16 Introduction to Telepathology MICHAEL B. SMITH The practice of medicine has been subject to economic, social, scientific, and technological forces that have altered the practice of the profession over the last several decades. In many cases, pressures have been applied by forces that have seemingly contradictory goals. Economic forces applied by the evolution of managed care have led to a reorganization of the medical infra- structure in the United States, which have resulted in increasing numbers of patients for individual providers to care for and the unavailability of medical care to larger and larger segments of the population. Concurrently, medicine has been under constant pressure, from both inside and outside the profession to find a way to care for the medically underserved, not only those created by the economic restructuring, but those who were underserved in the past, such as the geographically remote. While the appeasement of contradictory forces and pressures on priorities in medicine at a national level are a laborious, complicated process involving many social, economic, and philosophical issues, medical practitioners are having to deal with the problem of providing care to more and more patients dispersed over a greater and greater geo- graphic area on a daily basis. Pathology by its nature has been particularly prone to the pressures and problems of centralized care. Fortunately, advance- ments in the technology of telecommunications and computer science have offered practitioners an effective option in dealing with this problem. Telemedicine, or the use of telecommunications technology to send data, graphics, audio, or images between practitioners physically separated by a distance for the purposes of clinical care has been proffered as one aid in providing increased access in the face of centralized medical care.1 As a sub- set of telemedicine, telepathology is the transmission of histopathological images between different sites for diagnostic, consultative, educational, or quality assurance purposes. Great interest has been generated in the use of telepathology to increase the efficiency of histopathology laboratories in serving larger populations with either the same or decreasing resources. Although isolated incidences of the transmission of microscopic images for diagnosis occurred in the United States during the late 1960s and early 1970s, the first functioning long-distance telepathology network used on a 16. Introduction to Telepathology 269 routine basis was implemented in Europe at the University of Tromsø, Tromsø, Norway, in 1989.2–4 The university constructed a telepathology system utiliz- ing telephone lines to allow the evaluation of frozen sections performed at a remote hospital 400 km away above the Arctic Circle. Also in 1989, a telepathology network was established in France (Resintel) that evolved to link 32 sites throughout France and the islands of Martinique and Guadeloupe.5 Although the French network was not a commercial success, it was important because it proved that the technology available was capable of linking a complex network of stations, including some very remote sites, into a func- tioning telepathology system. Extensive networks of telepathology stations have not been developed in the United States, but many centers have carried out evaluations of telepathology systems that involve either a small number of submitting sites in this country or submissions from other countries. An example of a viable and functioning system is the telepathology link be- tween the Iron Mountain, Michigan, and Milwaukee, Wisconsin, Veteran’s Medical Centers.6 Pathologists at the medical center in Milwaukee, Wiscon- sin, are able to offer surgical pathology services to a remote facility that has an active surgical service without local pathology support. The U.S. military has been using telepathology to provide services to remote facilities on the Pacific rim, and in 1994 the Armed Forces Institute of Pathology instituted a telepathology service that reaches worldwide.7–8 Other telepathology services began going on line in recent years, with most originating from university systems such as the University of Arizona.9 Telepathology Systems Although there are number of options to choose from when constructing a telepathology system, the basic framework includes an image acquisition method, a method to compress and store the image, a way to transmit the image to a remote receiving station, and a way to display the image at the receiving station. When considering whether or not to institute telepathology, other issues such as format, reimbursement, and legal issues must also be taken into account. Acquiring the Image The most common use of telepathology to date has been as a method to perform histopathologic assessment from a site remote to the tissue section and microscope. The first step in this process is acquiring the image with a camera mounted to a light microscope. Of two options, the cheapest is to capture the image with a video camera, a method used in many large pathol- ogy practices for local microscopic video conferencing. It must be remem- bered, however, that most inexpensive video cameras on the market have not 270 M.B. Smith been configured for medical uses and as a consequence may not be adequate for telepathology in terms of resolution or color representation. Resolution is expressed in terms of pixels (picture elements) in columns and rows. The video camera uses a silicon grid of light-sensitive wells arranged in columns and rows termed a charge-coupled device (CCD). Each well in the CCD de- tects photons that are converted to an electrical charge, whose intensity de- pends on the amount of light striking the well, and then to a voltage signal, which is used to generate an image (analog signal). In general, the number of wells in the CCD reflects the clarity or resolution of the image produced. Many video cameras have 640 rectangular wells in the horizontal plane and 480 in the vertical plane (640H ´ 480V). As a point of reference, this is the standard established by the National Television Standards Committee (NTSC) and is the resolution seen on the home television set. The degree of resolution for telepathology has not been standardized, and the literature reports a wide range of degrees of spatial resolution, although 800H ´ 600V and 1024H ´ 1024V are reported with frequency.10 In contrast to radiology, whose use of teleradiology is much further advanced than pathology’s use of telepathology, color information in the image is of im- portance with both routine and special histologic stains. Since the CCD is a monochromatic device, it is necessary to manipulate the image to obtain three images in the primary colors, red, green, and blue (RGB). The most commonly utilized method is to place color filters over the CCD, devoting one third of the wells to each one of the primary colors. This method has the disadvantage of reducing resolution; hence, these types of cameras may not be optimal for telepathology. The image produced by the second method, having the light split by a prism to three separate CCDs, each with a separate color filter, is superior in both resolution and color. These types of cameras are, however, more expensive. The third method, using pulsed light of each of the primary colors to capture three separate images on a single CCD and then integrating the three images by computer, is a strategy used with great frequency in endoscopy cameras. To allow for storage, manipulation, and eventual transmission of an image, the analog video signal must be converted to the binary language of the computer. Conversion is accomplished with the use of the image capture board, usually in a desktop computer. The image capture board contains a device that samples the continuous voltage signal from the video camera and con- verts it to a numeric value, “digitizing” the image. The location and digital value of each pixel is stored in a second part of the image capture board, the image frame buffer, from which the computer can extract the data. Mono- chromatic video signal is encoded as 8 bits of data, with the value corre- sponding to the level of brightness or intensity of light. For “true color” imaging, imaging that approximates the range of the human eye, this means that 28 or 256 different shades of each primary color are encoded on each of three different channels. The total number of colors will be 224 (28 for each of the three primary colors), or 16.7 ´ 106 colors, with obvious implications for the size of the file necessary for the resultant image. 16. Introduction to Telepathology 271 An alternative to video cameras for capturing still images are digital cam- eras. Digital cameras convert light from the image into binary code within the camera, and as, no image capture board is required, the image can be down- loaded to the desktop computer via serial cable or PC card. Until recently, digital cameras were prohibitively expensive, but prices are now competitive with quality video cameras. The image sensor in many digital cameras is the CCD. However, some cameras have made use of a new sensor technology, complementary metal oxide conductor sensors (CMOS), which can be pro- duced cheaper than CCDs. Additionally, other functions such as image stabi- lization and compression can be built into the CMOS chip, making the camera smaller, lighter, and more efficient. Like video cameras, digital cameras have built-in image delay times, which vary with the make and model of the cam- era. The delay time in digital cameras is a reflection of the refresh rate, the time delay between pressing the shutter button and capturing the image (the camera first clears the image sensor, sets the white balance to correct for color, sets the exposure, and focuses, if using autofocus), and the recycle time (the time it takes to capture the image, process it, and store it).