Page 400 - Biomedical Engineering and Design Handbook Volume 2, Applications

378 SURGERY

Display of simulated
Simulated on computer surgical scene

Haptic
feedback

Control of the
surgical instrument

FIGURE 13.1 Surgical training simulator concept.

an interactive three-dimensional simulation milieu in which the surgeon, using haptic interfaces, can
manipulate, cut, or suture dynamically and geometrically correct models of organs and tissues sim-
ulated on a computer (Fig. 13.1). Development of a virtual environment-based simulator for surgi-
cal training is analogous to the flight simulators that are currently used for pilot training. Virtual
environments provide a setting in which there is no risk to patients and, therefore, less stress. They
are interactive and three-dimensional in contrast to books, and they are relatively inexpensive com-
pared to training in the operating room or animal labs. It also provides the trainees with the chance
for multiple and repeatable trials. Virtual environments also give a unique advantage as it is possible
to generate arbitrary anatomies and pathologies with which the surgeons can be trained for cases that
they will encounter only rarely during their entire career, but nonetheless must be capable of doing.
Virtual environment-based surgical simulation also permits standardization of training and accredi-
tation in surgery.

13.1 VIRTUAL ENVIRONMENTS: A GENERAL PERSPECTIVE

Our sense of physical reality is a construction from the symbolic, geometric, and dynamic informa-
tion directly presented to our senses. A large part of our sense of physical reality is a consequence
of internal processing, including our prior experiences, rather than something that is developed only
from the immediate sensory information we receive. The sense of reality can therefore be induced
by presenting artificially synthesized sensory stimuli to realize the sensory and motor consequences
1
of a real environment. A virtual environment is a real or an imagined environment that is simulated
on a computer and experienced by the user through artificially synthesized sensory stimuli. It is typ-
ically in the form of an interactive three-dimensional world created through computer graphics,
audio, and haptics.
Milgram 2,3 described the taxonomy of real, virtual, and mixed environments as a continuum. Real
and completely virtual environments form the ends of the continuum. In between these, there is a
variety of forms of mixed reality, where real and virtual environments mixed at different levels. In
an immersive virtual environment, the user is fully immersed in a completely computer-generated
artificial, three-dimensional world, where the goal is to achieve the user feel “present” within this
artificial world. In a nonimmersive virtual environment, the user remains as an observer working on
the artificial world from outside. Augmented reality is a form of mixed reality where perception is
predominantly from the real environments, while synthetic computer-generated data are overlaid to