**The Potential for Future Low-Cost Ka-Band Satellite Telemammography as
Demonstrated by NASA's Advanced Communications Technology Satellite
(ACTS)**

Robert J. Kerczewski, Gerald J. Chomos, Paul G. Mallasch,

Duc H. Ngo, Diepchi T. Tran, and Quang K. Tran

National Aeronautics and Space Administration

Lewis Research Center, Cleveland, Ohio

Brian A. Kachmar

Analex Corporation

Brookpark, Ohio

*ABSTRACT*

Telemammography using satellite communications can connect virtually any
patient in any location with mammography readers and breast cancer
experts located hundreds or thousands of miles away. Unfortunately,
satellite communications systems have historically been expensive and
difficult to use, making satellite telemammography an unaffordable
luxury. However, recent technological advances have resulted in the
capability of developing low cost, high capacity satellite
communications using the Ka-band frequency spectrum. The most important
of these advances have been tested and demonstrated by the National
Aeronautics and Space Administration's Advanced Communications
Technology Satellite (ACTS). By the year 2000, several companies are
expected to begin deploying regional or global satellite networks
offering low-cost services. Experiments with the ACTS satellite are
taking place to help develop and test technology which will allow
telemammography networks to be created with low-cost satellite links
reaching millions of currently underserved patients.

INTRODUCTION

The world is now often said to be in the "Information Age", with the
proliferation of computers and global telecommunications. From telephone
modems, to wireless local area computer networks, to the world wide web,
to cellular phones, to direct broadcast satellite TV, to
gigabit-per-second fiber-optic transmission, there is more digitally
encoded information moving more rapidly to more places than could have
ever been imagined just a decade ago. Yet, many remote and rural parts
of the US, as well as entire countries in the developing world, lack the
infrastructure for anything but the most primitive, low rate data
communications, if even that.

However, the requirement for significant and costly terrestrial
communications infrastructure in order to connect to the world, which is
beyond the economic reach of populations in developing areas, and beyond
economic justification for sparsely populated regions, is about to
disappear. More than \$40 billion worth of new regional and global
Ka-band satellite systems have been recently proposed which will offer
data transmission connectivity to every location on earth, requiring
only a small dish antenna of less than 1 meter in diameter. This latest
communications revolution has already begun with the launch of 17
satellites of the 66-satellite Iridium constellation, and will be in
full swing by the early 21^st^ century.

For those who want to make use of this revolutionary new capability with
applications now made practical by the low-cost and wide availability of
the proposed new systems, it now remains to develop the final enabling
technological links to connect their applications. This is where
satellite telemammography stands today.

This paper describes the state of the satellite communications
revolution and recent research efforts in satellite telemammography. In
particular, we will describe experiments being performed with NASA's
ACTS satellite, which has helped launch the satellite communications
revolution, and discuss how the telemammography application can best
take advantage of this revolution to help millions of patients reach the
mammography expertise they need.

NASA'S PIONEERING ACTS Ka-BAND SATELLITE PROGRAM

In September of 1993, NASA launched the Advanced Communications
Technology Satellite (ACTS), an experimental satellite designed to
develop and demonstrate advanced satellite communications technologies.
Primary among these technologies are the Ka-Band frequency range, never
before used for commercial applications, high-gain hopping antenna spot
beams, which provide high system capacity through frequency re-use and
allow very small earth station antennas, and on-board switching and
processing, which increase the quality of the communications link and
the flexibility of the satellite. During nearly four years of
experiments to date, over 100 organizations have worked with ACTS to
test and demonstrate technologies and applications such as science and
business networks, distance learning, telemedicine, supervisory control
and data acquisition, broadcast video, and aeronautical, maritime, and
land mobile communications^1,2^.

The advantages of the Ka-Band frequency spectrum include the ability to
generate higher antenna gains with smaller antenna sizes (compared to
lower frequency bands such as Ku- and C-Band), and the large currently
unused Ka-band spectrum, making high capacity systems possible. Chief
drawbacks of Ka-Band include the greater signal attenuation caused by
rain, compared to lower frequency bands, and the necessity of using
on-board switching and processing in order to take advantage of the
potential for enormous increases in system capacity. The ACTS
development and experiment program has been highly successful in
demonstrating that complex on-board processing hardware can be
successfully deployed in the severe space launch and operations
environment; to date the ACTS baseband processor continues to perform
far beyond even the most optimistic predictions. ACTS has also
demonstrated that the high gain spot beams, coupled with forward error
correction used during periods of rain attenuation, provide adequate
signal margin for a Ka-Band satellite to perform at extremely high
levels of availability.

PROPOSED Ka-BAND SYSTEMS AND THEIR POTENTIAL COST

The success of the ACTS Program has spurred an onslaught of proposed new
Ka-Band systems, both in the US and world wide, which make use of the
technologies developed and verified on-orbit by ACTS. The systems which
have filed with the US Federal Communications Commission (FCC) for
licenses to build and operate communications satellites include the low
earth orbit Teledesic system, as well as 13 geosynchronous satellites
and satellite networks, including GE Americom, Hughes Spaceway,
Lockheed-Martin Astrolink, Loral Cyberstar, and many others^3^. The FCC
has issued preliminary licenses to 12 of the proposed geosynchronous
systems as well as the Teledesic low earth orbit system. It remains to
be seen which of these will ultimately be deployed, but most experts
expect at least 3 or 4 to be financially viable. Most of the proposed
systems are being designed to be interoperable with terrestrial data
communications systems and will offer T1 (1.544 Mbps) and fractional T1
(384 kbps, 768 kbps) connectivity to mass consumer and business markets.
As a result, earth terminal and usage costs are expected to be very low.
In addition, most of the proposed systems are regional or global in
nature, resulting in worldwide interconnectivity requiring primarily the
satellite network, rather than a hodgepodge of various satellite and
terrestrial links as is currently required.

Table I presents the relevant U.S. proposed Ka-Band systems which have
been licensed by the Federal Communications Commission, and gives the
basic system specifications. Some system specifications may have
changed, but based upon the proposers' FCC filings, twelve licensed
systems will offer duplex data services at data rates significantly
higher than what is currently possible over telephone lines, a minimum
of 384 kbps. Ten of the twelve systems will offer T1 data rates, and all
will offer very small aperture terminals (VSAT) with antenna diameters
of 1-3 meters, or ultra-small aperture terminals (USAT) with antenna
diameters of 1 meter or less.

**TABLE I - Proposed U.S. Ka-Band Systems Offering Duplex T1-type Data
Services**

+------------+-----------+----+----------------+------------+--------+
| System     | Proposer  | O  | Number of      | Service    | A      |
|            |           | rb | Satellites,    | Data Rates | ntenna |
|            |           | it | Coverage       |            | Di     |
|            |           |    |                |            | ameter |
+------------+-----------+----+----------------+------------+--------+
| Teledesic  | Teledesic | L  | 288, Global    | Up to      | 0      |
|            | Corp.     | EO |                | T1/E1      | .3-1.5 |
|            |           |    |                |            | m      |
+------------+-----------+----+----------------+------------+--------+
| Echostar   | Echostar  | G  | 2, Regional    | T1/4 to T1 | 0.7-2  |
|            | Commu     | EO |                |            | m      |
|            | nications |    |                |            |        |
+------------+-----------+----+----------------+------------+--------+
| GE Star    | GE        | G  | 9, Global      | T1/4       | 0.75 m |
|            | Americom  | EO |                |            |        |
+------------+-----------+----+----------------+------------+--------+
| Galax      | Hughes    | G  | 20, Global     | T1 to 4T1  | 0.7m   |
| y/Spaceway | Commu     | EO |                |            |        |
|            | nications |    |                |            |        |
+------------+-----------+----+----------------+------------+--------+
| Ka-Star    | Ka-Star   | G  | 1, Regional    | T1/4 to T1 | 0.6-2  |
|            | Commu     | EO |                |            | m      |
|            | nications |    |                |            |        |
+------------+-----------+----+----------------+------------+--------+
| Astrolink  | Lockhe    | G  | 9, Global      | T1/4       | 0      |
|            | ed-Martin | EO |                |            | .6-1.2 |
|            |           |    |                |            | m      |
+------------+-----------+----+----------------+------------+--------+
| Cyberstar  | Space     | G  | 1-3,           | T1/4 to    | 0.7 m  |
|            | Syst      | EO | R              | 2T1        |        |
|            | ems/Loral |    | egional/Global |            |        |
+------------+-----------+----+----------------+------------+--------+
| Millenium  | Motorola  | G  | 4, Global      | T1/4 to T1 | 0.7 m  |
|            |           | EO |                |            |        |
+------------+-----------+----+----------------+------------+--------+
| NetSat 28  | NetSat 28 | G  | 1, Regional    | T1/4 to T1 | 1 m    |
|            |           | EO |                |            |        |
+------------+-----------+----+----------------+------------+--------+
| Orion      | Orion     | G  | 3,             | T1/4 to E1 | 0      |
|            | Network   | EO | R              |            | .7-1.2 |
|            | Systems   |    | egional/Global |            | m      |
+------------+-----------+----+----------------+------------+--------+
| PanAmSat   | PanAmSat  | G  | 2, Regional    | 56 kbps to | up to  |
|            |           | EO |                |            | 4 m    |
|            |           |    |                | 45 Mbps    |        |
+------------+-----------+----+----------------+------------+--------+

Notes: T1 is 1.544 Mbps; T1/4 is 384 kbps; 2T1 is 3.088 Mbps; 4T1 is
6.176 Mbps; E1 is 2.048 Mbps

NASA has been studying the emerging Ka-Band satellite market as well as
the proposed new Ka-Band satellite systems to assess the impact of the
ACTS Program and to determine future technology development
requirements. Satellite based services will be clearly most cost
effective for areas where comparable data rate terrestrial services are
unavailable^4^. Technology developments to be implemented in the
proposed new Ka-Band systems will allow substantial reductions in user
costs, creating an extremely competitive environment with terrestrial
services^5,6^. The proposed systems are scheduled for deployment
beginning around the year 2000. Although the companies involved are not
releasing their cost structures for competitive reasons, the general
consensus, based on analysis of system costs and projected revenues, is
that T1-rate connectivity will cost in the range of \$1-2 per minute,
with ultra-small aperture earth terminals (USATs), using antennas of one
meter or less in diameter, costing as low as \$1,000. A recent
NASA-sponsored study projects that continued improvements in technology
will lead to duplex E1-rate (2.048 Mbps) connectivity costing \$0.10 per
minute by the year 2010^7^.

SATELLITE TELEMAMMOGRAPHY AT T1 DATA RATES

The proposed new Ka-Band satellite systems will provide duplex data
services to a mass market, both requiring and ensuring that this will be
a low cost service. The global nature of coverage provided by satellites
means that any location can take advantage of this service, at the same
cost as any other location, regardless of the distance between the
transmitting and receiving sites. The application of satellites to
telemammography is a natural solution to the problem of providing
mammography screening services and direct contact with breast cancer
experts for millions of patients in remote, rural, and economically
depressed locations. The solution becomes much more practical with the
projected low cost and small earth station size being proposed in the
next generation systems. With current Ku-band satellite systems now
offering T1 rate VSAT connectivity, and the near-convergence on data
rates around T1 for the proposed new systems, T1 seems to be the
practical data rate of choice for low-cost satellite telemammography
systems of the future.

Researchers at General Electric Corporate Research and Development (GE
CR&D) and Massachusetts General Hospital (MGH) recognized the potential
for satellite telemammography at T1 data rates several years ago and
initiated research to enable T1-rate satellite telemammography. These
studies concentrated on DICOM-compatible mammography image transmission,
using a lossless image compression to improve transmission speed. The
transmission protocol issue was also studied; the normal internet-type
transmission protocol, TCP/IP (Transfer Control Protocol/Internet
Protocol) performs poorly over a long-delay transmission link, such as a
geosynchronous satellite link. The GE researchers modified the TCP/IP to
tolerate the delay and achieved 90% transmission efficiency, that is,
the average transmission rate was equal to 90% of T1. Over 100,000
mammography image data files have been transmitted over a Ku-band
T1-rate satellite link without error, taking an average transmission
time of about 3.5 minutes, which includes the effects of weather on the
Ku-Band link. This allows the implementation of a pipeline-mode
satellite telemammography screening process which will allow a patient
to have a mammography screening examination and receive the
remotely-interpreted results within about 40 minutes, the span of an
ordinary medical office visit^8,9,10^.

TECHNICAL ISSUES FOR T1-RATE SATELLITE TELEMAMMOGRAPHY

To take maximum advantage of the economy of next generation satellite
networks, methodologies for telemammography must be developed which
ensure rapid transmission of mammographic images at T1 data rates. This
will enable logistically practical satellite telemammography sessions,
in which images can be created at the screening site, transmitted to a
remote site for interpretation, and results returned to the patient
within the time frame of a normal patient clinical visit. Patients can
then receive screening results and act upon any follow-up
recommendations such as additional images or other diagnostic tests
during a single visit, reducing costs and improving convenience and
comfort of patients, especially those who must travel significant
distances for mammography screening services. In addition, reduction of
telemammography transmission time results in a direct cost savings in
satellite transmission charges. The GE CR&D/MGH studies have identified
and tested a pipeline methodology which combined with lossless image
compression enables this goal to be achieved. However, further
advancements in image compression will greatly improve the satellite
telemammography process and significantly reduce costs.

The current method of producing digital mammograms by digital scanning
of mammographic films will eventually be replaced by direct digital
mammography techniques. In either case, the resulting digital data file
can be 32-40 megabytes (Mb) or larger for each image^11^. At
conventional T1 transmission rates, this would require about 3.5 to 4
minutes per image; four images for a typical screening exam would take
14 to 16 minutes. In many cases, the four images from a previous year's
examination are used for comparison, resulting in a potential total
transmission time of 28 to 32 minutes. Lossless image compression
techniques can reduce the size of a mammography image file by about a
factor of about three without impacting the actual image information in
any way. Lossy image compression techniques can achieve substantially
higher compression ratios, however, some image information is lost.
Wavelet compression algorithms, discussed below, appear to be able to
achieve high compression ratios (at least 30:1) without removing image
information necessary for accurate interpretation and diagnosis,
although further study is needed to confirm this result for mammography.
An image compression ratio of 30:1 would result in a total transmission
time, including transmission of a previous exam (8 images total) of
about one minute. The resulting cost for transmission of the compressed
images, assuming the estimated costs for proposed new satellite systems
discussed above, is then \$1 to \$2, compared to \$16 to \$32 for 4
uncompressed images, or \$32 to \$64 for 8 uncompressed images. This is
a substantial reduction for remote rural locations where satellites are
the only alternative for telemammography, and makes satellite
telemammography cost competitive even in locations where there are other
data transmission alternatives. In addition, it should be noted that
digital data archiving costs can also be substantially reduced by using
image compression techniques. The use of 30:1 lossy compression results
in a factor of ten cost reduction compared to lossless compression. The
increase in transmission speed will also greatly ease the logistics of
transmitting mammography images and obtaining image interpretation
results within a single patient visit time frame.

Another significant area where technology development is necessary is in
the display of the digital mammography images. The largest
high-luminence display monitors can display 2,000 X 2,500 pixels, while
the image to be displayed can be as large as 4,000 X 6,000 pixels.
Although much research is being done, practical ways of displaying and
manipulating digital mammography images for fast and accurate image
interpretation have yet to be developed to the point of achieving wide
spread acceptance. However, this is a critical area for telemammography,
since all images transmitted will be in a digital format and the
alternative method of printing the digital images on film is costly,
time-consuming, and mitigates many of the advantages of digital
mammography.

A third important technology area for satellite telemammography is in
the interconnection of terrestrial systems and satellite links. We have
already discussed the transmission protocol problem and the GE CR&D/MGH
solution, which works very well. Additional incremental improvements are
possible which will allow increased data transmission efficiency over
the satellite link. The impact of satellite link errors, which are
usually more frequent than for terrestrial links, on the total
transmission time for mammography images, must be studied for Ka-band
links. The problems of interoperability for hybrid satellite/terrestrial
networks are also of interest because future telemammography networks
may very well include satellite links, terrestrial copper and fiber
lines, and hospital PACS networks.

Several aspects of these technical issues are being addressed in an ACTS
satellite experiment being jointly performed by the NASA Lewis Research
Center, the Cleveland Clinic Foundation (CCF), and the University of
Virginia (UVa), described below.

CLINICAL ISSUES FOR T1-RATE SATELLITE TELEMAMMOGRAPHY

Two primary clinical issues must be studied to enable T1-rate satellite
telemammography. One is the issue of diagnostic accuracy. Although
T1-rate satellite telemammography has been tested and simulated, there
has yet to be a study of the effects on diagnostic accuracy, especially
with the introduction of lossy image compression. It is essential to
test whether diagnostic accuracy can be maintained in a satellite
telemammography link. The image display, image compression, and
satellite link integrity issues all interact in potentially affecting
the overall diagnostic accuracy. The satellite link integrity issue can
be addressed by using transmission protocols and error correcting
techniques that insure that no digital errors occur in the transmitted
images. The image compression and display issues are difficult to
quantify, and therefore require extensive clinical studies.

The other important clinical issue is in the telemammography process
itself. The GE CR&D/MGH studies suggest that prompt-interpretation
mammography screening can be accomplished via satellites. The
NASA-CCF-UVa experiment is also oriented toward such a result. However,
to date no studies with actual patients have been attempted.

The NASA-CCF-UVa experiment, described below, is simulating the
end-to-end process as a necessary step toward studies with real
patients. It will also develop transmitted image databases which can be
used in future clinical studies of diagnostic accuracy.

APPLICATION OF WAVELET IMAGE COMPRESSION

A brief discussion of wavelet image compression is in order here, to
demonstrate the basis for applying this image compression technique to
satellite telemammography. Wavelets, a relatively new field of
mathematical theory and a specialized implementation of subband coding
is currently used by NASA Lewis to compress digital mammographic X-ray
images. Wavelets are sets of operations generated from a single function
using dilations and translations. Wavelet compression techniques provide
some of the best quality available today for transmitting and storing
very large volumes of superior quality, high compression ratio
performance digital imagery. For example, wavelets are being proposed
for consideration for the MPEG-4 video compression standard due to their
successful application in still-image and low rate video
compression^12^.

Wavelet compression works as a "transform-based compression." The first
step entails a transform that renders a sparse representation of the
image with no loss in data, wavelets consistently providing good sparse
representations for most image types. The transformed data's precision
is selectively reduced by a quantizer to attain the desired compression.
These quantized values cannot be restored to their original value as a
smaller number of bits now represent the transformed data; the higher
the compression ratio, the greater the quantization error. The last step
to reach the desired ratio is a lossless compression of the quantized
data using an entropy coder. Typically, standard run length encoding
(RLE) or Huffman coding techniques are used, but may be customized to
improve compression performance^13^. As discussed earlier, a compression
ratio of 30:1 can produce a dramatic cost reduction for image
transmission and storage, and can be justified based on positive
research results^14,\ 15^.

ACTS EXPERIMENTS IN T1-RATE SATELLITE TELEMAMMOGRAPHY

Several telemedicine experiments and demonstrations have been conducted
using ACTS, primarily by the Mayo Clinic. These experiments, included
speech pathology, teleradiology, medical education, and clinical
consulting between the Mayo Rochester site and remote rural sites in
Minnesota and South Dakota^16,17^. However, the demands of digital
mammography, particularly in terms of the resulting large data files,
and the complexity of the end-to-end telemammography process, lead to
the necessity of telemammography specific experiments.

In 1994, the University of Virginia and NASA Lewis Research Center
initiated research into satellite telemammography, joined soon
thereafter by the Cleveland Clinic Foundation. The purpose of this
research is to develop and demonstrate technologies and methods to
enable low-cost satellite telemammography using the enhanced
capabilities of the proposed new Ka-Band satellite systems. The
availability of NASA's ACTS satellite created an opportunity to
experiment with a satellite which was as technologically close to the
next generation of satellite systems as possible. The ACTS T1-VSAT (Very
Small Aperture Terminal) earth terminals and T1 network provide an
experimental prototype of future T1-rate regional and global satellite
systems^8^, and represent an ideal platform for the development and
demonstration of T1 satellite telemammography concepts. As ACTS is also
the only Ka-Band satellite in the Western hemisphere, it also provides
the only opportunity to study the impact of weather on Ka-band
transmission of data, data integrity being essential to telemammography.

Through a cooperative agreement, the NASA Lewis Research Center, the
Cleveland Clinic Foundation, and the University of Virginia, have
developed a pilot experiment to investigate the application of the ACTS
T1 satellite network to telemammography. T1-VSAT terminals located at
NASA Lewis, the Cleveland Clinic, and the University of Virginia are
being used to investigate several telemammography issues in an
experiment beginning in March, 1997 and scheduled to conclude in
October, 1997^19^. The experiment is called the Satellite
Telemammography Network Experiment (STN).

The STN Experiment has three parts. The first part focuses on
interoperability of the ACTS T1 satellite link with the terrestrial
portions of the telemammography network, and includes such issues as
data transmission protocol performance and satellite link performance.
The second part consists of simulating the end-to-end satellite
telemammography session, optimizing the process, and identifying
bottlenecks and possible solutions. The third part of the experiment
will collect a dataset of transmitted images for later clinical study.

Figure 1 shows the STN Experiment physical setup. Three ACTS T1-VSAT
earth stations are used. Earth Station #1 is located at NASA Lewis in
Cleveland, on the roof of the ACTS Master Control Facility, and is
connected to the telemammography workstation in another building via a
T1 line. Earth Stations #2 is also located at NASA Lewis. It is
connected to the telemammography workstation in the CCF Radiology
Department, about 15 miles away, through a commercial T1 transmission
line connected to a transfer workstation, and then through the Cleveland
Clinic's 10 Mbps local area network (LAN), rather than physically
locating the earth station at the Cleveland Clinic site. This was done
to reduce experiment costs, however the satellite network operates in
such a way that there is no operational difference, other than the need
to interconnect between satellite and commercial terrestrial resources.
An advantage is that it provides the opportunity to verify the
interoperability between satellite, commercial terrestrial, and LAN,
which will be important in future telemedicine networks. Earth Station
#8 is located at the University of Virginia in Charlottesville,
Virginia, and is directly connected to the telemammography workstation.

The physical configuration of the STN Experiment has been completed. All
of the links have been tested and mammography images have been
successfully transmitted between NASA Lewis and CCF, and between NASA
Lewis and UVa. We are currently using a NASA developed interface to
enable direct file transfers between the various telemammography
workstations. This method provides the full capacity of the T1 link to
be used, i.e., 100% link efficiency is obtained. However there is no
inherent error checking and correctly capability in this file transfer
technique, which is a built-in advantage of the TCP/IP protocol. We will
be including the TCP/IP protocol capability in the future, which will
also allow DICOM compatibility.

![](media/image1.emf){width="6.267361111111111in"
height="4.8180555555555555in"}

Figure 1 - Configuration of the Satellite Telemammography Network
Experiment

In research performed thus, commercial off-the-shelf software has been
utilized for wavelet compression of digital mammograms. NASA Lewis
applied a specialized image compression package designed specifically
for medical imaging. This software allowed efficient incorporation of
wavelet compression into existing applications and systems. Digital
X-rays with up to 16-bits of gray scale may be compressed to either a
user selectable compression ratio or to a user selectable distortion
level. The software also allows image compression solutions to
application developers and system integrators by providing linkable
libraries with a simple to use memory to memory application programming
interface.

RESULTS OF THE NASA-CCF-UVA SATELLITE TELEMAMMOGRAPHY NETWORK EXPERIMENT

The first part of the STN experiment is nearing completion. We have
verified the operation of the hybrid network, including the satellite
links and terrestrial portions. At the time of the preparation of this
paper, we have successfully transmitted over 500 images over the
network. No errors attributable to the communications links have
occurred. Transmission times of compressed images (30:1 wavelet
compression) are in the range of 5-7 seconds. It remains to implement
the TCP/IP protocol and demonstrate DICOM image transmission, and then
measure transmission times in the presence of rain.

The second part of the STN experiment, simulation of the satellite
telemammography session, will be started in late August. The
compression, transmission, and decompression of images has been tested
extensively. Image display software is being developed by the CCF, and
has been tested by radiologists. We are currently working to integrate
the entire process (compression, transmission, decompression, and
display). CCF is providing 4-image mammography cases which will be
transmitted from NASA Lewis to CCF and UVa, with NASA Lewis providing
the simulated role of remote mammography screening clinic. Some of the
simulated sessions will include live radiologists at the Cleveland
Clinic to perform image interpretation and diagnosis during the
simulated sessions.

The image compression and decompression has so far proven to be one of
the more interesting problems for telemammography. The wavelet
compression gives a qualitatively excellent result in that the
decompressed image cannot be distinguished from an image which was never
compressed, although actual clinical studies must be performed. The
compression algorithms can take some time to execute however, and this
can add considerably more time to the overall telemammography process.
Because it is a software-implemented algorithm, the image processing
time is dependent on the workstation hardware. Table II shows image
compression and decompression times for three different workstation
platforms. The processing time is more dependent on the RAM available to
the workstation than the CPU speed. However, even the Sun Ultra-2
requires 70 seconds for image compression, which is ten times the speed
for image transmission. A hardware implementation of the wavelet image
compression algorithms would likely be the ideal way to reduce
processing times to the range of a few seconds, but has yet to be
developed.

**TABLE II - Average Processing Times for Wavelet Image Compression and
Decompression**

  --------------- ------------ ---------- --------------- ----------------
  Workstation     CPU Speed    RAM        Compression     Decompression
  Platform                                Time            Time

  Sun Sparc-2     33 MHz       64 MB      16.5 minutes    7.0 minutes

  Sun Sparc-10    85 MHz       256 MB     3.5 minutes     1.5 minutes

  Sun Ultra-2     200 MHz      512 MB     70 seconds      22 seconds
  --------------- ------------ ---------- --------------- ----------------

The third part of the STN Experiment consists of compression and
transmission of approximately 60 mammography cases from NASA Lewis to
both UVa and CCF. These cases will be used for a pilot receiver
operating characteristic (ROC) clinical study of the diagnostic accuracy
of satellite telemammography. Up to 100 additional cases may be
transmitted in order to create a database large enough for a complete
study to be performed. No funding is available yet to perform the
complete study, but the images can be compressed, transmitted, and
stored for future study while the ACTS T1-VSAT earth stations are still
available.

CONCLUSIONS

Future T1-rate Ka-band satellite communications regional and global
networks will allow for low cost access to mammography and breast cancer
expertise for many millions of currently underserved patients. The first
such systems are projected to begin operation in the year 2000. However,
several technical and clinical issues must be addressed to enable
efficient and low-cost satellite telemammography. The technical issues
include satellite/terrestrial interoperability and data transmission
protocols, display of digital mammography images, and the application of
image compression. The clinical issues are the diagnostic accuracy of
satellite telemammography and the logistics of the end-to-end
telemammography process.

The interoperability issues have been addressed for the DICOM image
format, and additional work by NASA will optimize the efficiency of the
satellite link and overall data transmission for satellite
telemammography networks. Much additional research is required to
optimize the display of digital mammography images, however some display
software versions have been developed and are undergoing testing. In
image compression, wavelet algorithms appear to be the best current
method, and pending clinical testing should be able to provide a
compression ratio which will increase image transmission speed to
logistically practical levels while substantially reducing image
transmission and storage costs.

Extensive clinical testing will be required to verify that satellite
telemammography using lossy image compression will provide diagnostic
accuracy equivalent to current film-based (non-digital) methods. NASA,
CCF, and UVa are currently working to develop a database to enable such
testing. The optimization of the satellite telemammography process will
require improved implementations of the wavelet compression algorithms,
and perhaps a hardware implementation will ultimately be required. The
integration of the end-to-end satellite telemammography process is
currently being investigated, and will lead to the identification of
process bottlenecks and potential solutions. Software controlling the
entire process, including image management and archiving,
compression/decompression, image display, and patient and physician
scheduling where both are separated by large distances will also be
required.

The future for many millions of patients with no direct access to
mammography and breast cancer expertise is greatly improved due to the
imminent revolution in Ka-band satellite communications. Such access
will be enabled as researchers work to solve the technical and clinical
hurdles to convenient, efficient, and low cost satellite
telemammography.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge Dr. Samuel J. Dwyer III and Mr. David
Rigby of the University of Virginia, Department of Radiology, Dr.
Kimmerly A. Powell and Mr. Stefan Ganobcik of the Cleveland Clinic
Foundation Department of Biomedical Engineering, and Dr. William A.
Chilcote and Dr. David W. Piraino of the Cleveland Clinic Foundation,
Department of Radiology, Breast Imaging Section, for their contributions
to the development of the satellite telemammography research project.

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