Page 402 - Biomedical Engineering and Design Handbook Volume 2, Applications

380 SURGERY

realism and haptic feedback. Their simplicity makes them relatively inexpensive. They are typically
used for teaching widely-performed, relatively straightforward procedures with well-defined algo-
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rithms. Simulations of spinal biopsy, nerve blocks, vascular access, and interventional cardiology 12
are some successful examples of simulations of needle- and catheter-based procedures.
Minimally Invasive Surgery. Minimally invasive surgery is a revolutionary surgical technique,
where the surgery is performed with instruments and viewing equipment inserted through small inci-
sions (typically, less than 10 mm in diameter) rather than by making a large incision to expose and
provide access to the operation site. Minimally invasive operations include laparoscopy (abdominal
cavity), thoracoscopy (chest cavity), arthroscopy (joints), pelviscopy (pelvis), and angioscopy (blood
vessels). The main advantage of this technique is the reduced trauma to healthy tissue, which is the
leading cause of patients’ postoperative pain and long hospital stay. The hospital stay and rest peri-
ods, and therefore the procedure costs, can be significantly reduced with minimally invasive surgery.
However, minimally invasive procedures are more demanding on the surgeon, requiring more diffi-
cult surgical techniques.
The virtual environments-based training simulators in the literature are mostly for minimally
invasive surgery applications. This is not a coincidence. In addition to the need for better training
tools for minimally invasive surgery, the constraints which make minimally invasive surgery difficult
are the same reasons that make building simulators for minimally invasive surgery more manageable
with existing technology. It is significantly easier to imitate the user interface for minimally invasive
surgery, limited and well-constrained haptic interaction, and limited amount and quality of feedback
(visual and otherwise) available.
Examples of simulators for minimally invasive surgery include Refs. 13 to 16. Several commer-
cial laparoscopic surgery training simulators are also available, including systems developed by
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Surgical Science, Mentice, Immersion Medical, and Simbionix. 20
Open Surgery. In open surgery, the surgeon has a direct visual view of the operation site, and
directly interacts with the biological tissue for manipulation. Open surgery is significantly less struc-
tured compared to minimally invasive surgery. Furthermore, the surgeon has significantly more free-
dom of motion, and the amount and quality of tactile and visual feedback is higher. As a result,
simulation of open surgery is remains challenging. Considerable advances in haptic devices and
algorithms, deformable object modeling and simulation, user interface development, and real-time
computer graphics are needed for realistic simulation of open surgery. The existing simulations, as
a result, focus more on training simulators for individual skill rather than complete procedures.
Examples of open surgical simulators include Refs. 21 to 23.

13.2.2 Components of Virtual Environment-Based
Surgical Simulators
The construction of a virtual environment-based surgical simulation starts with development of
three-dimensional geometric models of the structures in the surgical anatomy (Fig. 13.2). The geo-
metric models are constructed from medical diagnostic images, and can be generic or patient spe-
cific. Typically, computerized tomography and magnetic resonance images are used for construction
of anatomical models. Computerized tomography images typically have higher image resolution.
Magnetic resonance images, on the other hand, have better contrast in soft tissues. Magnetic reso-
nance imaging is also preferable as it does not involve ionizing radiation. The volumetric data of the
medical diagnostic images are first segmented to identify individual anatomical entities, and then
converted to geometric models for use in the subsequent parts of the development. Two types of geo-
metric models are typically generated. Surface models are triangulated meshes that represent the
boundaries of the anatomical entities. Volumetric geometric models are tetrahedral meshes that rep-
resent the geometry of the interior of the anatomical entities. Surface geometry is used in graphical
rendering of the virtual environment, while volumetric geometry is used in simulation of the physi-
cal behavior of the anatomical entities.