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Wilkinson et al. Poster

Introduction
Materials and Methods
Results
Discussion

Clinical Experience with Commercially Available Neurosurgical Navigation Systems at Stanford

Eric P. Wilkinson, B.S.E., Hamid R. Abbasi, M.D., Ph.D., David P. Martin, M.D., and Ramin Shahidi, Ph.D.

INTRODUCTION

In the past decade, image guided surgery (IGS) systems have become commonplace in operating rooms throughout the country as adjuncts to surgeons' own knowledge and experience. As computing power and stereotactic theory has developed, multiple commercial image guidance systems have become available for utilization in cases in several surgical specialties, including neurosurgery, otolaryngology, and orthopaedic surgery. Such systems have been undergoing continual improvement as the technology has matured.

In the Department of Neurosurgery at Stanford University School of Medicine, commercial image guidance systems have been used for the past several years in the surgical management of patients with complicated intracranial and spinal pathology and are used alongside experimental systems used for surgical navigation research. Stanford is just one of many centers that have implemented this technology as an aid in certain procedures such as complex tumor, cerebrovascular, functional and stereotactic, spine, and pediatric cases.

New healthcare technologies are under increasing scrutiny in this age of cost-effectiveness analyses. It is critical to reflect on: 1) the types of cases that these systems are being used for, in order to adapt future systems to optimally display patient data during those types of surgery; and 2) the advantages and disadvantages (including time and effort) that commercial IGS systems have brought to surgery, particularly at this juncture where systems have become commonplace.

MATERIALS AND METHODS

To further understand the use of commercially available IGS systems at a major academic medical center, neurosurgical scheduling records from Stanford University Medical Center for the 33-month period beginning June 1, 1997 and ending March 1, 2000 were reviewed and cases utilizing commercial IGS packages were tabulated and categorized according to type of case. The number of cases per month were calculated, both for all types of cases as well as each type of case.

In addition, subjective comments from neurosurgeons were compiled regarding the advantages and disadvantages of the different commercial systems in use in the operating suite. Comments were provided on the systems from three different IGS suppliers: Radionics (Radionics Inc., Burlington, MA; http://www.radionics.com), BrainLab (BrainLab USA, Redwood City, CA; http://www.brainlab.com), and Elekta (Elekta Instruments, Inc., Norcross, GA; http://www.elekta.com). The systems are shown in Figure 1.

RESULTS

A total of 362 image-guided procedures were performed over the 33-month period. The number of cases in 1999 and 2000 increased markedly over 1997 and 1998, Tumor resection surgery (201 cases, 56%) was the most frequent indication, followed by cerebrovascular surgery (76 cases, 21%), functional neurosurgery (54 cases, 15%), spinal neurosurgery (19 cases, 5%) and miscellaneous (12 cases, 3%). Miscellaneous cases included ventriculostomies and other endoscopic procedures. Percentages of total cases by type of case are shown in Figure 2. the number of monthly cases, subdivided by type of case, are shown in stacked bar format in Figure 3.

Several neurosurgeons commented on the additional time needed to set up, register, and otherwise troubleshoot the image guidance systems. On average, using image guidance added 30-45 minutes to each case. The neurosurgeonsí subjective comments follow:

System Comparison

Radionics System

The Radionics system uses an active referencing and tracking system. In this system the infrared (IR) diodes send signals which are collected by two cameras; the position of each IR diode is then calculated by triangulation. Because the IR diodes need electricity, the active tools must always have a cable connection to the neuronavigation system. This requires advance preparation to sterilize the cabled components. The probe itself, however, is free of the cabling and may be autoclaved (Figure 4). This system is often employed for general neuronavigation use.

BrainLab System

This system is easy to use and provides tools for cranial and spinal neuronavigation. It uses the passive marker modality (Figure 4), which gives more flexibility in the setting up of the instruments in the OR; tools brought into its field of view are automatically recognized. The system accepts up to 7 markers which gives an accuracy up to 2 millimeters. Some tools are up to three times slower than on other systems. This system is frequently chosen when complicated OR setups require instrument flexibility.

Elekta System

This system is very reliable and utilizes an active registration and tracking system. A powerful feature of the system is the ability to use the operating microscope as a probe. The system requires a new calibration for each newly connected probe or microscope. The probes are in one segment, unlike the Radionics system, and cannot be autoclaved (Figure 4). The user interface for intraoperative registration is somewhat awkward.

DISCUSSION

The case data indicate that tumor and vascular cases predominate among image-guided procedures, with tumor cases making up the largest proportion. This is not surprising, as the complexities in choosing surgical approach and verifying operative location during complex tumor cases was an original impetus for the development of IGS systems. Other surgeries, including spinal and functional cases, are relatively new applications of IGS systems and the data reflect this.

The number of image-guided cases in 1999 and 2000 increased markedly from 1997 and 1998 values, particularly among functional, tumor, and spinal cases. This is due to a combination of factors during the last two years: 1) The hiring of additional faculty in functional, tumor, and spinal neurosurgery; 2) The creation of a dedicated surgical navigation service; and 3) Increasing familiarity with navigation equipment that comes with time and experience, leading to a higher tendency for the neurosurgeons to use the IGS systems during surgery.

Regular neuronavigation use, due to the time and effort required for its proper use, requires the work of a dedicated individual (trained in IGS technology) to acquire the imaging data, load it onto the guidance system, set up the system in the operating room, assist during the registration and navigation process, and take down the system following the procedure. It is essential that this individual or individuals be able to troubleshoot the frequent problems that occur during the daily use of IGS systems. This is a costly but necessary consideration when deciding to initiate an IGS program.

Cost considerations, as well as other challenges, including time investment and slowly increasing acceptance of image guidance systems as a regular aid in the operating room, will affect the development of new image guidance systems. A solid understanding of the time, procedural difficulties, and relative benefits and disadvantages of different systems is critical in the selection and use of IGS technology as well as in designing future innovations.

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