Interactive intraoperative localization using an infrared-based system

Computer-Assisted Planning and Intraoperative Navigation in the Management of Temporomandibular Joint Ankyloses

Temporomandibular joint ankyloses are a fusion of the mandibular condyle to the base of skull. Surgical advances have stemmed from innovation in computer planning, guidance, and intraoperative navigation, allowing surgeons to restore form and function with greater precision, predictability, and safety. Preoperative computer virtual surgical planning used the computed tomography scan data to render a 3-dimensional image that can be used for surgical simulations and fabrication of intraoperative aids. Temporomandibular joint reconstruction should be considered as a predictable option in the management of temporomandibular joint ankylosis. Intraoperative navigation allows for continuous real-time 3-dimensional positioning of instruments.

Assessment of the Accuracy and Errors of Head-Up Display by an Optical Neuronavigation System in Brain Tumor Surgery

BACKGROUND: A head-up display (HUD) in which navigational information is projected into the microscope view may enable surgeons to perform operations more efficiently. Projecting depictions of both tumor and important intracranial structures on the HUD may facilitate safe surgery.

OBJECTIVE: To investigate accuracy and errors regarding important intracranial structures, errors due to brain shifts, and preservation rates for important intracranial structures.

METHODS: A total of 184 surgeries in 172 patients were performed using this operation system. Postoperatively, we determined accuracy and errors for actual structures and virtual reality on the HUD and performed statistical analyses.

RESULTS: Preresection accuracy for important intracranial structures was highest for the internal carotid artery (ICA; 90.4%) and lowest for the posterior inferior cerebellar artery (53.6%). Differences between pre- and postresection accuracy were greatest, in descending order, for the cortical vein (P < .0001), V4 segment of vertebral artery (P < .0001), and anterior inferior cerebellar artery (P = .00780), whereas differences between pre- and postresection errors were smallest for the cranial nerve V (P = .500), middle cerebral artery (P = .0313), and ICA (P = .0313). Cases of poor preresection accuracy and large differences in pre- to postresection accuracy were seen in the prone position.

CONCLUSION: A reliable surgical resection rate was achieved using the HUD, and reliable preservation of important intracranial structures was also possible. Accuracy was concluded to be within an acceptable range.

Video-Assisted Navigation for Adjustment of Image-Guidance Accuracy to Slight Brain Shift

BACKGROUND

Information supplied by an image-guidance system can be superimposed on the operating microscope oculars or on a screen, generating augmented reality. Recently, the outline of a patient's head and skull, injected in the oculars of a standard operating microscope, has been used to check the registration accuracy of image guidance.

OBJECTIVE

To propose the use of the brain surface relief and superficial vessels for real-time intraoperative visualization and image-guidance accuracy and for intraoperative adjustment for brain shift.

METHODS

A commercially available image-guidance system and a standard operating microscope were used. Segmentation of the brain surface and cortical blood vessel relief was performed manually on preoperative computed tomography and magnetic resonance images. The overlay of segmented digital and real operating-microscope images was used to monitor image-guidance accuracy. Adjustment for brain shift was performed by manually matching digital images on real structures.

RESULTS

Experimental manipulation on a phantom proved that the brain surface relief could be used to restore accuracy if the primary registration shifted. Afterward, the technique was used to assist during surgery of 5 consecutive patients with 7 deep-seated brain tumors. The brain surface relief could be successfully used to monitor registration accuracy after craniotomy and during the whole procedure. If a certain degree of brain shift occurred after craniotomy, the accuracy could be restored in all cases, and corticotomies were correctly centered in all cases.

CONCLUSION

The proposed method was easy to perform and augmented image-guidance accuracy when operating on small deep-seated lesions.

From the idea to its realization: the evolution of minimally invasive techniques in neurosurgery

Minimally invasive techniques in neurosurgery evolved in two steps. Many minimally invasive concepts like neuronavigation, endoscopy, or frame based stereotaxy were developed by the pioneers of neurosurgery, but it took decades till further technical developments made the realization and broad clinical application of these early ideas safe and possible. This thesis will be demonstrated by giving examples of the evolution of four minimally invasive techiques: neuronavigation, transsphenoidal pituitary surgery, neuroendoscopy and stereotaxy. The reasons for their early failure and also the crucial steps for the rediscovery of these minimally invasive techniques will be analysed. In the 80th of the 20th century endoscopy became increasingly applied in different surgical fields. The abdominal surgeons coined as first for their endoscopic procedures the term minimally invasive surgery in contrast to open surgery. In neurrosurgery the term minimally invasive surgery stood not in opposiotion to open procedures but was understood as a general concept and philosophy using the modern technology such as neuronavigation, endoscopy and planing computer workstations with the aim to make the procedures less traumatic.

Interactive image guidance in skull base surgery using an opto-electronic device

The applicability of an image guidance frameless system based on an opto-electronic sensor device in skull base surgery was explored in this study. Five embalmed heads with external fiducial markers placed in noncoplanar points were scanned (CT scan) and different skull base approaches were reproduced in these specimens. The opto-electronic system is comprised of an infrared camera, a local rigid body, and a 24-light-emitting diode probe attached to different surgical instruments. DOS-based calibration and transformation software and Unix-based surgical planning software were also used. The anatomic landmarks identified during the dissection were matched with the corresponding points derived from computed tomographic (CT) scans. This information allowed the surgeon to develop a three-dimensional representation of the surgical field and to anticipate the next anatomic structure encountered during the dissection. This infrared device operated in real time, is not affected by external factors with regard to its accuracy, and does not interfere with standard neurosurgical techniques. This frameless system is helpful in minimizing the risk of morbidity and provides an accurate guide during the approach, as well as unobstructed access to the surgical field.

Rapid fabrication of custom patient biopsy guides

Image‐guided surgery is currently performed using frame‐based as well as frameless approaches. In order to reduce the invasive nature of stereotactic guidance and the cost in both equipment and time required within the operating room, we investigated the use of rapid prototyping (RP) technology. In our approach, we fabricated custom patient‐specific face masks and guides that can be applied to the patient during stereotactic surgery. While the use of RP machines has previously been shown to be satisfactory from an accuracy standpoint, one of our design criteria – completing the entire build and introduction into the sterile field in less than two hours – was unobtainable.⁽¹⁾ Our primary problems were the fabrication time and the nonresistance of the built material to high‐temperature sterilization. In the current study, we have investigated the use of subtractive rapid prototyping (SRP) machines to perform the same quality of surgical guidance, while improving the fabrication time and allowing for choosing materials suitable for sterilization. Because SRP technology does not offer the same flexibility as RP in terms of prototype shape and complexity, our software program was adapted to provide new guide designs suitable for SRP fabrication. The biopsy guide was subdivided for a more efficient build with the parts being uniquely assembled to form the final guide. The accuracy of the assembly was then assessed using a modified Brown‐Roberts‐Wells phantom base by which the position of a biopsy needle introduced into the guide can be measured and compared with the actual planned target. These tests showed that: 1) SRP machines provide an average technical accuracy of 0.77 mm with a standard deviation of the mean of 0.07 mm, and 2) SRP allows for fabrication and sterilization within three‐and‐a‐half hours after diagnostic image acquisition. We are confident that technology is capable of reducing this time to less than one hour. Further tests are being conducted to determine the registration accuracy of the face mask on the patient's head under IRB‐approved trials. The accuracy of this new guidance technology will be verified by judging it against current frame‐based or frameless systems.

PACS number: 87.57.Gg

Neuronavigation: geneology, reality, and prospects

Currently, neuronavigation is an indivisible and indispensable part of the neurosurgical reality with a significant potential impact in each neurosurgical procedure. The history of neuronavigation is quite short (< 3 decades), but full of highly promising achievements. The advent of neuronavigation would be unimaginable without the development of imaging technology, electronics, robotics, and space technology. The history of neuroradiology is reviewed briefly parallel with the detailed evolution of frame-based stereotaxy and its successor—neuronavigation. The historic milestones and the state of the art of neuronavigation are discussed in a genealogical manner. The future trends of neuronavigation as integrated with intraoperative CT, MR, and ultrasonography, as well as with robotic systems are outlined.

The impact of workflow and volumetric feedback on frameless image-guided neurosurgery

OBJECTIVE

During image-guided neurosurgery, if the surgeon is not fully orientated to the surgical position, he or she will briefly shift attention toward the visualization interface of an image guidance station, receiving only momentary "point-in-space" information. The aim of this study was to develop a novel visual interface for neuronavigation during brain tumor surgery, enabling intraoperative feedback on the entire progress of surgery relative to the anatomy of the brain and its pathology, regardless of the interval at which the surgeon chooses to look.

METHODS

New software written in Java (Sun Microsystems, Inc., Santa Clara, CA) was developed to visualize the cumulative recorded instrument positions intraoperatively. This allowed surgeons to see all previous instrument positions during the elapsed surgery. This new interactive interface was then used in 17 frameless image-guided neurosurgical procedures. The purpose of the first 11 cases was to obtain clinical experience with this new interface. In these cases, workflow and volumetric feedback (WVF) were available at the surgeons' discretion (Protocol A). In the next 6 cases, WVF was provided only after a complete resection was claimed (Protocol B).

RESULTS

With the novel interactive interface, dynamics of surgical resection, displacement of cortical anatomy, and digitized functional data could be visualized intraoperatively. In the first group (Protocol A), surgeons expressed the view that WVF had affected their decision making and aided resection (10 of 11 cases). In 3 of 6 cases in the second group (Protocol B), tumor resections were extended after evaluation of WVF. By digitizing the cortical surface, an impression of the cortical shift could be acquired in all 17 cases. The maximal cortical shift measured 20 mm, but it typically varied between 0 and 10 mm.

CONCLUSION

Our first clinical results suggest that the embedding of WVF contributes to improvement of surgical awareness and tumor resection in image-guided neurosurgery in a swift and simple manner.

Image-to-patient registration techniques in head surgery

Frame-based stereotaxy was developed in neurosurgery at the beginning of the last century, evolving from atlas-based stereotaxy to stereotaxy based on the individual patient's image data. This established method is still in use in neurosurgery and radiotherapy. There have since been two main developments based on this concept: frameless stereotaxy and markerless registration. Frameless stereotactic systems ('navigation systems') replaced the cumbersome stereotactic frame by mechanically and later also optically or magnetically tracked instruments. Stereotaxy based on the individual patient's image data introduced the problem of patient-to-image data registration. The development of navigation systems based on frameless stereotaxy has dramatically increased its use in surgical disciplines other than neurosurgery, but image-guided surgery based on fiducial marker registration needs dedicated imaging for registration purposes, in addition to the diagnostic imaging that might have been performed. Markerless registration techniques can overcome the resulting additional cost and effort, and result in more widespread use of image-guided surgery techniques. In this review paper, the developments that led to today's navigation systems are outlined, and the applications and possibilities of these methods in the field of maxillofacial surgery are presented.

Neuronavigation and surgery of intracerebral tumours

Approximately four decades after the successful clinical introduction of framebased stereotactic neurosurgery by Spiegel and Wycis, frameless stereotaxy emerged to enable more elaborate image guidance in open neurosurgical procedures. Frameless stereotaxy, or neuronavigation, relies on one of several different localizing techniques to determine the position of an operative instrument relative to the surgical field, without the need for a coordinate frame rigidly fixed to the patients' skull. Currently, most systems are based on the optical triangulation of infrared light sources fixed to the surgical instrument. In its essence, a navigation system is a three-dimensional digitiser that correlates its measurements to a reference data set, i.e. a preoperatively acquired CT or MRI image stack. This correlation is achieved through a patient-to-image registration procedure resulting in a mathematical transformation matrix mapping each position in 'world space' onto 'image space'. Thus, throughout the remainder of the surgical procedure, the position of the surgical instrument can be demonstrated on a computer screen, relative to the CT or MRI images. Though neuronavigation has become a routinely used addition to the neurosurgical armamentarium, its impact on surgical results has not yet been examined sufficiently. Therefore, the surgeon is left to decide on a case-by-case basis whether to perform surgery with or without neuronavigation. Future challenges lie in improvement of the interface between the surgeon and the neuronavigator and in reducing the brainshift error, i.e. inaccuracy introduced by changes in tissue positions after image acquisition.

Qualitative and quantitative accuracy of CAOS in a standardized in vitro spine model

Pedicle breach with screw implantation is relatively common. For clinical application of computer-assisted orthopaedic surgery, it is important to quantitatively know the accuracy and localization of any guidance modality. We ascertained the accuracy of computed tomography and C-arm-based navigated drilling versus conventional fluoroscopy using an artificial thoracic and lumbar spine model. The 3.2-mm diameter transpedicle drilling target was the center of a 4-mm steel ball fixed in the anterior left pedicle axis. After drilling, we used computed tomography to verify the position of the steel ball and the canal and visually explored for cortex perforation. Quantitative vector calculation showed computed tomography-based navigation had the greatest accuracy (median, d(thoracic) = 1.4 mm; median, d(lumbar) = 1.8 mm) followed by C-arm navigation (median, d(thoracic) = 2.6 mm; median, d(lumbar) = 2 mm) and the conventional procedure (median, d(thoracic) = 2.2 mm; median, d(lumbar) = 2.7 mm). Visual examination showed a decreased perforation rate in navigated drillings. We found no correlation between pedicle breaches and inaccurate drilling. The data suggest computer-assisted orthopaedic surgery cannot provide sub-millimeter accuracy, and complete prevention of pedicle perforation is not realistic.

Interventional and intraoperative MRI at low field scanner--a review

Magnetic resonance imaging (MRI) is a cutting edge imaging modality in detecting diseases and pathologic tissue. The superior soft tissue contrast in MRI allows better definition of the pathology. MRI is increasingly used for guiding, monitoring and controlling percutaneous procedures and surgery. The rapid development of interventional techniques in radiology has led to integration of imaging with computers, new therapy devices and operating room like conditions. This has projected as faster and more accurate imaging and hence more demanding procedures have been applied to the repertoire of the interventional radiologist. In combining features of various other imaging modalities and adding some more into them, interventional MRI (IMRI) has potential to take further the interventional radiology techniques, minimally invasive therapies and surgery. The term "Interventional MRI" consists in short all those procedures, which are performed under MRI guidance. These procedures can be either percutaneous or open surgical of nature. One of the limiting factors in implementing MRI as guidance modality for interventional procedures has been the fact, that most widely used magnet design, a cylindrical magnet, is not ideal for guiding procedures as it does not allow direct access to the patient. Open, low field scanners usually operating around 0.2 T, offer this feature. Clumsy hardware, bad patient access, slow image update frequency and strong magnetic fields have been other limiting factors for interventional MRI. However, the advantages of MRI as an imaging modality have been so obvious that considerable development has taken place in the 20-year history of MRI. The image quality has become better, ever faster software, new innovative sequences, better MRI hardware and increased computing power have accelerated imaging speed and image quality to a totally new level. Perhaps the most important feature in the recent development has been the introduction of open configuration low field MRI devices in the early 1990s; this enabled direct patient access and utilization of the MRI as an interventional device. This article reviews the current status of interventional and intraoperative MRI with special emphasis in low field surrounding.

Dynamic, three-dimensional optical tracking of an ablative laser beam

Surgical resection remains the treatment of choice for brain tumors with infiltrating margins but is currently limited by visual discrimination between normal and neoplastic marginal tissues during surgery. Imaging modalities such as computed tomography, magnetic resonance, positron emission tomography, and optical techniques can accurately localize tumor margins. We believe coupling the fine resolution of current imaging techniques with the precise cutting of midinfrared lasers through image-guided neurosurgery can greatly enhance tumor margin resection. This paper describes a feasibility study designed to optically track in three-dimensional space the articulated arm delivery of a noncontact ablative laser beam. To enable optical tracking of the laser beam focus, infrared-emitting diodes (IREDs) were attached to a handpiece machined for the distal end of the articulated arm of a surgical carbon dioxide laser. Crosstalk between the ablative laser beam and the tracking diodes was measured. The geometry of the adapted laser handpiece was characterized to track an externally attached passive tip and the laser beam focus. Target localization accuracies were assessed for both instrument points-of-interest and the sources of tracking errors were investigated. Stray infrared laser light did not affect optical tracking accuracy. The mean target registration errors while optically tracking the laser handpiece with a passive tip and the laser beam focus were 1.31+/-0.50 mm and 2.31+/-0.92 mm, respectively, and were equivalent to the errors tracking a 24-IRED pen probe from Northern Digital in a side-by-side comparison. The majority of error during ablation tracking derived from registration accuracy between physical space and the defined space of the ablation phantom and from an inability to freehand align the laser focus with the target in a consistent manner. While their magnitudes depend on spatial details of the tracking setup (e.g., number and distribution of fiducial points, working distance from the camera, etc.), these errors are inherent to any freehand laser surgery.

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.

Research progress in the last quarter of the 20th century at the University of Tokyo and Tokyo Women's Medical University

Professor Keiji Sano described the history of neurosurgery in Japan until 1975. After World War II, not only neurosurgery but all fields of medicine were devastated in Japan. Professor Sano contributed greatly to the reform and modernization of neurosurgery during that very difficult era in Japan. He performed much research by himself and also as a leader of research groups on stereotactic and functional neurosurgery, cerebrovascular diseases, head injuries, and brain tumors. He organized the Fifth International Congress of Neurological Surgery in Tokyo in 1973. I succeeded in the chairmanship of the Department of Neurosurgery of the University of Tokyo in 1981. We have performed research on the treatment of brain tumors and cerebrovascular diseases. To obtain the best results for brain tumor treatment, we have introduced several new radiotherapeutic methods, such as the gamma knife, heavy-particle irradiation, and the photon radiosurgery system. To improve surgical treatment, we have energetically engaged in medical engineering research on computer-assisted surgical systems (intraoperative monitoring and navigation systems). We have also performed much research on chemotherapy and immunotherapy. In the field of cerebrovascular diseases, the main research projects have been focused on the mechanism and treatment of vasospasm and brain edema after subarachnoid hemorrhage. I summarize the results of our research performed in the Department of Neurosurgery of the University of Tokyo until 1992 and at Tokyo Women's Medical University after 1992, in the last quarter of the 20th century.

The process and development of image-guided procedures

Medical imaging has been used primarily for diagnosis. In the past 15 years there has been an emergence of the use of images for the guidance of therapy. This process requires three-dimensional localization devices, the ability to register medical images to physical space, and the ability to display position and trajectory on those images. This paper examines the development and state of the art in those processes.

Nerve root infiltration of the first sacral root with MRI guidance

The purpose of this clinical trial was to describe the methodology and evaluate the accuracy of optical tracking-based magnetic resonance (MR)-guided infiltration of the first sacral (S1) root. Thirty-five infiltrations were performed on 34 patients with a 0. 23-T open C-arm magnet installed in a fully equipped operation room with large-screen (36 inches) display and optical navigator utilizing infrared passive tracking. T1 and T2 fast spin-echo (FSE) images were used for localizing the target and fast field echo for monitoring the procedure. Saline as contrast agent in single-shot (SS)FSE images gave sufficient contrast-to-noise ratio. Twenty-four patients had unoperated L5/S1 disc herniation, and 10 had S1 root irritation after failed back surgery. Needle placement was successful in 97% of the cases, and no complications occurred. Outcome was evaluated 1-6 months (mean 2.2 months) after the procedure and was comparable to that of other studies using fluoroscopy or computed tomography guidance. MR-guided placement of the needle is an accurate technique for first sacral root infiltration.

Accuracy and clinical applicability of a passive marker based frameless neuronavigation system

A passive marker system permits the inclusion of an unlimited number of instruments and other devices during frameless stereotaxy. The aim of this study was to evaluate the accuracy and clinical applicability of a passive marker based frameless image guided system (VectorVision; BrainLab, Heimstetten, Germany) developed for surgical planning and intraoperative image guidance. The system was first applied to a plastic phantom to determine the accuracy of the system by measuring the difference between the actual probe position and its analogous position on the monitor screen. The navigational device was subsequently applied to 40 procedures for brain tumours and cavernomas. The mean error value between the image on the monitor screen and the real location in the phantom and the clinical study was 1.45 mm (+/-0.99) and 4.05 mm (+/-3.62), respectively. Many different instruments could be employed as pointing devices. It was helpful in minimising the size of the craniotomy. An average lengthening of the surgical procedure of 20 minutes was experienced. The neuronavigation system proved to be a useful surgical tool to approach and detect lesions larger than 5 mm in diameter. The passive marker technology is intuitive and enables the surgeon to use his or her own instruments at any time as a pointing device, thus avoiding further costs for specially designed surgical equipment.

Intraoperative ultrasound for guidance and tissue shift correction in image-guided neurosurgery

We present a surgical guidance system that incorporates pre-operative image information (e.g., MRI) with intraoperative ultrasound (US) imaging to detect and correct for brain tissue deformation during image-guided neurosurgery (IGNS). Many interactive IGNS implementations employ pre-operative images as a guide to the surgeons throughout the procedure. However, when a craniotomy is involved, tissue movement during a procedure can be a significant source of error in these systems. By incorporating intraoperative US imaging, the target volume can be scanned at any time, and two-dimensional US images may be compared directly to the corresponding slice from the pre-operative image. Homologous points may be mapped from the intraoperative to the pre-operative image space with an accuracy of better than 2 mm, enabling the surgeon to use this information to assess the accuracy of the guidance system along with the progress of the procedure (e.g., extent of lesion removal) at any time during the operation. Anatomical features may be identified on both the pre-operative and intraoperative images and used to generate a deformation map, which can be used to warp the pre-operative image to match the intraoperative US image. System validation is achieved using a deformable multi-modality imaging phantom, and preliminary clinical results are presented.

Effect of optical digitizer selection on the application accuracy of a surgical localization system-a quantitative comparison between the OPTOTRAK and flashpoint tracking systems

Application accuracy is a crucial factor for stereotactic surgical localization systems, in which space digitization camera systems are one of the most critical components. In this study we compared the effect of the OPTOTRAK 3020 space digitization system and the FlashPoint Model 3000 and 5000 3D digitizer systems on the application accuracy for interactive localization of intracranial lesions. A phantom was mounted with several implantable frameless markers which were randomly distributed on its surface. The target point was digitized and the coordinates were recorded and compared with reference points. The differences from the reference points represented the deviation from the "true point." The root mean square (RMS) was calculated to show the differences, and a paired t-test was used to analyze the results. The results with the phantom showed that, for 1-mm sections of CT scans, the RMS was 0.76 +/- 0. 54 mm for the OPTOTRAK system, 1.23 +/- 0.53 mm for the FlashPoint Model 3000 3D digitizer system, and 1.00 +/- 0.42 mm for the FlashPoint Model 5000 system. These preliminary results showed that there is no significant difference between the three tracking systems, and, from the quality point of view, they can all be used for image-guided surgery procedures.

Computer-assisted resection of cerebral arteriovenous malformations

OBJECTIVE

A series of 22 patients with arteriovenous malformations (AVMs) were surgically treated using computer-assisted image guidance. The value of image guidance for nidus definition and detection of feeding arteries and draining veins was assessed.

METHODS

Seven of the 22 patients presented with hemorrhage. The sizes of the AVMs ranged from 1 to 8 cm. Six patients underwent preoperative embolization. For 18 patients (81.8%), the AVMs were located in highly eloquent areas. A passive-marker-based neuronavigation system (BrainLab, Heimstetten, Germany) was used for intraoperative image guidance. Segmentation of the pathological vessels was performed preoperatively, on the basis of 2-mm helical computed tomographic angiographic slices, to obtain three-dimensional reconstructions of the AVMs. Temporary clips were initially placed on all identifiable feeding arteries, for intranidal pressure reduction before AVM dissection. Dissection of the AVMs was then performed along the main draining veins, as identified by neuronavigation. Patient follow-up monitoring ranged from 3 to 16 months (median, 7 mo).

RESULTS

The computer-calculated registration accuracy ranged between 1.1 and 3.1 mm (median, 1.4 mm). Exact nidus definition was possible for all 22 patients. The principal draining veins were also identified for all patients. Feeding arteries could be detected after the segmentation process when the vessels were at least 3 mm in diameter (19 patients). Complete collapse of the AVMs was achieved with initial clip application for 3 patients; partial intranidal pressure reduction was observed for 12 patients. No significant decompression by feeder clipping was possible for pre-embolized AVMs. Perioperative mortality and morbidity rates were 0 and 14%, respectively.

CONCLUSION

This image-guided technology allows observation of the relationship between AVMs and adjacent brain structures, increasing spatial orientation during surgery. Definition of an optimal surgical approach and early localization of feeding arteries for temporary occlusion minimize tissue manipulation and enhance the safety of direct dissection along the draining veins, which is necessary in eloquent areas.

Intraoperative imaging techniques in the treatment of brain tumors

Despite significant advances in medical imaging techniques and their routine preoperative use, real-time intraoperative information regarding anatomy remains of indisputable importance to neurosurgeons. Intraoperative displacement of the brain tissue caused by surgical retraction or the resection cavity itself, as well as shift caused by cerebrospinal fluid leakage, may result in alteration of the surgical anatomy of the lesion and surrounding structures. Neurosurgical navigation methods are beneficial in providing accurate intraoperative information regarding the anatomy of the surgical field. Furthermore, interactive image guidance may decrease incision lengths, operating times, and postoperative morbidity. This review focuses on recent developments in neurosurgical navigational techniques that enable real-time anatomic visualization during brain tumor surgery.

Transpedicle screw fixation of the cervical spine

The use of posterior cervical spine fixation has become increasingly popular in recent years. Dissatisfaction with lateral mass fixation, especially at the cervicothoracic junction, has led spine surgeons to use cervical pedicle screw fixation for reconstruction in numerous cervical spine disorders. The biomechanical advantage of a three-column fixation device implanted to secure an unstable cervical spine has proven to be a valuable tool in the spine surgeon's armamentarium. Successful placement of a pedicle screw in the cervical spine requires a sufficient three-dimensional understanding of pedicle morphology to allow accurate identification of the ideal screw axis. Variability in cadaveric based morphometric measurements used to guide the surgeon in the placement of a pedicle screw has raised legitimate concerns as to whether transpedicle fixation can be applied without significant neurovascular complications. The emergence of computer assisted image guidance systems may be implemented in the operative protocol to improve the accurate placement of a pedicle screw. The indications for placement of a pedicle screw in the cervical spine are beginning to evolve. Only surgeons experienced in transpedicle screw fixation and surgery of the cervical spine should perform this method of instrumentation.

MR-guided procedures using contemporaneous imaging frameless stereotaxis in an open-configuration system

Frameless MR-guided procedures have had limited application using conventional closed magnets, due largely to the technical difficulties involved. As a result of in-room MR image-monitoring capabilities, new open-design magnets now allow frameless stereotaxis using contemporaneous imaging to guide more invasive procedures. We evaluate our clinical experience with this new technique. An open-design 0.2 T magnet (Siemens OPEN) combined with an in-room monitor was used for 33 frameless MR-guided procedures (aspiration cytology, biopsy, and/or treatment) in a variety of locations in the head, neck, spine, brain, pelvis, and abdomen. Success of the procedure was based on the ability to accurately position the instrument in the target region to allow biopsy and/or treatment. The open-design magnet allowed the physician to directly access the patient for frameless stereotaxis as the procedure was performed. The in-room monitor provided contemporaneous imaging feedback during the procedure for successful placement of the instrument in the target region. Twenty-eight biopsy and five treatment procedures were performed. In all cases the technique resulted in successful placement of the instrument within the target tissue to complete the procedure. MR-guided procedures using contemporaneous imaging frameless stereotaxis are possible in an open-design magnet with in-room image monitoring and offer exciting possibilities for further development.

Computed intraoperative navigation guidance--a preliminary report on a new technique

OBJECTIVE

To assess the value of a computer-assisted three-dimensional guidance system (Virtual Patient System) in maxillofacial operations.

DESIGN

Laboratory and open clinical study.

SETTING

Teaching Hospital, Austria.

SUBJECTS

6 patients undergoing various procedures including removal of foreign body (n=3) and biopsy, maxillary advancement, and insertion of implants (n=1 each).

INTERVENTIONS

Storage of computed tomographic (CT) pictures on an optical disc, and imposition of intraoperative video images on to these. The resulting display is shown to the surgeon on a micromonitor in his head-up display for guidance during the operations.

MAIN OUTCOME MEASURES

To improve orientation during complex or minimally invasive maxillofacial procedures and to make such operations easier and less traumatic.

RESULTS

Successful transferral of computed navigation technology into an operation room environment and positive evaluation of the method by the surgeons involved.

CONCLUSIONS

Computer-assisted three-dimensional guidance systems have the potential for making complex or minimally invasive procedures easier to do, thereby reducing postoperative morbidity.

History of spinal cord stereotaxy

Stereotactic and functional neurosurgery has experienced a remarkable degree of development during the last 50 years, from the plaster of Paris frame of Spiegel and Wycis to the technology of frameless stereotaxis. Although predominantly used for intracranial procedures, stereotaxy has its roots in experimental studies of the spinal cord. The field of spinal cord stereotaxy has not received the same amount of attention as supratentorial surgery, but there have been significant contributions to the field that have helped to further our understanding of spinal cord anatomy and physiology. Now that frameless stereotaxis has reached clinical practice, there may be further developments in the field of spinal surgery: this technique may prove useful for spinal fusion operations and, possibly, intramedullary operations as well.

The interactive use of magnetoencephalography in stereotactic image-guided neurosurgery

OBJECTIVE

To expand the use of magnetoencephalography (MEG) functional mapping in the operating room as well as preoperatively, a method of integrating the MEG sensorimotor mapping information into a stereotactic database, using computed tomographic scans, magnetic resonance imaging scans, and digital angiography, was developed. The combination of functional mapping and the stereotactic technique allows simultaneous viewing of the spatial relationship between the MEG-derived functional mapping, the radiological/structural anatomic characteristics, and the pathological abnormality.

METHODS

MEG data were collected using a MAGNES II Biomagnetometer and were incorporated into the COMPASS frame-based and REGULUS frameless stereotactic systems. The transformation process, by calculating a translational vector and a rotation matrix, integrates functional and anatomic information that is then directly available intraoperatively in the stereotactic database. This procedure was employed in 10 patients undergoing computer-assisted stereotactic volumetric resections for lesions involving the sensorimotor cortex. The principles of coregistration and coordinate transformation are reviewed in the context of preoperative functional mapping. We introduce innovations to apply these techniques to intraoperative stereotactic systems.

RESULTS

Tests of the accuracy of the intraoperative integration of functional information in patients and calibration phantoms indicated close agreement with earlier preoperative methods. The intraoperative availability of functional information was a significant aid to the surgeon because it provided more accurate information on the location of functional tissue than could be derived solely by radiological criteria.

CONCLUSION

The real-time availability of functional mapping information in an interactive fashion can reduce surgical risk and minimize functional morbidity. Within the ever-expanding realm of functional mapping and image-guided neurosurgery, further progress and integration of these methods is critical for resection of lesions involving eloquent cortex.

Clinical evaluation of a system for precision enhancement in spine surgery

Most techniques in segmental spinal fixation surgery rely on the identification of predefined targets with the help of anatomical landmarks and on intraoperative use of image intensifiers. However, because there is no direct link between the image information, the accessible spinal anatomy, and the action of surgical instruments several potential problems and possible complications are still involved. A novel system for spinal surgery has been designed allowing for the real-time, intraoperative localization of surgical instruments in medical images. In practice this was achieved by combining image-guided stereotaxis with advanced optoelectronic position sensing techniques. Modules were developed for image data processing, surgical planning and simulation, and various intraoperative procedures. A detailed validation of the system was performed indicating an overall accuracy to be better than the slice distance of the spinal image used. In an in-vitro setting 20 pilot holes for pedicle screws were prepared in human cadaveric lumbar spines. An analysis in 77 histological cuts showed an ideal location in 70 and only minor cortex engagement in seven sections. In vivo the system has been successfully applied in three posterior low lumbar stabilizations with overall 15 transpedicular screws. RELEVANCE--:This article focuses on the clinical evaluation of a computer-assisted surgery system and its application to the operating theatre for transpedicular fixation of the spine. The given approach effectively keeps the surgeon 'in the loop' and requires only minor modifications of the established surgical techniques and associated instruments. The results of this study indicate that advanced computer-assisted techniques may significantly improve the accuracy and safety of surgical interventions of the spine. The proposed technique may in future be adapted to other applications in orthopaedic surgery.