Учебники / Computer-Aided Otorhinolaryngology-Head and Neck Surgery Citardi 2002

FIGURE 1.5 CAS platforms provide software tools that semi-automatically create accurate three-dimensional models from two-dimensional CT data. This model was made within several minutes on the StealthStation Cranial 3.0 system (Medtronic Surgical Navigation Technologies, Louisville, CO). Before this technology was available, models were not as good, and the process of creating models was time-consuming, expensive, and difficult.

1.5 NEW PARADIGM

The surgical endeavor encompasses distinct but overlapping phases of data collection, diagnosis, planning, and execution. These processes draw upon the collective knowledge base of medicine as well as the surgeon’s intuition. CAS in its various manifestations can positively influence each of these various aspects of surgical care.

Since the advent of modern medicine in the late nineteenth century, physicians have sought methods to peer within body spaces. It was accurately believed that visualization would yield more accurate diagnosis and more effective treatment. Eventually, technology began to provide the means for visualization within body spaces—CT and MR provide anatomical information that would have been unimaginable 50 years ago. In addition, minimally invasive surgical techniques, which rely upon telescopes and other optical devices, provide phenomenal surgical access through tiny ‘‘portholes.’’ All of this technology still requires a great

FIGURE 1.6 The software tools that are offered with CAS surgical navigation systems provide unique perspectives that traditional approaches do not. In this instance, LandmarX 3.0 (Medtronic Xomed, Jacksonville, FL) provides a coronal-sagittal ‘‘cut’’ view that highlights the complex frontal recess pneumatization pattern in this patient. Standard coronal CT views do not portray the depth that this ‘‘cut’’ view shows.

deal of mental extrapolation by the surgeon—unless CAS is employed. For instance, the surgeon must mentally reconstruct three-dimensional relationships from two-dimensional planar imaging data, and then this mental model must be applied to the surgical field. Furthermore, minimally invasive surgery relies upon two-dimensional images afforded by surgical endoscopes. Each level of extrapolation introduces potential errors and inaccuracies.

CAS should be considered another tool for the surgeon. CAS provides easy ways to manipulate and view imaging data, and the resultant understanding that the surgeon garners from such manipulations can be directly applied in the operating room through surgical navigation. In these ways, CAS makes the surgical endeavor more precise.

Furthermore, CAS expands the capabilities of surgical care. By providing new vistas on imaging data, CAS can yield previously unrecognized information. CAS also may facilitate delicate surgical procedures. The next generation of CAS platforms will doubtlessly advance surgical care as surgeons recognize the limitations of current technologies, and engineers develop new solutions.

Surgeons can also use computer-based technologies for the more mundane aspects of patient care. The quantity of information is simply immense. Traditional paper records, files and books cannot adequately store this material in a simple way that facilitates retrieval and use. Computers, and more specifically, computer-based communications (such as the Internet), have an obvious role.

The emphasis on the physician-surgeon as an information manager should not dehumanize the delivery of patient care. The amount of information that guides each patient encounter is overwhelming; it is undeniable that even routine medical care now relies upon ever-increasing amounts of medical information. Without specific measures, this avalanche of information will overwhelm the humanistic aspects of the patient-physician relationship.

The mere use of computers does not exacerbate this problem; in fact, computer-based technologies, by offering efficient means for information management, may represent a solution to the information avalanche. CAS applications do not dehumanize the patient-physician relationship; in fact, by increasing available physician time, they may reinject a traditional humanistic element in patient care.

CAS should not be dismissed as a novelty item. CAS applications are diverse and powerful, and they will influence surgical practice for many years. In many ways, the introduction and widespread adoption of CAS will revolutionize how surgeons care for patients.

CAS is an enabling technology. It provides a means for the collection, organization, and manipulation of information and images. CAS will never substitute for the physician in the patient-physician relationship, and it will never replace surgical expertise. In the end, surgeons will rely upon CAS so that they can deliver better patient care.

The technological developments that are powering CAS are leading to new models for diagnosis, disease management, and surgical procedures. Increasingly surgeons are now integrating CAS platforms into their practices. The resultant CAS-driven paradigm represents a critical advance in contemporary surgery, since CAS provides solutions to current challenges and opens new diagnostic and therapeutic vistas for patient care.

REFERENCES

1.Reinhardt H, Meyer H, Amrein E. Computer-aided surgery: Robotik fu¨r Hirnoperationen? Polypscope plus 1986; 6:1–6.

2.International Society for Computer-Aided Surgery. Computer-aided surgery: aims and scope. www.iscas.org/aims.html 1999.

data from this CT scan were transferred into an IBM PC XT computer located in the operating room. This computer was linked to an operating microscope that had been outfitted with an acoustic localizer. In the operating room, the microscope was fixed on each of the three fiducial markers, and a sonic digitizer recorded their unique positions. The position of the patient relative to the microscope could be calculated through triangulation. The reformatted CT scan was projected through the microscope to the surgeon’s eye via a small television monitor. While this frameless device was less cumbersome than framed systems, its accuracy was somewhat lacking (average: 2.0 mm; range: 0.7–6.0 mm).

Watanabe et al. devised the Neuronavigator, a three-dimensional digitizer that had a jointed arm with a surgical probe [5]. The six freely mobile arm joints each contained a potentiometer. Based on the known arm segment lengths and data from the potentiometers, the intraoperative computer (PC-9801E; NEC, Japan) could calculate the relationships of the segments to each other and thus accurately determine the probe tip position. Before surgery, three metal fiducials fiducial markers were placed on the patient’s face, and a CT scan was obtained at 10 mm slice thicknesses (2–5 mm thickness for small lesions). Hard copy images were then scanned into the computer. The position sensor arm was used to correlate the patient’s intraoperative position to the CT scans. The average error of this system in the operating room was 3 mm.

In 1988, Reinhardt et al. reported on a computerized digitizing arm composed of three aluminum shells containing four potentiometers [6]. Data from the potentiometers were analyzed by an Apple IIE computer (Apple, Cupertino, CA) and then overlaid on a preoperative CT scan imaged by a video camera. The patient’s position on the operating table was correlated using plastic fiducial rods attached to a rigid headrest. A clinical accuracy of 2 mm was reported.

The concept of stereotactic surgery was clearly described in 1991 by Guthrie and Adler [7]. They noted that when a digital image of a patient is obtained by CT scanning or magnetic resonance imaging (MRI), any point within the digital image space can be assigned an x, y, or z value, known as a ‘‘image coordinate.’’ The correlation requires a minimum of three noncolinear points common to both the image space and the stereotactic (i.e., patient) space.

Guthrie (personal communication) became disenchanted with framed stereotaxis because ‘‘the frame dictated the case,’’ rather than acting as an aid to the surgeon. Thus, work was undertaken on the Operating Arm System (Radionics, Boston, MA), an optically encoded multijointed arm coupled to a computer (Silicon Graphics, Mountain View, CA). In this system, skin staples were placed as fiducial markers on the patient’s scalp, and then a preoperative CT scan was obtained. In the operating room, registration (namely the mapping of the image space with the patient space) was accomplished by touching the staples in a specific order. The computer matched the CT coordinates of the staples with the coordinates received by the operating arm, and the position of the probe tip was

shown as a cursor on the computer screen. The reported accuracy of the system was better than 3 mm.

In 1991, Watanabe et al. reported on the use of a new Neuronavigator system for neurosurgery in 68 patients [8]. The authors believed that their maximum intraoperative error of 2.5 mm was acceptable. The upgraded Neuronavigator Version II (Mizuho Medical Co., Ltd., Tokyo) incorporated the Microsoft Windows 3.2 operating system along with several new features, including a target alarm (Figure 2.2). As the probe approached the target (e.g., tumor), an alarm sounded to indicate close proximity to the target.

Kato et al. described an electromagnetic digitizer for used in computerassisted neurosurgery in 1991 [9]. Preoperatively, plastic tubes filled with contrast material were placed at four points for a fiducial reference system, and a CT or MRI scan was obtained. Slices of 5 mm thickness were obtained, and a maximum of 24 image slices could be loaded into the computer system. In the operating room, a magnetic field source was attached to the patient, and a sensing probe was used to calibrate the patient’s position. Experience with 10 neurosurgical patients demonstrated an accuracy of about 4 mm.

Also in 1991, Leggett et al., who were employees of ISG Technologies, reported their work with the Viewing Wand (ISG Technologies, Mississauga, Ontario, Canada), a localizer that had a six-jointed counterbalanced arm with a sterilizable distal probe (Figure 2.3) [10]. An accuracy of 2–3 mm was reported for skull-base tumor resection, optic nerve decompression, and transphenoidal biopsy. Using a plastic human skull and a custom-designed Plexiglas phantom, Zinreich et al. found the Viewing Wand comparable in accuracy to framed stereotactic systems [11].

In a system described by Laborde et al., 50 to 70 2 mm CT slices were reformatted into a three-dimensional (3D) virtual image prior to neurosurgery [12]. For preoperative planning, new software allowed the virtual model to be manipulated so that the surgeon could see the relationship of the pathology to the surrounding tissues. The intraoperative accuracy of 3 mm was enhanced by repeating the registration process.

Barnett et al. published a preliminary report on a frameless, armless system with four components: a probe with two ultrasonic emitters, a receiver microphone array fixed to the operating table, hardware for the timing and control of signal production and reception, and an intraoperative computer [13]. Before surgery, fiducial markers were placed, and a CT or MRI scan was obtained. Microphones arranged in specific positions on the receiver array detected ultrasonic signals generated sequentially by the probe emitters. Localization of the probe tip was calculated based on the time-interval delay of the emitted pulses. An error of 1.5 mm was reported for the initial five patients, whose preoperative scans had been performed at a slice thickness of 1 mm.

In another article, Barnett et al. reported on the use of an ultrasonic localizer

FIGURE 2.2 The Neuronavigator (as developed by Watanabe et al.) incorporated an electromechanical tracking system as well as a computer workstation. The electromechanical arm was rigidly fixated to the operating table, and the patient’s head was held rigidly in place.

(COMPASS, Stereotactic Medical Systems, Rochester, MN) in 52 craniotomies [14]. The mean error of the device was 4.8 mm. The authors concluded that although the unit was a reasonable guide for surgery, its imprecision made it unacceptable as a replacement for a framed system.

Klimek et al. in 1993 noted that deep-seated orbital lesions were difficult to access through an endonasal approach and that frameless stereotaxy systems could be advantageous in revision cases or in situations where there was bleeding