Pre-activating the mesial temporal lobe facilitates learning

While numerous neuroimaging studies have been conducted to examine brain activities associated with different cognitive tasks, few have focused on the effects of temporary increase in blood oxygen level on subsequent cognitive performance. The present study aimed to study this temporary hemodynamic change on subsequent learning. Using the novel picture encoding task (NPET) to activate the hippocampus, the present functional magnetic resonance imaging study showed that the level of blood oxygen level-dependent signals in the mesial temporal lobe associated with NPET positively predicted memory performance after engaging in the NPET for normal controls and patients with temporal lobe epilepsy. In addition, patients demonstrated significantly greater improvement on memory performance than normal controls. Though the improvement was transient, these results provided a neuro-physiological evidence to support our previous hypothesis that the functioning of a specific brain region can be facilitated by performing a task mediated by the same region.

Multilayer image grid reconstruction technology: four-dimensional interactive image reconstruction of microsurgical neuroanatomic dissections

OBJECTIVE

Cadaveric dissection is the gold standard for training physicians in various surgical specialties. However, limitations in acquiring and storing sufficient cadaveric material, recent pressures in training opportunities, and progress in digital image technology have led to advances in virtual or artificial visual means to augment surgical training. For training neurosurgeons, the appearance of reality is still crucial for learning anatomic structures and procedures. We developed a four-dimensional (including time) multilayer digital image reconstruction technology (MIGRT) that allows users to manipulate a "volumetric" set of photographic image data from exquisite cadaveric intracranial dissections and to navigate through stages of neurosurgical procedures as the dissection progresses.

METHODS

A robotic microscope with two digital cameras was used to capture dissection images, usually in stereoscopic mode. A grid space was created to define positions at which images are captured. Images were acquired from identical angles at the same grid coordinates but at different stages of various dissections.

RESULTS

Image data are reconstructed according to the sequence of acquisition into a multilayer image grid system by the MIGRT software. The single interactive, four-dimensional montage is viewable a on common computer platform.

CONCLUSION

MIGRT uniquely focuses on capturing anatomic content that preserves natural appearances, including procedure, texture, and color, which is far superior and preferable to images and a reconstructed image environment based on artificial or animated concepts. MIGRT shows time-dependent changes in procedures, provides depth perception by stereoscopy or unique sequential motion, and allows simultaneous interactivity at each step of the procedure.

Three-dimensional reconstruction of registered and fused Chinese Visible Human and patient MRI images

Radiological images are commonly used as important tools in medical diagnoses and treatment. Different modalities of medical images provide uniquely different content. Hence, it is natural and desirable to combine different image modalities to obtain additional new information to enhance clinical assessment. However, given the current technology, radiological images are not always sufficiently informative to permit diagnosis and treatment. In order to address this problem, we fused selected portions of the Chinese Visible Human (CVH) dataset with MRI images from a patient. Specifically, we segmented the caudate nucleus, the lentiform nucleus, and the thalamus in the CVH dataset and then registered and fused this dataset with corresponding MRI images using both rigid and nonrigid registration techniques. After rigid and nonrigid registration, the CVH and MRI images largely coincided with each other. The shape, relationship, and position of focal areas and neural structures were clearly displayed. Using volume and surface rendering, these images were three-dimensionally reconstructed to display the neural structures of interest within the brain. These structures can be rotated at will and observed from different angles. Our research indicates that the fusion of CVH and patients' MRI images can enhance the amount of neural information available to physicians and lay a foundation for the clinical use of the CVH dataset.

LUCY: A 3-D Pelvic Model for Surgical Simulation

Development of 3-D models of human anatomy for use in virtual reality simulators is anticipated to enhance surgical training. These models may be a valuable resource for gaining mastery of minimal-access procedures. The pelvis portion (hip to upper-thigh) of a 32-year-old female cadaver was frozen and sectioned axially in approximately 2-mm increments as the first step in producing an accurately representative 3-D model of the human female pelvis. Photographic exposures of the entire series of 95 sections were then converted to digital format. Adobe PhotoShop masks for each structure were created and converted into wire-frame and surface-textured models; this aggregate model set was named "LUCY." To date, 3-D representations of 40 pelvic structures (over 2200 individual masks) have been modeled In conjunction with haptic technology, these virtual anatomic models will enable users to practice fundamental surgical manipulations and procedures such as tubal ligation and ovariectomy. The deployment of surgical-simulation models such as LUCY may facilitate technical-performance aspects of surgical training, particularly those associated with minimal-access procedures. Manipulations and procedures can be practiced over the Internet, providing a host of flexible options to enhance the surgical curricula.

Model of surgical procedures for multimodal image-guided neurosurgery

OBJECTIVE

Improvement of the planning stage of image-guided surgery requires a better anticipation of the surgical procedure and its anatomical and functional environment. This anticipation should be provided by acquisition of multimodal medical images of the patient and by a better understanding of surgical procedures. In this paper, we propose improvements to the planning and performance of multimodal image-guided neurosurgery through the use of information models related to neurosurgical procedures.

MATERIALS AND METHODS

A new generic model of surgical procedures is introduced in the context of multimodal image-guided craniotomies. The basic principle of the model is to break down the surgical procedure into a sequence of steps defining the surgical script. In the model, a step is defined by an action. The model assigns to each surgical step a list of image entities extracted from multimodal preoperative images (i.e., anatomical and/or functional images) which are relevant to the performance of that particular step. A semantic validation of the model was performed by instantiating the model entities for 29 surgical procedures.

RESULTS

The resulting generic model is described by a UML class diagram and a textual description. The validation showed the relevance of the model, confirming the main underlying assumptions. It also provided some leads to improve the model.

CONCLUSION

While further validation is needed, the initial benefits of this approach can already be outlined. It should add real value to the different levels of image-guided surgery, from preprocessing to planning, as well as during surgery. Models of surgical procedures can manage image data according to the surgical script, which should lead to better anticipation of surgery through the development of simulation tools. Furthermore, the models may improve the performance of surgery using microscope-based neuronavigation systems by making it possible to adapt both visualization and interaction features of multimodal preoperative images according to the model.

Intraoperative three-dimensional visualization of the pyramidal tract in a neuronavigation system (PTV) reliably predicts true position of principal motor pathways

BACKGROUND

This prospective study employs anisotropic diffusion-weighted (ADW) magnetic resonance imaging for the integration of individual spatial information concerning the principal motor pathways into the operating room during microneurosurgery in the central region. We hypothesize that the three-dimensional (3-D) visualization of the pyramidal tract position (PTV) in a neuronavigation system based on ADW provides valid information concerning the position and extension of the principal motor pathways.

METHODS

A total of 13 consecutive patients with lesions adjacent to the pyramidal tracts and the central region underwent microneurosurgery with the help of pyramidal tract visualization (PTV). An ADW sequence obtained preoperatively was fused to an anatomic navigation sequence. The 3-D reconstructions of the precentral gyrus (PG), the pyramidal tract, and the tumor were available in a customized neuronavigation system during surgery. Intraoperatively the PG was identified on the basis of the aforementioned data. Electric motorcortex stimulation (CS) was used to directly verify the PG location and indirectly the fiber tract position.

RESULTS

In 11 cases (92%) the prediction of the principal motor pathways' position was correct. In one case of a meningioma, according to PTV, the tumor was falsely localized postcentrally. In the case of a precentral cavernoma, no motor response could be elicited by cortical stimulation.

CONCLUSION

Intraoperative PTV on the basis of ADW provides the neurosurgeon with reliable information concerning the position of the principal motor pathways during intracranial procedures as proved with intraoperative electrophysiological testing. The technique has the potential to reduce operative morbidity. PTV is straightforward and can be adapted to other customized neuronavigation devices.

The Application of Rapid Prototyping Techniques in Cranial Reconstruction and Preoperative Planning in Neurosurgery

The value of rapid prototype models of the skull in our craniofacial and neurosurgical practice was analyzed. Individual skull models of 52 patients were produced by means of rapid prototyping techniques and used in various procedures. Patients were divided into three groups as follows: group I (26 patients) requiring corrective cranioplasty 1) after resection of osseous tumors (15 patients) and 2) with congenital and posttraumatic craniofacial deformities (11 patients), group II (10 patients) requiring reconstructive cranioplasty, and group III (16 patients) requiring planning of difficult skull base approaches. The utility of the stereolithographic models was assessed using the Gillespie scoring system. The esthetic and clinical outcomes were assessed by means of the esthetic outcome score and the Glasgow Outcome Score, respectively. Simulation of osteotomies for advancement plasty and craniofacial reassembly in the model before surgery in group I reduced operating time and intraoperative errors. In group II, the usefulness of the models depended directly on the size and configuration of the cranial defect. The planning of approaches to uncommon and complex skull base tumors (group III) was significantly influenced by the stereolithographic models. The esthetic outcome was pleasing. The indications for the manufacture of individual three-dimensional models could be cases of craniofacial dysmorphism that require meticulous preoperative planning and skull base surgery with difficult anatomical and reconstructive problems. The stereolithographic models provide 1) better understanding of the anatomy, 2) presurgical simulation, 3) intraoperative accuracy in localization of lesions, 4) accurate fabrication of implants, and 5) improved education of trainees.

Image-guided craniotomy for cerebral metastases: techniques and outcomes

OBJECTIVE

The purpose of the present study was to analyze the outcomes after craniotomies for brain metastases in a modern series using image-guided technologies either in the regular operating room or in the intraoperative magnetic resonance imaging unit.

METHODS

Neurosurgical outcomes were analyzed for 49 patients who underwent 55 image-guided craniotomies for excision of brain metastases during a 5-year period. Tumors were located in critical and noncritical function regions of the brain. A total of 23 craniotomies for tumors in critical brain were performed using intravenous sedation anesthesia; craniotomies for noncritical function brain regions were completed under general anesthesia. The patients were also divided into Radiation Therapy Oncology Group recursive partitioning analysis (RPA) classes on the basis of age, Karnofsky Performance Scale scores, state of primary disease, and presence or absence of extracranial metastases.

RESULTS

There was no perioperative mortality. Gross total resection, as verified by postoperative contrast-enhanced computed tomography or magnetic resonance imaging, was achieved in 96% of patients. The median anesthesia time was 4.25 hours, and the median length of hospital stay was 3 days. In 51 symptomatic cases, there was complete resolution of symptoms in 70% (n = 36), improvement in 14% (n = 7), and no change in 12% (n = 6) postoperatively. No patient who was neurologically intact preoperatively deteriorated after surgery, and 93% of patients maintained or improved their functional status. Only two patients (3.6%) with significant preoperative deficits had increased long-term deficits postoperatively. The mean follow-up was 1 year, and the local recurrence rate was 16%. The median survival of the entire group was 16.23 months (17.5 mo in RPA Class I, 22.9 mo in RPA Class II, and 9.8 mo in RPA Class III).

CONCLUSION

Gross total resection of brain metastases, including those involving critical function areas, can be safely achieved with a low morbidity rate using contemporary image-guided systems. RPA Class I and II patients with controlled primary disease benefit from aggressive treatment by surgery and radiation.

Plastination and computerized 3D reconstruction of the temporal bone

The purpose of this study was to generate a computerized 3D reconstruction of the temporal bone and intratemporal structures. A plastination technique was used to obtain equidistant serial thin sections of 1.2 mm thickness and, on an SGI workstation, a Contour-Marching Cubes algorithm was selected to reconstruct the temporal bone and intratemporal structures in three dimensions. All reconstructed structures can be represented individually or jointly and rotated in any plane. Any diameter and angle of a structure can be conveniently measured. The capability of reconstructing individual and combined images of intratemporal structures, viewing them from all surgical angles, and accurately measuring their spatial relationships gives skull base and otologic surgeons important guidance. The reconstructed model can also be used for resident education, rehearsal of an unfamiliar surgery, and for developing a new surgical approach.

Surgical navigation in the open MRI

The introduction of MRI into neurosurgery has opened multiple avenues, but also introduced new challenges. The open-configuration intraoperative MRI installed at the Brigham and Women's Hospital in 1996 has been used for more than 500 open craniotomies and beyond 100 biopsies. Furthermore the versatile applicability, employing the same principles, is evident by its frequent use in other areas of the body. However, while intraoperative scanning in the SignaSP yielded unprecedented imaging during neurosurgical procedures their usage for navigation proved bulky and unhandy. To be fully integrated into the procedure, acquisition and display of intraoperative data have to be dynamic and primarily driven by the surgeon performing the procedure. To use the benefits of computer-assisted navigation systems together with immediate availability of intraoperative imaging we developed a software package. This "3D Slicer" has been used routinely for biopsies and open craniotomies. The system is stable and reliable. Pre- and intraoperative data can be visualized to plan and perform surgery, as well as to accommodate for intraoperative deformations, "brain shift", by providing online data acquisition.

Future perspectives in intraoperative imaging

Of all the advances in imaging science in the past twenty years, none has had a greater impact than Magnetic Resonance Imaging. Since its introduction as a diagnostic tool in the mid-1980's, MRI has evolved into the premier neuroimaging modality, and with the addition of higher field magnets, we are able to achieve spatial resolution of such superb quality that even the most exquisite details of the brain anatomy can be visualized. With the implementation of intraoperative, neurosurgical MRI, we can not only monitor brain shifts and deformations; we can achieve intraoperative navigation using intraoperative image updates. In the future, intraoperative MRI can be used not only to localize, target, and resect brain tumors and other lesions but also to fully comprehend the surrounding cortical and white matter functional anatomy. In addition to the inclusion of new imaging methods such as diffusion tensor imaging, new therapeutic methods will be applied. Especially encouraging are the promising results in MRI-guided Focused Ultrasound Surgery, in which the non-invasive thermal ablation of tumors is monitored and controlled by MRI. With the clinical introduction of these advances, intraoperative MRI is changing the face of Neurosurgery today.

Cross-modal sensory processing in the anterior cingulate and medial prefrontal cortices

One of the principal functions of the nervous system is to synthesize information from multiple sensory channels into a coherent behavioral and perceptual gestalt. A critical feature of this multisensory synthesis is the sorting and coupling of information derived from the same event. One of the singular features of stimuli conveying such information is their contextual or semantic congruence. Illustrating this fact, subjects are typically faster and more accurate when performing tasks that include congruent compared to incongruent cross-modal stimuli. Using functional magnetic resonance imaging, we demonstrate that activity in select brain areas is sensitive to the contextual congruence among cross-modal cues and to task difficulty. The anterior cingulate gyrus and adjacent medial prefrontal cortices showed significantly greater activity when visual and auditory stimuli were contextually congruent (i.e., matching) than when they were nonmatching. Although activity in these regions was also dependent on task difficulty, showing decreased activity with decreasing task difficulty, the activity changes associated with stimulus congruence predominated.

Intracranial navigation by using low-field intraoperative magnetic resonance imaging: preliminary experience

OBJECT

Intracranial navigation by using intraoperative magnetic resonance (iMR) imaging allows the surgeon to reassess anatomical relationships in near-real time during brain tumor surgery. The authors report their initial experience with a novel neuronavigation system coupled to a low-field iMR imaging system.

METHODS

Between October 2000 and December 2001, 70 neurosurgical procedures were performed using the mobile 0.12-tesla PoleStar N-10 iMR imaging system. The cases included 38 craniotomies, 15 brain biopsies, nine transsphenoidal approaches, and one drainage of a subdural hematoma. Tumor resection was performed using the awake method in seven of 38 cases. Of the craniotomies, image-confirmed complete or radical tumor resection was achieved in 28 cases, subtotal resection in eight cases, and open biopsies in two cases. Tumor resection was controlled with the use of image guidance until the final intraoperative images demonstrated that there was no residual tumor or that no critical brain tissue was at risk of compromise. In each stereotactic biopsy the location of the biopsy needle could be verified by intraoperative imaging and diagnostic tissue was obtained. Complications included a case of aseptic meningitis after a biopsy and one case of temporary intraoperative failure of the anesthesia machine. Awake craniotomies were performed successfully with no permanent neurological complications.

CONCLUSIONS

Intraoperative MR image-based neuronavigation is feasible when using the Odin PoleStar N-10 system for tumor resections that require multiple other surgical adjuncts including awake procedures, cortical mapping, monitoring of somatosensory evoked potentials, or electrocorticography. Use of the system for brain biopsies offers the opportunity of immediate verification of the needle tip location. Standard neurosurgical drills, microscopes, and other equipment can be used safely in conjunction with this iMR imaging system.

Preoperative evaluation of neurovascular compression in patients with trigeminal neuralgia by use of three-dimensional reconstruction from two types of high-resolution magnetic resonance imaging

OBJECTIVE

To assess the value of three-dimensional (3-D) images reconstructed from 3-D constructive interference in steady state (3-D-CISS) and 3-D fast inflow with steady-state precession (3-D-FISP) images for the visualization of neurovascular compression in patients with trigeminal neuralgia.

METHODS

Twenty-four consecutive patients with trigeminal neuralgia underwent preoperative 3-D-FISP and 3-D-CISS imaging. 3-D reconstruction of nerves and vessels was performed with the use of a volume-rendering method. We compared the 3-D reconstructed images with intraoperative findings.

RESULTS

3-D-CISS and 3-D-FISP images scanned from the same position clearly delineated the trigeminal nerve and vessels. 3-D reconstructed images showed the spatial relationship between the trigeminal nerve and causative vessels. The responsible arteries were identified from the 3-D reconstructed images, which closely simulated the microscopic operative view.

CONCLUSION

3-D reconstructions from two types of high-resolution magnetic resonance images (3-D-CISS and 3-D-FISP) are very useful for creating preoperative simulations and in deciding whether to perform surgery in patients with trigeminal neuralgia.

Brain activation during facial emotion processing

Functional neuroimaging studies have helped identify neural systems involved in cognitive processing and more recently have indicated limbic activation to emotional stimuli. Some functional magnetic resonance imaging (fMRI) studies have reported increased amygdala response during exposure to emotional stimuli while others have not shown such activation. The present study was designed to test the hypothesis that activation of the amygdala is related to the relevance of the emotional valence of stimuli. Healthy young participants (7 men, 7 women) were studied in a high-field (4 tesla) scanner using blood oxygenation-level dependent (BOLD) signal changes in a blocked "box car" design. They viewed facial displays of happiness, sadness, anger, fear, and disgust as well as neutral faces obtained from professional actors and actresses of diverse ethnicity and age. Their task alternated between emotion discrimination (indicating whether the emotion was positive or negative) and age discrimination (indicating whether the poser was older or younger than 30). Blocks contained the same proportion of emotional and neutral faces. Limbic response was greater during the emotion than during the age discrimination conditions. The response was most pronounced in the amygdala, but was also present in the hippocampus and circumscribed voxels in other limbic regions. These results support the central role of the amygdala in emotion processing, and indicate its sensitivity to the task relevance of the emotional display.

Neural correlates of successful and unsuccessful verbal memory encoding

Recent neuroimaging studies suggest that episodic memory encoding involves a network of neocortical structures which may act interdependently with medial temporal lobe (mTL) structures to promote the formation of durable memories, and that activation in certain structures is modulated according to task performance. Functional magnetic resonance imaging (fMRI) was used to determine the neural structures recruited during a verbal episodic encoding task and to examine the relationship between activation during encoding and subsequent recognition memory performance across subjects. Our results show performance-correlated activation during encoding both in neocortical and medial temporal structures. Neocortical activations associated with later successful and unsuccessful recognition memory were found to differ not only in magnitude, but also in hemispheric laterality. These performance-related hemispheric effects, which have not been previously reported, may correspond to between-subject differences in encoding strategy.

Tumor detection by virtual cystoscopy with color mapping of bladder wall thickness

PURPOSE

We determine the value of color mapping of bladder wall thickness for detection of tumor as a component of virtual cystoscopy.

MATERIALS AND METHODS

A total of 31 subjects with hematuria and/or a history of bladder tumor underwent helical computerized tomography of the pelvis after distention of the bladder with air. Three-dimensional (D) models were constructed, and thickness of the wall was color mapped according to a fixed and validated mm. scale. Axial source images and 3-D models were reviewed and graded for the presence of wall thickening. A comparison was made with findings on conventional cystoscopy in 31 patients and pathological specimen in 13.

RESULTS

Compared with conventional cystoscopy, the analysis of axial image yielded a sensitivity of 0.80, specificity 0.90, positive predictive value 0.80 and negative predictive value 0.90 for the presence of tumor. Examination of color mapped 3-D renderings resulted in 0.83, 0.36, 0.42 and 0.71, respectively.

CONCLUSIONS

Thin axial computerized tomography of the air distended bladder shows promise as a potential screening tool for bladder cancer. The low specificity of color mapped 3-D renderings makes the technique inappropriate for screening. It may valuable for guiding urologists to additional suspicious sites in a patient with a known tumor.

Local and remote visualization techniques for interactive direct volume rendering in neuroradiology

The increasing capabilities of magnetic resonance (MR) imaging and multisection spiral computed tomography (CT) to acquire volumetric data with near-isotropic voxels make three-dimensional (3D) postprocessing a necessity, especially in studies of complex structures like intracranial vessels. Since most modern CT and MR imagers provide limited postprocessing capabilities, 3D visualization with interactive direct volume rendering requires expensive graphics workstations that are not available at many institutions. An approach has been developed that combines fast visualization on a low-cost PC system with high-quality visualization on a high-end graphics workstation that is directly accessed and remotely controlled from the PC environment via the Internet by using a Java client. For comparison of quality, both techniques were applied to several neuroradiologic studies: visualization of structures related to the inner ear, intracranial aneurysms, and the brainstem and surrounding neurovascular structures. The results of pure PC-based visualization were comparable with those of many commercially available volume-rendering systems. In addition, the high-end graphics workstation with 3D texture-mapping capabilities provides visualization results of the highest quality. Combining local and remote 3D visualization allows even small radiologic institutions to achieve low-cost but high-quality 3D visualization of volumetric data.

Three-dimensional visualization of the pyramidal tract in a neuronavigation system during brain tumor surgery: first experiences and technical note

OBJECTIVE

To integrate spatial three-dimensional information concerning the pyramidal tracts into a customized system for frameless neuronavigation during brain tumor surgery.

METHODS

Four consecutive patients with intracranial tumors in eloquent areas underwent diffusion-weighted and anatomic magnetic resonance imaging studies within 48 hours before surgery. Diffusion-weighted datasets were merged with anatomic data for navigation purposes. The pyramidal tracts were segmented and reconstructed for three-dimensional visualization. The reconstruction results, together with the fused-image dataset, were available during surgery in the environment of a customized neuronavigation system.

RESULTS

In all four patients, the combination of reconstructed data and fused images was a helpful additional source of information concerning the tumor seat and topographical interaction with the pyramidal tract. In two patients, intraoperative motor cortex stimulation verified the tumor seat with regard to the precentral gyrus.

CONCLUSION

Diffusion-weighted magnetic resonance imaging allows individual estimation of large fiber tracts applicable as important information in intraoperative neuronavigation and in planning brain tumor resection. A three-dimensional representation of fibers associated with the pyramidal tract during brain tumor surgery is feasible with the presented technique and is a helpful adjunct for the neurosurgeon. The main drawbacks include the length of time required for the segmentation procedure, the lack of direct intraoperative control of the pyramidal tract position, and brain shift. However, mapping of large fiber tracts and its intraoperative use for neuronavigation have the potential to increase the safety of neurosurgical procedures and to reduce surgical morbidity.

Intraoperative magnetic resonance imaging: considerations for the operating room of the future

Recent technological advances have made possible the introduction of the magnetic resonance imaging (MRI) system into the operating room to guide neurosurgical interventions. We review the possibilities and limitations associated with various open-configuration magnet designs, including systems from the Phillips, Siemens, General Electric, Odin and IMRIS designs. This technology has been shown to be a feasible adjunct to current neurosurgical management of intracranial brain tumors for both biopsy and resection procedures and shows significant potential applications for epilepsy surgery, spine surgery and for minimally invasive interventional techniques. Combined with other surgical planning modalities, intra-operative MRI scanners provide an evolutionary influence on the design of today's operating room.

Three-dimensional integration of brain anatomy and function to facilitate intraoperative navigation around the sensorimotor strip

We studied 12 patients with brain tumors in the vicinity of the sensorimotor region to provide a preoperative three-dimensional visualization of the functional anatomy of the rolandic cortex. We also evaluated the role of cortex-muscle coherence analysis and anatomical landmarks in identifying the sensorimotor cortex. The functional landmarks were based on neuromagnetic recordings with a whole-scalp magnetometer, coregistred with magnetic resonance images. Evoked fields to median and tibial nerve and lip stimuli were recorded to identify hand, foot and face representations in the somatosensory cortex. Oscillatory cortical activity, coherent with surface electromyogram during isometric muscle contraction, was analyzed to reveal the hand and foot representations in the precentral motor cortex. The central sulcus was identified also by available anatomical landmarks. The source locations, calculated from the neuromagnetic data, were displayed on 3-D surface reconstructions of the individual brains, including the veins. The preoperative data were verified during awake craniotomy by cortical stimulation in 7 patients and by cortical somatosensory evoked potentials in 5 patients. Sources of somatosensory evoked fields identified correctly the postcentral gyrus in all patients. Useful corroborative information was obtained from anatomical landmarks in 11 patients and from cortex-muscle correlograms in 8 patients. The preoperative visualization of the functional anatomy of the sensorimotor strip assisted in designing the operational strategy, facilitated orientation of the neurosurgeon during the operation, and speeded up the selection of sites for intraoperative stimulation or mapping, thereby helping to prevent damage of eloquent brain areas during surgery.

Automated segmentation of MR images of brain tumors

An automated brain tumor segmentation method was developed and validated against manual segmentation with three-dimensional magnetic resonance images in 20 patients with meningiomas and low-grade gliomas. The automated method (operator time, 5-10 minutes) allowed rapid identification of brain and tumor tissue with an accuracy and reproducibility comparable to those of manual segmentation (operator time, 3-5 hours), making automated segmentation practical for low-grade gliomas and meningiomas.

Computer assisted oral and maxillofacial surgery--a review and an assessment of technology

Advances in the basic scientific research within the field of computer assisted oral and maxillofacial surgery have enabled us to introduce features of these techniques into routine clinical practice. In order to simulate complex surgery with the aid of a computer, the diagnostic image data and especially various imaging modalities including computer tomography (CT), magnetic resonance imaging (MRI) and Ultrasound (US) must be arranged in relation to each other, thus enabling a rapid switching between the various modalities as well as the viewing of superimposed images. Segmenting techniques for the reconstruction of three-dimensional representations of soft and hard tissues are required. We must develop ergonomic and user friendly interactive methods for the surgeon, thus allowing for a precise and fast entry of the planned surgical procedure in the planning and simulation phase. During the surgical phase, instrument navigation tools offer the surgeon interactive support through operation guidance and control of potential dangers. This feature is already available today and within this article we present a review of the development of this rapidly evolving technique. Future intraoperative assistance takes the form of such passive tools for the support of intraoperative orientation as well as so-called 'tracking systems' (semi-active systems) which accompany and support the surgeons' work. The final form are robots which execute specific steps completely autonomously. The techniques of virtual reality and computer assisted surgery are increasingly important in their medical applications. Many applications are still being developed or are still in the form of a prototype. It is already clear, however, that developments in this area will have a considerable effect on a surgeon's routine work.

AI planning and scheduling in the medical hospital environment

Hospital management is a hard task due to the complexity of the organization, the costly infrastructure, the specialized services offered to different patients and the need for prompt reaction to emergencies. Artificial Intelligence planning and scheduling methods can offer substantial support to the management of hospitals, and help raising the standards of service. This editorial presents an overview of the achievements reported in therapy planning and hospital management together with a general roadmap of the published research in Artificial Intelligence planning and scheduling. Finally, a discussion for the future research and development in this area concludes the presentation.

Feasibility of brain volumetric analysis and reconstruction of images by transfontanel three-dimensional ultrasound

Based on the authors' experience with reconstruction of the heart using three-dimensional echocardiography, the authors assessed the feasibility of three-dimensional reconstruction of brain images using transfontanelle ultrasound in selected cases of infants with abnormal intracranial findings. A conventional 5-MHz ultrasound transducer inside a transducer holder was rotated 180 degrees around its vertical axis using a computer-controlled stepper motor to acquire multiple sequential cross-sections of the brain. The raw digital data of this three-dimensionally recorded dataset were transferred to a PC-based workstation for further analysis. The reconstruction of the three-dimensional brain images and volumetric analysis were undertaken using a new dedicated software capable of three-dimensional reconstruction and volumetric analysis (Echo-PAC-3D, version 1.2 Beta, GE Vingmed, Horton, Norway). The reconstruction of sequential slices from the stored three-dimensional data allowed the visualization of the epicortical extension and volumetric measurements of the focal ischemic infarction in the superior tempoparietal lobe in a 2-week-old newborn with a focal ischemic brain lesion. In other 2-week-old newborns, the extension and volume of a periventricular hemorrhage was visualized by three-dimensional reconstruction of coronal cross-sectional images from the acquired three-dimensional dataset. The three-dimensional reconstruction of the lateral ventricles allowed the three-dimensional visualization and estimation of ventricular dilatation in milliliters in an 8-week-old infant with hydrocephalus. Three-dimensional reconstruction of brain images and volume estimation of brain lesions and cavities by ultrasound may provide new insights into the morphology and extension of ultrasonographically visible brain lesions.

Mixed capillary/lymphatic malformation with coexisting port-wine stain: treatment utilizing 3D MRI and CT-guided sclerotherapy

BACKGROUND

Lymphatic malformation, a benign malformation of the skin and the subcutaneous tissues, is divided into two major groups: the classical and the localized forms. Pathologically lymphatic malformation often consists of sequestered lymphatic cisterns with thick muscle walls lying deeply in the subcutaneous tissue. Communicating via dermal lymphatic channels with superficial pseudovesicles, they can vary in size depending on the pressure transmitted by the cisterns beneath.

METHODS

We present a patient with mixed capillary/lymphatic malformation and coexisting port-wine stain since birth. To demonstrate the anatomic extent and the subcutaneous involvement we performed a 3D reconstruction of a magnetic resonance imaging (MRI). The diagnostic procedures, therapeutic possibilities, and complications regarding this rare appearance are reviewed.

RESULTS

Good results could be obtained with CO2 laser vaporization of the superficial lesions and computed tomography (CT)-guided transcutaneous sclerotherapy for the deeper cisterns with doxycycline.

CONCLUSION

The combination of CO2 laser treatment and sclerotherapy with doxycycline seems to present a treatment option for cutaneous and subcutaneous lymphangioma circumscriptum with rare side effects.

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.

Accuracy and limitation of functional magnetic resonance imaging for identification of the central sulcus: comparison with magnetoencephalography in patients with brain tumors

The aim of the present study was to clarify the accuracy and limitation of functional magnetic resonance imaging (fMRI) for the identification of the central sulcus affected by brain tumors. Twelve normal volunteers and 11 patients with intracranial tumors adjacent to the central sulcus underwent fMRI and magnetoencephalography (MEG). Three patients were evaluated again after surgery. fMRI was performed with a 1.5 Tesla scanner during repetitive opening and closing of each hand. Cross-correlation function was used to identify activation areas, and the central sulcus was defined as the nearest sulcus to the highest activation spots that were determined by elevating correlation coefficient threshold. Somatosensory-evoked fields were measured using a whole head MEG system. The central sulcus was defined as the nearest sulcus to the N20m for the median nerve stimulus. fMRI and MEG coincided in defining the central sulcus in all 24 hemispheres of volunteers and all 10 examined nonaffected hemispheres of patients. The fMRI-defined central sulcus coincided with the MEG-defined central sulcus in nine (82%) but did not in two (18%) affected hemispheres of patients. The preoperative mismatch disappeared after surgery in one of the two patients. The present study indicates that fMRI successfully defined the central sulcus in most of the patients with brain tumors. However, in a few cases, fMRI was not reliable probably due to venous flow changes by tumor compression and/or compensational activity by brain tissues surrounding the primary sensorimotor cortex. For precise functional assessment of the brain affected by intracranial tumors, combination of fMRI and MEG will be recommended.

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.

Computer-based imaging and interventional MRI: applications for neurosurgery

Advances in computer technology and the development of open MRI systems definitely enhanced intraoperative image-guidance in neurosurgery. Based upon the integration of previously acquired and processed 3D information and the corresponding anatomy of the patient, this requires computerized image-processing methods (segmentation, registration, and display) and fast image integration techniques. Open MR systems equipped with instrument tracking systems, provide an interactive environment in which biopsies and minimally invasive interventions or open surgeries can be performed. Enhanced by the integration of multimodal imaging these techniques significantly improve the available treatment options and can change the prognosis for patients with surgically treatable diseases.

Computer-generated microsurgical anatomy of the basilar artery bifurcation. Technical note

The authors' goal was to develop a computer graphics model to represent the microsurgical anatomy of the basilar artery (BA) bifurcation and surrounding structures to simulate surgery of a BA bifurcation aneurysm performed via the transsylvian approach. The source of the input data was a variety of publications that showed detailed anatomy of the area. A computer graphics model of the area near the BA bifurcation including relevant structures, such as perforating branches or cranial nerves, was depicted in detail. A BA bifurcation aneurysm was added to the computer graphics model and it was rotated to simulate the transsylvian approach. After the internal carotid artery was displaced using a virtual retractor, the aneurysm was exposed, thus providing an understanding of the three-dimensional surgical orientation of the area. Designing a standard anatomical model on the basis of data culled from a variety of publications and adding morphological changes by using a virtual retractor to displace structures that obstruct the view along a critical path at the base of the brain are useful strategies of computer manipulation for surgical simulation in open microneurosurgery. This methodological tool would be useful in teaching surgical microanatomy and in introducing a new navigational system for virtual reality. Both concept and technical details are discussed.

Computer-generated surgical simulation of morphological changes in microstructures: concepts of "virtual retractor." Technical note

The authors' goal was to develop a computer graphics model to simulate the displacement and morphological changes that are caused by the retraction of fine intracranial structures. The authors developed an application program to interpolate the contour of models of an artery and a retractor. The center of the displacement was determined by spatial coordinates, and the shape of the displacement of the arterial model was calculated using a cosine-based formula with representation of a brain retractor. This computer graphics model was applied to the simulation of the displacement and morphological changes that occur when retraction is performed in the optic nerve. An illustrative case is presented, in which the optic nerve was displaced by a retractor to simulate the surgery performed in a carotid cave aneurysm of the internal carotid artery. The authors have named this methodological tool a "virtual retractor." This new navigational system for open microneurosurgery would be useful in teaching surgical microanatomy and in presurgical operative planning.

A method for assessing the accuracy of intersubject registration of the human brain using anatomic landmarks

Several groups have developed methods for registering an individual's 3D MRI by deforming a standard template. This achievement leads to many possibilities for segmentation and morphology that will impact nuclear medical research in areas such as activation and receptor studies. Accordingly, there is a need for methods that can assess the accuracy of intersubject registration. We have developed a method based on a set of 128 anatomic landmarks per hemisphere, both cortical and subcortical, that allows assessment of both global and local transformation accuracy. We applied our method to compare the accuracy of two standard methods of intersubject registration, AIR 3.0 with fifth-order polynomial warping and the Talairach stereotaxic transformation (Talairach and Tournoux, 1988). SPGR MRI's (256 x 256 x 160) of six normal subjects (age 18-24 years) were derformed to match a standard template volume. To assess registration accuracy the landmarks were located on both the template volume and the transformed volumes by an experienced neuroanatomist. The resulting list of coordinates was analyzed graphically and by ANOVA to compare the accuracy of the two methods and the results of the manual analysis. ANOVA performed over all 128 landmarks showed that the Woods method was more accurate than Talairach (left hemisphere F = 2.8, P < 0.001 and right hemisphere F =2.4, P < 0.006). The Woods method provided a better brain surface transformation than did Talairach (F = 18.0, P < 0.0001), but as expected there was a smaller difference for subcortical structures and both had an accuracy <1 mm for the majority of subcortical landmarks. Overall, both the Woods and Talairach method located about 70% of landmarks with an error of 3 mm or less. More striking differences were noted for landmark accuracy </=1 mm, where the Woods method located about 40% and Talairach about 23%. These results demonstrate that this anatomically based assessment method can help evaluate new methods of intersubject registration and should be a helpful tool in appreciating regional differences in accuracy. Consistent with expectation, we confirmed that the Woods nonlinear registration method was more accurate than Talairach. Landmark-based anatomic analyses of intersubject registration accuracy offer opportunities to explore the relationship among structure, function and architectonic boundaries in the human brain.

Computer-assisted three-dimensional reconstruction of head and neck tumors

OBJECTIVE

Because head and neck tumors reside in a complex area, having a three-dimensional (3-D) model of the patient's unique anatomical features may assist in the delineation of pathology. The authors describe a new computer technique of 3-D anatomical reconstruction from two-dimensional computed tomography (CT) and magnetic resonance (MR) data and discuss how it represents a step forward in the continuing evolution of 3-D imaging.

STUDY DESIGN

The authors selected three patients with solitary head and neck tumors and reconstructed their anatomy in a 3-D format for study. The tumors represented locations in the nose and central skull base (patient 1), temporal bone (patient 2), and neck (patient 3).

MATERIALS AND METHODS

MR and CT images from the individual patients were electronically transferred to workstations in the Surgical Planning Laboratory of the authors' institution. Registration (or fusion) was carried out between the MR and CT images. The desired anatomic components underwent segmentation (identification and isolation). Assembly of the segmented images was performed and the resulting structures were integrated to produce a 3-D model.

RESULTS

3-D models of the following were constructed and displayed in an interactive format on high-capacity computer workstations: 1) a skull base sarcoma with extension into the nasopharynx and nose; 2) an acoustic neuroma with internal auditory canal involvement; and 3) a metastatic recurrence of a tongue base squamous cell carcinoma in the posterior triangle of the right side of the neck with extension to the skull base.

CONCLUSION

The authors' Surgical Planning Laboratory has developed a 3-D reconstruction technique that has several new features. The models provided a very good 3-D interactive representation of the tumors and patient anatomy. The need now exists to develop this method of 3-D reconstruction of head and neck tumors for potential applications in treatment, research, and medical education.

VoxeLine: a software program for 3D real-time visualization of biomedical images

The architecture and implementation of VoxeLine, a new interactive environment for display and analysis of 2D and 3D images in real-time, is discussed. This modular software project comprises two main parts: a user part (without programming expertise) and a programming part which permits its adaptation to specific problems. VoxeLine has the ability to deal with almost all sorts of data types encountered in the biomedical field (e.g. images, vectors). Another important feature is its ability to show datasets in all directions without duplicating data into the main memory. This feature allows VoxeLine to be used on machines with limited memory capacities and power. Real-time 3D manipulations (10 Hz for a 256 x 256 x 124 MRI dataset) are possible on a classic monoprocessor architecture such as a personal computer.

Three-dimensional multi-scale line filter for segmentation and visualization of curvilinear structures in medical images

This paper describes a method for the enhancement of curvilinear structures such as vessels and bronchi in three-dimensional (3-D) medical images. A 3-D line enhancement filter is developed with the aim of discriminating line structures from other structures and recovering line structures of various widths. The 3-D line filter is based on a combination of the eigenvalues of the 3-D Hessian matrix. Multi-scale integration is formulated by taking the maximum among single-scale filter responses, and its characteristics are examined to derive criteria for the selection of parameters in the formulation. The resultant multi-scale line-filtered images provide significantly improved segmentation and visualization of curvilinear structures. The usefulness of the method is demonstrated by the segmentation and visualization of brain vessels from magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA), bronchi from a chest CT, and liver vessels (portal veins) from an abdominal CT.

Clinical application of functional magnetic resonance imaging in presurgical identification of the central sulcus

OBJECT

The authors sought to evaluate the advantages and limitations of functional magnetic resonance (fMR) imaging when it was used regularly in the clinical context to identify the central sulcus.

METHODS

A 1.5-tesla MR system comprising a spoiled gradient recalled acquisition in the steady-state functional sequence and a cross-hand cancellation analysis method were used to evaluate 50 surgical candidates with centrally located space-occupying lesions in the brain. Three-dimensional (3-D) models of the patient's head and brain showing the relative position of the tumor and the eloquent cortex were obtained in each case. A selective and reproducible focal activation was found, indicating the probable central sulcus position in 41 patients (82%). Direct cortical stimulation confirmed the fMR findings in 100% of 22 intraoperatively assessed patients. Failure to identify the central sulcus occurred in 18% of cases and was mainly a consequence of intrinsic damage in the primary sensorimotor region that resulted in severe hand paresis.

CONCLUSIONS

Although specific factors were identified that contributed to reduced sensitivity of fMR imaging in the clinical context, the present study supports functional assessment and 3-D representation of specific surgical situations as generally feasible in common practice.

Virtual otoscopy

Imaging techniques assist the surgeon in diagnosis of disease, surgical planning, and providing image guidance during surgery. Endoscopy has the drawback of being a minimally invasive procedure and limiting visualization to the inner surface of the lumen. Ultrasound, CT, and MR imaging show volumes of tissue beyond the lumen wall; however, their planar, two-dimensional representations require mental reconstruction of anatomic structures, which often proves difficult with the small, complex structures within the temporal bone. To improve three-dimensional visualization of the inner ear, we successfully completed a virtual model that can be displayed as a contiguous, three-dimensional luminal view, known as virtual otoscopy, which emulates traditional endoscopy. A concomitant global view and a view of the related CT slice adds a distinct advantage in the presentation and study of this complex organ. Advances in computer and software technology may overcome the time and cost factors that, at present, limit widespread use of virtual otoscopy. Overall, virtual otoscopy stands as a promising new visualization technique for elucidation of the middle ear, inner ear, and temporal bone structures.

Frameless stereotactic lesion contour-guided surgery using a computer-navigated microscope

BACKGROUND

The Zeiss MKM System is a recently developed computerized operating microscope for image-guided neurosurgery. The clinical advantages, reliability, accuracy, and limitations of this technique were investigated.

METHODS

Since February 1995, 78 consecutive frameless stereotactic image-guided procedures were performed in 73 patients (30 males, 43 females; mean age, 46.9 years; range, 16-77 years) for tumor surgery (50/64.1%), cavernoma removal (16/20.5%), and functional procedures (12/15.4%). Skin markers (74 cases) or bone markers (4 cases) and a standard imaging protocol (2-mm cranial computed tomography (CCT) in 59 cases/1.5-mm magnetic resonance imaging (MRI) in 19 cases) were used.

RESULTS

The main advantages were pre-operative skin incision, craniotomy and corticotomy planning, and determination of lesion boundaries. Useful registration and system reliability were noted in 97% (76/78) of the procedures. A significant improvement in registration accuracy was observed over the test period from a mean of 4.8 mm (SD = 3.36; Cases 1-25) to a mean of 2.2 mm (SD = 0.86; Cases 26-78). This resulted in an improvement in application accuracy from <5 mm in 71% (Cases 1-25) to <2 mm in 95% (Cases 26-78) of cases, and the accuracy led to successful localization of the lesion in every case. Accuracy was reliable at the beginning of every procedure, but degraded to values >5 mm by the end of the procedure in 29% (22/78) of cases. MRI cases achieved higher application accuracy values (2.1 mm mean) than CT cases (3.7 mm mean).

CONCLUSIONS

The system offers a reliable alternative to frame-assisted stereotactic craniotomies in lesion targeting, but would need an intraoperative image update for resection guidance.