Chayagraphics is uniquely positioned to offer the customers end to end solutions from hardware to software, from setting up a Digital Radiography system to deploying a Teleradiology system to enable seamless transmission of data from point a to point n.
The elements of a teleradiology system
A teleradiology system consists of an image acquisition section and an image display/interpretation section, connected by a communications system (i.e., a network). A Picture Archiving and Communications System (PACS) is a sister technology of teleradiology that also allows storage and archiving, as well as transmission, of digital images within an enterprise -- typically a hospital.
Standards for teleradiology
The American College of Radiology, which has more than 30,000 members, is the principal organization of radiologists, radiation oncologists and medical physicists in the United States. The ACR periodically defines new standards for radiological practice to help advance the science of radiology and to improve the quality of service to patients.
In 1994, the ACR developed a standard for teleradiology [37]. This standard defines goals, qualification of personnel, and equipment guidelines, as well as licensing, credentialing, liability, communication, quality control and quality improvement issues. The standard was intended to serve as a model for all physician and health care workers using teleradiology.
According to the ACR, the goals of teleradiology include: providing consultative and interpretative radiological services in areas of demonstrated need; making services of radiologists available in medical facilities without on-site radiologist support; providing timely availability of radiological images and radiological image interpretation in emergency and non-emergency clinical care areas; facilitating radiological interpretation in on-call situations; providing subspecialty radiological support as needed; enhancing educational opportunities for practicing radiologists; promoting efficiency and quality improvement; and sending interpreted images to referring providers. The personnel involved include physicians, technologists, physicists, engineers and/or communication or image systems specialists. The equipment guidelines cover two basic categories of teleradiology systems: small and large matrix sizes. Small matrix (lower resolution) systems include computed tomography (CT), magnetic resonance imaging (MRI), ultrasound, nuclear medicine and digital fluorography. According to the ACR standard the small matrix digitization (acquisition) systems should produce 500 pixel x 500 pixel x 8 bit images or better and the small matrix display systems should produce a 500 x 480 x 8 bit display or better. Large matrix systems include digitized radiographic films and computed radiography. For these, the digitization systems should produce 2000 x 2000 x 12 bit images or better and the display systems should produce a 2000 x 2000 x 8 bit display or better.
The ACR standard requires that both small and large matrix systems include a capability for image sequence selection for transmission and display, annotation capabilities at the transmitting station including patient data and brief patient history, provision for interactive windowing at the transmitting site and provision for compression (for improved transmission rates and reduced archiving/storage requirements). For the transmission of images and patient data, the ACR standard requires that new technology systems should include the ACR/NEMA data format standard and the DICOM network standard (see below) [1,3]. For the display, the ACR requires that the luminance of the grey scale monitors should be at least 50 foot-lamberts (170 cd/m2). For large-matrix displays, the ACR requires interactive windowing, magnification, inversion and rotation functions, and the capability of making accurate linear measurements. For small matrix systems, the ACR requires accurate reproduction of the original study. The availability of a patient database and of software security protocols is also required.
Image acquisition
Image acquisition is commonly performed by a film digitizer, converting conventional radiographs to digital form for transmission over a network. Two different techniques are used in film digitization, which employ either lasers or charged coupled devices (CCD).
Laser digitizers offer very good contrast and spatial resolution, but are more expensive than CCD digitizers. The latter offer comparable spatial resolution, but their contrast or grey-scale resolution is lower. However, since their performance is improving, it is foreseeable that they will become the technology of choice, because they are less expensive, smaller and easier to maintain.
An alternative to image capture onto conventional film, followed by digitization, is computed radiography (CR). CR uses phosphor storage plates to directly obtain digital images and offers broader dynamic range, which is particularly useful for applications such as portable radiographs. Because CR is becoming widespread, and its use is likely to increase, film digitization will eventually become obsolete.
Other common devices for image acquisition are CT and MR scanners. Digitization is still sometimes necessary because, although CT and MR systems generate digital data, the image formats are often not made available by the manufacturers, so that data conversion into standard formats for transmission is required.
Image acquisition can also be carried out by frame grabbing, where the analog output from a digital display, such as CT, MR or ultrasound is converted into a digital image, normally 512 x 512 x 8 bits. Video frame grabbing suffers from several limitations: data can be lost in the analog-to-digital conversion, and various window settings must be used to obtain suitable representations for bone, soft tissue, lung etc. This results in an increase in the data transmitted and in the number of images reviewed by the radiologist.
Nevertheless, video frame grabbing is used in many teleradiology systems [10] owing to economic considerations and to the absence of established standards in some medical imaging environments.
Another important aspect of image acquisition is that in many cases a sequence of images is necessary to evaluate a specific clinical problem. This is the case for echocardiograms, which are normally videotaped and then reviewed subsequently by a radiologist or cardiologist, and for coronary arteriography and ventriculography imaging, which are recorded as cine films normally reviewed at a later stage. Unless a brief but representative sequence of images can be singled out this results in a great quantity of data, whose cost-effective storage and transmission creates serious problems. Serious storage and transmission problems arise also in mammography, because of the extremely high spatial resolution requirements. A minimum resolution of about 4000 x 5000 x 12 bits is regarded as indispensable for an 8 x 10 inch (20 x 25 cm) field of view. After acquisition, images are transmitted to an interpretation site using local area networks (LANs) or wide area networks (WANs). Transmission can take place either directly to a workstation or to an image server that can distribute the images to one of several workstations. In this case the technologies of PACS at the transmission place are used, including storage facilities.
Image display
Display monitors are crucial to teleradiology, which depends on the ability to display images that are perceived to be identical to those available on conventional or laser printed film. . From the observer’s point of view, the displayed image has three important attributes: fidelity, informativeness and attractiveness. Image fidelity from the observer’s point of view can be expressed in term of spatial resolution, grey scale resolution, grey scale linearity and noise. Image informativeness can be expressed in terms of the visibility of diagnostically important features or as the detectability of some specific abnormality. Image attractiveness relates to the aesthetic properties of the displayed picture.
Grey scale monitors are used for primary diagnosis for CT, magnetic resonance imaging, digital fluoroscopy, ultrasound and scintigraphy, and more recently for thoracic and musculoskeletal radiology.
Image transmission
The choice of the telecommunication medium for a teleradiology system requires finding a costbenefit trade-off between expense and bandwidth. The higher the bandwidth, the more rapid the transmission and the greater the capacity of the network—and the higher the cost. The main aspects to be taken into account for the telecommunications solution for a teleradiology system are the number of cases to be sent, the average size of the files, the required turnaround time and the peak activity.
Local area networks (LAN)
A LAN is an information transmission medium equally shared by all connected stations, limited to a local area without crossing any public areas. The transmission speed in LANs is typically between 4 Mbps and 100 Mbps. LANs generally have a service diameter of not more than a few kilometers and are completely owned by a single organization. The medium performance LANs are based on Ethernet, whereas for high performance LANs there are several standards, such as FDDI, 100 Mbps Ethernet and ATM.
Wide area networks (WAN)
WANs typically span entire regions or countries, have data rates below 1 Mbps and are owned by multiple organizations. The data rate that can be achieved commonly with a fast modem on the standard public telephone network (the PSTN) is 28.8 Kbps, although faster rates, to about 44 Kbps, are possible.
ISDN services are quite widespread, but in some locations transmitting medical images over ordinary telephone lines may be the only possibility. Image transmission over the Internet is now possible. However, image transmission speed over the Internet is often low in practice since the efficiency of the transfer depends on the global throughput at the time at which the transmission takes place. At present, the Internet can be useful in teleradiology for education and training, but its potential use would increase if dedicated medical networks become available so that the global traffic on the network is not heavily influenced by commercial information.
The highest performance transmission protocol for image communication is Asynchronous Transfer Mode (ATM). However, this service is not widely available at present and normally requires fiber optic cabling between the transmitting and the receiving station. ATM is a packet switching technology, in which the data to be transmitted is divided into cells (packets) which may arrive from various sources in a random and discontinuous fashion. ATM provides integrated support for a variety of communication services, due to its ability to manage asynchronous and synchronous traffic, to scale according to demand-oriented growth, to integrate different communication systems and to support virtual networking. Although ATM technology is very recent, ATM products and services are now becoming available, and it is felt that ATM technology is emerging as a leading candidate for medical image transmission in both LAN and WAN applications.
Image compression
Many teleradiology systems include image compression facilities, in order to obtain transmission rates compatible with an efficient teleconsulting service and to reduce storage requirements. Image compression may be lossless (reversible) or lossy (irreversible). The advantage of lossless compression is that the original image can be recovered - there can therefore be no subsequent claim that important information was lost as a result of the compression process, which could be crucial in the event of legal action. The advantage of lossy compression is that higher degrees of compression can be achieved and therefore transmission times reduced.
Conformance with the DICOM standard
The DICOM standard provides a rigorous treatment of the issue of conformance, specifying levels of conformance in terms of specifically-defined service classes in which the functional units are precisely described. Moreover, the structure of a manufacturer’s conformance claim is explicitly defined. This does not prevent manufacturers from implementing any function in their software. However if they claim to conform to the DICOM standard the conformance claim precisely states which services are supported by their product and which are not.
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