Page 414 - Biomedical Engineering and Design Handbook Volume 2, Applications

392 SURGERY

CIS systems are instances of an emerging paradigm of human-computer cooperation to accom-
plish delicate and difficult tasks. In some cases, the surgeon will supervise a CIS system that carries
out a specific treatment step such as inserting a needle or machining bone. In other cases, the CIS
system will provide information to assist the surgeon’s manual execution of a task, for example,
through the use of computer graphic overlays on the surgeon’s field of view. In some cases, these
modes will be combined.
From an engineering systems perspective, the objective can be defined in terms of two inter-
related concepts:

• Surgical CAD/CAM systems transform preoperative images and other information into models of
individual patients, assist clinicians in developing an optimized interventional plan, register this
preoperative data to the patient in the operating room, and then use a variety of appropriate
means, such as robots and image overlay displays, to assist in the accurate execution of the
planned interventions.
• Surgical assistant systems work interactively with surgeons to extend human capabilities in car-
rying out a variety of surgical tasks. They have many of the same components as surgical
CAD/CAM systems, but the emphasis is on intraoperative decision support and skill enhance-
ment, rather than careful preplanning and accurate execution.
Two other concepts related to CIS are surgical total information management (STIM) and surgi-
cal total quality management (STQM), which are analogous to total information management and
total quality management in manufacturing enterprises.
Table 14.1 summarizes some of the factors that must be considered in assessing the value of CIS
systems with respect to their potential application. Although the main focus of this chapter is the
technology of such systems, an appreciation of these factors is very important both in the develop-
ment of practical systems and in assessing the relative importance of possible research topics.
The CIS paradigm started to emerge from research laboratories in the mid-1980s, with the intro-
duction of the first commercial navigation and robotic systems in the mid-1990s. Since then, a few
hundreds of CIS systems have been installed in hospitals and are in routine clinical use, and a few
tens of thousands of patients have been treated with CIS technology, with their number rapidly
growing. The main clinical areas for which these systems have been developed are neurosurgery,
orthopedics, radiation therapy, and laparoscopy. Preliminary evaluation and short-term clinical
studies indicate improved planning and execution precision, which results in a reduction of com-
plications and shorter hospital stays. However, some of these systems have in some cases a steep
learning curve and longer intraoperative times than traditional procedures, indicating the need to
carry out preoperative analysis and elaborate a surgical plan of action. This plan can range from
simple tasks such as determining the access point of a biopsy needle, to complex gait simulations,
implant stress analysis, or radiation dosage planning. Because the analysis and planning is specific
to each surgical procedure and anatomy, preoperative planning and analysis software is usually cus-
tomized to each clinical application. These systems can be viewed as medical CAD systems, which
allow the user to manipulate and visualize medical images, models of anatomy, implants, and sur-
gical tools, perform simulations, and elaborate plans. To give the reader an idea of the current scope
of these systems, we will briefly describe two planning systems, one for orthopedics and one for
radiation therapy.
In orthopedics, planning systems are generally used to select implants and find their optimal
placement with respect to anatomy. For example, a planning system for spinal pedicle screw inser-
tion shows the surgeon three orthogonal cross sections of the acquired CT image (the original xy
slice and interpolated xz and yz slices) and a three-dimensional image of the vertebrae surfaces. The
surgeon selects a screw type and its dimensions, and positions it with respect to the anatomy in the
three cross-sectional views. A projection of the screw CAD model is superimposed on the images,
and its position and orientation with respect to the viewing plane can be modified, with the result
displayed in the other windows. Once a satisfactory placement has been obtained, the system stores
it with the screw information for use in the operating room. Similar systems exist for total hip and
total knee replacement, which, in addition, automatically generate in some cases machining plans