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Health Care: Delivery, Education, Communication

Telemedicine Systems and Telecommunications


4. Information Capture

The types of information that are relevant to telemedicine can be divided into five broad categories:

  • documents,
  • electronic medical records,
  • still images,
  • audio,
  • video.

4.1 Documents

Documentary information (e.g. reports, letters or static medical records) can be transmitted in digital form, if the information already exists as a computer text file. Alternatively, paper documents can be digitized using a flatbed scanner or a document camera, and then transmitted as still images (see below). Note, however, that, for non-urgent cases, copies of written records can be posted to the consultant end of the link in advance, or paper documents can be faxed before or during a telemedicine session. Even in the age of digital telemedicine, the use of the postal service can represent a very cost-effective way of transferring large quantities of information from one place to another; the disadvantage involves the delay and the human interaction required.

4.2 Electronic Medical Records

Traditional paper-based records are gradually being replaced by electronic medical records (EMRs). At present, the EMR is a hodge-podge of heterogeneous, proprietary systems that rarely interoperate successfully. Efforts are underway to create a highly interoperable EMR system, where data can flow across the health-care continuum seamlessly.[6][7] EMRs will allow instant access to a patient's record, including the business operations such as billing and reimbursement.

4.3 Still images

Two major classes of image are important in telemedicine - those of unspecified quality and those where the diagnostic needs (and hence legal consequences) dictate a particular image quality (Figure 1). The difference can best be appreciated by considering the difference between photocopies of images and the originals - a photocopy may be perfectly legible and acceptable for many purposes, but fine detail present in the original may have been lost. For some types of image this can be crucial, and the requirements have been particularly well studied for radiographs.[8]

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Figure 1: Image quality in a still picture is usually defined in terms of the numbers of picture elements in the image (pixels) and the numbers of their black and white - or colour - levels. (a-d) show the same X-ray image digitized at different resolutions: 240, 120, 60, 30 dots/inch. (e-h) show the same X-ray images displayed with different numbers of grey levels per pixel: 255, 15, 5 and 2.

For many telemedicine purposes, a simple photographic image may be sufficient. For instance, low-cost digital cameras now provide very good imaging quality and may be adequate to capture an image of a skin lesion for teledermatology or a view down a microscope for telepathology.[9] Alternatively, an inexpensive flatbed scanner can be used to digitize photographs or charts such as electrogram (ECG) traces (Figure 2). If the scanner is equipped with the appropriate transparency attachment, then 35mm slides or X-ray films can also be scanned. Where relatively simple diagnoses are required, such basic equipment may be more than adequate, e.g. for emergency room assessment of X-rays of a simple fracture.

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Figure 2: A flatbed scanner can be used to digitize a paper record. With a suitable backlight, X-ray films can also be digitized (photo credit: B. Harnett).

Another inexpensive method is to capture still images using a video camera, possibly one that is specially designed for imaging documents (Figure 3). In addition, many diagnostic instruments now provide a video output, for example ultrasound scanners. Still images can be recorded with a video capture card on a personal computer (PC) and a suitable screen capture program.

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Figure 3: A document camera is an alternative method of digitizing X-ray films. Note the use of black cardboard masks around the region of interest.

When high-quality diagnostic images are required, the equipment involved can be costly. Modern diagnostic imaging devices are often equipped with digital outputs, which allow images to be transmitted between sites. However, it is common for telemedicine links to be set up in situations where the patient side of the link has old or outdated equipment. In this case, it may be necessary to purchase specialized equipment, such as high-resolution X-ray film digitizers, which are much more expensive (10-20 times) than flatbed scanners designed to work with PCs.

Digital Imaging and Communications in Medicine (DICOM) is an established standard for digital image transmission in radiology; it defines how images of clinical quality are distributed via networks.

4.4 Audio

At its simplest, voice transmitted by telephone or radio can be used for some remote diagnoses. Although the telephone system has been designed for voice transmission, it is not necessarily ideal for all types of medical sound transmission. Telephones use analogue (Box 2) transmission, which is therefore susceptible to noise and loss of quality, particularly over long distances. Digital signal transmission offers many advantages, particularly since digital signals can be transmitted over networks for long distances without degradation. It is also possible to process a digital signal in various ways, including compressing it so that a live or recorded voice requires less data to be transmitted than the original signal (see below for further information about compression).

Most modern PCs are equipped with a sound card that is suitable for capturing audio for telemedicine purposes. No special equipment is required other than a suitable microphone. In some cases, it is also possible to connect these cards directly to the equipment that is being used; for example, the audio output of an ultrasound scanner can be connected to the PC. Another option is simply to use an ordinary telephone line as the audio portion of the session. This frees up more bandwidth for video.

Box 2: Analogue and Digital

An analogue signal is one whose magnitude is continuously variable. For example, an electrical signal might have a magnitude of about 1.2 V (measured with an inexpensive voltmeter), while a more expensive instrument might show it to be 1.2345 V. The value measured depends on the resolution of the instrument.

In contrast, a digital signal can vary - or be measured - only in discrete steps. The digital representation of the same voltage might show it to be 1.2 V the adjacent levels being perhaps 1.0 V and 1.4 V. Increasing the sensitivity of the measurement does not alter the value.

To transmit an analogue signal requires, in principle, a perfect transmission path. In the case of an electrical voltage, any resistance in the transmission path will reduce the voltage at the receiver site. Analogue transmission, such as between the subscriber's house and the telephone exchange, is therefore susceptible to the introduction of noise. In contrast, the transmission of a digital signal is perfect. The huge advantage from the perspective of telemedicine is that transmission quality becomes independent of distance: a telemedicine transmission between two locations in the same city will work as well as transmission between two locations on different continents.

4.5 Video

A common view of telemedicine is that it only involves realtime video images transmitted between remote sites for the purposes of consultation between a doctor and a patient. This is certainly one form of telemedicine, although it is by no means the only one. In cases where video transmission is considered appropriate, the issue arises of what video quality is required, since unsurprisingly the higher the quality, the higher the cost of the equipment and the transmission. In the majority of applications, commercial videoconferencing units provide the most straightforward solution to the problem of transmitting video pictures for telemedicine. Generally speaking, such units provide video pictures that are not as good as broadcast quality television (TV), although in many clinical applications this does not seem to matter.[10] When considering this question, it is worth bearing in mind that the users' opinions will be influenced, even if subconsciously, by the domestic TV that they are used to watching (Box 3).

A wide range of telemedicine equipment and accessories is available commercially. A benefit of using commercial suppliers is the technical assistance that they can provide, which includes setting up the working connection and (in most cases) a help desk for technical problems. Many suppliers can perform software upgrades and fault-finding by logging on to the equipment from their home base. For those without technical knowledge or access to in-house technical support, this may be important to the success of a telemedicine project.

Box 3: Video Standards

There are two common broadcast TV video standards: National Television Standards Committee (NTSC), which is used in Japan and North America, and Phase Alternating Line (PAL), which is used in much of Europe. The two systems have different display characteristics:

  1. 525 lines/picture at 30 pictures/s (NTSC),
  2. 625 lines/picture at 25 pictures/s (PAL).

The standard called common intermediate format (CIF), which is widely used for videoconferencing, was introduced to provide compatibility between the two video standards. Thus, it is possible to videoconference between the USA (where the camera and monitor operate to the NTSC standard) and say Europe (where the camera and monitor operate to the PAL standard). CIF is 288 lines/picture at 30 frames/s. The resulting quality of a CIF video picture is not very different from that of a normal TV picture.

4.6 Compression of Video Signals

Commercial videoconferencing units all use compression techniques to reduce the quantity of data being transmitted, and therefore the communication costs. This means that the units at either end of a link must be compatible, i.e. the same compression and decompression algorithms must be employed. To ensure that equipment from different manufacturers is interoperable, international standards have been defined by the International Telecommunication Union (ITU) (Table 2). Provided that each telemedicine site has a system embracing the proper standards, it is possible to conduct videoconferencing sessions between pieces of equipment supplied by different manufacturers. This applies not just to the basic transmission of video and audio, but also to additional features such as the control of cameras at the remote site, and the exchange of data between PCs that are being used in the videoconferencing session. Equipment that does not adhere to standards should be avoided.

Compression is a rapidly developing area of computing science, where the objective is to maximize the file compression and minimize the information loss.

Protocol Purpose
H.320 The oldest of the multimedia communication protocols. Defines a videotelephone operating on ISDN.
H.324 A newer protocol defining videotelephony for the standard telephone network (PSTN). Poorer-quality pictures, because of the restricted bandwidth of the PSTN compared with ISDN. Since H.324 can also be used on ISDN, it may supersede H.320 in due course.
H.323 A newer protocol defining videotelephony for LANs and the Internet.
T.120 A family of protocols to allow computer-supported cooperative working in conjunction with videotelephony.

Table 2: ITU Protocols

4.7 Videoconferencing Equipment

Videoconferencing has traditionally required equipment which was expensive to buy and to run, and was large and complicated to operate. At first it could be used only in fixed studio installations, but miniaturization made possible the development of the 'rollabout' unit, which could be moved between rooms within a building. The basis of the equipment is the CODEC (coder/decoder), which handles the compression of video pictures prior to transmission, and the decompression of the received pictures prior to display. Rollabout units are still widely used, particularly in business, and generally deliver highquality video pictures (up to 2 Mbit/s transmission) on large display monitors with high-quality sound.

More recently, as the trend to miniaturization has continued, portable videoconferencing units have appeared, in which all the components except the display screen are integrated into a single unit. Such 'set-top' units require only connecting to a domestic TV to form a good-quality videoconferencing system (Figure 4).

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Figure 4: A set-top videoconferencing unit.

Further technological development has resulted in the videoconferencing functions becoming available on a plug-in card for PCs. This means that an ordinary PC can be used as a personal 'desktop' videoconferencing workstation delivering reasonable quality video on a smaller screen and with generally lowerquality sound; nonetheless, these may be adequate for many purposes. It is also possible to use the PC's own processor to encode video for transmission, i.e. the PC operates as a software CODEC (Figure 5).

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Figure 5: Desktop videoconferencing software (photo credit: B. Harnett).

The merits of the different families of videoconferencing system are summarized in Table 3.

Type Quality of Video & Audio Cost Usage
Studio High High Large Group
Rollabout High High Small Group
Set-Top Low/Medium Low Personal/Small Group
Desktop Low/Medium Low Personal
PSTN Low Low Personal

Table 2: ITU Protocols

Much of the technology to capture the different types of information required in telemedicine will be available in any well-equipped modern office, but most telemedicine applications aim to provide services to poorly equipped remote sites that may not have even the most basic computer equipment. A major part of the overall cost of setting up a telemedicine system may be purchasing such straightforward items for the patient consultation end of the link.

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