Teleradiology Today. Applications

Transcription

1 Teleradiology Today a report by H K Huang Professor and Director of Informatics, Childrens Hospital of Los Angeles/University of Southern California and Chair Professor of Medical Informatics, The Hong Kong Polytechnic University H K Huang is Professor and Director of Informatics in the Department of Radiology at the Childrens Hospital Los Angeles/University of Southern California, US. He is also Chair Professor of Medical Informatics at The Hong Kong Polytechnic University. Mr Huang pioneered in Picture Archiving and Communication System (PACS) research. Mr Huang developed PACS at University of California at Los Angeles (UCLA) in 1991, and the hospital-integrated PACS at the University of California at San Francisco (UCSF) in He has co-authored and authored seven books and published over 200 articles. Mr Huang is a consultant for many hospitals in developing PACS worldwide. He was inducted into the EuroPACS Society, as an Honorary Member for his contribution in PACS, in October 1996, the American Institute of Medical and Biological Engineering as a Founding Fellow, for his contribution in medical imaging, in March 1993 and the Royal College of Radiologists, UK, as an Honorary Fellow for his contribution in PACS research and development, in November Introduction Telemedicine and teleradiology can improve healthcare delivery turnaround time and achieve cost savings. 1,2 These technologies have become increasingly important as healthcare delivery systems in the US gradually change from fee-for-service to managed care. During the past few years, there has been a trend of primary care physicians joining health maintenance organisations (HMOs). HMOs purchase smaller hospitals and form hospital groups under the umbrella of HMOs. In addition, academic institutions form consortia to compete with other local hospitals and HMOs. This consolidation allows the elimination of duplication and the streamlining of healthcare services among hospitals. There are two models in telemedicine and teleradiology: the referring physician or healthcare provider can either consult with an individual specialist at various places through a network or they can request opinions from a consolidated expert centre where different types of consultation services are provided. In this discussion, the expert centre model is focused on as this is the current trend in the healthcare delivery system. In the expert centre consultation process, three modes are possible: telediagnosis, teleconsultation and telemanagement. 3-5 For telediagnosis, the patient s examination results and imaging studies are examined at a remote site, and data and images are transmitted to the expert centre for diagnosis. The urgency of this service is nominal and turnaround can take between four hours to one day. For teleconsultation, the turnaround time is about half an hour, the patient may still be waiting at the examination site, while the referring doctor requests a second opinion or diagnosis from the expert centre. For telemanagement, the patient may still be on the gantry or in the examination room at the remote site and the expert provides immediate management care to the patient in situ. On account of these three different operational modes, the technology requirements in telemedicine and teleradiology are different. In general, teleradiology can be considered as a subset of telemedicine dealing with the transmission and display of images in addition to other patient-related information between a remote site and an expert centre. The technology requirement for teleradiology is more stringent than that of general telemedicine because it involves images. Basically, telemedicine without teleradiology requires only very simple technology. An information system (IS), such as Hospital Information System (HIS), gathers all of the necessary patient information, examination results and diagnostic reports, arranges them in proper order at the referring site and transmits them through telecoms technology to a workstation at the expert centre. Teleradiology Background The managed care trend in the healthcare industry creates an opportunity to form expert centres in radiology practice. In this model, radiological images 1 1. H K Huang (1997), Telemedicine and Teleradiology Technologies and Applications, Min Invas Theray, Vol. 5 6, pp H K Huang (1999), PACS: Basic Principles and Applications, John Wiley & Sons, NY, p J N Stahl, J Zhang, C Zeller, E V Pomerantsev, S L Lou, T M Chou and H K Huang (2000), Tele-conferencing with Dynamic Medical Images, IEEE Trans Inform Tech Biom, Vol. 4, No.1, pp J Zhang, J N Stahl, H K Huang, X Zhou, S L Lou and K S Song (2000), Real-time teleconsultation with high resolution and large volume medical images for collaborative health care, IEEE Trans Inform Tech Biom, Vol. 4, No.1, pp J N Stahl, J Zhang, T M Chou, C Zellner, E V Pomerantsev and H K Huang (2000), A New Approach to Teleconferencing with Intravascular Ultrasound and Cardiac Angiography in a Low-Bandwidth Environment, RadioGraphics, 20, pp. 1,495 1,503.

2 Teleradiology Today and related data are transmitted between examination sites and expert centres through telecoms. This type of radiology practice is loosely called teleradiology. Figure 1 shows an expert centre model in teleradiology. In this expert centre model, rural clinics, community hospitals and HMOs rely on radiologists at the centre for consultation. The turnaround time requirement determines the technology that is needed and the cost involved. The Reason for Teleradiology The managed-care trend in healthcare delivery expedites the formation of teleradiology expert centres. However, even without the healthcare reform, teleradiology is still an extremely important component in radiology practice for the following reasons. First, teleradiology secures images for radiologists to read so that no images will be lost accidentally in transit. Second, teleradiology reduces the reading cycle time from when the image is formed to when the report is completed. Third, since radiology is subdivided into many subspecialities, even a general radiologist requires an expert s second opinion frequently. The availability of teleradiology will facilitate seeking the second opinion. Fourth, teleradiology increases radiologists income since no images are lost accidentally and subsequently not read. The healthcare reform adds two more reasons. It saves healthcare costs since an expert centre can serve multiple sites, thereby reducing the number of radiologists that are required. It improves the efficiency and effectiveness of healthcare because turnaround time is faster and the repeat rates decrease since there will be no loss of images. Defining Teleradiology Generally speaking, teleradiology means that an image is sent from the examination site to an expert site where a radiologist will make the diagnosis. The report is sent back to the examination site where a primary physician can prescribe the patients treatment immediately. Teleradiology can be very simple or extremely complicated. In the simple case, images are sent from a computerised tomography (CT) scanner, for example, in the evening to the expert centre using lower quality equipment and communication technology. During off-peak hours, evenings and weekends, there may not be a radiologist at the examination site to cover the service. This type of teleradiology does not require highly sophisticated equipment. The second type of teleradiology is more complicated, with four different models starting from Figure 1: The Expert Centre Model in Teleradiology Telediagnosis 4 24 hrs Table 1: Four Models in Teleradiology simple to complicated in ascending order, as shown in Table 1. The complications occur when information from the radiology information system (RIS)/historical images are required for comparison with the current examination. In addition, complications arise when the examination and dictation are required to be archived and appended to the patient image data file. Teleradiology is relatively simple to operate when no archiving is required. However, when archiving and retrieval of previous information relating to the same patient is required, the operation becomes complicated. Teleradiology and PACS Historical Images/RIS* Archive Simple no no Simple to complicated yes no Complicated no yes Most complicated yes yes * Radiology Information System (RIS) Teleradiology Primary Care Physicians/Patients from Rural Clinics, Community Hospitals, HMOs Radiological Examinations Images and Information Transmitted to the Expert Centre Radiologists Make Diagnosis Table 2: Differences Between Teleradiology and PACS Telerad PACS Image capture digitiser/dicom DICOM Display technology same same Networking WAN* LAN** Storage duration short long Compression yes maybe * Wide area network (WAN) * * Local area network (LAN) Teleconsultation 1/2 hr Telemanagement almost realtime When the teleradiology service requires patient s historical images as well as related information, teleradiology and Picture Archiving and Communication System (PACS) become very 2

3 Figure 2: A Generic Teleradiology Set-up Direct Digital Digitiser: Vidicon, Laser Scanner Images Formatted Image Data DSO t-1, DS3, ATM, Internet 2 Workstation HIS/RIS Patient-related Information Management Software Fax/Phone Referring Site Phone line Fax/Phone Expert Centre 3 Table 3: Teleradiology Components Imaging acquisition device Image capture Data reformatting Transmission Storage Display Reporting Billing similar. 2 Table 2 shows the differences between teleradiology and PACS. The major differences between them are in the methods of image capture, communication and storage duration. Some current teleradiology still uses a digitiser as the primary method of converting a film image to digital format, although the trend is moving towards using the Digital Imaging and Communication of Medicine (DICOM) standard. In networking, teleradiology uses lower speed wide area networks (WANs) compared with the much higher speed local area network (LAN) that is used in PACS. In teleradiology, image storage is mostly short term, whereas in PACS it is long term. Teleradiology relies heavily on image compression for faster transmission speed, whereas PACS may or may not. In general, a typical examination generates between 10MBs and 40MBs or much higher now with volume magnetic resonance imaging (MRI), volume zoom CT and digital mammography. The high extreme is in digital mammography, which generates 160MBs per examination. To transmit 160MBs of information through WAN requires a very high bandwidth communication technology. Teleradiology Components Table 3 lists the teleradiology components 2 and Figure 2 shows a generic schematic of their connections. Among these components, reporting and billing are other common business entities, which are not discussed here. Image Acquisition Device Devices generating images in teleradiology applications include CT, MRI, computed radiography (CR), ultrasound imaging, nuclear medicine (NM), digital subtraction angiography (DSA), digital fluorography (DF), digital mammography and film digitiser. Images from these acquisition devices are first generated from the examination site and then sent through the communication network to the expert centre if they are already in digital format. If these images are stored on films, they need to be digitised by a film scanner at the examination site. Image Capture In image capture, if the original image data is on film, either a video frame grabber or a laser film digitiser can be used to convert them to digital format. A video frame grabber, although low in cost, produces very low quality digital images and is not recommended. A laser film digitiser produces highquality digital data and is used more widely. Data Reformatting After the images are captured, it is advantageous to convert these images and the related data to industry standards because multiple vendors equipment can then be used in the teleradiology chain. Two common standards used in the imaging industry are DICOM for images and Health Level 7 (HL7) for textual data. 2 Storage At the receiving end of the teleradiology chain, a local storage device is required before the image is displayed. The capacity of this device can range from several hundred megabytes to 100GBs. A long-term archive, such as a digital linear tape (DLT) library, may be needed at the expert centre for historical images and radiology information retrieval, and current examination and diagnosis archival.

4 Teleradiology Today Display Workstation Single or multihead workstations with flat panel display and image display software are required for primary diagnosis. Communication Networking Important components in teleradiology are communication networks. Since most teleradiology applications are not conducted thought an intranet, that is, within the same hospital complex, but through the Internet, which involves interhealthcare facilities in metropolitan areas or at longer distances, the communication technology involved requires WANs. A WAN can be wireless or with cables. In wireless WAN, some of the available technologies are microwave transmission and communication satellites. Wireless WAN has not been used extensively due to its cost. Table 4 shows cable technology that is available in WANs. These WAN technologies are available through either a longdistance or local telephone carrier. The cost of using WAN is a function of transmission speed and the distance between sites. Therefore, within a fixed distance, for a digital system level zero (DS-0) line which has a low transmission rate, the cost is fairly low compared with DS-3, which is much faster but more expensive. Most of the private lines, for example T1 and T-3, are point-to-point and the cost also depends on the distance between connections. Table 5 gives an example showing the relative cost between DS-0 and T-1 lines between Childrens Hospital Los Angeles/University of Southern California (USC) and St John s Hospital, Santa Monica, CA, 15 miles apart in the Los Angeles metropolitan area. Using T-1 for teleradiology is very popular. Some larger companies lease several T-1 lines from telephone carriers and sub-lease portions of them to smaller companies for teleradiology applications. User-friendliness User-friendliness includes both the connections of teleradiology equipment at the examination site and the expert centre, and the simplicity of using the display workstation at the expert centre. Userfriendliness means that the complete teleradiology operation should be as automatic as possible, requiring only minimal user intervention. For the image workstation to be user-friendly requires three criteria: Table 4: Wire Technologies Available in Wide Area Networks (WANs) Technology Speed DS-0 (Digital Service) 56Kb/s DS-1 dial up 56Kb/s to 24x56=1.34Mb/s DS-1 Private Line (T-1) 1.544Mb/s Integrated Service Digital Network (ISDN) 56Kb/s to 1.544Mb/s DS-3 Private Line (T-3) 28 DS-1 = 45Mb/s Asynchronous transfer mode (ATM) 155Mb/s or more Internet 2 backbones 100Mb/s or more Table 5: Wide Area Network Cost Using DS0 (56Kb/s) and T-1 (1.5Mb/s) between USC and St John s Hospital 15 Miles DS0 T-1 Up-front investment US$500 Up-front investment US$6,700 Modems (2) US$400 T1 DSU/CSU WAN interface (2) US$1,500* Installation (2) US$100 Router (2) US$3,000 T-1 Installation US$1,200 Local connection (2) US$1,000 T-1 monthly charge: US$556 * DSU/CSU: Data service unit/channel service unit as of July 2001 image and related data pre-fetch; automatic image sequencing at the display; and automatic look-up table, image rotation and unwanted background removal from the image. Advance Technologies Four state-of-the-art and emerging technologies in teleradiology will be discussed: communication, image compression, image workstations, and image authenticity and integrity. Internet 2 and the Next-generation Internet During the past few years, the Internet has encountered unexpected demands by various applications including medical imaging. The characteristics of medical imaging, especially in teleradiology, are different from other types of data in two aspects: its file size is very large and some image examinations require near-realtime transmission for practical use. The standard Internet, therefore, has not been able to fulfil the transmission bandwidth requirement in daily clinical applications. The problem of high-speed transmission of large volume medical images has become very critical. Internet 2 is an infrastructure of high-speed communication (over 2Gb/s), currently consisting of the California Research and Education Network (CalREN-2), the very high performance Backbone Network Service (vbns) and the Abilene. The next- 6. F Yu, K Hwang, M Gill and H K Huang (2000), Some Connectivity and Security Issues of NGI in Medical Imaging applications, Journal of High Speed Networks, 9, pp

5 Figure 3: A two 2,000 Line Flat Panel Workstation Displaying a Posterior anterior (left) and a Lateral (right) Digital Chest Image Table 6: Time Estimated to Transmit a 184MBs Mammography Examination Under Various Network Environments Local ATM (measured Internet T1 NGI (nationwide: NGI (regional: 90Mb/s San Francisco (estimated (estimated SF Washington DC SF Bay area (SF) local area) 200Kb/s) 1.55Mb/s) estimated based based on on 5Mb/s) >15Mb/s) 16.4 seconds 2.04 hours 15.8 minutes 4.9 minutes < 1.64 minutes generation Internet (NGI) initiative that was sponsored by the US government in 1996 based on multi-agency federal research and development programmes is the application of Internet 2. Internet 2 infrastructure and NGI applications provide an opportunity for the medical community to tackle the image transmission problem. 6 At the global level, CalREN-2, vbns and Abilene provide readily available, high-speed backbones and administrative infrastructure. At the local level, the users are in the process of learning how to connect the hospital and clinic environments to these backbones. The advantages of using Internet 2 for teleradiology is its high speed and low operational cost once the local site is connected to the backbones. The disadvantage is that the local site has to upgrade its conventional Internet infrastructure to the high-speed Internet 2 architecture which tends to be very costly. Table 6 shows the Internet 2 performance compared with the private asynchronous transfer mode (ATM) optical carrier level three (OC-3) (155Mb/s) as of today. 7 9 Display Workstations State-of-the-art diagnostic workstation consists of two 2,000-line flat panel displays, a display board, a high-end PC computer, 100GBs storage and associated display software. It can display the first image from a disk in one to two seconds. The hardware of such a workstation costs about US$15,000. User-friendly software with similar cost to the hardware is required for easy and convenient use by the radiologist at the workstation (see Figure 3) H K Huang and S L Lou (1999), Telemammography: A Technical Overview, A G Haus and M J Yaffe, eds. RSNA Categorical Course 1999, Oak Brook, IL, pp S L Lou, E A Sickles, H K Huang, et al. (1997), Full-Field Direct Digital Telemammography: Technical Components, Study Protocols, and Preliminary Results, IEEE Transactions on Information Technology in Biomedicine, Vol. 1, No.4, pp H K Huang, A W K Wong and X Zhu (1997), Performance of Asynchronous Transfer Mode (ATM) Local Area and Wide Area Networks for Medical Image Transmission in Clinical Environment, Journal Comp. Med. Imag. & Graphics, 21 (3), pp

6 Teleradiology Today Image Compression Teleradiology requires image compression because of the slow speed and high cost of WAN. To achieve image compression without loss, current technology can reach between 3:1 to 2:1 compression ratios, whereas in lossy image compression using cosine transform-based Moving Picture Experts Group (MPEG) and Joint Photographic Experts Group (JPEG) hardware and software, 20:1 to 10:1 compression ratios can be obtained with acceptable image quality. The latest advance in image compression technology uses the wavelet transform. This has the advantage over cosine transform for higher compression ratio and better image quality after decompression. However, hardware for wavelet is not available. Image reconstruction from a compressed file is in a progressive manner in that a lower resolution image is first reconstructed almost instantaneously and displayed. From the expert s viewpoint, the image is transmitted through the network almost in realtime. Higher quality images are reconstructed continuously to replace the previous ones until the original image is reconstructed and displayed. Image Data Authenticity and Integrity Often, image transmission in teleradiology is through public networks. For this reason, trust in image data becomes an important issue. Trust in image data is characterised in terms of privacy, authenticity and integrity of the data. 10 Privacy refers to the denial of access to information by unauthorised individuals. Authenticity refers to validating the source of a message. Integrity refers to the assurance that the data was not modified accidentally or deliberately in transit. Privacy is the responsibility of the public network provider, based on firewall and password technologies, whereas authenticity and integrity are the responsibility of the end-user. Authenticity and integrity are kept based on the concept of public and private keys digital signature encrypted with existing algorithms while the image is being generated. In general, the public and private keys digital signature concept consists of seven steps: private and public keys set up a method in assigning public and private keys between the examination site and the expert centre; image pre-processing to segment objects of interest from the background and extract patient Table 7: Teleradiology Trade-off Parameters information from the DICOM image header at the examination site while the image is being generated; image digest to compute an image digest (digital signature) of the image based on its characteristics using the existing algorithms; data encryption to produce a digital envelope containing the encrypted image digest and corresponding patient information from the image header; data embedding to embed the digital envelope into the image as a further security; the image with the embedded digital envelope is sent to the expert site; and the expert centre receives the image with the embedded digital envelope, decrypts the image and the signature and compares the digital signatures before and after the transmission to validate the image integrity. Three Teleradiology Models Off-hour Reading Image Capture Workstat Compress Comm Tech Quality X X X Turnaround time X X X Cost X X X X The off-hour reading model is to take care of the off-hour reading, including in evenings, at weekends and during holidays, when most radiologists are not available at the examination sites. In this set-up, image acquisition devices at different examination sites, including hospitals and clinics, are connected to an off-hour reading centre with medium or low-grade transmission speed. The connections are mostly direct digital with the DICOM standard. The reading centre is equipped with network switches and various types of workstations that are compatible with the images being generated by imaging devices at examination sites. The staffing includes technical personnel that are taking care of the communication networks and workstations, and radiologists who come in during the evenings, weekends, and holiday shifts and perform online digital reading. They provide preliminary impressions and transmit these to the examination site instantaneously. The radiologists at the examination sites verify the reading and sign off the reports the next day. 10.X Zhou and H K Huang (2000), Authenticity and Integrity of Digital Mammogrpahy Image, IEEE Trans. Medical Imaging, Vol. 20, No.8 (to appear). 6

7 Application Service Provider Model Important Issues in Teleradiology The application service provider (ASP) model is a business venture that aims to take care of the radiology diagnosis of examination sites where onsite radiology interpretation is unavailable. This model can be for equipment only or for equipment and radiologists. In the former, an ASP entity sets up a technical centre housing network equipment and workstations. It also provides a turn-key connectivity for the examination site where images would be transmitted to the centre. The examination site can hire its own radiology to perform reading at the centre or the centre can provide radiologists for the reading. Web-based Teleradiology Web-based teleradiology is mostly used for hospital or larger clinics to distribute images to various parts of the hospitals or clinics or outside based on Web technology. A Web server is built where filtered images from PACS are either pushed from the PACS server or pulled by the Web server. Filtered images in the Web server are then available for clients to view. The clients can be referring physicians who simply want to take a look at the images or for radiologists to make a remote diagnosis. Web-based teleradiology is very convenient and low cost to set up because most technologies are readily available, especially within the hospital intranet environment. The drawback is that since the Web is a general technology, the viewing capability and conditions are not as good as in a PACS workstation where the set-up is more customised to the medical imaging display. Image Quality and Cost Trade-off Parameters Table 7 shows the teleradiology trade-off parameters between image quality, turnaround time and cost. These three parameters are effected by four factors: the method of image capture, the type of workstations used, the amount of image compressed and the communication technology selected. The cost in teleradiology is determined by all of these four factors. Image Authenticity and Integrity Since teleradiology uses public communication to transmit images, two issues arise: the way in which the patient s confidentiality can be ensured; and the authenticity and integrity of the image emerging technologies of data security are being researched and developed. 10 Medical Legal Issues There are four major medical legal issues in teleradiology: privacy, licensure, credentialing and malpractice liability issues. The American College of Radiology (ACR) Standard for Teleradiology, adopted in 1994, defines guidelines for qualifications of both physician and nonphysician personnel, equipment specifications, quality improvement, licensure, staff credentialing, and liability. These guidelines need to be re-evaluated from time to time. 8