Frameless stereotaxic integration of CT imaging data: accuracy and initial applications

A Priori Information Based Time-Resolved 3D Analysis of the Trajectory and Spatial Orientation of Fast-Moving Objects Using High-Speed Flash X-ray Imaging

This paper shows that the X-ray analysis method known from the medical field, using a priori information, can provide a lot more information than the common analysis for high-speed experiments. Via spatial registration of known 3D shapes with the help of 2D X-ray images, it is possible to derive the spatial position and orientation of the examined parts. The method was demonstrated on the example of the sabot discard of a subcaliber projectile. The velocity of the examined object amounts up to 1600 m/s. As a priori information, the geometry of the experimental setup and the shape of the projectile and sabot parts were used. The setup includes four different positions or points in time to examine the behavior over time. It was possible to place the parts within a spatial accuracy of 0.85 mm (standard deviation), respectively 1.7 mm for 95% of the errors within this range. The error is mainly influenced by the accuracy of the experimental setup and the tagging of the feature points on the X-ray images.

Simulation of surgery for supratentorial gliomas in virtual reality using a 3D volume rendering technique: a poor man's neuronavigation

OBJECTIVE

Different techniques of performing image-guided neurosurgery exist, namely, neuronavigation systems, intraoperative ultrasound, and intraoperative MRI, each with its limitations. Except for ultrasound, other methods are expensive. Three-dimensional virtual reconstruction and surgical simulation using 3D volume rendering (VR) is an economical and excellent technique for preoperative surgical planning and image-guided neurosurgery. In this article, the authors discuss several nuances of the 3D VR technique that have not yet been described.

METHODS

The authors included 6 patients with supratentorial gliomas who underwent surgery between January 2019 and March 2021. Preoperative clinical data, including patient demographics, preoperative planning details (done using the VR technique), and intraoperative details, including relevant photos and videos, were collected. RadiAnt software was used for generating virtual 3D images using the VR technique on a computer running Microsoft Windows.

RESULTS

The 3D VR technique assists in glioma surgery with a preoperative simulation of the skin incision and craniotomy, virtual cortical surface marking and navigation for deep-seated gliomas, preoperative visualization of morbid cortical surface and venous anatomy in surfacing gliomas, identifying the intervenous surgical corridor in both surfacing and deep-seated gliomas, and pre- and postoperative virtual 3D images highlighting the exact spatial geometric residual tumor location and extent of resection for low-grade gliomas (LGGs).

CONCLUSIONS

Image-guided neurosurgery with the 3D VR technique using RadiAnt software is an economical, easy-to-learn, and user-friendly method of simulating glioma surgery, especially in resource-constrained countries where expensive neuronavigation systems are not readily available. Apart from cortical sulci/gyri anatomy, FLAIR sequences are ideal for the 3D visualization of nonenhancing diffuse LGGs using the VR technique. In addition to cortical vessels (especially veins), contrast MRI sequences are perfect for the 3D visualization of contrast-enhancing high-grade gliomas.

Intraoperative Image Guidance during Endoscopic Sinus Surgery

Endoscopic sinus surgery (ESS) is one of the most commonly performed procedures in otorhinolaryngology and is associated with a definite risk for both intraoperative and postoperative complications. Intraoperative image guidance is expected to have a major effect on procedures such as ESS by allowing the clinician to more efficiently remove pathology and by improving surgeon confidence and knowledge of anatomy, particularly in revision procedures or in patients with altered anatomy. As a consequence, complications during these pro-’ cedures will decrease and patient safety will increase. Several guidance modalities are available including computed tomography (CT), magnetic resonance imaging (MRI), and fluoroscopy. This article will describe current applications of each of these three techniques with respect to ESS while focusing on innovative techniques that use MRI and CT to provide intraoperative guidance with unmatched convenience, reliability, and utility.

Malleable Registration Mask: Application of a Novel Registration Method in Image Guided Sinus Surgery

Image-guided systems are becoming more widely used in endoscopic sinus and skull base surgery. All systems require initial registration to correlate the CT scan images to the patient's anatomy. Multiple registration techniques can be used. The ideal technique is one that is easy, reproducible, and provides the most accurate registration in the least amount of time. This study used an optical-based image-guided system (LandmarX) to test a unique mask registration technique and compared it to a previously used anatomic registration technique. Twenty-one patients were scanned with the mask and underwent surgery. Registration was performed using both the registration mask and the anatomic landmarks. Mean registration error and time were recorded. Results are reported for 20 patients. Mean registration error for the mask technique was 0.96 mm and took a mean of 41 seconds. Anatomic registration error using five or six points resulted in a mean initial error of 2.08 mm and took 31.2 seconds. Mean final anatomic registration error was 1.53 mm, requiring reregistration of a mean of 4.6 points, and took 106 seconds. Statistically significant differences were obtained between the two techniques with regard to registration error and time to final registration. We found that the registration mask technique is a more reliable technique in ease, accuracy, and time of registration. This technique should be especially beneficial to the less experienced image-guided surgeon.

Endoscopic Transnasal Pituitary Surgery: Report on 180 Cases

The endoscopic transnasal approach is an evolving technique for treating lesions in the sella turcica. Since this method was introduced at our institution 4 years ago, the majority of transsphenoidal procedures are performed with it. The records of all patients having endoscopic transnasal hypophysectomy at the Mayo Clinic during the last 4 years were reviewed retrospectively. The criteria analyzed were safety, functional and cosmetic outcome, and complications. During the 4-year period, the operative procedure was modified to improve operative exposure and safety. The results of our review showed a significant decrease in length of hospital stay, reduced operative time, reduced need for nasal packing, and elimination of a sublabial incision. The complication rate was equivalent to that reported for the traditional transseptal transsphenoidal approach. As the neurosurgeons at our institution gained experience with this approach, an increasing number of pituitary microadenomas were resected safely and successfully. In addition, because of the limited septal dissection, this approach is particularly helpful for revision operations. This approach also can be used for the full range of pituitary lesions and in conjunction with adjunctive techniques, including frontal craniotomy and -knife irradiation. Currently, the endoscopic transsphenoidal approach is the method preferred for surgically treating pituitary lesions in adults at our institution.

Accurate external localization of the left frontal cortex in dogs by using pointer based frameless neuronavigation

BACKGROUND

In humans, non-stereotactic frameless neuronavigation systems are used as a topographical tool for non-invasive brain stimulation methods such as Transcranial Magnetic Stimulation (TMS). TMS studies in dogs may provide treatment modalities for several neuropsychological disorders in dogs. Nevertheless, an accurate non-invasive localization of a stimulation target has not yet been performed in this species.

HYPOTHESIS

This study was primarily put forward to externally locate the left frontal cortex in 18 healthy dogs by means of a human non-stereotactic neuronavigation system. Secondly, the accuracy of the external localization was assessed.

ANIMALS

A total of 18 healthy dogs, drawn at random from the research colony present at the faculty of Veterinary Medicine (Ghent University), were used.

METHODS

Two sets of coordinates (X, Y, Z and X″, Y″, Z″) were compared on each dog their tomographical dataset.

RESULTS

The non-stereotactic neuronavigation system was able to externally locate the frontal cortex in dogs with accuracy comparable with human studies.

CONCLUSION AND CLINICAL IMPORTANCE

This result indicates that a non-stereotactic neuronavigation system can accurately externally locate the left frontal cortex and paves the way to use guided non-invasive brain stimulation methods as an alternative treatment procedure for neurological and behavioral disorders in dogs. This technique could, in analogy with human guided non-invasive brain stimulation, provide a better treatment outcome for dogs suffering from anxiety disorders when compared to its non-guided alternative.

Multimodal navigated skull base tumor resection using image-based vascular and cranial nerve segmentation: A prospective pilot study

Background:

Skull base tumors frequently encase or invade adjacent normal neurovascular structures. For this reason, optimal tumor resection with incomplete knowledge of patient anatomy remains a challenge.

Methods:

To determine the accuracy and utility of image-based preoperative segmentation in skull base tumor resections, we performed a prospective study. Ten patients with skull base tumors underwent preoperative 3T magnetic resonance imaging, which included thin section three-dimensional (3D) space T2, 3D time of flight, and magnetization-prepared rapid acquisition gradient echo sequences. Imaging sequences were loaded in the neuronavigation system for segmentation and preoperative planning. Five different neurovascular landmarks were identified in each case and measured for accuracy using the neuronavigation system. Each segmented neurovascular element was validated by manual placement of the navigation probe, and errors of localization were measured.

Results:

Strong correspondence between image-based segmentation and microscopic view was found at the surface of the tumor and tumor-normal brain interfaces in all cases. The accuracy of the measurements was 0.45 ± 0.21 mm (mean ± standard deviation). This information reassured the surgeon and prevented vascular injury intraoperatively. Preoperative segmentation of the related cranial nerves was possible in 80% of cases and helped the surgeon localize involved cranial nerves in all cases.

Conclusion:

Image-based preoperative vascular and neural element segmentation with 3D reconstruction is highly informative preoperatively and could increase the vigilance of neurosurgeons for preventing neurovascular injury during skull base surgeries. Additionally, the accuracy found in this study is superior to previously reported measurements. This novel preliminary study is encouraging for future validation with larger numbers of patients.

Introduction: Intraoperative spinal imaging and navigation

Image-guided surgery (IGS) has been evolving since the early 1990s and is now used on a daily basis in the operating theater for spine surgery at many institutions. In the last 5 years, spinal IGS has greatly benefitted from important enhancements including portable intraoperative CT (iCT) coupled with high-speed computerized stereotactic navigation systems and optical-based camera tracking technology.

The silent loss of neuronavigation accuracy: a systematic retrospective analysis of factors influencing the mismatch of frameless stereotactic systems in cranial neurosurgery

BACKGROUND

Neuronavigation has become an intrinsic part of preoperative surgical planning and surgical procedures. However, many surgeons have the impression that accuracy decreases during surgery.

OBJECTIVE

To quantify the decrease of neuronavigation accuracy and identify possible origins, we performed a retrospective quality-control study.

METHODS

Between April and July 2011, a neuronavigation system was used in conjunction with a specially prepared head holder in 55 consecutive patients. Two different neuronavigation systems were investigated separately. Coregistration was performed with laser-surface matching, paired-point matching using skin fiducials, anatomic landmarks, or bone screws. The initial target registration error (TRE1) was measured using the nasion as the anatomic landmark. Then, after draping and during surgery, the accuracy was checked at predefined procedural landmark steps (Mayfield measurement point and bone measurement point), and deviations were recorded.

RESULTS

After initial coregistration, the mean (SD) TRE1 was 2.9 (3.3) mm. The TRE1 was significantly dependent on patient positioning, lesion localization, type of neuroimaging, and coregistration method. The following procedures decreased neuronavigation accuracy: attachment of surgical drapes (DTRE2 = 2.7 [1.7] mm), skin retractor attachment (DTRE3 = 1.2 [1.0] mm), craniotomy (DTRE3 = 1.0 [1.4] mm), and Halo ring installation (DTRE3 = 0.5 [0.5] mm). Surgery duration was a significant factor also; the overall DTRE was 1.3 [1.5] mm after 30 minutes and increased to 4.4 [1.8] mm after 5.5 hours of surgery.

CONCLUSION

After registration, there is an ongoing loss of neuronavigation accuracy. The major factors were draping, attachment of skin retractors, and duration of surgery. Surgeons should be aware of this silent loss of accuracy when using neuronavigation.

Quantitative error analysis for computer assisted navigation: a feasibility study

PURPOSE

The benefit of computer-assisted navigation depends on the registration process, at which patient features are correlated to some preoperative imagery. The operator-induced uncertainty in localizing patient features-the user localization error (ULE)-is unknown and most likely dominating the application accuracy. This initial feasibility study aims at providing first data for ULE with a research navigation system.

METHODS

Active optical navigation was done in CT-images of a plastic skull, an anatomic specimen (both with implanted fiducials), and a volunteer with anatomical landmarks exclusively. Each object was registered ten times with 3, 5, 7, and 9 registration points. Measurements were taken at 10 (anatomic specimen and volunteer) and 11 targets (plastic skull). The active NDI Polaris system was used under ideal working conditions (tracking accuracy 0.23 mm root-mean-square, RMS; probe tip calibration was 0.18 mm RMS). Variances of tracking along the principal directions were measured as 0.18 mm(2), 0.32 mm(2), and 0.42 mm(2). ULE was calculated from predicted application accuracy with isotropic and anisotropic models and from experimental variances, respectively.

RESULTS

The ULE was determined from the variances as 0.45 mm (plastic skull), 0.60 mm (anatomic specimen), and 4.96 mm (volunteer). The predicted application accuracy did not yield consistent values for the ULE.

CONCLUSIONS

Quantitative data of application accuracy could be tested against prediction models with iso- and anisotropic noise models and revealed some discrepancies. This could potentially be due to the facts that navigation and one prediction model wrongly assume isotropic noise (tracking is anisotropic), while the anisotropic noise prediction model assumes an anisotropic registration strategy (registration is isotropic in typical navigation systems). The ULE data are presumably the first quantitative values for the precision of localizing anatomical landmarks and implanted fiducials. Submillimetric localization is possible for implanted screws; anatomic landmarks are not suitable for high-precision clinical navigation.

Practical Applications of Image-Guided Navigation during Anterior Craniofacial Resection

Intraoperative image-guided navigation allows the surgeon to identify anatomic landmarks obscured by overlying normal tissue, neoplasms, infection, or previous surgery. This case presentation illustrates some of the practical applications of the ISG image-guided navigation system during anterior cranial base surgery. The advantages and the pitfalls of the ISG system are discussed.

Endoscopic trans-sphenoidal removal of cholesterol granuloma of the petrous apex: case report and literature review

OBJECTIVE

We report a case of cholesterol granuloma of the petrous apex which was surgically treated via an endoscopic trans-sphenoidal approach.

METHODS

Case report and review of the literature concerning cholesterol granulomas of the petrous apex and their management.

RESULTS

The lesion was approached endoscopically via a bilateral sphenoidotomy with removal of the vomer. A large cholesterol granuloma was evacuated and marsupialised. The patient made an uneventful recovery.

CONCLUSION

Trans-sphenoidal access to the petrous apex represents an alternative route for the drainage and ventilation of cholesterol granulomas. This approach is the technique of choice when the cholesterol granuloma abuts the posterior wall of the sphenoid sinus. The trans-sphenoid approach, unlike other lateral approaches to the petrous apex, spares cochlear and vestibular function and allows post-operative endoscopic follow up.

Intraoperative repositioning assessment using navigation system in zygomatic fracture

BACKGROUND

Intraoperative repositioning assessment in the zygomatic fracture operation is very important in achieving adequate facial symmetry. A navigation system that has been developed in neurosurgery has recently been applied in the otolaryngol, orthopedic, and maxillofacial surgeries. We used a navigation system (Stealth Station TREON; Medtronic) in zygomatic fracture operation, and found it useful in performing accurate reduction and confirming the symmetry.

METHODS

We applied a navigation system in 6 patients with zygomatic bone fracture. Navigation aided reduction of the bone fracture was performed by evaluating intraoperative procedures: (1) an evaluation by measuring the distances from the midline of the face and (2) an evaluation by comparing the affected side to the mirror image of the nonaffected side. A method using the distance from the midline of the face was performed in 3 cases, and a method using the mirror image of the nonaffected side was used in 6 cases.

RESULTS

Accurate reduction and symmetry were confirmed during the operation in all patients. Good symmetry was confirmed in postoperative computed tomographic scan. It was useful in performing accurate reduction of the fractures and confirming the symmetry of the face.

CONCLUSIONS

We suggest that the system can also be applied for the treatment of untreated facial fractures requiring osteotomy and of comminuted facial fractures with third-bone fragments and for the evaluation of bone graft.

Computer assistance for intraoperative navigation in ENT surgery

The intraoperative need for exact orientation during interventions in the paranasal sinuses and the augmented need for navigational aids in lateral skull base surgery have lead to the development of computer-aided tools during the last fifteen years. These tools, which provide the position of a tool or a pointer in the patient's preoperative radiologic imaging, have quickly gained a wide acceptance for revision surgeries and the surgical treatment of complex pathologies in Ear-, Nose- and Throat (ENT-) surgery. Currently, the use of such systems is spreading from academic centers to smaller hospitals and will become a standard tool in the near future. We review the present state of computer-aided surgery (CAS) systems, based on our experience as clinical and research centers with a long experience in the field, provide some technological background information and, based on selected cases, show the merits of this technology. The systems we have been working with cover a wide variety of intraoperative navigational systems in ENT surgery (Easy Guide, MedScan II, MKM, SNN, STN, SurgiGATE ORL, Treon, VectorVision, Viewing Wand, [without claiming completeness]), and virtually the whole area of ENT surgeries: macroscopic, (video-)endoscopic and microscopic procedures. The 3D tracking technologies involved cover mechanical, optical (active and passive), magnetic and robotic principles. The visualization tools used are computer monitors, video monitors, head-up-displays and the microscope's oculars, thus spanning the area from pointer-systems to real navigators and a surgical telepresence demonstrator, implementing the majority of available patient-to-image referencing strategies. Clinically, the systems can be operated with an acceptable accuracy of around 1 mm, whereas in laboratory settings and in cadaver studies application accuracy may be pushed to its limits: the physical resolution of the radiologic imaging used for navigation.

Computer-assisted and frameless stereotaxy: the initial Australian experience

The trends towards minimally invasive surgery coupled with the increasing use of computer software and hardware have led to an increasing use of stereotactic neurosurgery as a part of mainstream neurosurgery. Computer-assisted and frameless stereotactic systems allow the performance of stereotactic procedures without the need for the mechanical linkage to a stereotactic frame. St Vincent's Hospital, Sydney, has used the Radionics Operating Arm System since March 1994 in 106 cases for stereotactic biopsy, localization of superficial lesions and volumetric resection of tumours. The Operating Arm System uses mechanical digitizers and has the advantages of being able to be used for both framed-based and frameless stereotactic procedures, simplicity of use, and the arm as a 'mouse' software program allowing the surgeon control of the computer program within the sterile operative field.

Neurocognitive Effects of Repetitive Transcranial Magnetic Stimulation in Patients with Cerebrovascular Disease Without Dementia

Aims: The results of our pilot study suggested that one session of high frequency rTMS applied over the left dorsolateral prefrontal cortex (DLPFC) might induce measurable positive effects on executive functioning in patients with mild cognitive impairment of the vascular type without dementia (MCI-V). The aims of the current study were to replicate the results of our pilot study using a frameless stereotaxy as opposed to the standard and routinely used procedure. We also studied the effects of low frequency rTMS. Patients and method: Seven patients with MCI-V participated in a randomized, controlled, blind study with a crossover design. Each patient received 10 Hz and 1 Hz stimulation over the left DLPFC (an active stimulation site) or the motor cortex (MC; a control stimulation site). Frameless stereotaxy was used to target the DLPFC. The order of sites and frequencies was randomized. A short battery of neuropsychological tests was performed to evaluate executive function, working memory, and psychomotor speed. Results: One session of both high and low frequency rTMS was well tolerated and safe in terms of the cognitive after-effects in patients with MCI-V. We did not observe any significant frequency dependent or stimulation site-dependent cognitive effects of rTMS. Conclusion: We found neither positive nor negative significant effect of either low or high frequency rTMS applied over the DLPFC or the MC, while a mild positive site-specific effect of 10 Hz rTMS was observed in our pilot study on the Stroop interference results. These results suggested that MCI-V is a heterogeneous and poorly defined entity and, thus, rTMS might be useful in a subpopulation of this group of patients.

Transcranial magnetic stimulation and the challenge of coil placement: a comparison of conventional and stereotaxic neuronavigational strategies

The combination of transcranial magnetic stimulation (TMS) with functional neuroimaging has expanded the potential of TMS for human brain mapping. The precise and reliable positioning of the TMS coil is not a simple task, however. Modern frameless stereotaxic systems allow investigators to base navigation either on the subject's structural magnetic resonance imaging (MRI), functional MRI data, or the use of functional neuroimaging data from the literature, so-called "probabilistic approach." The latter assumes consistency across individuals in the location of task-related "activations" in standardized stereotaxic space. Conventional nonstereotaxic localization of brain areas is also a common method for defining the coil position. Our aim was to evaluate the accuracy of five different localization strategies in one single study. The left primary motor cortex (left M1-Hand) was used as target region. Three approaches were based on real-time frameless stereotaxy using information based on either anatomical or functional MRI. The remaining two strategies relied either on standard cranial landmarks (i.e., the International 10-20 EEG system) or a standardized function-guided procedure (i.e., the spatial relationship between the left and right M1-Hand). The results were compared to a TMS-based mapping of the primary motor cortex; center of gravity of motor-evoked potentials (MEP-CoG) was calculated for each subject (n = 10). Our findings suggest that highest precision can be achieved with fMRI-guided stimulation, which was accurate within the range of millimeters. Very consistent results were also obtained with the "probabilistic" approach. In view of these findings, we discuss the methods and special characteristics of each localization strategy.

Computer aided surgery: concepts and applications in rhinology

Computer-aided surgery (CAS) has become relevant in a growing number of disciplines. This article will describe the history and principals of CAS and explain some of the technical issues, applications, and outcomes for CAS in the domain of rhinology.

Image-guided ultrasonography for recurrent cystic gliomas

BACKGROUND

Long-term survival of patients with recurrent gliomas depends on the extent of resection. Thus, the desirability of an intra-operative imaging modality that can augment the resection extension without affecting vital surrounding structures is more than obvious. It was the aim of the present study to evaluate a possible benefit of image-guided intra-operative ultrasonography for the surgery of recurrent gliomas.

METHOD

The authors performed ultrasonography-assisted image-guided resection of recurrent gliomas in 16 patients. An ultrasound device (IGSonic) was integrated into the VectorVision2 navigation system (BrainLAB, Heimstetten, Germany). The IGSonic Probe 10V5 was connected to the VectorVision Navigation station via an IGSonic Device Box. Following patient registration, MRI based neuronavigation was used to determine the skin incision and the bone flap. Before opening the dura, the underlying structures were explored by ultrasound combined with the corresponding MR images. The navigated ultrasound displayed the sonographic image of the intracranial anatomy on the navigation screen in a composed overlay fashion.

FINDINGS

The integration of intra-operative ultrasound into neuronavigation system offered quick and helpful intra-operative images in all 16 procedures. Due to the specific ultrasonic characteristics of the solid and the cystic parts, our technique created highly useful images in 10 patients with cystic recurrences. In these, user friendly images were obtained that were easy to understand even for neurosurgeons without major experience in intra-operative ultrasound.

CONCLUSIONS

Neurosonography is a time- and cost-effective technology offering intra-operative imaging. The improved orientation and visualization of tumour remnants, adjacent ventricles, and the enhanced intra- and peri-tumoural vasculature is one of the main advantages of ultrasonography-assisted image-guided surgery, which is most obvious during surgery for cystic gliomas.

Application Accuracy of Automatic Registration in Frameless Stereotaxy

OBJECTIVE

We compared the application accuracy of an infrared-based neuronavigation system when used with a novel automatic registration with its application accuracy when standard fiducial-based registration is performed.

METHODS

The automatic referencing tool is based on markers that are integrated in the headrest holder we routinely use in our intraoperative magnetic resonance imaging (MRI) setting and can be detected by the navigation software automatically. For navigation targeting we used a Plexiglas phantom with 32 notched rods of different heights. The phantom was fixed in the head holder and multiple optimized gradient echo slices containing the clamp-integrated markers were acquired. After that we measured a T1 MPRAGE sequence with a slice thickness of 1.0 mm for navigation. The deepest points of the surface of the rods were defined as target points in image space. In three measurement series we referenced the phantom once with 4, once with 7 fiducials and twice automatically. In one series we performed only one automatic registration. The localization error was measured 3 times per rod and registration.

RESULTS

The median localization errors for standard registration with 7 fiducials were between 1.2 and 3.05 mm. With 4 fiducials, medians were in the range from 1.87 to 2.21 mm. For the automatic registration we obtained median localization errors between 0.88 and 2.13 mm. In 6 of the 8 samples that were compared the automatic registration showed an application accuracy that was highly significantly better (p < 0.001 in most cases) than that of fiducial-based standard registration.

CONCLUSION

The application accuracy found for automatic referencing is at least not worse than that for standard registration no matter whether 4 or 7 fiducial markers were used. Therefore, its use in the operating room is feasible. In combination with intraoperative MRI it may become a favorable alternative to standard fiducial-based registration especially when an intraoperative update of navigation data is necessary.

Image-guidance for surgical procedures

Contemporary imaging modalities can now provide the surgeon with high quality three- and four-dimensional images depicting not only normal anatomy and pathology, but also vascularity and function. A key component of image-guided surgery (IGS) is the ability to register multi-modal pre-operative images to each other and to the patient. The other important component of IGS is the ability to track instruments in real time during the procedure and to display them as part of a realistic model of the operative volume. Stereoscopic, virtual- and augmented-reality techniques have been implemented to enhance the visualization and guidance process. For the most part, IGS relies on the assumption that the pre-operatively acquired images used to guide the surgery accurately represent the morphology of the tissue during the procedure. This assumption may not necessarily be valid, and so intra-operative real-time imaging using interventional MRI, ultrasound, video and electrophysiological recordings are often employed to ameliorate this situation. Although IGS is now in extensive routine clinical use in neurosurgery and is gaining ground in other surgical disciplines, there remain many drawbacks that must be overcome before it can be employed in more general minimally-invasive procedures. This review overviews the roots of IGS in neurosurgery, provides examples of its use outside the brain, discusses the infrastructure required for successful implementation of IGS approaches and outlines the challenges that must be overcome for IGS to advance further.

Evaluation of registration techniques for spinal image guidance

Object

Paired point matching alone and paired point matching combined with surface matching are the two techniques used for the registration step in preoperative computerized tomography–based spinal image guidance. In the present study the authors sought to compare paired point–matching registration alone with paired point matching supplemented with surface matching to determine if the addition of surface matching improves navigational accuracy.

Methods

Pedicle screws were placed in three embalmed human cervicothoracic spinal specimens during image guidance to serve as a reference points. The specimens were then rescanned, and each level was registered using paired point matching alone and then by paired point supplemented with surface matching. Navigational accuracy was assessed by placing the stereotactic probe in the center of the screw head, and measuring the apparent distance between the screw head and probe on the computer monitor. Statistical analysis was used to compare the registration error and navigational error between the two techniques.

Seventy-five screws were placed at 46 vertebral levels. The mean registration error for the paired point matching/surface matching technique (0.5 mm) was significantly lower (p < 0.001) than that of the paired point matching alone technique (1.2 mm); however, the intertechnique difference in navigational error was nearly equivalent (1.3 mm compared with 1.4 mm) and statistically insignificant (p > 0.05).

Conclusions

Although the addition of surface matching to paired point registration significantly decreased the mean registration error, the actual navigational accuracy between the two techniques was equivalent when easily distinguishable points were meticulously selected. The use of paired point matching alone did not compromise the accuracy of navigation and is likely to result in decreased operating time.

Scale-invariant registration of monocular endoscopic images to CT-scans for sinus surgery

In this paper, we present a novel method for intra-operative registration directly from monocular endoscopic images. This technique has the potential to provide a more accurate surface registration at the surgical site than existing methods. It can operate autonomously from as few as two images and can be particularly useful in revision cases where surgical landmarks may be absent. A by-product of video registration is an estimate of the local surface structure of the anatomy, thus providing the opportunity to dynamically update anatomical models as the surgery progresses. Our approach is based on a previously presented method [Burschka, D., Hager, G.D., 2004. V-GPS (SLAM):--Vision-based inertial system for mobile robots. In: Proceedings of ICRA, 409-415] for reconstruction of a scaled 3D model of the environment from unknown camera motion. We use this scaled reconstruction as input to a PCA-based algorithm that registers the reconstructed data to the CT data and recovers the scale and pose parameters of the camera in the coordinate frame of the CT scan. The result is used in an ICP registration step to refine the registration estimates. The details of our approach and the experimental results with a phantom of a human skull and a head of a pig cadaver are presented in this paper.

Historical perspective on image-guided sinus surgery

Image-guided surgery has undergone rapid evolution, to the point where it is now a technology that is surgeon-friendly, relatively easy to set up, and reliable, making it a realistic and worthwhile option for endoscopic sinus surgery. Technologies will continue to advance as the market forces push companies to produce systems that are more accurate, faster, and more convenient. Head-tracking methodologies will likely progress away from headsets toward more reliable and safer modalities. Further integrations of surgical instrumentation, the ability to update images intraoperatively, and advancements in real-time imaging and robotics are likely to continue ata rapid rate.

Accuracy and cost analysis of image-guided sinus surgery

The use of image guidance in FESS has become widespread over the past several years. Numerous studies involving large numbers of patients illustrate the accuracy of these systems. In addition, case reports concerning patients who have extensive sinonasal neoplasms or distorted anatomy serve to demonstrate the usefulness of IGS. Studies by Metson et al [22] and Fried et al [23] have also investigated the surgeons' opinions of IGS. The vast majority of sinus surgeons have been pleased with the systems' ease of use and accuracy. Increased confidence in precisely localizing anatomical structures was the primary benefit. The major drawback to using image-guided systems was the increased operative time. Despite this, almost all surgeons who were questioned reported that they expect to increase their use of IGS in the future. By giving the surgeon real-time localization of surgical instruments, IGS could result in safer and more thorough surgery. This effect could have major implications for difficult surgeries in which distorted anatomy or extensive disease might otherwise result in incomplete eradication of the disease process. Studies examining these issues are necessary before a final conclusion can be drawn as to whether the accuracy achieved with current systems is truly beneficial and the cost is worth incurring.

Endoscopic Surgery of the Anterior Skull Base

OBJECTIVES/HYPOTHESIS

Traditional surgical approaches to the anterior skull base often involve craniotomy, facial incisions, disruption of skeletal framework, tracheotomy, and an extended hospital stay. As experience with endoscopic sinus surgery has grown, the techniques and equipment have been found to be adaptable to treatment of lesions of the anterior and central skull base. A minimally invasive endoscopic approach theoretically offers the advantages of avoiding facial incisions, osteotomies, and tracheotomy; surgery should be less painful, recovery quicker, and hospital stays should be shorter. The study attempted to assess endoscopic approaches to the anterior and central skull base for its ability to achieve those goals.

STUDY DESIGN

Retrospective review of 72 cases performed at a single institution from November 1996 to July 2003. A subgroup of 15 patients who underwent endoscopic approach to their pituitary tumors was compared with a similar group of 15 patients who underwent traditional open trans-sphenoidal surgery for their pituitary tumors.

METHODS

Patient records were analyzed and information tabulated for age, sex, disease, location of lesion, operative time, use of image-guided surgical systems, blood loss, length of intensive care unit stay, duration of operative pain, length of postoperative hospitalization, complications, and completeness of resection.

RESULTS

Of the cases, 86.1% were performed exclusively endoscopically, and 13.9% used a combination of endoscopic and open techniques. An image-guided surgical system was used in 83% of cases. Hospital length of stay was 2.3 days for the exclusively endoscopic group as opposed to 8 days for the combined group. With the patients with pituitary tumors, operative times were similar between the two groups (255.13 vs. 245.73 min), blood loss was less in the endoscopic group (125.33 vs. 243.33 mL), pain duration was shorter in the endoscopic group (10 of 15 patients pain free on postoperative day 1 vs. 2 of 15 patients pain free in the open group), and intensive care unit stay and hospital length of stay were both shorter in the endoscopic group. Complication rates and completeness of resection was similar in both groups, although the open group had a higher rate of complications related to the approach to the sella.

CONCLUSION

The study demonstrated the safety and efficacy of judicious endoscopic approaches to anterior skull base lesions. An outcomes assessment in pituitary surgery demonstrates advantages of an endoscopic approach in appropriate cases.

Der anterosigmoidale Zugang

BACKGROUND AND OBJECTIVE

The antero- or persigmoid approach preserves all functional structures of the petrous bone and, therefore, is an alternative to the classic laterobasal approaches for exploring the petroclival region. As high morbidity is assumed and it is a time consuming procedure, this approach is not well known.

METHODS AND PATIENTS

Initially, a cadaver study using computer assisted surgery was used to determine the surgical workflow before we optimized our surgical procedures.

RESULTS

In a series of 7 patients with benign tumors growing from the petrous apex to the petroclival region, we were able to resect all tumors completely via the anterosigmoidal surgical corridor using computer assisted surgery.

CONCLUSIONS

The navigation-guided anterosigmoidal approach is an excellent method, allowing a good overview of the petroclival region. In patients suffering from complex petroclival tumors, it offers a real chance to achieve complete microsurgical tumor resection without functional defects by an interdisciplinary neuro-oto-surgical session.

[Precision of navigation-assisted surgery of the thoracic and lumbar spine]

The goal of these studies was to evaluate the accuracy of in vivo and in vitro application of CT- and C-arm-based navigation at the thoracic and lumbar spine. With CT based navigation, 82 pedicle screws were consecutively inserted, 53 into the thoracic and 29 into the lumbar spine. Seven (13%) perforations were detected at the thoracic spine and two (7%) at the lumbar spine. Additionally, minor perforations below the thread depth were seen in six (11%) thoracic and in two (7%) lumbar instrumentation. With C-arm-based navigation, 74 screws were consecutively placed into 38 thoracic and 36 lumbar pedicles. Perforations were noted in ten (26%) thoracic and four (11%) lumbar implants. Minor perforations were observed in another nine (24%) thoracic and ten (28%) lumbar pedicles. The observer-independent and standardized in vitro study based on a transpedicular 3.2-mm drill hole aiming a 4-mm steel ball in a plastic bone model showed pedicle perforations of the drill canal only in thoracic vertebrae, 1 of 15 in CT-based and 3 of 15 in C-arm navigation. The quantitative calculation of the smallest distance between the central line through the drill canal and the center of the steel ball resulted in 1.4 mm (0.5-4.8 mm) for the CT-based navigation at the thoracic spine and in 1.8 mm (0.5-3 mm) at the lumbar spine. For the C-arm based navigation the distance was 2.6 mm (0.9-4.8 mm) for the thoracic spine and 2 mm (1.2-3 mm) for the lumbar spine. In our opinion, the clinical results of the comparative accuracy of CT- and C-arm-based navigation in the present study showed moderate advantages of the CT-based technique in the thoracic spine, whereas CT- and C-arm based navigation had comparable perforation rates at the lumbar pedicle. The results of the experimental study correlated with the clinical data.

Computer-aided navigation in neurosurgery

The article comprises three main parts: a historical review on navigation, the mathematical basics for calculation and the clinical applications of navigation devices. Main historical steps are described from the first idea till the realisation of the frame-based and frameless navigation devices including robots. In particular the idea of robots can be traced back to the Iliad of Homer, the first testimony of European literature over 2500 years ago. In the second part the mathematical calculation of the mapping between the navigation and the image space is demonstrated, including different registration modalities and error estimations. The error of the navigation has to be divided into the technical error of the device calculating its own position in space, the registration error due to inaccuracies in the calculation of the transformation matrix between the navigation and the image space, and the application error caused additionally by anatomical shift of the brain structures during operation. In the third part the main clinical fields of application in modern neurosurgery are demonstrated, such as localisation of small intracranial lesions, skull-base surgery, intracerebral biopsies, intracranial endoscopy, functional neurosurgery and spinal navigation. At the end of the article some possible objections to navigation-aided surgery are discussed.

Intraoperative ultrasound imaging: comparison of pathomorphological findings in US versus CT, MRI and intraoperative findings

Since 1987, Ultrasound (US) is performed routinely as real time navigation system in our neurosurgical practice. In 374 cases with different pathologies the preoperative CT and MRI images were compared with the intraoperative US images and the operative findings. In all instances, the lesion could be localized and described in detail. US findings correlated with the findings an CT/MRI, concerning size and shape of lesions. US allowed the differentiation of more structural details within tissue compartments. The demarcation of gliomas was not as well defined in US as compared to CT/MRI, which correlated with the intraoperative situation. As for CT/MRI imaging, a correlation between US findings and histopathology of the lesion was not possible. In our opinion. intraoperative US imaging is an excellent tool for localization of cerebral and medullar lesions and for detailed description of their interior. This indicates a widespread applicability of this method in neurosurgery as an anatomical link between preoperative imaging and the reality of the operative field.

Passive marker computer-aided sinonasal and cranial base surgery: observations from a learning curve

To assess the feasibility of passive marker computer-aided surgery in a single institution, we performed 22 procedures in 21 patients with disorders including sinonasal tumors (n = 9), fungal sinusitis (n = 4), recurrent polyps (n = 3), chronic sinusitis (n = 3), and cerebrospinal fluid rhinorrhea (n = 2). Passive marker computer-aided surgery was successful in 19 of the 21 patients. The accuracy was on the order of 1.35 mm. Probe conversion, rotation, and cordlessness were helpful in all 19 cases. The system helped with landmarks (n = 14), margins (n = 7), skull base (n = 6), orbit (n = 5), and approach (n = 4). Computer-aided surgery accurately confirmed the location of an instrument and demonstrated tumor-normal tissue interfaces. It aided the surgeon in procedures on the sinonasal area and cranial base. The potential advantages of a passive marker system as compared with other available technologies center around the ability to convert and/or rotate virtually any instrument to a cordless imaging probe on demand during the operation.

Clinical evaluation of postoperative sinonasal surgical patients

Rhinosinusitis is a very common upper respiratory illness. Functional endoscopic sinus surgery has been successfully utilized in the surgical treatment of medically refractory rhinosinusitis. The endoscopic approach has also been extended to various skull base lesion and sinonasal neoplasms. This paper provides a brief overview of the clinical aspect of evaluating sinonasal surgical patients. Judicious use of nasal endoscopy and importance of CT imaging of the sinuses are discussed. Emphasis is placed on establishing communication between the sinus surgeon and radiologist to facilitate evaluation of the sinonasal surgical patients. liming and specific types of imaging studies before any revision sinus surgery are discussed. Major complications associated with endoscopic sinus surgery are reviewed.

The use of an image guidance system in retrieving lost medial rectus muscles

INTRODUCTION

Finding a lost medial rectus muscle can be difficult. We present 2 patients in whom image guidance technology assisted in the recovery of a lost medial rectus muscle.

METHODS

Two patients (ages 19 and 33), both with lost medial rectus muscles, underwent computerized tomography of their heads, faces, and orbits. The muscles were both lost after strabismus surgery 7 and 19 years ago, respectively. These images were then loaded into an image guidance system (LandmarX, Xomed Co, Jacksonville, Fla) and served as a "map" to locate the lost medial rectus muscle intraoperatively. Using a transnasal endoscopic approach, the lamina papyracea was exposed. The area of the lamina closest to the lost medial rectus was identified using a guidance probe. After the periorbita was exposed, the guidance probe was used to confirm the location of the medial rectus muscle. The muscle was then isolated transnasally and passed into the orbit using forceps. It was then sutured onto the globe.

RESULTS

The medial rectus was identified transnasally and reattached to the globe in both cases. Adduction improved from complete deficits in both patients to 80% and 50% adduction deficits, respectively.

DISCUSSION

The transnasal endoscopic approach to retrieve the medial rectus has been described before. For these patients, image guidance technology successfully identified the appropriate areas for the surgeons to locate the lost muscle. The use of this technique decreased operative times and reduced the extent of the dissection required, which should also reduce long-term scarring.

CONCLUSION

Image guidance technology, with its capability of 3-dimensional images, can be used to assist surgeons in finding lost medial rectus muscles.