Dec 20, 1989 - trator with duplex optical fiber. The concentrator allows up to eight connections. An example of the cluster design is a concentrator connected.
183
Computer r’
.
.
Radiologic
Paul S. Cho,
Daniel
A picture archiving and communication consists of four components: acquisition
J. Valentino,
system devices,
(PACS) a host
computer, an image archive, and display stations (which include video monitors and printers). These four components are connected by an image communication network. Each component has a computer or a processor that controls the image transfer. The speed of the communication depends on the type of processor used, the physical media containing the processors, and the software or the protocol that controls the communication between the processors. Connecting these components may be the most difficult technical task in a PACS implementation. Although the implementation of the American College of Radiology/National Electrical Manufacturers’ Association (ACR/NEMA) communication standard might
alleviate
some
time before major for their equipment.
methods emerging Broadband
of the
imaging
difficulties,
it will
manufacturers
In this
paper,
we
still
adopt
be a long
this standard
describe
some
used in radiologic image communication network technologies.
current
and other
Video
The simplest
.
Image Communication
S. L. Lou,
H. K. Huang,1
method
Methods
Albert
W. K. Wong,
transmission
is the broad-
band video communication system. A broadband communication system uses a single or double coaxial cable that can be connected anywhere along its length for immediate twoway access to information. The term broadband refers to the fact that information is transmitted over a wide band of radio frequencies. A video image (RS-170 signal) at the transmitting end is encoded and converted to the radio frequency range
communication
and Brent
K. Stewart
to either continue,
system.
The
same
change
sequence,
of such a broadband broadband
system
video also
can be used for monitoring CT and sonographic examinations. For example, we can select channel 2 for MR, channel 3 for CT, and channel 4 for sonography. The advantage of the broadband communication system is that it is inexpensive and is capable of transmitting images in real time. The dis-
H. K. Huang. July 1990 0361-803x/90/1551-0183
the technologist
or abort the study. Figure 1 shows the architecture
Received December 20, 1989; accepted after revision February 21 , 1990. This work was supported in part by Public Health Service Grant No. AOl CA39063, awarded Services, and by the UCLA Department of Radiological Sciences Research Fund. 1 All authors: Medical Imaging Division, Department of Radiological Sciences, UCLA Medical AJR 155:183-186,
K. K. Chan,
and is decoded at the receiving end, very much the same as in cable television technology. Each 5i 2 x 5i 2 pixel image can be assigned to a given 6-MHz channel in the 5-540 MHz frequency range. This broadband signal is then placed onto the broadband cable and mixed with the other channels during the transmission. At the receiving end of the cable, a television tuner (broadband demodulator) simply tunes to the appropriate channel and demodulates the broadband information back into an RS-i 70 signal, which can be displayed on a video monitor. Theoretically, 60 simultaneous channels can be supported, with each channel transmitting 51 2 x 51 2 pixel images at 30 frames/sec. Broadband video communication can be used to monitor examinations of patients. An example is the MR image monitoring system. This system is for monitoring examinations performed in an MR trailer that is located outside the hospital. Because it is not practical for the radiologist to be in the trailer for every examination, it is convenient to have the technologist perform the examination and send real-time MR images to the radiologist for immediate consultation. The radiologist views the images as the study is being performed and in-
structs of image
Page
0 American Roentgen Ray Society
by the National Cancer Institute, School,
Department
Los Angeles, CA 90024-1721
.
of Health and Human
Address reprint requests to
HUANG
184
ET AL.
AJR:155, July 1990
Standard DR1 1 -W emulator boards that implement this interface are now available for many computers. The effective performance of this image transfer method from the Digital
Progressive /lntertsc.d
converter
Equipment
Corporation’s
VAX computer
to other devices
is
less than i 0% of the specification, between 50 and 70 kilobytes/sec; from the SUN (Mountain View, CA) computer to other devices, it is about 1 00 kilobytes/sec. In radiology applications, the DR1 1 -W is used for connecting a host computer and an image acquisition device or a printer. For example, it is used in computed radiography systems [i } and laser film scanners and printers [2]. The computed radiography system developed by Fuji Photo Ltd. (Tokyo, Japan) and distributed by Philips, Siemens, and Toshiba uses this transfer method to send the image to an external computer.
Ethernet
Fig. 1.-Architecture
of a broadband
monitoring MR examinations. MR Images sent to modulator, which converts video
video communication
system
for
from the scanner’s console are signals to a certain RF range.
Converted signal is sent to head end, which assigns it to a broadband channel. Signal is broadcast through cable and received by any station tuned to this channel with demodulator.
advantage is that images that appear on the monitor are volatile and therefore cannot be stored or retrieved later. Also, the image quality may not be sufficient for primary diagnosis because the image is from a video monitor and the coaxial broadband cable degrades the video signal.
Parallel
Transfer
(DRI 1-W)
The DR1 i -W computer board uses a i 6-bit parallel transfer interface designed by Digital Equipment Corp. (Boston, MA) in the late 1 970s. The specification of the transfer speed is about 1 megabyte/sec; this translates to sending a 1 K x 1 K pixel image through the parallel communication cables in 1 sec. The drawback of this communication method is that the cable length between the two host computers (or processors) is very short, normally less than 50 ft. It is possible to use a pair of fiber-optic modems to extend the distance between the acquisition device and the host computer to about 1000 ft. This connection is convenient if the computed radiography system is located at a common processing area in the radiology department and the host computer is at a remote location.
Communication
The Ethernet with Transmission Control Protocol/Internet Protocol (TCP/IP) is the most popular serial digital communication method, almost a standard in every computer built in the late 1980s. The maximum signaling speed of Ethernet is 10 megabits/sec. In practice, we can achieve about 10-40% of its maximum speed. Ethernet was designed for transmission of text information (small files) and is not suitable for image (large files) communication. Early experience with use of Ethernet for image communication [3] was not encouraging. However, recent improvements in both the hardware and software protocol of Ethernet technology are promising. In the following paragraphs, we discuss our clinical experience with standard Ethernet communication methods. For this discussion, it is advantageous to distinguish between the communication from an image acquisition device to a host computer and that from a host computer to an image archival or display station. In the case of transmitting
images
from an acquisition
device
to a host computer,
the
transmission speed on Ethernet is very slow. One reason is that the transfer speed is constrained by the older generation
computer
used
in the acquisition
device,
which
was
not
designed for image communication. When a digital image must be transmitted, the technologist pushes a key on the device console to start the image transmission. Table 1 (left columns) shows our experience with this mode of image transmission. It takes about 30 sec to send a CT scan (16
bits/pixel),
4 sec for an MR image (8 bits/pixel),
and 8 sec for
a sonogram (8 bits/pixel) from the acquisition device to the host computer, without use of image compression. The speed of transferring an image from the host computer to either the image archival or the display station is much higher. This is because we are no longer limited by the acquisition device and can select suitable computers for the host, as well as for the archival and display stations. Table 1 (right columns) shows image transfer speed from the host
computer
to a display
station
in a clinical
environment.
For
example, the communication between the VAX (Maynard, MA) and the PC/AT computer (IBM, Poughkeepsie, NY) can reach about 100 kilobytes/sec. This means that this combination can transmit an MR, a CT, and a sonography image from the host computer to the display station in 2, 5, and 4 sec, respectively. The transfer rate can reach about 200 kilobytes/sec if both the host computer and the display station
RADIOLOGIC
AJA:155, July 1990
TABLE
1: Ethernet
Communication Acquisition
Point-to-Point
Device
Rate for Radiologic
185
Images Host Computer
to Host Computer
Protocol)
GE 9800 CT (Eclipse - Sun/Ethernet) FONAR MR (AT/Excellan -+AT/ExceIIan, FTP) ATL Sonography (XT/Excellan -+ VAX/Excellan, (AT/Excellan -+ VAX/Excellan, File transfer
COMMUNICATION
Speed in
Technique (Computers/Manufacturer,
a
Transfer
IMAGE
Computer
kilobytes/sec 14 30-40
VAX VAX
FTP)
14
Sun
FTP)
42
to Archival
Computer (Manufacturer)
Statio n and Display Speed in kilobytes/sec
Protocol
AT FTP#{176} (Excellan) AT Data Link (MICOM) Sun FTP (Sun)
40 100 180
protocol.
computer are SUNs. As the acquisition device is dictated by the manufacturer, the computer for the device cannot be changed. Thus, the speed from the acquisition device to the host computer cannot be improved unless the manufacturer upgrades
the acquisition-device
computer.
On the other
hand,
the host computer, the display station computer, and the archival computer can be selected by the user for high-speed communication purposes. From the data shown in Table 1 it is clear that the slowest communication link in a PACS module is from the acquisition device to the host computer.
Otherclusters
,
Image
Communication
Networks
The DR1 1-W interface allows the connection of only two computers, and Ethernet performance degrades drastically when more than two computers are connected (see Figure 4). Thus, both methods are good only for point-to-point image transfer and are not suitable for image networking. In order to have good throughput in image networking, use of the concept of clusters is important. A cluster can be loosely defined as a PACS module or a group of imaging components within which images are transmitted. Figure 2 shows the architecture of a cluster. A major component in a cluster is the hub. The function of a hub in an imaging network is to relay image information rapidly between sources and destinations. In this design, there are two hubs; one accepts images acquired from acquisition devices, the other accepts images sent by the host computer, and both accept images sent by other clusters. The image transfer rate from acquisi-
tion devices to the first hub is slow because of the older computers used in the acquisition devices. However, the image transfer in the display
rate from other station through
fast. The second
clusters to the host computer the second hub can be very
hub also is used to transmit
images
very
quickly to different display stations. Once the images are in a display station, they are stored in a local high-speed magnetic disk and can be retrieved and displayed rapidly. As we do not anticipate that manufacturers will change the computers in their acquisition devices, the image communication speed from the device to the host computer will remain slow. However, we can design high-speed communication with
state-of-the-art
technology
and a hub, between hubs, stations and image archival
Emerging
Other Clusters
Communication
We have some preliminary communication technologies
between
and between
the
host
a hub
computer
and display
stations. Technologies experience with three emerging using fiber optics as the corn-
Fig. 2.-Connectivity within a cluster. Image transfer rate from an acquisition device to hub is relatively slow because of processor and network controller used in acquisition device. However, transfer rate between all other components fast. OD = optical disk.
media.
munication
ture (Canstar
when
using
host adaptor
The first is a rooted-tree
Super
100 network,
and hub can be very
network
Toronto,
architec-
Canada).
The
Canstar nents-the
Super 100 network consists of two major compoconcentrator (or hub), with a 1 00 megabit/sec
transfer
rate, and the host-interface
unit, with a 10 megabit/
sec transfer rate (will be upgraded to a faster quarter, 1 990). The host-interface unit is inserted plane of the host computer and is connected to trator with duplex optical fiber. The concentrator
rate in first in the backthe concenallows up to
eight
design
connections.
concentrator
An example
connected
of the cluster
to four acquisition
devices,
is a
one host
computer, a second concentrator, and two display stations. Figure 3 shows the experimental setup of the Canstar network; we compared the performance of this network with that
of a standard
comparison.
Ethernet.
Although
Figure
4 shows
the host-interface
results
of one
unit is currently
lim-
ited to 1 0 megabits/sec, the Canstar performs much better than the Ethernet does. The second network is the fiber distributed data interface (FDDI) with a token ring architecture [4]. FDDI is used as the Ethernet; no computer program modification by the user is necessary. The specification for the speed of this communication method is 1 00 megabits/sec. Figure 5 shows some
preliminary Another
results with this communication new
high-speed
testing is a star topology
communication
architecture
network. network
(UltraNet,
we are
Ultra Network
Technologies, San Jose, CA) [5]. The maximum signaling speed of this network is 1 gigabit/sec. Figure 5 shows some
preliminary
results of a comparison
of this network
with other
186
HUANG
ET AL.
July 1990
AJR:155,
#{149}3 4000 .
3500
‘%
3000
2500
G)
2000
g
U.
1500
.
1000
-
E 500 -
IFig. 3.-A
rooted-tree
network
architecture
for image communication.
Ethernet
Concentrator is connected to four computers. Transfer rate of concentrator is 100 megabits/sec and that of host interface unit (H.l.u.) is 10 megabits/ sec. This experimental setup is to compare transfer speed between Canstar Super 100 network, Ethernet, and fiber distributed data interface (FDDI). E.l. = Ethernet interface.
____________________________________________ ‘3
600
_______________________ Ethernet:
-P1-
600 550
CanstarSuperloo:
-A--
500
550
_j
500
‘
450
450
their
performance
400
400
video
is most
350
350
the
300
300
in the image
C
250
250
an output
device
.2
oo
oo
However,
these
150
150
communication
100
100
may degrade
50
50
0
0
; -
g
-
c I-
0
1
2
3
4
5
6
8
7
of Communication
Process
parallel
in a clinical
useful
Ultranet
with
the
network.
technologies
The
patients,
DR-i
an image acquisition
broadband
the Ethernet
1 W are
best
device to another
suited
for
component
is used
for connecting
such
as the film laser
printer
to the network.
three
methods
in a PACS the image
are not adequate
network.
quality.
transfer
The
video
In the case
for image broadband
of Ethernet
rate is too slow.
Three
network architecture, the and the star topology-hold
communication results transmit
of radiologic
images.
show that the star a 2K pixel image
and
emerging
that use fiber optics as the communication
dia-the rooted tree token ring architecture,
experimental Ultranet can
and
DR-i 1 W also
DR-i 1 W, the image
rapid
environment.
for monitoring
transfer
connecting
for
Number
FDDI
Fig. 5.-Point-to-point comparison of performance of four communication methods: Ethernet, Canstar, fiber distributed data interface (FDDI), and ultraNet. A point-to-point model was used. Computers used were a SUN 3/160 and a SUN 3/260 running UNIX 4.0 operating system. Communication protocol used was Transmission Control Protocol/Internet Protocol. UltraNet is almost 10 times faster than Ethernet. 3100 kilobytes/sec can be translated to transmitting a 2K x 2K image in 1.3 sec.
g
____________________
Canstar Super 100
me-
FDDI with promise
Preliminary
topology with the in 1 .3 sec. If this
Fig. 4.-Performance of Ethernet and Canstar network when number of connections increases in a centralized model. In this model, one computer is used as server and all others are clients. Server sends out images (e.g.,
performance could be sustained throughout chiving and communication systems network,
central storage) and client requests images (e.g., a display station). Buffer size is 2 kilobytes, and measurement is from computer memory to com-
the requirement of image communication in a digital radiology department. We are in the process of designing an experiment
puter
memory.
kilobytes/sec
For Ethernet,
performance
to 60 kilobytes/sec
when
decreases
number
increases from one to seven. This result clearly Ethernet and Canstar as image communication connections becomes large.
drastically
of server-client
from 365
pairs
to optimize
the performance
of this network.
shows limitation of use of network when number of
REFERENCES 1 . Kangarloo
networks
the picture arit would satisfy
H, Boechat MI, Barbaric Z, et al. Two-year
clinical experience
the same test conditions. These results show that, for point-to-point communication, this star topology network can transmit a 2K x 2K pixel image in 1 .3 sec.
2. Lo SC, Taira AK, Mankovich NJ, Huang HK, Takeuchi H. Performance characteristics of a laser scanner and laser printer system for radiological
Conclusions
4. Templeton
We
used
under
have discussed image-transfer
our experience with methods for radiology
three commonly and measured
with a computed
radiography
system.
AJR 1988;151
:605-608
imaging. Comput Radiol 1986;10:227-237 3. Templeton AW, Owyer SJ Ill, Johnson JA, et al. An on-line digital image management system. Radiology 1984;1 52:321 -325 AW,
Cox
GG,
Owyer
SJ Ill. Oigital
image
management
works: current status. Radiology 1988;1 69: 193-1 99 Huang HK, Mankovich NJ, Taira AK, et al. PACS for radiological state of the art. Crlf Rev Diagn Imaging 1988;28:383-427
net-
images:
