Nothin’ but ‘net?

Editorial

Nothin’ but ‘net? Kirk N. Garratt, MD Rochester, Minn

See related article on page 241. With the world having watched the Gulf War unfold live from Baghdad as well as the surface of Mars (up to 240 million miles away) being probed as it was happening, unrealistic expectations about immediate image transmission are perhaps forgivable. With the proliferation of powerful home computers and development of the Internet, we anticipate that digital images may be drawn into our homes or workplaces with little delay and high fidelity. However, even a novice Internet surfer knows the frustration of delays in downloading large files, especially image-intensive files. We’re told the delays have to do with the limitations the current network of copper cables to move large amounts of data. In this issue of the Journal, Tobis et al1 describe their use of commercial telecommunications technologies for the transmission of angiographic and intravascular ultrasound images from a catheterization laboratory to a core laboratory 40 miles away. The images were transmitted with minimal delay (near real-time), allowing monitoring of the procedure while it was being conducted. The core lab personnel were thereby able to confirm that the patient qualified for inclusion in the protocol under study, ensure that the particulars of the protocol were followed faithfully, and offer advice to the operators regarding how to conduct the case. The authors found that the system facilitated the intended monitoring function in 39 (98%) of 40 cases and permitted the expert core lab personnel to influence the conduct of the case in a manner that may have improved the final outcome in 23 (58%) cases. The authors contend that the system used allowed transmission of data that was not significantly degraded (as evidenced by comparative studies between original and transmitted images showing modest differences in averaged values of quantitative parameters). They conclude that commercial telecommunications systems can From the Division of Cardiovascular Diseases and Internal Medicine, Mayo Clinic and Foundation. Reprint requests: Kirk N. Garratt, MD, 200 First St SW, Mayo Clinic, Rochester, MN 55905. Am Heart J 1999;137:187-9. 0002-8703/99/$8.00 + 0 4/1/92713

be useful in linking core labs with practicing cardiac labs during procedures to support clinical studies and perhaps improve clinical outcomes. The findings of this study are both enticing and disappointing. This report is exciting in that it shows how far we have come: actually bringing an expert from a remote site into a lab while a patient is on the table and having his or her virtual participation in a procedure. No telemedical image file transfer system has been challenged with the task of providing near realtime data transfer of the massive image files generated by coronary angiography and intravascular ultrasound. These files are truly huge: a single frame of uncompressed digital angiographic data requires 250 to 500 kilobytes of storage space and memory. Because most laboratories acquire images at 30 frames per second and studies may involve more than 2 minutes of recorded images, it is clear that the storage and transmission requirements are formidable. Echocardiographic images are also very large: a single full-frame, full-color transthoracic echocardiographic video image may consume 3 megabytes (MB). In this report transfer of such complex images was accomplished by using technologies that are readily available today. However, when critically examined a few very important facts surface. The cable used to connect the cardiac lab with the core lab was a point-to-point service T1 fiberoptic cable capable of transmitting data at a maximum rate of 1.544 megabytes per second. Although this data transfer rate is impressive for “routine” uses such as Internet access, these rates are quite limiting when very large image files are being transmitted. To transfer cineangiograms without compression requires around 7.5 MB/s (approximately 0.25 MB/frame × 30 frames/s). If a TI line is used, either data have to be moved at less than near real time or it must be compressed. The role of compression has been addressed by the Digital Imaging and Communications In Medicine (DICOM) Cardiovascular Information Working Group, a team of physicians, engineers, and physicists committed to defining standards to be used in the transport of digital medical image data. Lossless compression algorithms allow modest data compression (3:1), but significant data compression requires some loss of data.

188 Garratt

Based on work showing that Joint Photographic Experts Group (JPEG) 20:1 lossy compression resulted in no significant problem with image interpretation, this compression algorithm has been incorporated in the DICOM standard for echocardiographic data.2 The use of this compression algorithm for intravascular ultrasonic data was not addressed by this committee (standards for intravascular ultrasound are currently being developed by the working group). This degree of data compression has not been accepted for cineangiographic images. At the 1998 American College of Cardiology (ACC) meeting, the results of an ACC/ESC (European Society of Cardiology) study on JPEG lossy cineangiographic compression were shown. This study concluded that motion JPEG compression of >6:1 resulted in unacceptable image artifact. (For information about DICOM, compression and this study see the ACC DISC ‘96 tutorial at http://www.xray.hmc.psu.edu/dicom/acc_tut/tutorial.html#Tutorial_Outline). Tobis et al1 used data compression of 200:1 for transfer of echocardiographic and angiographic data. The compression algorithm used was a proprietary one owned by VTEL, a Texas-based telecommunications company, and was designed to support teleconferencing. This degree of compression has not been studied to determine impact on image interpretation, and this algorithm has not been evaluated for medical image transfer applications. Although the authors note that transfer resulted in a trivial difference in average angiographic stenosis measurements (from 0.7 ± 0.3 mm to 0.8 ± 0.3 mm), the paired t test indicated a highly significant difference (P = .008). This can only be true if each image pair (original and transferred) did not match very well, even though the averaged values were similar. The plot comparing the distribution of differences between measurements made from original and transferred images confirms that the differences were greatest when small vascular dimensions were measured, but even structures in the 3 to 4 mm range had an error of up to 0.75 mm. The error was bidirectional, indicating that the system didn’t systematically underestimate or overestimate. The only angiographic measurements that fared well in this analysis were the lesion length and pretreatment reference vessel diameters, measurements that involved relatively large values (several millimeters) and that should have been less sensitive to the effects of image compression. The intravascular ultrasound image data were less affected by compression, although the mea-

American Heart Journal February 1999

surements involving the smallest values (minimum stent area) again proved the most sensitive to the effects of compression. If this degree of commercial compression is problematic and T1 cables are limited, what is the solution? One alternative is to examine other compression algorithms, and that is being done. Newer techniques such as wavelet compression3 introduce far less image artifact and can produce excellent image fidelity at compression ratios of 30:1 or greater. Another approach is to exploit more sophisticated telecommunications systems to support faster data transfer. Workers at Mayo Clinic recently completed a series of experiments designed to test a complex system incorporating very broad bandwidth ground fiberoptic cables (OC-3 cables with maximum data transfer rates of 155 MB/s) and an advanced communications technology satellite commissioned by the Defense Advanced Research Projects Administration (maximum data transfer rate of 644 MB/s). Using this system, uncompressed angiographic and transthoracic echocardiographic images were transferred at rates approaching near real time, and the system proved useful for remote support of catheterization procedures involving adult and pediatric patients.4 Intravascular ultrasound images were not tested with this system. Of course, this system is not available publically and couldn’t be used to support routine image transfer between medical centers today, but it does represent the potential of telecommunications technology in 1998. It is also worth noting that data compression is cheap and system bandwidth is expensive, so the final use of a medical telecommunications system will depend on finding the best balance between these 2 forces. Tobis et al1 cite 4 important areas of potential application for near real-time catheterization procedural data transfer: (1) physician training, (2) clinical conferencing, (3) support for clinical trials, and (4) support for clinical procedures. Remote training requires replication of the most accurate and lifelike environments possible; high ratio data compression will be inappropriate for this application. Conferencing, on the other hand, is far less image critical and can be supported with 200:1 compression. The expense of establishing high-bandwidth, high-fidelity telecommunications systems may preclude their routine use for monitoring clinical trials, even though the principal conclusion of the current study supports the effectiveness of this application. On the other hand, failure to comply strictly with study protocols can have tremendous fall-

American Heart Journal Volume 137, Number 2

out. The ROBUST study of intragraft thrombolysis5 and the recent GRII coronary stent (Cook Cardiology, Bloomington, Ind) trial were both “negative” studies, yet in both cases there were significant questions about protocol violations that may have influenced the final results. The impact of these trial results have been tremendous: apparent lack of efficacy for urokinase and the GRII stent have essentially driven these products from the market. In the future, companies may decide to spend whatever is necessary to confirm protocol compliance, and it is possible that high-bandwidth telecommunications capabilities will be required of medical centers wishing to participate in device trials. The final point is the most intriguing. If images could be transferred quickly with high fidelity from a catheterization laboratory to an angioplasty expert at a remote site, then it might be possible for novel support systems to replace conventional ones. Already there is a discrepancy between the number of American hospital centers reporting angioplasty services (18%) and those reporting cardiothoracic surgical services (16%).6 The need for urgent cardiac surgery among properly selected patients treated with modem equipment and techniques is low,7 and the expense associated with establishing new cardiothoracic surgical programs (estimated at several million dollars) is great. Furthermore, most hospital centers have the ability to transport patients (or physicians/surgeons) rapidly by ground or air when necessary (ie, backup systems are available). Thus the use of high-fidelity telecommunications systems to bring experienced angioplasty operators virtually into remote angioplasty procedures may expand angioplasty services into less populated areas at reasonable cost. At Mayo Clinic, this practice model is being explored as a system for providing remote sup-

Garratt 189

port for angioplasty procedures at regional hospitals without on-site cardiothoracic surgical services. The current work by Tobis et al1 represents an important step in the progression from tradition-based to digitally based catheterization systems. Although the telecommunications technology used has shortcomings for large image, file-intensive applications and the compression used was probably excessive, the principle proven was good: It is possible for those of us whose professions depend on faithful transmission of imaging data to make technology work for us in the expansion of our practices and clinical investigative efforts.

References 1. Tobis J, Aharonian V, Mansukhani P, Kasaoka S, Jhandyala R, Son R, et al. Video networking of cardiac catheterization laboratories. Am Heart J 1999;137:241-9. 2. American College of Cardiology. DISC 1996 Tutorial. Available from: URL:http://www.xray.hmc.psu.edu/dicom/acc_tut/tutorial.html 3. Erickson BJ, Manduca A, Palisson P, Persons KR, Earnest F IV, Savcenko V, et al. Wavelet compression of medical images. Radiology 1998;206:599-607. 4. Garratt KN, Holmes DR Jr, Wondrow MA, Khandheria BK, Mitchell MP, Bengali AR, et al. Remote angiographic consultation during interventional procedures using complex telecommunications network [abstract]. J Am Coll Cardiol 1998;31(supplA):8A. 5. Hartmann JR, McKeever LS, O’Neill WW, White CJ, Whitlow PL, et al. Recanalization of chronically occluded aortocoronary saphenous vein bypass grafts with long-term, low dose direct infusion of urokinase (ROBUST): a serial trial. J Am Coll Cardiol 1996; 27:60-6. 6. Cutler DM, McClellan M. The determinants of technological change in heart attack treatment. Working paper series: working paper 5751. Cambridge (MA): National Bureau of Economic Research; 1996. 7. Ellis SG, Miller DP, Brown KJ, Omoigui N, Howell GL, Kutner M, et al. In-hospital cost of percutaneous coronary revascularization. Critical determinants and implications. Circulation 1995;92:741-7.