Jon Harald Kaspersen1 , Thomas Lang0, Frank Lindseth1 1 SINTEF Health Research, Medical Technology, 7465 Trondheim, Norway
Image-guided surgery (IGS) is an evolving technology used to carry out minimally invasive procedures. The majority of developed systems for IGS are designed for neurosurgery  although systems for other clinical applications are emerging, such as otologic procedures  and liver surgery . In the most advanced systems available today, IGS may provide the surgeon with two- (2D) and three-dimensional (3D) visual "road maps" of a patient's anatomy corresponding to the position of the surgical instruments used. Minimally invasive surgery allows access to difficult-to-reach anatomy, minimizes trauma to the patient, and, hence, can result in a shorter convalescence and hospital stay and reduced pain for the patient after surgery. Prior to the development of IGS, surgeons performing e.g. minimally invasive laparoscopic surgery could only see the surface area visible from the laparoscope. This surface-view technology is limited because the surgeon must correlate the patient's medical images (MR/CT/ultrasound) mentally with the operative field to determine the location of vital anatomical structures that lie beyond the view of the monocular laparoscope. Stereoscopic laparoscopes add depth perception to the view, but this does not solve the problem of not knowing what it looks like beneath the surface. IGS overcomes this limitation and provides the surgeon with real-time enhanced visualization .
The use of intraoperative ultrasound has been found valuable due to its relatively low cost and the possibility to generate 3D anatomical visual information within seconds, especially in neurosurgery     . In other areas such as prostate brachytherapy, 3D ultrasound has been used for visual guidance when positioning seed implants .
An IGS system combines a high-speed computer system, specialized software and tracking technology. On this computerized system the actual movements of surgical instruments are correlated with the patient's preoperative medical images and are displayed on the system's monitor. The precision of computerized instrument localization and navigation is critical to maneuvering safely within concealed anatomy and for the surgeon to perform more precise and careful surgery. However, most IGS systems are based on preoperative images, sometimes acquired the day before surgery. This means that as surgery proceeds, the images are continuously becoming less representative of the true patient anatomy. Introducing intraoperative imaging modalities such as ultrasound can solve this problem .
In traditional laparoscopic surgery, only the endoscope camera is used for guidance of the procedure. However, by introducing other guidance methods, the outcome of laparoscopic procedures may be improved. In section 1, we present initial experience with 3D navigation technology based on preoperatively acquired MRI or CT data sets used in combination with a laparoscopic navigation pointer. This technology offers the surgeon a better overview of structures not readily visible with conventional endoscope technology, and, hence, improves the guidance of laparoscopic surgery.
Before we describe an in-house navigation system under development, we present a brief overview of image-guided minimally invasive surgery with reference to Figure 12-1. Patient treatment using IGS systems involves several important steps, of which some are more critical than others for obtaining the optimal therapy of the patient. These steps are shown in Figure 12-1, and involve: 1) preoperative image acquisition, data processing and preoperative image visualization for optimal diagnostics as well as satisfying preoperative therapy decision and planning, 2) accurate registration of preoperative image data and visualization in the operating room for accurate and optimal planning just prior to surgery, 3) intraoperative imaging for updating images for guidance as well as intraoperative visualization and navigation for safe, efficient and accurate IGS in the OR, and finally, 4) postoperative imaging and visualization for adequate evaluation of patient treatment.
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