Medical Applications Involving Virtual Environments

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Medical Applications Involving Virtual Environments

New Jersey Institute Of Technology

CIS 732

Eric Antonelli

December 17, 2001

Table of Contents





Historical perspective


Current Information Systems



rtual Environments

spaces systems


conferencing systems


Collaborative virtual environments




System examples


Telepresence systems



Collaborative augmented environments


tion and artificiality


Spatial representations



Medical Applications and Virtual Environments

Computer Integrated dexterous work


Medical Simulations



Current Surgical Aspects

guided surgery


Preoperative plann





Medical Education



Anatomical simulations


Surgical Simulations



Collaborative Medical Environments










As medicin
e enters the twenty
first century it is apparent that computer technology will
change the delivery of healthcare. In particular, the use of virtual environments represent
a future where virtual worlds mix with actual patient data to form an augmented real


system where complicated medical procedures are simplified leading to improved patient
care and reduced cost. There are five basic types of virtual reality categories these are
spaces, spatial video
conferencing, collaborative virtual environmen
telepresence systems and collaborative augmented environments. Each possesses unique
features and functions that allow for degrees of artificiality, spatiality and user
transportation. Medical education has made use of virtual environment simulations

train healthcare professionals using computer generated anatomical models thus allowing
for medical procedure training and the improvement of user hand eye coordination.
Virtual environments have also made advances possible in preoperative planning, i
guided surgery and in computer mediated communication as a means to enhance
collaboration and to change and extend the medical knowledge base.


The way in which healthcare is delivered is changing, that is there are forces within
ne and external to the field that are bringing about change. For instance, managed
care, a means of limiting the cost of medical treatment, initiated by the insurance industry
has pressured the healthcare industry to rethink doctor
patient interactions an
d medical

There have been major strides in the treatment disease, however, there are aspects of
medicine that have changed little since the time of the Egyptians or Greeks. Since the
time of Hippocratus, doctor
patient interaction has change
d little. There are still
interpersonal interactions allowing the physician to unravel a patient's aliment. On the
other hand, technological advances can be seen in all disciplines of medicine. These
include the development of antibiotics and vaccinatio
ns enabling many scourges of man
such as syphilis or smallpox to be controlled or eradicated. One of the major advances to
medicine as been the ability to non invasively peer inside the human body through the
use of imaging techniques including X rays of
dense tissues and magnetic resonance


imaging (MRI) or to understand physiological processes using positron emission
tomography (PET). Therefore, most advancement to medicine has been technological,
and health care professionals as well as society as a who
le have become dependent on
technology. Simply stated, the ability of technology and computing to further modernize
and change healthcare and its delivery is limitless.

At present the bulk of healthcare applications deal with information systems that c
mostly of administrative applications such as strategic decision
support, enterprise wide
networks or with clinical support applications. With clinical support applications, the
patient's medical record that contains temporal physiological informat
ion and treatment
modalities is the basis for the system. The incorporation and retention of patient
information using information technology such as distributed computer
based patient
record databases and clinical support systems enhances the overall qua
lity of care as well
as constraining medical costs.

"Most healthcare organizations and integrated delivery systems operate separate clinical
services information systems, particularly in areas such as pharmacy, clinical laboratory
and radiology" (1). The

laboratory information system is the most common type of
application system. Broadly speaking, these system are concerned with automation of
routine laboratory practices and fall into two categories, those involved in actually
automating the testing proc
ess itself and those involved in the processing of laboratory
data. Another category is the pharmacy information system. "This type of application
has been used to check prescriptions, monitor medications administered to patients as


well as monitoring dr
ug therapies for possible adverse reactions" (2). One of the more
advanced systems concerns the viewing and storage of radiological data. These systems
are used by radiologists to view and interpret actual patient data in the form of images.
These image
s have been acquired through radiological procedures such as X ray or
magnetic resonance imaging. It is this category of clinical application that is leading the
way in the use of virtual environments because it deals extensively with three
dimensional vo
lumes and the rendering of surfaces.

Virtual Environments

The dependence of our society on computer technology has lead to the blending of reality
with the silicon world. The use of virtual reality, a computer
generated illusion of three
dimensional space
, can be found in many aspects of business and science. The
technology itself are varied, what is specific about shared
space technology is that user
exploits spatial properties such as movement and containment in order to carry out a
particular task or f
or communication. For instance, virtual reality systems can be used as
a mode of simulation, where that simulation represents an aircraft control system, a
theater where poetry is read, or a three
dimensional sectioned human body. Most of
these systems a
re networked enabling multiple users to participate, manipulate objects
and share experiences within a proxy of reality. "More precisely, virtual environments
involve the merging of the numerically modeled space in the computer with the user's
l three
dimensional space" (3).


There are five basic types of virtual reality categories these include media
spaces, spatial
conferencing, collaborative virtual environments, telepresence systems and
collaborative augmented environments (4). Media
spaces are often used in offices and
are used to enhance the existing workspace. This type of system makes use of integrated
audio and visual technology. The basis for this category is the placement of various
cameras in a room so as to give the users di
fferent views of the activities of others.
spaces can be best described as social systems where individuals located at distant
sites may collaborate on long term projects. The drawbacks to these systems include
difficulty in sharing text documents,
the manipulation of objects and only modest
peripheral awareness.

Spatial video conferences can be considered an advancement to the media
category. This type of conferencing also makes use of integrated audio and visual
technology however it imp
roves on peripheral awareness and instead relies on gaze

direction. "Gaze
direction has been identified as a major element of conversation
management and helps in understanding the viewpoints of others when engaged in
collaborative work" (4). This princ
iple of gaze
direction is what separates this
technology from that of media
spaces. Many spatial video conferencing systems have
the ability to manipulate documents and make use of shared drawing surfaces. There are
limitations to this system as far as t
he number of individuals that may participate must
remain low and participates can not dynamically enter and leave the space.


Up to this point, both systems use mixed audio and visual technology as a proxy for face

face communication. The intention
of virtual reality is to bring individuals together
over great distances and could be best described as a means of reducing time involved in
travel. The above systems do not attempt to augment or replace reality with actual or
modified representations of
the real world. However, collaborative virtual environments
(CVE) attempt to do exactly that, the replacement of reality. Collaborative virtual
environments make use of networked virtual reality systems to support group work and
activities. The main con
cept behind the use of a virtual environment is the users are
replaced with alternate representations, or avatars. The users in the space can change
their locations and view perspectives, interact with others in the space as well as
manipulate data repres
ented as objects unlike other systems where data and
communications are located in separate windows. Additionally, collaborative virtual
environments aim to provide an integrated, explicit, and persistent context for
cooperation that combines both the part
icipants and their information into a common
display space (4, 5). Because of these reasons the category of virtual reality lends itself
to certain medical situations, especially surgical applications.

What remains similar in many virtual reality systems

is the creation and utilization of
avatars. Avatars, derived from the Indian word for one regarded as an incarnation, serve
as a physical proxy for the user. The avatars fall into several categories based on
appearance. Some of the more common avatar c
lasses include animal representations,
cartoon characters and abstract avatars which may have shocking or unusual form. The
users of these types of avatars usually wish to remain anonymous another intent is that


they may attempt to adopt some or all of th
e character's qualities. "Therefore, in many
cases there is a psychological relationship between the user and their avatar" (6). Some
users who are not concerned with anonymity prefer to utilize actual user images and are
known as real
face avatars.

virtual environments people may communicate and setup social spaces through the
utilization of avatar proxies. "As with humans, avatars have defined areas of perception
the closest being the manipulation range where objects can be moved or inspected, next

the audio perception range and finally the visual perception range" (7). Communication
in this three
dimensional environment can take place using text messaging or voice
additionally, this communication must take place synchronously (8). Voice is the

preferred method of communication because it is the most natural form associated with
human behavior (9). When voice communication is used facial animation can be added
to the avatar. So the character can visually project emotion with a smile or a frown

thus adding to the realism of the experience.

Two examples of sophisticated collaborative virtual environments include MASSIVE
(Model, Architecture and System for Spatial Interaction in Virtual Environment). Other
systems include DIVE (Distributed I
nteractive Virtual Environment) and the large
military system known as NPSNET. "MASSIVE allows for the complete implementation
of spatial model of interactions and includes network
supported communication of up to
twenty users" (10). It also possesse
s an advanced interaction model that allows users to


generate and manipulate objects within the virtual world. The most current version of the
system strives for data consistency and the ability to build or structure worlds.

World structuring in as syste
m such as MASSIVE is based on the concept of locales.
This is a technique, which allow for the formation of appropriately sized "chucks" of
information. Locales provide a means of structuring and composing a virtual world
according to spatial characteris
tics. The locale is the fundamental unit of the virtual
world, it could represent a distinct region such as a room or surgical suite (7, 10, 11).
The locale may also contain virtual objects as varied as a table, a wall or a surgeon's
scalpel. With the l
ocale representation of space there is no global coordinate system
instead each locale contains its own independent coordinate system. The complete
virtual world and associated objects are linked together using inter
locale links.

Many examples of low co
st virtual reality systems can be found on the World Wide Web.
Two of most familiar are Activeworld and Onlive Traveler; however, both differ in their
metaphors. Activeworld is intended as an actual replacement of civilization with towns,
streets and bui
ldings, with the system operating in a modified browser. Whereas, Onlive
Traveler is a communication based system that requires a downloadable client (Figure 1).

Still other systems are based on open technologies such as virtual reality modeling
e (VRML) and open GL. This is the case with the DeepMatrix system, which is a
web based three
dimensional multi
user system. The significance of this system is that it
focuses on e
commerce and it is the first system that utilizes Java on all levels to a


full platform independence on client as well as the server side. Therefore, as a system, it
is highly applicable in areas that rely on high user accessibility as is required in B2C e

Another category of virtual environments is teleprese
nce systems. These systems allow
users to experience and manipulate objects in remote physical space through computer
and communication technology (4, 11). Telepresence applications typically involve the
creation of a physical proxy of the remote person
in the form of a robot which has
cameras attached to it and which can move through the physical environment (4). This
technology also provides the same immersion as found in the collaborative virtual

The final category of virtual environment
s is what is termed the collaborative augmented
environment. This type of system attempts to mix virtual environments and reality
therefore they are called shared
space systems. "The advantage of this virtual
environment is the ability to overlay graphica
l objects onto a real world scene with some
degree of dynamic registration between the two" (4). As an example, in shared
systems, multiple users may manipulate a virtual object from across a physical space (4).
An alternate approach to the use of m
ixed spaces includes the ability to augment real
objects with specific digital information to enhance the user interaction with the physical
object. Peripheral information such as sound and light further add to the enhancement.
The long
term goal of coll
aborative augmented environments is to provide the natural
integration of digital and physical information.


When dealing with systems utilizing telepresence, collaborative virtual environments or
spaced environments all must include dimensions of a
rtificiality transportation,
and spatiality. All the above must work together at various levels to provide some degree
of user immersion. Transportation is the dimension that deals with the extent to which a
group of users and objects leave behind their
local space and enter a new remote or
virtual space in order to communicate with others or to perform set of tasks. The degree
of transportation from the real world can be little to as much as totally immersion as is
the case with a CAVE, a room system wh
ose surfaces project multiple synchronized
images to completely simulate abstract reality. At an intermediate levels of
transportation participants find split levels of involvement, where users attend to aspects
of both their immediate physical environmen
t and that of virtual reality (4).

Artificiality is the dimension concerned with the degree to which a virtual space is either
synthetic or based on the physical world. With synthetic artificiality, deals with spaces
that are totally independent or dev
oid of human external reality and synthetic information
may include electronic synthesized sounds and three
dimensional geometric
representations. Actual physical information may be represented as an image of a face or
body as well as electronic documents

The last dimension that concerns shared
space virtual environments is the concept of
spatiality. The fundamental attributes of this dimension include containment, topology,
distance, orientation and movement (4, 10). Of the above attributes movement o


participants is considered necessary and lends itself to the development of distance and
orientation. Movement also allows for the exploration of digital spaces and also plays a
role in dynamic group formation (5).

Medical Applications and Virtual Envi

Medicine is in a state of transition whereby virtual environments and scientific
visualization has furthered patient care and medical education. Virtual reality is being
used to enhance medicine in four main areas: education and training, medical

planning and casualty care, virtual prototyping and rehabilitation and psychiatric therapy
(12). The use of virtual environments is being applied to a wide range of medical
disciplines, including remote and local surgery, surgical planning as we
ll as treatment of
phobias and other causes of psychological distress. It is also used for the visualization of
data intensive medical record set.

Today, surgery remains mostly a visual and manual discipline. What this amount to is
that many aspects of

medicine require dexterous work, or the ability match hand
coordination with the specific task at hand. Therefore, the use of virtual environments,
especial those involved in actual surgical procedures or training in virtual simulators must
mimic phys
ical interactions with instruments, eye coordination and medical planning.

The concept that medicine is a dexterous task is central to the development of virtual
medical environments. These systems must allow for delicate work of actual surgical
tations that can be performed for hours on end without strain. Such systems


already exist for brain and heart surgery, certain minimally invasive techniques and
craniofacial repair. "Therefore, the approach of medical simulations is to bring the
modeled work object such as a three
dimensional medical image, a scalpel,
cutting tool or laser into the user's natural work volume" (13). Additionally, as a surgeon
performs dexterous work he is usually within one foot or so of his work, this affords goo
depth perception and reduces arm strain. So when one attempts to develop system to
replace reality the above concerns must be taken into account.

The key to dexterity is hand eye coordination. "In the abstract, a mouse cursor seems far
better than a

finger, pointing more precisely at a point in the monitor screen" (13).
However, in three
dimensional systems stereo vision as well as the position of the user's
body is of importance. Therefore, it is both the physical state of the user's body, the
ition of the head and the arms as well as vision that must come together in the
accomplish a given task.

When merging the user's workspace with that of the computers it is of importance that the
user must be able to perceive an objects relative location a
nd to have some sort of tactile
sense for the object. The sense of touching can be accomplished through the use of a
generalized tool handle this is what the user actually manipulates. The virtual tool
becomes the "working end" and it may portray various

surgical instruments such as a
scalpel blade or a laser. "It is generally understood that if the user can see the tool and
feel the tool then the perception matches" (13).


Medical virtual environments augment vision and dexterity in various ways. The

common setup for these types of systems makes use of a virtual workbench metaphor.
The virtual workbench is composed of a mix of physical items and computer
objects (Figure 2). The physical items include a tool handle or some other type o
f input
device. The mouse is a poor metaphor for a scalpel handle and must be replaced using
specialized devices with electro
magnetic and mechanically linked three
input sensors. Other equipment that is required for realism and to match user

includes stereo glasses, high
resolution monitor and workstation (13, 14).

Current Surgical Aspects

Until recently, it has been considered by many physicians and laymen alike that surgery
was extreme, exploratory in some instances, and fraug
ht with complications due to the
lack exact patient data. However, with the advent of computer technology and
specifically the use of this technology coupled to imaging systems has expanded and
enhance medical procedures.

Today, image
guided surgery ha
s been used to help guide surgeons to targets during
actual operations. In this method virtual reality is augmented with actual patient data in
the form of surface and volume renderings as well as the simulation of tissue behavior.
This form of augmented

virtual reality is used in conjunction with an interventional
imaging system and surgical suite in order to perform minimally invasive techniques
leading to fewer infections and more rapid recovery (14). The system makes use of


dynamic visual feedback us
ed to create intraoperative three
dimensional representations
as opposed to standard radiography or two
dimensional volume reconstructions

(Figure 3).

As with most disciplines, surgery requires practice. This may present itself even to a
skilled practit
ioner due to the complications of unique cases. Virtual environments have
been used under these circumstances as a means of preoperative planning. Preoperative
planning allow the surgeon to review a particular case in a virtual setting making use of
al patient data. This then allows for the view and implement of alternative
procedures. Since this occurs prior to patient involvement, costs, time and hopefully
complications are reduced.

Telemedicine is the application of computer and communication
technologies to support
the facilitation of healthcare to patients at remote locations. These types of systems have
been used with much success when assisting in remote operations. This usually takes the
form of a medical specialist at one site and a train
ed general practitioner or surgeon by
the patient's side. Telemedicine requires audio and video equipment, fiber optics,
interfaces to surgical instrumentation as well as the ability to transmit radiological
information. Telemedicine has yet to integrate
virtual reality.

Although telemedicine does not support the virtual environment, it has set a milestone for
the penetration into the medical community. In particular, these systems have been
incorporated into military usage. An example of this technolog
y is the Joint Medical



Telemedicine or JMO
T (15). This system was designed to transmit and
receive near real time, far
forward medical data under battlefield conditions. "It makes
use of digital scopes, digital blood and urine laboratories,

physiological monitors, digital
radiography and ultrasound" (15). The use of medical information technology in austere
theaters of operations was implemented by the military to expand resources and to reduce
medical personnel to enemy fire.

Medical Ed

The field of medical education was the first medical discipline to exploit the power of
virtual environments (3). The use of virtual environments provides a unique education
resource for the study of anatomical structure and medical procedures. On
e of the central
issues in medical education is to provide a realistic sense of the inter
relation of
anatomical structures in three
dimensional space. Using virtual environments, the student
of medicine can repeatedly explore the anatomical structures of
interest in both normal
and diseased states. The user of the system may then visualize various anatomical
features in exploded view for better comprehension of complex morphologies and the
underlying physiological processes. The above becomes impossible a
nd largely
unethically with human subjects and is economically unrealistic or cumbersome at the
laboratory level or with cadavers.


Another advantage of using virtual reality systems for medical education is that the
demonstration and exploration of variou
s anatomical systems can be combined with other
educational resources (Figure 4). For instance, a predefined medical instructional
exercise pertaining to a specific anatomical structure or organ can be created with expert
voice annotations as a means of
guidance. The student may then further explore using the
above exercise and then use the simulation as a study guide for a possible class
examination. The value of virtual environment simulators is in the teaching of cognitive
as well as manual skills. T
hat is individuals who practice the discipline of surgery must
become dexterous and continually practice hand
eye coordination.

The Medical College of Georgia and the Georgia Institute of Technology have developed
an example of a working medical surgery

simulation. The stimulator enables ophthalmic
surgeons to practice delicate procedures using a virtual eye a stereoscopic microscope
and force feedback surgical instrument that continuously report orientation and position.
The system functionality is mo
difiable and allows for the substitution of instruments and
evaluation of training record and playback functions. The virtual component of the
simulator is the computer
generated eye and the interaction of the eye with the surgical
instrumentation. The e
ye, itself, is represented by a series of deformable three
dimensional models. The model represents various anatomical structures such as the
sclera, iris, zonules and retina. All the above tissues are textured with actual human eye
images. As in the li
ving state, both the lens and the cornea were modeled as semi
transparent objects. When the virtual eye makes contact with an associated surgical


instrument, the eye deforms and a proportional amount of tactile feedback is registered by
the user.

This e
xample serves to explain the basis of hybrid model systems, which are currently in
wide use. The virtual objects, especially smooth surface organs and related structures are
currently composed of polygonal surfaces using the two
dimensional textures or im
"mapped" onto them. This can produce a realistic effect as far as representing actual
tissue; however inaccuracies can be ascertained when object are viewed from various
angles (15).

Presently, evaluation and testing protocols are being developed to
determine how the
virtual environment simulators can contribute to surgical education. For example, it must
be demonstrated that there is a measurable improvement through outcome analysis. In
other words, there must be an improvement in a relevant dimens
ion such as shorter
surgical time, shorter training periods to train learners, lower the complication rate or
simply lower overall costs.

Training of doctors in the surgical theater itself brings increased risk to the patient due to
inexperience and long
er surgical procedures. The result is to cause an increase stress on
the already constrained healthcare system because new surgical procedures require
training by other doctors, who are already inundated by their own clinical schedules. The
continued train
ing of healthcare professionals regarding new procedures in rural or
remote settings is difficult and surgical training opportunities present themselves on a


case basis (1, 2). The best solution to this problem depends on the development
and accept
ance of medical training simulators that offer sufficient transportation and
artificiality. This enables a surgeon a degree of "practice time", under computer control,
to perfect ones technique as part of a preoperative planning method. This concept of
recise computer monitored training stems from the analogy of flight simulator training
where a pilot learns aircraft instrumentation and flight characteristics prior to real
flight responsibilities.

Collaborative Medical Environments

As in other pr
ofessions, the medical community participates in conferences and other
forms of collaboration. Meetings may also involve professional or technical
consultations regarding patient cases leading to improved care. The normal practice has
included the tradit
ional face
face meetings or phone communication. "The use of
computer media communication and in particular collaborative virtual environments can
be used to enhance collaboration and to change and extend the medical knowledge base"

Within a c
ollaborative environment or workspace several issues regarding user
descriptions must be recognized. The most apparent is a sense of location within the
virtual world, next is identity, which leads to the ability to distinguish other participates
and to r
etain individual identifies over time. Since much of human communication is


visual other issues such as facial expressions and gestures need to be considered when
using virtual environments in computer mediated communication (6).

The conference has pla
yed a long
standing tradition in professional circles, playing a
central role in informal and formal knowledge building and social network maintenance
(). It has been through the use of networked computer technology that has led to changes
in the meeting
planning and social experiences of the participants. In particular, on line
computer conferences show a great promise for changing methods of collaboration. This
technology has the ability to reduce logistics and other organizational factors as well as
uickly representing data in various formats. However, more importantly the peer
collaboration can include a larger pool of users thereby adding content and also allowing
for horizontal communication (16).

A major problem that needs to be addressed in usi
ng virtual environments as a means of
computer mediated communication are the problems of coping with inconsistencies due
to network delays in collaborative virtual environments. The cause of these delays may
be attributed to low bandwidth, network distan
ce or geographical distance. Since these
shared environments involve participants are remote sites any delay in communication
may potentially break the consistency between users and their replicated environments (5,
16). The issue of a temporal delay caus
ing latency in voice data or decrease object
response would be considered a nuisance in normal computer media communication
however, some medical collaboration may be simultaneous with patient procedures. The


use of collaborative environment in life
cal systems therefore necessitates that
latency be reduced through dedicated high
speed connections.


The widespread use of computer technology in our society has led to changes in many
aspects of business, science and education. This has le
d to the development and
exploration new problems, changed workflow, altered data representations and made
available vast amounts of information. Furthermore, the ability of computer systems to
present information as either descriptive or prescriptive has

empowered individuals and
generated social ramifications (18).

The next step in enabling computer system users is the ability to replace reality with a
virtual environment. That is, the incorporation of a shared
space where users can
collaborate, inves
tigate complex objects, or train for complex tasks. There are five basic
types of virtual reality categories these are media
spaces, spatial video
collaborative virtual environments, telepresence systems and collaborative augmented
ts. Each has specific attributes that have been tailored based on task or on an
aspect of computer mediated communication.

At present, medical virtual environments deal mainly with the presentation of gross
anatomical structures for educational purposes
or for the augmentation of surgical
techniques using intraoperative three
dimensional imaging. In these systems, real
patient data is incorporated and then used for preoperative planning and medical training.


Telemedicine is the application of compu
ter and communication technologies to support
the facilitation to healthcare to patients at remote locations has yet to incorporate virtual

The delivery of healthcare is a team effort with many individuals possessing various
skills contributing t
o successful patient outcomes. However, the ability to use virtual
environments in team training has not been explored up to this point. For instance, a
surgical team is a group generally consisting of a surgeon, an anesthetist and one or more
s. The emphasis in the development of virtual reality systems so far has
emphasized either education of a signal member or the presentation of patient data.
Future work needs to include virtual environments for the training of entire teams
allowing for c

There are challenges to be overcome in order to augment and further increase the realism
of virtual environments. For instance some medical disorders present themselves to the
healthcare professional as a malodor or as frictional sounds a
s is the case with various
joint abnormalities. At this time, there is no technology incorporated into these systems
to simulate odor or sound feedback. Additionally, force feedback of instruments is crude
and in particular tactile feedback especially of

soft tissues is lacking.

The ultimate goal of medicine is to enter a new era of understanding of disease at the
molecular level. Computer technology along with molecular techniques has enabled
researchers to sequence the entire human genome. As the b
iochemical and genetic causes


of basic human disorders are elucidated new individually tailored therapeutics will be
developed. In the future what will be needed is the ability to link genetic database
information, real
time patient pathology at the micro
scopic level coupled with augmented
virtual reality treatment systems used by expert teams as a means of collaboration and
ultimately successful patient treatment.


1) Charles Austin and Stuart Boxerman (1997)
Information Systems for Hea
lth Services


edition. Health Administration Press. Chicago Illinois.

2) McGlynn, E., Damberg, C., Kerr, E. and Brook, R. (1998)
Health Information
. Rand Publications.Washington, D.C.

3) Zajtchuk, R. and Satava, R. (September
1997) Medical applications of virtual reality
Communications of the ACM Volume 40. Issue 9. 63

4) Benford, S., Greenhalgh, C., Reynard, G., Brown, C., and Koleva, B. (1998)
Understanding and constructing shared spaces with mixed
reality boundries. AC
Transactions on computer
human interactions. Vol. 5. No. 3. 185

5) Jackson, R., Taylor, W., and Winn, W. (February 1999) Peer collaboration and virtual
environments. Proceedings of the 1999 ACM symposium on Applied computing. 121

6) Craven,
M., Benford, S., Greenhalgh, C., Wyver, J., Brazier, C.J., Oldroyd, A. and
Regan, T. (September 2000) Ages of avatar. ACM Proceedings of the third international
conference on collaborative virtual environments. 189


7) Saar, K. (February 1999) VIRTUS
. ACM Proceedings of the fourth symposium on the
virtual reality modeling language. 141


8) Greenhalgh, C., Purbrick, J., Benford, S., Craven, M., Drozd, A. and Taylor, I.
(October 2000) Temporal links. Proceedings of the 8th ACM international confer

9) Vaghi, I., Greenhalgh, C., and Benford, S. (December 1999) Coping with
inconsistency due to network delays in collaborative virtual environments

Proceedings of the ACM symposium on virtual reality software and technology. 42

10) Gre
enhalgh, C., Purbrick, J., and Snowdon, D. (September 2000) Inside MASSIVE
3. ACM Proceedings of the third international conference on collaborative virtual
environments. 119

11) Kaplan, S. and Fitzpatrick, G. (August 1997) Designing support for remo
te intensive
care telehealth using the locales framework. ACM Proceedings of the conference on
Designing interactive systems. 173

11) Tanriverdi, H. and Iacono, C.S. (December 2000) Knowledge barriers to diffusion of
telemedicine. ACM Proceedings of
the international conference on Information systems.


12) Lowery, J. (December 1998) Getting started in simulation in healthcare

ACM Proceedings of 1998 conference on winter simulation. 31

13) Poston, T. and Serra, L. (May 1996) Dextrous vir
tual work

Communications of the ACM Volume 39 Issue 5. 37

14) Yoo, T. and Rheingans, P. (1999) Digital design of a surgical simulator for
interventional MR imaging ACM Proceedings of the conference on Visualization. 393

15) Rodger, J. and Pen
dharkar, P. (2000) Using telemedicine in the Department of
Defense. Communications of the ACM Volume 43. Issue 3. 19

16) Jones, M (September 2000) collaborative virtual conferences

ACM Proceedings of the third international conference on collaborativ
e virtual
environments. 19


17) Benford, S., Greenhalgh, C., Craven, M., Walker, G., Regan, T., Morphett, J. and
Wyver, J. (December 2000) Inhabited television. ACM Transactions on Computer
Human Interaction (TOCHI) Volume 7 Issue 4.

18) Turoff, M
. (September 1997) Virtuality. Communications of the ACM Volume 40.
Issue 9. 38