimal communication requirement between the AFIP and case referring laboratories can be as modest as a conventional telephone line. Using such a simple link over 200 cases have been successfully refereed for diagnostic consultation. The AFIP Telepathology Program's mission encompasses: Tele-diagnostics. In the first year of telepathology service, the AFIP furnished three pathology laboratories in the states of South Carolina, Tennessee and Ohio with telepathology send/receive units, provided brief on-site technical training and established access to structured formal anatomic pathology diagnostic consultation. It was evident from our experience that a diagnostic telepathology service can be established successfully with minimal resources, at a modest cost and with no significant disruption to the normal operation of a consultation center. We also concluded that addressing medical, technical, human ergonomics, administrative, and legal elements of the service is indispensable to service success. Tele-didactics. The AFIP telepathology service unit in the commonwealth of Puerto Rico, deployed in January 1994, serves pathologists of the U.S. Navy, VA Medical Department, Puerto Rico Health Sciences Center, University del Caribe and local private laboratories. Access to the service is through the telepathology station at the University of Puerto Rico, Department of Pathology, Rio Piedras, Puerto Rico. This station is unique among our user base since it is an academic center with established consultation and education roles to regional pathologists and an Accredited Pathology Residency Training Program. Telemetry of quality. To use telepathology as a means of quality assessment we provided an easy to operate telepathology station to a smaller pathology laboratory. The participating laboratory is to select 100 random cases, provide copies of the pathology reports and digitize four to five images that justify the rendered diagnosis. This preliminary trial is still underway. The AFIP telepathology program's major effort has been in non-real-time systems. However, we currently are exploring real-time system options based on pathology specific needs and the emerging advanced communication technologies. Project RavenCare Project RavenCare will conduct multidisciplinary research on the computer and communication technologies, hardware and software, necessary for the development and demonstration of a prototype health care delivery system suitable for traditionally underserved areas. Using a general purpose high performance multimedia workstation,2~ the MS 5000, as our primary research and development platform, research will be conducted into the computer architecture and telemedicine-relevant capabilities such as data compression, image processing, and computer aided diagnosis necessary to design an optimized telemedicine workstation, the TS 9000. The developmental testbed and prototype telemedicine system for Project RavenCare will consist of MS 5000 workstations in four locations (a village clinic in Hoonah, Alaska, a hospital in Sitka, Alaska, Georgetown University Medical Center and the University of Washington) that will be linked at T-1 speed via the NASA Advanced Communication Technology Satellite (ACTS). Project RavenCare aims at developing a comprehensive telemedicine system to support high
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resolution radiology images with wide dynamic range, color still pictures, video images, text data, audio data, a multimedia database and integrated communication capability as well as intelligent decision support. Figure 1 illustrates the RavenCare Project Network.
The Akamai Project Georgetown University was a digital imaging network system (DINS) research and demonstration site chosen to deploy, test and evaluate two prototype DINS networks. The research project produced excellent results that laid the foundation for the current Medical Diagnostic Imaging Support (MDIS) project of deploying filmless radiology. Georgetown is establishing a research and demonstration program to find pathways tO develop telemedicine capable MDIS network. This project called Akamai is establishing a technological and clinical foundation for electronic patient care capability that transcends the time and distance barriers in patient care today. This project aims at supporting the peace time and war time health care as well as disaster relief efforts in the Pacific using enhanced MDIS technology. Figure 2 highlights the global communication network for the Akamai project. Tripler Army Medical Center (TAMC) in Hawaii will be linked with Pacific rim sites using the existing communication capability. Georgetown will be connected to TAMC through a T-1 ground line and NASA's ACTS. The project consists of three parts: (1) Establishment of deployable telemedicine and teleradiology links from Pacific Rim DoD clinics to TAMC, (2) Implementation of a film]ess electronic medical imaging environment and teleradiology hub at TAMC, and (3) Establishing a research site and project support team at Georgetown University Medical Center for technology assessment and integration of new imaging and communication technologies.
Teleradiology in Korea The teleradiology (TR) system in Korea32 will provide the ability to acquire diagnostic medical images at remote sites and to electronically transmit them to the central Steerable
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Figure 2. AkamaiTe|emedicineProjectand NASA/ARPAACTSProject. site--either the 121 Evacuation hospital in Seoul or the 51st Tactical Fighter Wing (TFW) hospital at Osan AFB for clinical diagnosis and consultation. The TR system will improve the speed and quality of radiology service and reduce the dependency on radiographic films that require expensive logistical support. These goals can be achieved by: (1) medical image acquisition, (2) diagnostic image transmission, (3) soft copy image diagnosis, and (4) electronic diagnostic reporting. The system is highly modular and subcomponents can be transported to other sites, if necessary, to meet the changing nature of US troop deployment in Korea. Figure 3 shows locations of medical facilities in Korea and two types of high speed communication lines to move diagnostic images. The TR system will be installed in two phases. Figure 3 depicts the completed network at the end of Phase II. Necessary communication capabilities, T-I lines and 256 Kbps lines are currently available through in-country DoD assets. The 121 EVAC Hospital with 3 radiologists will be the primary hub to provide teleradiology service to the health care facilities shown in Figure 3. Camp Walker, Osan AFB and Camp Red Cloud will function as secondary hubs relaying the images from the remote sites over 256 Kbps lines to 121 EVAC over faster communication links of T-1 line. R E M A I N I N G M A J O R ISSUES While teleradiology has become a mature technology, many issues still remain to be investigated as related to telemedicine and tele-imaging in general. One of the most
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important upcoming areas of investigation and research is that of a comprehensive intelligent database system for tele-imaging. This will help the use of tele-imaging for education purposes. Another issue is how the use of tele-imaging will affect the professional relationships among clinicians but also between the physicians and the supporting staff. In other words, the impact of tele-imaging on the health care environment and the practice of medicine as we know it today. The third major issue to be investigated is the cost of communication technology especially in regard to telemedicine and tariffs imposed on interstate communications. Finally, Georgetown is involved in research on computer aided diagnosis and the ways in which this technology can act as a tool to enhance the productivity and accuracy of the physician's diagnosis.
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