Page 433 - Biomedical Engineering and Design Handbook Volume 2, Applications

COMPUTER-INTEGRATED SURGERY AND MEDICAL ROBOTICS 411

instrument and target anatomy. One common approach is to display a circle or ellipse representing
likely registration uncertainty, but significant advances are needed both in the modeling of such
errors and in the human factors associated with their presentation.
One limitation of video overlay systems is the limited resolution of current-generation video
cameras. This is especially important in microsurgical applications, where the structures being operated
on are very small, or in applications requiring very good color discrimination. Consequently, there is
also interest in so-called optical overlay methods in which graphic information is projected into the
62
optical path of a microscope or presented on a half-silvered mirror 63,64 so that it appears to be super-
imposed on the surgeon’s field of view in appropriate alignment. The design considerations for these
systems are generally similar to those for systems using video displays, but the registration problems
tend to be even more demanding and the brightness of the display can also be a problem.
All of the common interfaces (mice, joysticks, touch screens, push buttons, foot switches, etc.)
used for interactive computer applications are used to provide input for surgical systems as well. For
preoperative planning applications, these devices are identical to those used elsewhere. For intraop-
erative use, sterility, electrical safety, and ergonomic considerations may require some design mod-
48
ifications. For example, the LARS robot repackaged the pointing device from an IBM Thinkpad ®
computer into a three-button “mouse” clipped onto the surgeon’s instruments. As another example,
a tracked stereotactic wand has been used to provide a configurable “push button” interface in which
functions are selected by tapping the tip of the pointer onto a sterilized template. 65
Surgeons routinely use voice to communicate with operating room personnel. Further, their hands
(and feet) are frequently rather busy. Accordingly, there has long been interest in using voice as a
two-way command and control system for surgical applications. 35,48,66–68
Force and haptic feedback is often important for surgical simulation 68,69 and telesurgery
applications. 19,21,70–73 Again, the technical issues involved are similar to those for other virtual-reality
and telerobotics applications, with the added requirement of maintaining sterility and electrical safety.

14.3.8 Systems
Computer-integrated surgery is highly systems oriented. Well-engineered systems are crucial both
for use in the operating room and to provide context for the development of new capabilities. Safety,
usability and maintainability, and interoperability are the most important considerations. We discuss
them briefly next.
Safety is very important. Surgical system designs must be both safe, in the sense that system fail-
ures will not result in significant harm to the patient and the system will be perceived to be safe. Good
system design typically will require careful analysis of potential failure sources and the likely conse-
quences of failures. This analysis is application dependent, and it is important to remember that care
must be taken to ensure that system component failures will not go undetected and that the system will
remain under control at all times. Wherever possible, redundant hardware and software subsystems
should be provided and cross-checked against each other. Rigorous software engineering practices
must be maintained at all stages. Discussion of general safety issues for surgical robots may be found
in Refs. 22 and 74–77. An excellent case study of what can happen when good practices are ignored
may be found in Ref. 78, which discusses a series of accidents involving a radiation therapy machine.
Many discussions of safety in CIS systems tend to focus on the potential of active devices such
as robots or radiation therapy machines to do great harm if they operate in an uncontrolled manner.
This is a valid concern, but it should not be forgotten that such “runaway” situations are not usually
the main safety challenge in CIS systems. For example, both robotic and navigation assistance sys-
tems rely on the accuracy of registration methods and the ability to detect and/or compensate for
patient motion to ensure that the surgical instruments do not stray from the targeted anatomy. A
human surgeon acting on incorrect information can place a screw into the spinal cord just as easily
as a robot can. This means that analysis software and sensing must be analyzed just as carefully as
motion control. Surgeons must be fully aware of the limitations as well as the capabilities of their
systems and system design should include appropriate means for surgeons’ “sanity checking” of sur-
gical actions.