computer. (Sparc LX;. Sun Microsystems,. Mountain. View, CA). Direct digital CT and. MR examinations from Mount ... College of Radiology/National. Electrical.
1S33
Computers
Asynchronous Transfer Image Communication H. K. Huang1,
Image
Ronald
communication
archiving
and
L. Arenson,
is an important
communication
systems
William
Mode P. Dillon,
component (PACS)
S. L. Lou,
in picture
and
teberadiob-
ogy applications. Currently, local area networks (LAN5) and wide area networks (WAN5) use different technologies for image communication. Asynchronous transfer mode (ATM) is an emerging technology that can be used for both LANs and WANs. This article describes experimental results using an ATM network to transmit CT scans and digitized radiographs between the University of California, San Francisco (UCSF) and Mount Zion Hospital, an affiliated community hospital in the San Francisco Bay area. The WAN connection between the two hospitals is via an ATM main switch at Pacific Bell, a local communicatlon
carrier
located
in Oakland,
CA,
which
uses
Technology
single-
mode optical fibers. Preliminary results show that, using the ATM Optical Carrier Level 3 (OC3) (1 55 Mblts/sec) specification, it takes 1 .3 sec and 2.7 sec to transmit a 10-Mbyte digitized radiograph and a 20-Mbyte CT scan, respectively, between the two locations. Encouraged by these results, we have designed and implemented an ATM WAN and LAN between UCSF and Mount Zion Hospital. This Is the first of a three-phase project of installing a WAN serving four hospitals and one clinic in the San Francisco Bay area.
Background A PACS or a teleradiobogy system consists of four components: image acquisition devices, several computers, an archival unit, and display workstations. These components are connected by an image communication network. The PACS or the teleradiobogy system also needs to connect to
Todd
Bazzill,
in Radiology
for Radiologic Albert
W. K. Wong
other medically related databases, such as a hospital information system or a radiology information system. If the communication network is within a local area connected by cables, the network is considered an LAN. If the network requires telecommunication carriers like a telephone company, microwave dishes, or a satellite, it is called either a metropolitan area network (MAN) or a WAN, depending on the distance between nodes. For this discussion, WAN is used to represent both MANs and WANs. Because the communication media used for LANs and WANs are different, the technology for their applications is also different. In general, technologies for LANs are more versatile, and their costs are lower than those for WANs. We have reported on some LANs that have signaling rates as high as 1 gigabit/sec with realization of 24 Mbits/sec in radiobogic LAN applications (compared with the standard Ethernet signal rate of 10 Mbits/sec with realization of 800 Kbits/sec) [1-3]. On the other hand, radiobogic applications using WANs have been limited to the dial-up digital services zero and one. The latter, with a maximum speed of 1 .544 Mbits/sec, is sometimes referred to as the Ti [4]. Although the higher-speed digital service three is available, its application is limited by costs and serviceability. Therefore, a gap in technology development and required cost exists between LANs and WANs. The current concept in radiobogic image communication is that no physical or logical boundaries should exist between LANs and WANs (Holman BL et al., presented at the NCI, NIH, and Conjoint Committee Conference on Diagnostic Radiology,
Received
November 23, 1994; accepted after revision January 20, 1995. in part at the CaIREN (California Research and Education Network) inauguration meeting, San Francisco, October 1994. Supported in part by NLM HPCC Program NO1-LM-4-3508 and by CaIREN ATMN-007. 1 All authors: Department of Radiology, University of California, San Francisco, 530 Parnassus Ave., Am. CL-i 58, San Francisco, CA 94143-0628. respondence to H. K. Huang.
Presented
AJR
1995;164:1533-1536
O36i-8O3/95/i646-i533
© American
Roentgen Ray Society
Address
cor-
HUANG
1534
November 1994). Forthis reason, ATM for both LANs and WANs has become the emerging technology [5]. ATM is a method for transporting information that splits data into fixed-length cells (53 bytes). Each cell consists of S bytes of header information pertinent to the ATM transmission protocol and 48 bytes of information. It is based on the virtual circuit-oriented packet-switching theory developed for telephone circuit switching applications [6]. Our department has received two grants to set up an ATM WAN and LAN for transmission of radiobogic images and rebated medical data. This network connects five sites: UCSF; Mount Zion Hospital; San Francisco Veterans Administration Medical Center; San Francisco General Hospital; and San Francisco Magnetic Resonance Center. Each site will have an ATM switch that connects to the main ATM switch in Oakland, CA. Figure 1 shows the ATM connections in the testing area. UCSF serves as the expert center, and its ATM switch is connected to the departmental PACS infrastructure. Other sites are considered satellites. Images and related patient data are transmitted from the satellite sites to UCSF for interpretation and consultation. The ATM network provides us with an opportunity to study both LANs and WANs using a single technology. This article describes the first phase of this study: the connection between UCSF and Mount Zion Hospital. We describe an experiment that demonstrates the successful connection of a WAN and an LAN in a clinical setting with a single highspeed communication technology. We provide the performance statistics based on this experiment and illustrate the implementation of the ATM network between the two sites.
The Sateblfte
Site: Current
Clinical
Operational
Environment
Mount Zion Hospital has a GE 9800 helical CT scanner (Milwaukee, WI) and a Siemens 1 .O-T MR IMAPCT scanner (Iselin, NJ) that are connected to an acquisition computer (Sparc LX; Sun Microsystems, Mountain View, CA). Direct digital CT and MR examinations from Mount Zion Hospital are transmitted to UCSF as follows: The acquisition computer acquires both direct digital CT and MR images automatically during scanning opera-
ET AL.
AJA:i64,
June
tions using a method similar to that described previously [7]. After an examination is completed, the entire study is reformatted to the ACR/NEMA (American College of Radiology/National Electrical Manufacturers Association) standard with UCSF shadow group header information, which contains information aboutthe patient’s examination and historythat is relevantto the UCSF clinical environment. The formatted image data is then immediately transmitted from Mount Zion Hospital to UCSF’s PACS through a Ti line for display and for long-term archiving. For this study, we developed an automatic time log in the UCSF PACS that tabulates the time required for each stage after the PACS detects the completion of an examination [7]. The stages include image transmission from the scanner to the acquisition computer at the satellite site, image reformatting, image transmission from the satellite site to UCSF, image archiving at the PACS controller, and image display in the viewing room. We randomly selected 600 CT scans with an average size of 20 Mbytes per scan and recorded the average time required to complete each of the five stages. The result was about 800 sec, of which 200 sec was for the Ti communication [8]. We also recorded the time required to send a 10Mbyte digitized radiograph through the Ti line (about 100 sec). These times were used as a baseline against which the ATM technology was compared.
The
ATM
Experiment:
Experimental
Set-Up
and
Simulation
We performed the following experiment to evaluate the performance of the ATM 0C3 WAN and LAN between UCSF and Mount Zion Hospital. Table 1 lists the test equipment we used, and the experimental set-up is shown in Figure 2. At Mount Zion Hospital, an ASX 200 ATM switch (FORE, Warrendale, PA) is connected to a Sparc20 computer (Sun Microsystems, Mountain View, CA) with an S-bus ATM adapter board (FORE) using two multimode optical fibers. This ASX 200 ATM switch is connected to the ATM main switch via single-mode optical fibers. At UCSF, another ASX 200 ATM switch is connected to SparciO, 20, and 690 MP computers using multimode optical fibers. A Sparc2O computer was used to simulate the acquisition computer at Mount Zion Hospital; a Sparc2O and 690 MP computer were used to simulate the display workstation computer and the PACS controller computer at UCSF, respectively. During the experiment, we turned the connection(s) on and off as needed. The ATM WAN and LAN throughputs were measured under various conditions.
TABLE I : Test Equipment Used for the Asynchronous Mode Experiment Between the University of California, Francisco and Mount Zion Hospital
Asynchronous Mbits/sec)
Fig. 1.-The San Francisco Bay area. Five clinical sites(Universlty of CalIfomla, San Francisco; Mount Zion Hospftal; San Francisco Veterans Administration Medical Center (VA Medical Center]; San Francisco General Hospftal; and San Francisco Magnetic Resonance Center(SFMRC])are connected wIth asynchronous transfer mode (ATM) test network through main ATM switch at Pacific Bell, Oakland, CA. PacBell = PacIfic Bell.
1995
Transfer San
transfer mode (ATM) optical carrier level 3 (OC3, 155 switch
at Pacific
Bell,
Oakland,
CA
ATM switch (ASX 200; FORE, Warrendale, PA) ATM SONET (Synchronous Optical NETwork) 0C3 adaptor within the ASX 200 switch Sun Sparc20, 10, 690 MP computers View, CA)
S-bus ATM adaptor boards (FORE)
(Sun Microsystems,
boards Mountan
AJR:164,
June
ATM TECHNOLOGY
1995
FOR
IMAGE
COMMUNICATION
TABLE 2: Asynchronous Performance Statistics
1S3S
Transfer
Mode Optical
Wide
area
Local
Network
Path 1: From Mount Zion Hospital Sparc2o (Sun Microsystems, Mountain View, CA) to UCSF Sparc20 Path 2: From UCSF Sparc20 to Mount Zion Hospital Sparcl0
Carrier
area
Level 3
Aggregate
Network
60.64
60.64
-
-
66.64
66.64
48.80
76.96
(Sun Microsystems)
Paths 1 and 2 concurrently
28.16
itized radiographs and CT body images. The digitized radiographs used were 1 0 Mbytes each, and the CT scans were about 20 Mbytes per examination. Six hundred sets of each type of examination were transmitted and measured. The statistical variance of transmission rate within each type of examination was less than 1 The results were used as a comparison against those obtained by the Ti method, as shown in Table 3. %.
Fig. 2.-Experimental
set-up
for the asynchronous
transfer
mode
(ATM)
(OC3 specification, 155 Mbits/sec transfer rate) wide area network (WAN) and local area network (LAN) throughput test between University of Callfomla, San Francisco and Mount Zion Hospital using the ATM switch in Oakland, CA. Path marked with number 1 is for WAN performance measurement, path marked with number 2 for LAN performance measurement. Paths 1 and 2 combined is for both WAN and LAN measurement. PacBell = Pacific Bell, MM = multimode fibers, SM = single-mode fibers.
Results Simulation
We first measured the ATM WAN performance by activating only the path marked with the number 1 in Figure 2. ATM LAN performance was measured by activating only the path marked with the number 2 in Figure 2. However, the PACS controller computer (Sparc69O MP) was running continuously, representing the background communication activities. The performance of both networks was measured by activating paths 1 and 2 simultaneously. The performance ofthe connection between the 690 MP and the ASX 200 was not measured because its performance represented image archiving, which always has a bower priority in the PACS design. The simulation used the following parameters: image buffer size of 128 K, measurement from computer memory to computer memory, a data set size of 256 Mbytes, and the Transmission Control ProtocoVbnternet Protocol (TCP/IP) communication protocol. Table 2 shows that the ATM WAN performance is about 60 Mbits/sec and the ATM LAN is 66 Mbits/sec (or close to 40% of the 155 Mbits/sec signaling rate). When combining the WAN and the LAN concurrently, their performances decrease by 46% and 73%, respectively, but the aggregate performance reaches 77 Mbits/sec.
Discussion We have successfully completed an ATM performance test between UCSF and Mount Zion Hospital using an 0C3 link with a transmission rate of 155 Mbits/sec. Experimental results demonstrate that we can obtain a transmission rate of about 60 Mbits/sec in both the LAN and the WAN. This performance can be translated as sending a 10-Mbyte digitized radiograph in 1 .3 sec or a 20-Mbyte CT scan in 2.7 sec. We believe this rate would satisfy most radiobogic image communication requirements. Our experimental results were based on the TCP/IP protocol. We have yet to optimize the ATM communication protocol, which could potentially improve its performance by 20-25%. Because this experiment is a simulation, we have to extrapolate these results in the clinical environment. First, the images transmitted during the simulation were not obtained directly from the CT scanner host computer or from the laser film digitizer; they were from the acquisition computer. In an actual clinical network, a bottleneck occurs between the scanner/digitizer and the acquisition computer because performing a CT scan or
TABLE 3: Transmission Time Required Between Mount Zion Hospital and the University of California, San Francisco Using a Ti line and Asynchronous Transfer Mode Optical Carrier Level 3
10-Mbyte
Ti linea
Transmission
of Digitized
Radiographs
and CT Scans
Using the same experimental set-up, path 1 to measure the WAN performance
we activated for transmitting
transfer
only dig-
20-M byte CT Study
One
Two
One
Image
Images
Study
100 sec (1 .6 mm)
Asynchronous
Radiograph
1 .3 sec
One Current and One Historical
200 sec
200 sec
400 sec
(3.4
(3.4
(6.7
mm)
2.7 sec
mm)
2.7 sec
mm)
5.4 sec
modeb
aTransmission bTransmission
rate rate
= =
1 .5 Mbits/sec, 155 Mbits/sec,
realization realization
rate rate
= =
100K/sec. 7.5 Mbytes/sec.
1S36
HUANG
digitizing a radiograph takes time. Second, aside from the acquisition node, we want to know if the simulation results can represent the remaining network performance in the clinical environment. This issue can be addressed by the characteristics of the ATM switches and adapter boards. First, ATM switch operation is, in principle, different from Ethernet connections. In the case of Ethernet, the transmission speed is reduced drasticabby when the number of connections increases. On the other hand, because the ATM switch operates in a star architecture, it has an aggregate data rate of 2.5 gigabits/sec at the switch. Until the number of connections to the switch reaches this limit, the performance between nodes would not deteriorate, regardless of the number of connections. When the switch reaches this limit, a second switch can be added. As forthe performance at the computer connection, the ATM transmission rate depends only on the computer into which the ATM adapter board is inserted. Because we are using Sparc-series computers in the clinical environment, we do not anticipate a change in the ATM transmission performance. Thus, we are confident that the results from this simulation would be a good representation of an ATM network in a clinical environment. Encouraged by this result, we have designed atotal ATM WAN and LAN between UCSF and Mount Zion Hospital. Figure 3 shows the first phase ofthe system configuration. In this configuration, the existing Ti line is used as the back-up link for the WAN. For those PACS components with older computer buses thatthe ATM technology does not support, we use a LAN access
ET AL.
AJA:164,
June 1995
(LAX-20) that converts the ATM connection to an Ethernet connection. This technology is called the Star Ethernet conf iguration. In this configuration, each connection can achieve a rate of 10 Mbits/sec, and the performance of each connection is not reduced by other connections. Examples in this category of computers in UCSF PACS are the 2K display stations that use the older Sun computers with a VME-bus backplane. This network architecture has been implemented, and we are designing experiments to measure its performance. ATM technology is supported by the ATM Forum [9], a consortium of over 500 private companies and universities. The development trends in ATM technology are moving toward a universal standard. The research trends are in ATM adaptable layer algorithm development, which will allow an optimal method for high-speed transmission of multimedia radiobogic information including images, reports, video, voice, and text. The list price of the ATM switch or the ATM LAN access switch is equivalent to that of an Ethernet router, but the ATM adapter board is lower than the fiber-distributed data interface board [1]. We anticipate that the price of ATM hardware cornponents will drop drastically in the next 2 years and will then be affordable by most radiology departments. The ATM LAN has no cost besides the switches and adapter boards if the fiber-optic cables are already in place. On the other hand, the hidden cost of the ATM WAN is the long-distance connections that depend on the charges posted by the carriers who own the transcontinental and transoceanic fiber-optic cables. It is imperative thatthe radiobogic community demonstrate the usefulness of this technology in health-care delivery so that the cost of using these cables will come down. The beauty of the ATM technology is that even if the ATM WAN is still too high to be cost-effective in the near future, we can still use the Ti line for the WAN, as shown in Figure 3, and the ATM LAN architecture remains functionally intact. We expectATM to become the standard communication technology in the near future. switch
REFERENCES 1
.
Huang HK, Lou SL, Cho PS, methods. AJR 1990;155:i83-186
et al. Aadiologic
image
communication
2. Stewart BK, Lou SL, Wong WK, Huang HK. An ultrafast network for com-
Fig. 3.-Implementation of first phase of asynchronous transfer mode area network (WAN) and local area network(LAN) configuration of California, San Franclsco(UCSF). WAN is connected by ATM switch ASX-200 at UCSF and LAN access switch LAX-20 at Mount Zion Hoepital through main ATM swftch in Oakland, CA In this phase, LAX-20 is chosen at Mount ZIon Hospital because most computer equipment there still uses older computer bus archftecture. However, connection between two
(ATM)wide at Universfty
switches at Mount Zion Hospital and UCSF is true ATM speed. In this architecture, Ti line is used as WAN back-up. PACS = picture archiving and cornmunicatlon system, Acq = acquisition device, SONET = Synchronous Optical NETwork, CaIREN = California Research and Education Network, Mux = multiplexer, OC-3c = optical canter level 3, US = ultrasound, NM = nuclear medicine, DFS = digItal fluoroscopy, Mbps = megabits/sec.
munication of radiologic images. AJR 1 991 156:835-839 3. Huang HK, Wong WK, Lou SL Stewart BK. Architecture of a comprehensive radiologic imaging network. IEEEJ SelAreas Commun 1992:10:1188-1196 4. Stewart BK, Dwyer SJ, Huang HK, Kangarloo H. Design of a high speed high resolution teleradiology system. PACS VI, SPIE 1992;1654:66-80 5. McDysan DE, Spohn DL. ATM theory and application. New York: McGrawHill, 1995
6. Cavanaugh JD, Salo TJ. Internetworking ed. Advances in local and metropolitan Computer Society Press, 1994 7. Lou SL, Huang HK. Assessment
with ATM WANs. In: Stallings W, area networks. New York: IEEE
of a neuroradiology
PACS
in the clinical
environment. AJR 1992;1 59:1321-1327 8. Lou SL, Huang HK, Bazzill T, Gould AG, Dillon WP, Schomer BG. Interhospital CT image communication: T-i line versus carrier service. Radiology 1994;193(P):33i 9. The ATM Forum. ATM user-network interface specification, version 3.0,
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