Digital imaging and communications in medicine

Digital imaging and communications in medicine (DICOM) is both a standards development organization and a set of technical standards for the transfer of medical images among computer systems. When "medical images" are mentioned, many people immediately think of X-rays and other methods in radiology and nuclear medicine that create pictures of structures or activity invisible to the human eye. On reflection, however, the problem space does not consist exclusively of the transfer of specialized imaging equipment. In other words, DICOM is a technical solution to the specific issues of teleradiology, and to the broader aspects of the image-related aspect of telemedicine.

There are many aspects of medical examination, in which a specialist may recognize something not obvious to a more general clinician. For example, dermatological diagnosis relies strongly on visual examination of the skin, perhaps under magnification, perhaps under special illumination, but basically ways that the dermatologist looks at the patient's skin. If a nurse-practitioner, in a remote area, has a patient with an unusual skin lesion, the experience of the dermatologist is just as distant as a magnetic resonance imaging scanner. Teledermatology is a very real service; a simple digital color photograph of the lesion may provide enough information for a dermatological diagnosis. The dermatologist may need to interact with the patient, with the remote clinician providing remote hands to show the skin response to pressure and release (i.e., diascopy ), or perhaps viewing the lesion under a Wood's light that will demonstrate ultraviolet fluorescence.

Other specialties, such as opthalmology, may need instruments to be positioned on the patient, but the needed information is still basically visual.

Of course, it may be possible to gain the benefits of more instrument-dependent imagery. It is quite common, for example, for rural hospitals not to need an in-house radiologist for emergency room night coverage, as long as the radiologist can see the X-ray. When X-rays were dependent on film, the process of waiting for the film to dry, and then scanning it into machine-readable form was cumbersome. Modern digital X-ray, however, uses an electronic sensor rather than film. That digital image will look exactly the same, viewed on a suitable display workstation next to the emergency room, or halfway around the world. There is a good deal of mutual night radiology coverage, for example, between Australia and the United States.

There are, however, important differences, when consulting on an Australian patient, if the radiologist is in the same building, in the same city, or across the world. It is trivial to transmit a large file over a local area network connecting the ER to the radiology office in the hospital. It may or may not be trivial to send a large image file through the networks available in the same local area, and it can be significant to transfer it over long distances.

DICOM Organization

Secretariat functions for the DICOM work are under the National Electrical Manufacturers Association (NEMA), which is a recognized support group for a number of standardization activities.

Transmission and compression

There are multiple 10 gigabit per second undersea cables going to other continents from Australia. If, for example, there were only ordinary telephone lines between the hospital and the radiologist, it would take a significant time to transfer a single image. Indeed, if multiple views were to be examined, it might be faster for the local radiologist to get out of bed, dress, and drive to the hospital.

If the hospital had a high-speed satellite link over which images could be transmitted, however, it would take an equal time, over the high-speed path, to reach local or remote satellite receivers. A hybrid approach might be appropriate, with the satellite serving to get the digitized image to a coastal city where an optical undersea cable terminates. At the other end, if the viewing radiologist only had telephone lines to her office, there indeed might need to be a satellite terminal there. If, however, either the local cable TV provider had a satellite data receiver at the local cable head end, a cable modem is quite fast enough to transfer the image. Also, the head end might connect to terrestrial high-speed optical networks.

Even when high-speed media are available, if the image file size can be reduced, without loss of quality, and without expensive conversion equipment, reducing the file improves transfer efficiency. Data compression techniques may be very relevant, but the techniques used must comply with DICOM specifications for loss-free compression, or with a level of loss that does not compromise clinical quality. There are loss-free compression methods, and also methods that cause different amounts of loss, trading compression and possibly loss against file size.

Interoperability and standards

Compression

JPEG, MPEG

Communications

DICOM files can be transferred over the Internet, or private Internet Protocol network, in compliance with the appropriate communications standards of the Internet Protocol Suite]

Web access

Working with the International Organization for Standardization (ISO) Technical Committee 215, DICOM is producing an international standard for World Wide Web Access to DICOM Objects. DICOM is already a European standard.

Terminology and indexing

DICOM utilizes rele-vant parts of other mature standards such as LOINC, SNOMED,

Quality

DICOM works with the the Breast Imaging Reporting and Data System (BI-RADS®) coordinated by the American College of Radiology, working with the National Cancer Institute of the National Institutes of Health, the Centers for Disease Control, the Food and Drug Administration, the American Medical Association, the American College of Surgeons, and the College of American Pathologists.

Electronic health records

DICOM works jointly with the Health Level 7 standards development group, to ensure that their formats are compatible, and DICOM images can be incorporated into electronic health records compliant with the HL7 specification.

Other applications

Trauma

Focused Assessment with Sonography for Trauma (FAST) is a procedure, using a basic medical ultrasound unit, to examine a patient for the presence of free fluid in body cavities, such as the peritoneum or pericardium