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584 Image-Guided Surgery

navigational operations. The presentation of multimoda- and visualization of the three-dimensional (3D) anatomy.
lity-based images has to be merged into a single model Thesevolumetricmodelssupportsurgicalplanningand/or
in which anatomy and pathology have to be distinguished simulations to define and optimize access strategies and to
but integrated into the same intuitive framework. Therapy simulate planned trajectories (Kikinis et al., 1996). When
systems have to be linked with imaging systems to consti- these models are registered to the patient’s actual anatomy,
tute a complete therapy delivery system. At the same time they relate image-based coordinate locations in the surgi-
a multidisciplinary team has to be created which com- cal field. The use of sensors or tracking devices enables
bines surgeons, interventionalists, imaging experts, and the surgeon to navigate and carry out procedures using all
computer scientists. the preoperative multimodality-based information, which
Such an environment is radically different from the con- is tied together in the model. Acquisition, display, and vi-
ventional operating room. The surgeon’s view of the sur- sualization of an image in surgery is different from that
face of the operational field is coupled by images showing in diagnosis. Preoperative images can be acquired with
what is beyond the visible surface. This leads to a definite optimal quality and without seriously limiting the imag-
change in surgical approaches and methods and results ing time. Intraoperative guidance, however, limits the time
in a close integration of image-based information with acceptable for imaging. To fully integrate acquisition and
surgical procedures. This new integrated setting is not op- display, intraoperative imaging has to be dynamic and pri-
timized yet and it has been the subject of intense research marily defined by the procedure (Fig. 1).
(Jolesz and Shtern, 1992). The overall goal of IGT is to The navigational systems display images interactively
integrate all the accessible information (both preoperative with orientation and location defined by the position of
and intraoperative imaging data) into a single complete sensors attached to surgical instruments or other tracked
operational therapy delivery system. devices. Interactive image guidance can direct the surgeon
These therapy delivery systems can be suited to dif- to the target using on-line trajectory optimization. By dis-
ferent applications. These call for interdisciplinary teams playing alternative access routes, surgical planning can be
from various clinical specialties to work together with performed at the operating room table. Navigational sys-
engineers and computer scientists using not only surgi- tems (frameless stereotaxy) have a relatively good accu-
cal and radiological methods, but biomedical engineering racy and they are feasible unless the surrounding anatomy
principles in the process of combining imaging and ther- is changing significantly during the procedure.
apy devices. It is anticipated that this emerging field will In combination with navigational and interactive dis-
embrace 1ess-invasive therapy options and will result in play tools preoperative models can aid a variety of di-
better clinical outcomes and reduced cost. agnostic and therapy applications. For diagnosis, the pri-
mary objective is detection and description of a lesion.
I. IMAGE-GUIDANCE METHODS For therapy, the purpose is localization and targeting. For
AND TECHNOLOGIES surgery and targeted therapy, it is essential to know the
exact position and 3D extent of the abnormality and its
IGT systems use preoperatively acquired images to cre- relationship to the surrounding anatomy. The representa-
ate models which can be used for localization, targeting, tion of anatomic structures and their functions along the

FIGURE 1 The concept of image-guided surgery.