[Simulation in surgical training]. / Op.-Simulation in der Chirurgie.

BACKGROUND: Patient safety during operations hinges on the surgeon's skills and abilities. However, surgical training has come under a variety of restrictions. To acquire dexterity with decreasingly "simple" cases, within the legislative time constraints and increasing expectations for surgical results is the future challenge. OBJECTIVES: Are there alternatives to traditional master-apprentice learning? MATERIALS AND METHODS: A literature review and analysis of the development, implementation, and evaluation of surgical simulation are presented. RESULTS: Simulation, using a variety of methods, most important physical and virtual (computer-generated) models, provides a safe environment to practice basic and advanced skills without endangering patients. These environments have specific strengths and weaknesses. CONCLUSIONS: Simulations can only serve to decrease the slope of learning curves, but cannot be a substitute for the real situation. Thus, they have to be an integral part of a comprehensive training curriculum. Our surgical societies have to take up that challenge to ensure the training of future generations.

Effect of smoking on retrobulbar blood flow in thyroid eye disease.

PurposeTo evaluate the effect of smoking on retrobulbar blood flow parameters by color Doppler imaging in patients with thyroid eye disease.Patients and methodsIn this observational case series, blood flow parameters in the ophthalmic artery, superior ophthalmic vein, central retinal artery, and vein were determined by color Doppler imaging in patients with thyroid eye disease. Patients were grouped as smokers and non-smokers. Never smokers and those who had stopped smoking for at least 1 year before onset of ophthalmopathy were considered as non-smokers. A thorough ophthalmic examination including Hertel exophthalmometry was performed. Orbital CT scan was also carried out in all patients.ResultsFifty-one orbits from 30 patients between 21 and 62 years old (mean±SD: 40.8±12.0) were enrolled in this study. Smokers had greater proptosis and more active and sever disease. (P<0.05) Muscle involvement based on CT scan did not vary in smokers and non-smokers. Maximum velocity (3.78±1.74 vs 5.27±2.14, P<0.001; t-test) and minimum velocity (1.74±0.78 vs 3.26±1.36, P =0.014; t-test) in superior ophthalmic vein were significantly lower in smokers than non-smokers. Even after adjusting for age, sex, and clinical activity score and severity, smokers had a lower minimum velocity in superior ophthalmic vein (P =0.01; ANCOVA analysis).ConclusionCigarette smoking may correlate with increase in orbital venous congestion in thyroid eye disease.

[Space-occupying lesion of the nasopharynx and skull base]. / Unklarer Prozess des Nasopharynx und der Schädelbasis.

We report the case of a 73-year-old female patient who presented with an asymptomatic tumor of the nasal cavity and nasopharynx as well as bilateral hydromyrinx. MRI scan showed a bilaterally symmetric liquor-intense mass of the skull base, which proved to be a transsphenoidal meningocele. Since the finding was incidental and symptoms were absent, high-risk surgical intervention was not recommended.

A new tool for the navigated placement of intracerebral chemotherapy catheters.

OBJECTIVE: The aim of this report is to illustrate a method for the precise placement of chemotherapeutic delivery catheters with the aid of computer-assisted navigation systems. MATERIALS AND METHODS: We have developed a cannula which can be referenced to our navigation system (BrainLab (®)) to advance and position catheters. The cannula has a length of 10 cm. In the case of a ventricular puncture, CSF will drain through holes at the tip and a side port of the cannula to caution the surgeon. The cannula is fixed to the BrainLab (®) adapter ML and navigated with a BrainLab (®) vector vision (®) system. Using the puncture software, the placement is planned and executed. After placing the cannula as planned, the mandrin is removed and the primed catheter moved forward. When resistance is felt the cannula is withdrawn over the catheter. Further catheters can be placed similarly. RESULTS: Initial phantom tests showed a good target accuracy. Clinically we have used the cannula in 7 cases with good accuracy. CONCLUSION: This newly designed tool is easy to handle and well integrated into the navigation system. It provides the means to place catheters precisely to the planned position. Potentially it can be combined with every navigation system using adaptable reference systems.

Effects of positioning and notching of resurfaced femurs on femoral neck strength: a biomechanical test.

PURPOSE: To assess the effects of positioning and notching of resurfaced femurs on the mechanical strength of third-generation saw bone (TGSB) femurs using an in vitro analogue bone model. METHODS: 30 TGSB femurs were equally divided into 6 resurfaced femur groups (intact, anatomic, varus, valgus, anatomically notched, and valgus notched) for testing the load to failure, stiffness, and total energy. RESULTS: Compared to the intact femurs, the load to failure in all resurfaced femurs was significantly decreased by 29 to 57%. Among the resurfaced femurs, valgus and anatomic femurs had the highest load to failure, followed by valgus notched, varus, and anatomically notched femurs. Notching weakened the construct by a further 24 to 30%. CONCLUSION: To minimise the risk of femoral neck fracture, resurfaced femoral heads should be placed in an anatomic or valgus orientation, and the superior cortex of the femoral neck should remain intact.

Entry points for catheter placement in convection-enhanced delivery--a retrospective anatomic analysis.

INTRODUCTION: Planning the trajectories for catheter positioning in convection-enhanced delivery (CED) is delicate. The bulk flow follows the path of least resistance. Additional factors such as the varying tumor location and the functional relevance of the surrounding brain areas add to complicate the trajectory planning even further. Therefore several criteria have been established, dealing with the correct general entry and target point position. The goal of our study was to analyze the trajectories for CED catheters placed in our department to find preferable entry point positions. METHODS: We retrospectively looked at 51 trajectories for CED catheters planned with neuronavigation during 2003-2005 for 21 patients with supratentorial malignant gliomas. We evaluated the entry points for their anatomic position, the functional relevance of the area and their parameter to reach the important white matter tracts for CED. This was done using the anatomic literature, macroscopical studies in our laboratory on human autopsy brains and MR imaging. RESULTS: Most tumors were located in the fronto-temporo-parietal region. For these locations catheters were predominantly placed via the superior parietal lobule and the superior frontal gyrus. Looking at the anatomic literature and our laboratory results we characterized these areas with properties predisposing them for catheter placement as having wide superficial gyri and few deep sulci. In addition, they have far less functional relevance than the surrounding eloquent areas. Most relevant white matter tracts can be reached from these entry points. Accordingly, we have defined 2 areas that appear most suitable as entry points in CED catheter placement: the superior parietal lobule and superior frontal gyrus. CONCLUSION: Inserting CED catheter via the described entry points will presumably save time in planning and reduce side effects.

Neuronavigation and resection of lesions located in eloquent brain areas under local anesthesia and neuropsychological-neurophysiological monitoring.

BACKGROUND: The aim of this study was to determine the safety and maximal extension of tumor resection achievable with a combination of awake craniotomy under local anesthesia, neuronavigation, and continuous neuropsychological and neurophysiological monitoring in patients with lesions within the eloquent brain. METHODS: We have performed 55 resections of different pathologies with neuronavigation on 52 patients from January 1998 to December 2002. Mean age was 49 years, the male to female ratio was 37 to 15. All patients underwent a continuous examination by a neuropsychologist and repetitive cortical stimulations during the resection, and a 3-month postoperative neurological examination to determine functional outcome. Neurological outcome and results of resection of patients with gliomas were compared to a control group of 27 patients with lesions in the central region who were operated under general anesthesia during the same time period. RESULTS: Tumor resection was stopped when a macroscopic total cytoreduction was achieved, or at the onset of neurological dysfunction. There was a higher rate of complete tumor resection (77% vs. 33%) and a lower rate of neurological deterioration (33% vs. 12%) in the study group compared to the control group. Overall, a complete resection in the study group was achieved in 40 patients (72%), a partial resection in 28%. Five patients developed a new deficit during surgery which resolved completely after a change of surgical strategy, 14 patients had a new deficit after surgery which improved within 3 months in 6 patients. There was no operative mortality. CONCLUSION: The combination of neuronavigation with cortical stimulation and repetitive neurological and language examinations allows a more radical resection of tumors in eloquent brain areas, otherwise considered as inoperable.

Radiation dose of the lens in trans-sphenoidal pituitary surgery: pros and cons of a conventional setup using fluoroscopic guidance and CT-based neuronavigation.

BACKGROUND AND PURPOSE: We determined the radiation dose in patients' lenses during pituitary surgery with either conventional fluoroscopy or CT-guided neuronavigation. MATERIALS AND METHODS: Thermoluminescent dosimeters (TLD-100H) were attached to the lenses of an anthropomorphic Alderson-Rando head phantom. Simulation of the conventional setup of continuous fluoroscopy (61 kV peak, 2.01 mAs) with collimation and automatic exposure control was used with 1 TLD being removed every 5 seconds, followed by another experiment with 1 being removed every 30 seconds. For CT-guided neuronavigation, a spiral of 3-mm-thick sections without gap was performed (140 kV, 220 mA). Patients' charts (n = 87) were reviewed in terms of radiation exposure and perioperative complications. RESULTS: Radiation dose is distance-dependent (P < .002), with an exposure-time-dependent linear increase (R(2) = 99.27, P < .0001) close to the primary beam only. The radiation dose of the CT (mean, 39.39 mGy) was fivefold higher compared with the maximal time of 3 minutes (8 mGy) reached in our patients by using the conventional setup. CT offers more detailed 3D anatomy available at any time intraoperatively. Tolerance doses needed to develop cataracts were not reached, and perioperative complications occurred without significant differences (Mann-Whitney U test, P = .39) using either method. Continuous use of fluoroscopy reached the mean value of CT after 14.33 minutes. CONCLUSION: Neuronavigation provides better anatomic information and avoids repetitive exposure and accumulation to the staff, with the disadvantage of an increased radiation exposure to the patient causing at least no acute harm. Long-term effects are hard to prove but cannot be neglected either.

MR spectroscopy in patients with intracranial meningiomas.

With magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS), we tried to get more pre-operative information in patients with suspicious meningioma concerning the histologic diagnosis especially regarding WHO Grades I and II meningiomas. Apart from the known spectra and metabolites such as choline, creatine and N-acetyl-aspartate (NAA), recent publications have shown that lactate is often found in necrotic tumor tissue. Within a 2 year period, 39 patients with an intracranial meningioma were studied with MRS. In 62.5% of histologic atypical meningiomas (WHO Grade II), a lactate peak could be demonstrated in the pre-operative MRS. Interestingly, also patients with multiple meningiomas show different spectra of their tumors.

Activation of the supplementary motor area (SMA) during voluntary pelvic floor muscle contractions--an fMRI study.

To identify cortical and subcortical regions involved in voluntary pelvic floor muscle control, functional magnetic resonance imaging (fMRI) was performed at 1.5 T in thirty healthy subjects (15 women, 15 men). The participants performed rhythmical (1 Hz) pelvic floor muscle contractions, which imitated the repetitive interruption of voiding. Since previous reports concerning the representation of pelvic floor muscles in the cortex of the medial wall are inconsistent, a conservative statistical threshold (FWE-corrected P<0.05) was used to detect the most robust foci of activation, and cytoarchitectonic probability maps were used to correlate the results with structural anatomical information. We found a strong and consistent recruitment of the supplementary motor area (SMA), with foci of peak activity located in the posterior portion of the SMA, suggesting that this region is specifically involved in voluntary pelvic floor muscle control. Further significant activations were identified bilaterally in the frontal opercula, the right insular cortex and the right supramarginal gyrus. They may reflect the attentive processing and evaluation of visceral sensations. Weaker signals were detected in the primary motor cortex (M1) and the dorsal pontine tegmentum. There was no significant correlation between bladder volumes and brain activation induced by pelvic floor muscle contractions. We found no significant gender-related differences.

[MRI of carotid stents: influence of stent properties and sequence parameters on visualization of the carotid artery lumen]. / MRT bei Karotisstents: Einfluss von Stenteigenschaften und Geräteparametern auf die Darstellbarkeit des Karotislumens.

PURPOSE: To evaluate MR artifacts of carotid artery stents and to optimize stent properties and sequence parameters. MATERIAL AND METHODS: Four carotid artery stents - Wallstent (mediloy), Precise (nitinol), ACCULINK (nitinol) and a stent prototype (nitinol) - were investigated in a flow model of the cervical vessels. The model was made of silicon tubing and a flow pump that produces realistic flow curves of the carotid artery. To investigate the effects of magnetic susceptibility and radiofrequency induced shielding artifacts, turbo spin echo and gradient echo sequences as well as CE-MRAs were measured. To improve the visualization of the stent lumen in a CE-MRA, flip angle as well as geometry and covering of the stent prototype were altered. RESULTS: Susceptibility artifacts in stents of the carotid artery only influence the lumen visualization at the proximal and distal end of the braided mediloy stent. A change of stent coverings has no significant influence on radiofrequency artifacts, whereas a reduction in linking elements between stent segments and a change in diameter of stent struts improves visualization of the stent lumen. By increasing the flip angle in a CE-MRA, visualization of the stent lumen is possible in both mediloy and nitinol stents. CONCLUSION: The choice of stent material and changes in stent geometry as well as the optimization of the flip angle of the CE-MRA may reduce susceptibility and radiofrequency artifacts, rendering feasible the CE-MRA of a stented carotid artery.

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.

Processing and visualization for diffusion tensor MRI.

This paper presents processing and visualization techniques for Diffusion Tensor Magnetic Resonance Imaging (DT-MRI). In DT-MRI, each voxel is assigned a tensor that describes local water diffusion. The geometric nature of diffusion tensors enables us to quantitatively characterize the local structure in tissues such as bone, muscle, and white matter of the brain. This makes DT-MRI an interesting modality for image analysis. In this paper we present a novel analytical solution to the Stejskal-Tanner diffusion equation system whereby a dual tensor basis, derived from the diffusion sensitizing gradient configuration, eliminates the need to solve this equation for each voxel. We further describe decomposition of the diffusion tensor based on its symmetrical properties, which in turn describe the geometry of the diffusion ellipsoid. A simple anisotropy measure follows naturally from this analysis. We describe how the geometry or shape of the tensor can be visualized using a coloring scheme based on the derived shape measures. In addition, we demonstrate that human brain tensor data when filtered can effectively describe macrostructural diffusion, which is important in the assessment of fiber-tract organization. We also describe how white matter pathways can be monitored with the methods introduced in this paper. DT-MRI tractography is useful for demonstrating neural connectivity (in vivo) in healthy and diseased brain tissue.

CURVES: curve evolution for vessel segmentation.

The vasculature is of utmost importance in neurosurgery. Direct visualization of images acquired with current imaging modalities, however, cannot provide a spatial representation of small vessels. These vessels, and their branches which show considerable variations, are most important in planning and performing neurosurgical procedures. In planning they provide information on where the lesion draws its blood supply and where it drains. During surgery the vessels serve as landmarks and guidelines to the lesion. The more minute the information is, the more precise the navigation and localization of computer guided procedures. Beyond neurosurgery and neurological study, vascular information is also crucial in cardiovascular surgery, diagnosis, and research. This paper addresses the problem of automatic segmentation of complicated curvilinear structures in three-dimensional imagery, with the primary application of segmenting vasculature in magnetic resonance angiography (MRA) images. The method presented is based on recent curve and surface evolution work in the computer vision community which models the object boundary as a manifold that evolves iteratively to minimize an energy criterion. This energy criterion is based both on intensity values in the image and on local smoothness properties of the object boundary, which is the vessel wall in this application. In particular, the method handles curves evolving in 3D, in contrast with previous work that has dealt with curves in 2D and surfaces in 3D. Results are presented on cerebral and aortic MRA data as well as lung computed tomography (CT) data.

MR imaging-guided prostate biopsy with surgical navigation software: device validation and feasibility.

Magnetic resonance (MR) imaging--guided prostate biopsy in a 0.5-T open imager is described, validated in phantom studies, and performed in two patients. The needles are guided by using fast gradient-recalled echo and T2-weighted fast spin-echo images. Surgical navigation software provided T2-weighted images critical to targeting the peripheral zone and the tumor. MR imaging can be used to guide prostate biopsy.

An integrated visualization system for surgical planning and guidance using image fusion and an open MR.

A surgical guidance and visualization system is presented, which uniquely integrates capabilities for data analysis and on-line interventional guidance into the setting of interventional MRI. Various pre-operative scans (T1- and T2-weighted MRI, MR angiography, and functional MRI (fMRI)) are fused and automatically aligned with the operating field of the interventional MR system. Both pre-surgical and intra-operative data may be segmented to generate three-dimensional surface models of key anatomical and functional structures. Models are combined in a three-dimensional scene along with reformatted slices that are driven by a tracked surgical device. Thus, pre-operative data augments interventional imaging to expedite tissue characterization and precise localization and targeting. As the surgery progresses, and anatomical changes subsequently reduce the relevance of pre-operative data, interventional data is refreshed for software navigation in true real time. The system has been applied in 45 neurosurgical cases and found to have beneficial utility for planning and guidance. J. Magn. Reson. Imaging 2001;13:967-975.

Serial intraoperative magnetic resonance imaging of brain shift.

OBJECTIVE: A major shortcoming of image-guided navigational systems is the use of preoperatively acquired image data, which does not account for intraoperative changes in brain morphology. The occurrence of these surgically induced volumetric deformations ("brain shift") has been well established. Maximal measurements for surface and midline shifts have been reported. There has been no detailed analysis, however, of the changes that occur during surgery. The use of intraoperative magnetic resonance imaging provides a unique opportunity to obtain serial image data and characterize the time course of brain deformations during surgery. METHODS: The vertically open intraoperative magnetic resonance imaging system (SignaSP, 0.5 T; GE Medical Systems, Milwaukee, WI) permits access to the surgical field and allows multiple intraoperative image updates without the need to move the patient. We developed volumetric display software (the 3D Slicer) that allows quantitative analysis of the degree and direction of brain shift. For 25 patients, four or more intraoperative volumetric image acquisitions were extensively evaluated. RESULTS: Serial acquisitions allow comprehensive sequential descriptions of the direction and magnitude of intraoperative deformations. Brain shift occurs at various surgical stages and in different regions. Surface shift occurs throughout surgery and is mainly attributable to gravity. Subsurface shift occurs during resection and involves collapse of the resection cavity and intraparenchymal changes that are difficult to model. CONCLUSION: Brain shift is a continuous dynamic process that evolves differently in distinct brain regions. Therefore, only serial imaging or continuous data acquisition can provide consistently accurate image guidance. Furthermore, only serial intraoperative magnetic resonance imaging provides an accurate basis for the computational analysis of brain deformations, which might lead to an understanding and eventual simulation of brain shift for intraoperative guidance.

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.

Integration of interventional MRI with computer-assisted surgery.

Interventional MRI (IMRI) has entered into a new stage in which computer-based techniques play an increasing role in planning, monitoring, and controlling the procedures. The use of interactive imaging, navigational image guidance techniques, and image processing methods is demonstrated in various applications. The integration of intraoperative MRI guidance and computer-assisted surgery will greatly accelerate the clinical utility of image-guided therapy in general and interventional MRI in particular. J. Magn. Reson. Imaging 2001;13:69-77.