Paranasal sinusitis is one of the most common diseases in otorhinolaryngology field. The symptoms include nasal discomforts, such as nasal obstruction, purulent rhinorrhea, post-nasal drip, hypernasal voice, foul odor in nose, hyposmia and anosmia, and non-nasal symptoms, such as headache, facial fullness sensation, sore throat, otalgia, teethache and chronic cough. It comprises a spectrum of medical conditions that are characterized by inflammation in paranasal sinuses. According to the disease duration, they are divided into acute (< 4 weeks), subacute (4 to 12 weeks) and chronic paranasal sinusitis (>12 weeks). In the acute stage of sinusitis, most patients recover after adequate medical treatment, such as administration of antibiotics, anti-inflammatory agents and mucolytic agents. However, if the symptoms of paranasal sinusitis persist more than 12 weeks, chronic inflammatory process leads to irreversible structural changes of paranasal sinuses, such as polyp formation, blockage of sinus ostium. With multiple potential inflammatory triggers acting through various physiologic pathways, it appears that chronic paranasal sinusitis may be a syndrome with multiple etiologies and a common endpoint for a variety of nose and sinus diseases. In this chronic stage of disease, surgical management instead of medical treatment becomes a mainstream of treatment modalities.
Endoscopic sinus surgery (ESS) for the treatment of sinus disease has been a common otolaryngological surgical procedure since the mid-1980s, with an expanding role in the management of orbital, facial bone and skull base diseases (1,2). Computer-aided surgery (CAS) technology has been developed to assist surgeons in achieving better anatomical localization since the 1990s (3,4), and may help prevent potential sinus complications such as orbital damage, cerebrospinal fluid leakage and carotid artery injury (5). Based on real-time image guidance in association with
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endoscopy, CAS systems may help to improve the intraoperative precision of orientation
(6,7) using either computed tomography (CT) or Magnetic Resonance Imaging (MRI) (8). Among the commercially available CAS systems, both optical and electromagnetic tracking systems have become popular, as they are more accurate and convenient than electromechanical (9) or sonic tracking systems (10). The optical tracking system was developed earlier than the electromagnetic system and was the first to be widely adopted in the clinical setting because of its high degree of accuracy (1). Numerous studies (4,11-16) have analyzed its performance under both clinical and laboratory conditions. Claes et al.
(11) conducted a cadaveric study for comparisons of navigation errors of conventional fiducial marker registration and anatomical landmark registration using an active optic navigation system (OptoTrak 3020®). The results showed matching with external fiducials on the face results in smaller navigation error than matching with anatomical landmarks. The accuracy was comparable and acceptable in the fiducial marker group (mean=2.13 ± 1.42 mm). Eliashar et al. (12) demonstrated accurate anatomical localization with less than 2 mm localization error. (1.1~2.0 mm, mean =1.6mm) in 94% (32/34) live sinus surgeries using an active optic navigation system (LandmarX®).
In 2 out of 34 surgeries, the localization errors were more than 2 mm (2.2 and 2.3 mm).
They were still considered as acceptable errors because there is general consensus that 3-mm navigation error is clinical acceptable and applicable (13). The same optic navigation system (LandmarX®) was used in Metson’s clinical study (14). The navigation errors of 754 sinonasal surgeries performed by 34 physicians were analyzed, and the mean accuracy of anatomical localization at the start of surgery was 1.69 ± 0.38 mm. Snyderman et al. (15) used a passive optic navigation system (Stryker®) in 50 endoscopic, anterior cranial base procedures, and the accuracy was evaluated after fiducial marker registration. The results revealed that the mean error of initial
registration was 2.8 mm (1.4~7.1 mm). Anon (4) used an active optic navigation system (OptoTrak 3020®) in 24 endoscopic sinus surgeries. Accuracy measurements were recorded after fiducial marker registration and the overall accuracy was 1.88 ± 1.04 mm.
Klimek et al. (16) recorded the accuracy of laboratory condition and that of live surgery using a passive optic navigation system. Laboratory accuracy measurements were obtained on a Plexiglas model with known coordinates of fiducial markers, before and after predefined table movement. Intraoperative accuracy measurements were recorded from 24 patients undergoing endoscopic sinus surgery with fiducial marker referencing technique. The result demonstrated laboratory accuracy to 0.86 ± 0.94 mm. After table movements, the accuracy decreased to 1.12 ± 0.99 mm, 1.05 ± 0.96 mm, 1.15 ± 1.04 mm and 1.54 ± 1.25 mm, respectively, in four different positions. Intraoperative accuracy was 1.14 ± 0.57 mm. Briefly, the accuracies of optic navigation systems under laboratory conditions, in cadaveric studies and live surgeries are good and acceptable, either using fiducial marker registration or using anatomical registration.
The development of electromagnetic tracking systems for surgical use was limited by ferromagnetic distortion that adversely affected system accuracy until certain hardware and software advances were recently reported (4,17-19). Using fiducial marker registration, Anon (4) reported the electromagnetic navigation (InstaTrak®) accuracy were within 0.96 ± 0.86 mm after localization measurement of 10 dry skull bases. Fried et al. (19) presented a multicenter clinical study (n=55) that evaluated the electromagnetic navigation (InstaTrak®) systems’s capability for localizing anatomical structure in critical surgical sites when performing endoscopic sinus surgery. The results showed mean accuracies in autoheadset registration group and fiducial registration group were 2.28 mm and 1.97mm, respectively. Although optic navigation systems were widely adopted before; currently, the electromagnetic systems are much more popular in North
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America due to advanced accuracy. There are only few studies concerning the navigation accuracy of newly-developed electromagnetic systems at present; therefore, one purpose of this study is to further analyze the performance of new electromagnetic navigation system (Medtronic S7®).
Navigation accuracy is highly dependent on the registration process, which establishes the correlation between specific landmarks and stored image data. Various registration methods have been proposed, based on external fiducial markers (20), anatomical landmarks (21) and contour-based registration (10,22), respectively. Anatomical landmark registration has been commonly used with an acceptable precision in a variety of practical situations, as it utilizes natural markers and is non-invasive (21). The surface registration procedure that aligns the unique facial contours eliminates the long preparation time of the usual registration technique and is thus clinically convenient
(23,24). Thus far, the accuracy of surface registration for optical tracking systems has been shown to be satisfactory in a variety of studies (22-25). Ledderose et al. (25) assessed the accuracy of surface laser registration using a passive optic navigation system (VectorVisionCompact®) on two cadaver heads. Repeated measurements were performed for 10 times and averaged. The resulting overall accuracy was 1.13 ± 0.53 mm, ranging from 0.77 to 1.76 mm, and thus proved to be clinically sufficient (13). Raabe et al. (22) evaluated the accuracy of another passive optic navigation system (Polaris®) using laser registration in live surgeries. The mean accuracy was 2.4 ± 1.7 mm. Stelter et al. (24) present their experience with a passive optic navigation system (VectorVisionCompact®) using laser registration for endoscopic sinus surgery on 368 patients. The clinical plausibility test produced an average deviation of 1.3 mm. Schlaier et al. (23) evaluate the registration accuracy and practicability of the passive optic navigation system (VectorVisionCompact®) with a laser registration technique in
comparison to marker registration. Thirty-five patients were registered by paired-point registration. In 16 patients, a second registration was carried out using a special laser pointer. The marker registration proved to be more accurate than the surface registration with regard to localization of anatomical landmarks and target fiducials (1.31 ± 0.87 mm vs. 2.77 ± 1.64 mm; p < .01). Nevertheless, the data for electromagnetic systems using surface registration is lacking for both live surgery and cases of cadaveric dissection. Accordingly, the precision of the surface registration used in electromagnetic tracking systems needs to be further evaluated. To our knowledge, this study presents the first investigation of the efficiency of system preparation and the three-dimensional accuracy of the surface registration used in electromagnetic tracking systems in live endoscopic sinus surgery.
In addition, comparisons of optic and electromagnetic systems using fiducial marker-matching registration or anatomical landmark registration were conducted in previous studies (1,26). Optic navigation systems were proved to be more accurate than electromagnetic navigation systems under laboratory condition (1) and in cadaveric study (mean error = 0.12 vs. 0.37mm, p < .05) (26). How about the performance of these two navigation systems using newly-developed surface registration technique? Is the optic navigation system still more accurate than the newly-developed electromagnetic navigation system under clinical condition? So far, comparisons between optic and electromagnetic systems using surface registration have not been reported, either in live surgery or cadaveric dissection. In the second part of our study, we investigate the anatomical precision of the two different navigation systems using surface registration in the course of live endoscopic sinus surgery on the same patients, and to share our experience with their use in clinical practice.
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