Endoscopy guided by an intraoperative 3D ultrasound-based neuronavigation system.

OBJECTIVE: We have investigated the feasibility of using 3D ultrasound-based neuronavigation for guiding neuroendoscopy. METHODS: A neuronavigation system with an integrated ultrasound scanner was used for acquiring the 3D ultrasound image data. The endoscope with a tracking frame attached was calibrated to the navigation system. The endoscope was guided based on intraoperative 3D ultrasound data in 9 operations. In 5 of the operations, ultrasound angiography data were also obtained. Updated image data (e. g., more than one 3D ultrasound dataset) were obtained in 6 of the operations. RESULTS: We found that the image quality of 3D ultrasound was sufficient for image guidance of the endoscope. Planning of the entry point and trajectory as well as finding optimal sites for fenestration were successfully performed. Blood vessels were visualized by 3D ultrasound angiography. In one procedure of third ventriculostomy, the basilar artery was visualized. Updated image data were quickly obtained, and in two of the cases, a reduction of the size of cysts was demonstrated. CONCLUSIONS: 3D ultrasound gives accurate images of sufficiently high quality for image guidance of neuroendoscopy. Updated 3D ultrasound datasets can easily be acquired and may adjust for brain shift. Ultrasound angiography image data are also available with this technology and can visualize vessels of importance.     

SonoWand, an ultrasound-based neuronavigation system

OBJECTIVE: We have integrated a neuronavigation system into an ultrasound scanner and developed a single-rack system that enables the surgeon to perform frameless and armless stereotactic neuronavigation using intraoperative three-dimensional ultrasound data as well as preoperative magnetic resonance or computed tomographic images. The purpose of this article is to describe our two-rack prototype and present the results of our work on image quality enhancement. DESCRIPTION OF INSTRUMENTATION: The system consists of a high-end ultrasound scanner, a modest-cost computer, and an optical positioning/digitizer system. Special technical and clinical efforts have been made to achieve high image quality. A special interface between the ultrasound instrument and the navigation computer ensures rapid transfer of digital three-dimensional data with no loss of image quality. OPERATIVE TECHNIQUE: The positioning system tracks the position and orientation of the patient, the ultrasound probe, the pointer, and various surgical instruments. This makes it possible to update the three-dimensional map during surgery and navigate by ultrasound data in a similar manner as with magnetic resonance data. METHODS: The two-rack prototype has been used for clinical testing since November 1997 at the University Hospital in Trondheim. EXPERIENCE AND RESULTS: The image quality improvements have enabled us, in most cases, to extract information from ultrasound with clinical value similar to that of preoperative magnetic resonance imaging. The overall clinical accuracy of the ultrasound-based navigation system is expected to be comparable to or better than that of a magnetic resonance imaging-based system. CONCLUSION: The SonoWand system enables neuronavigation through direct use of intraoperative three-dimensional ultrasound. Further research will be necessary to explore the potential clinical value and the limitations of this technology.     

Multimodal image fusion in ultrasound-based neuronavigation: improving overview and interpretation by integrating preoperative MRI with intraoperative 3D ultrasound.

OBJECTIVE: We have investigated alternative ways to integrate intraoperative 3D ultrasound images and preoperative MR images in the same 3D scene for visualizing brain shift and improving overview and interpretation in ultrasound-based neuronavigation. MATERIALS AND METHODS: A Multi-Modal Volume Visualizer (MMVV) was developed that can read data exported from the SonoWand neuronavigation system and reconstruct the spatial relationship between the volumes available at any given time during an operation, thus enabling the exploration of new ways to fuse pre- and intraoperative data for planning, guidance and therapy control. In addition, the mismatch between MRI volumes registered to the patient and intraoperative ultrasound acquired from the dura was qualified. RESULTS: The results show that image fusion of intraoperative ultrasound images in combination with preoperative MRI will make perception of available information easier by providing updated (real-time) image information and an extended overview of the operating field during surgery. This approach will assess the degree of anatomical changes during surgery and give the surgeon an understanding of how identical structures are imaged using the different imaging modalities. The present study showed that in 50% of the cases there were indications of brain shift even before the surgical procedure had started. CONCLUSIONS: We believe that image fusion between intraoperative 3D ultrasound and preoperative MRI might improve the quality of the surgical procedure and hence also improve the patient outcome.     

Integration of a 3D ultrasound probe into neuronavigation

Background  

Intraoperative ultrasound (iUS) allows the generation of real-time data sets during surgical interventions. The recent innovation of 3D ultrasound probes permits the acquisition of 3D data sets without the need to reconstruct the volume by 2D slices. This article describes the integration of a tracked 3D ultrasound probe into a neuronavigation.     

Functional neuronavigation. Fusion of functional MRI data in a neuronavigation system

Neuronavigation systems integrating functional magnetic resonance imaging data have been reported recently, but generally without many details about methodology. We propose an easy method to perform functional neuronavigation by integrating functional MRI data analyzed with the Statistical Parametric Mapping 99 reference software, in the Stealth Station which is the most common neuronavigation system. Users of this new and promising technique, which requires further validation, must be aware of its limitations. Functional MRI data seem to be the major source of imprecision. As a result we do not yet recommend the use of functional neuronavigation without the control of direct cortical stimulations.     

A-mode ultrasound-based intra-femoral bone cement detection and 3D reconstruction in RTHR.

Due to the difficulty of determining the 3D boundary of the cement-bone interface in Revision Total Hip Replacement (RTHR), the removal of the distal intra-femoral bone cement can be a time-consuming and risky operation. Within the framework of computer- and robot-assisted cement removal, the principles and first results of an automatic detection and 3D surface reconstruction of the cement-bone boundary using A-mode ultrasound are described. Sound propagation time and attenuation of cement were determined considering different techniques for the preparation of bone cement, such as the use of a vacuum system (Optivac, Biomet). A laboratory setup using a rotating, standard 5-MHz transducer was developed. The prototype enables scanning of bisected cement-prepared femur samples in a 90 degrees rotation range along their rotation axis. For system evaluation ex vivo, the distal femur of a human cadaver was prepared with bone cement and drilled (? 10 mm) to simulate the prosthesis cavity in a first approximation. The sample was cut in half and CT scanned (0.24 mm resolution; 0.5 mm distance; 0.5 mm thickness), and 3D voxel models of the manually segmented bone cement were reconstructed, providing the ground truth. Afterwards, 90 degrees segments of each ex-vivo sample were scanned by the A-mode ultrasound system. To obtain better ultrasound penetration, we used coded signal excitation and pulse compression filtering. A-mode ultrasound signal detection, filtering and segmentation were accomplished fully automatically. Subsequently, 3D voxel models of each sample were calculated. Accuracy evaluation of the measured ultrasound data was performed by ICP matching of each ultrasound dataset ( approximately 8000 points) to the corresponding CT dataset and calculation of the residual median distance error between the corresponding datasets. Prior to each ICP matching, an initial pre-registration was calculated using prominent landmarks in the corresponding datasets. This method yielded a median distance error in the region of 0.25 mm for the cement-bone interface in both femur halves.     

Clinical evaluation of a novel ultrasound-based bladder volume monitor

OBJECTIVE: Bladder volume monitors may be useful for surveillance of bladder volume and urine production in urologic patients. Therefore, we designed an ultrasonic bladder volume monitor and evaluated it in vitro using phantoms and in vivo in one male volunteer. The purpose of this study was to perform a more thorough in vivo evaluation of our monitor in urologic patients to investigate biological effects and variance over a wide range of bladder volumes. MATERIAL AND METHODS: Thirty urologic patients of either gender were examined using the bladder volume monitor, which is based on seven phased array ultrasonic transducers arranged in a circular pattern to optimize detection of the bladder walls. The monitor was set up to record bladder volume every 30 s during two sequential cystometries with infusion rates of 30 and 60 ml/min. The measured volumes were analyzed using regression analysis to determine volume increments (slopes), offset volume (intercept) and correlation (Pearson's correlation coefficient). RESULTS: In the male patients, the median correlation coefficient between the infused and measured volumes was 0.97 and the slope was 0.68 ml/ml, thus warranting a correction factor of approximately 1.47 with no general volume offset. In the female patients, small bladders were generally outside the field of view of the monitor. Consequently, the correlation coefficients and slopes were 0.834 (median) and 0.43 (mean), respectively, whereas volume offsets were generally negative. CONCLUSIONS: For examinations in male patients, the performance of the bladder volume monitor was adequate. However, for examinations in female patients, a minor redesign of the transducer unit is necessary to insure proper operation.     

Image-guided endoscopic ventriculostomy with a new frameless armless neuronavigation system.

OBJECTIVE: Complications resulting from imprecise placement of the ventriculoscope and reduced visibility through the endoscopic lens under certain conditions during third ventriculostomy have been reported in the literature. The following is a report of our first experience with image-guided endoscopic ventriculostomy. MATERIALS AND METHODS: Between September 1996 and October 1997, 11 patients diagnosed with aqueduct stenosis were found to be eligible for image-guided neuroendoscopy. The image-guided system (BrainLab, Heimstetten, Germany) links a freehand probe, tracked by a passive-marker sensor system, to a virtual computer image space. A 4-mm rigid ventriculoscope (Storz Instruments GMBH, Tuttlingen, Germany) was used. RESULTS: Eight patients improved clinically directly after surgery, two patients stabilized, and one patient improved only after insertion of an additional ventriculo-peritoneal shunt. The computer- calculated registration accuracy ranged from 1. 1 to 3.1 mm (median 1.4 mm) using 3-mm computed tomographic slices. The accuracy of the tool tip calibration for the endoscope was in the range of 0.35-0.9 mm (mean = 0.47 +/- 0.21). The described technique provided maximal flexibility for the surgeon and helped in performing a safe and accurate endoscopical procedure. CONCLUSIONS: Although not all cases of ventriculostomy require additional image guidance, we found the technique to be helpful in patients with atypical or large ventricles, in cases where orientation became difficult owing to bloody or blurry cerebrospinal fluid, and in patients with small foramina of Monroe, where the entrance angle of the endoscope needs precise definition for an atraumatic procedure to be performed.     

Integrated neuronavigation system with intraoperative image updating.

OBJECTIVE: Recently, MRI has entered the field of image-guided surgery as a new intraoperative imaging modality. In spite of its obvious benefits, this type of iMRI scanner has some drawbacks that have limited its utilization. The goal of the work presented here was to overcome some of these disadvantages. METHODS: A system that allows intraoperative images to be acquired during surgery and have the ability to conduct surgery outside the constraints of the narrow gap of the open magnet was implemented. Ability to conduct tasks inside the scanner with real-time image guidance was also maintained. The system allowed navigation with neuronavigation tools both inside the gap of an open magnet and outside the magnet, utilizing two different optical camera-sets and a dynamic reference frame. Automatic patient registration was implemented. RESULTS: The average difference between tracking position measured outside and inside the magnet was 0.8 +/- 0.1 mm. CONCLUSION: In the work presented in this note we have introduced a dynamic reference frame to compensate for transport of the patient to a location outside the scanner employing a second camera set. The integrated system showed adequate accuracy.     

Accuracy evaluation of a CAS system: laboratory protocol and results with 6D localizers, and clinical experiences in otorhinolaryngology.

OBJECTIVES: The objective of the study reported in this article was to evaluate (1) localizer inaccuracies, one of the major sources of errors in Computer-Assisted Surgery (CAS) systems, and (2) the final errors obtained using surface-based registration in ear, nose, and throat (ENT) surgery. These objectives were met through (1) a technical evaluation of the accuracy and usability of several optical localizers under laboratory test conditions, and (2) a clinical measure of the global errors obtained when using a CAS system including one of the standard localizer systems (Flashpoint 5000) in Functional Endoscopic Sinus Surgery (FESS). PATIENTS AND METHODS: The technical evaluation of localizers consisted of series of geometric tests on four commercial systems. Clinical evaluation included the development of a laboratory CAS system using a markerless, skin surface registration method. This was based on a standard optical digitizing system (Flashpoint 5000), which eliminates the need for the second CT scan, which is normally performed specifically to process the position of the fiducial markers. Global accuracy was then evaluated on 20 patients by subjective and visual comparison when placing a calibrated pointer on anatomical landmarks. RESULTS: The results of the technical study indicate that the four commercial systems tested have levels of inaccuracy deemed acceptable for most CAS applications, including ENT surgery. The clinical study obtained a registration and calibration accuracy of less than 1.5 mm in 89.2% (SD = 0.20 mm) of the cases studied. Our markerless skin surface points registration method is reliable, and allows patient head movements during the procedure. The accuracy tests performed show that this type of system can be used for ENT surgery with satisfaction. CONCLUSION: CAS systems enable the surgeon to have a more thorough understanding of the complicated anatomy of paranasal sinuses, and may be especially helpful in revision surgery when normal anatomic landmarks are lacking. Further studies are necessary in FESS to improve the CAS systems that are currently available, and to determine whether these systems can minimize the overall risk of complications.     

3D ultrasound-based navigation for radiofrequency thermal ablation in the treatment of liver malignancies

BACKGROUND: The aim of the study was to compare three methods for ultrasound-based guidance of a radiofrequency probe into liver tumors in a model setup. METHODS: The liver model tumors were placed inside excised calf livers, and the radiofrequency probe was guided into the center using either a new 3D navigation method or two conventional 2D methods-freehand scanning and a method based on a biopsy guide. We performed 54 experiments, measuring the physical distance (all methods) and image distance (3D method only) from the tip of the probe to the center of the tumors. RESULTS: Based on the physical measurements alone, the biopsy-based guiding performed better than both the 2D freehand and the 3D navigation method. However, the 3D image measurements showed that the tip of the probe was better positioned in the center of the model tumors for the 3D navigation method as compared to the physical measurement results for the 2D methods. CONCLUSION: Although it was easier to position the radiofrequency probe accurately using the 3D image display technique, movement of the model tumor during 3D navigation is a challenge.     

Image fusion of MR images and real-time ultrasonography: evaluation of fusion accuracy combining two commercial instruments,a neuronavigation system and a ultrasound system

Summary Objective. The aim of our study was to evaluate MRI/Ultrasonography fusion accuracy depending on three ultrasonographic parameters.Method. An ultrasonography and MRI compatible model was created, consisting of a plastic box, which contained 3 objects. MRI scans were performed with 128 sagittal slices. The objects were segmented and 3D reconstructions were created. A special ultrasound adapter with 3 reflective markers was fixed to the ultrasound probe. Thus, the probe could be tracked by the navigation system (Vector Vision², BrainLab, Heimstetten, Germany) and the segmented shape of the 3D-objects obtained from the MR images were overlaid onto the ultrasound display (Elegra, Siemens, Erlangen, Germany). The dependency of fusion accuracy on different depth of ultrasound display, different distances between probe and objects and different angles between the axis of the ultrasound probe and the centre of the spheres was evaluated. 435 single measurements were performed.Findings. Overall fusion accuracy was 1.08mm±0.61mm (mean ± standard deviation) for spheres and 1.6mm±1.1mm for arrow heads. If the ultrasound probe was directed more tangentially to the surface of the spheres the fusion became increasingly inaccurate (P<0.05). Fusion accuracy decreased the more distant the US probe was held to the object (P<0.05). Different depth of ultrasound display had no significant effect on fusion accuracy.Conclusions. Highly accurate fusion of MR images and real-time ultrasonography could be achieved. However, careful interpretation of the fused data is necessary, when different angles and distances of the US probe to the object are concerned.     

Clinical application of a neuronavigation system in transsphenoidal surgery of pituitary macroadenoma

The utility of a neuronavigation system in the transsphenoidal surgery of pituitary macroadenoma was evaluated, and improvement of the surgical outcome is discussed. From 1997 to 2003, a total of 63 patients (male:female=41:22, mean age 58.3 years) with pituitary macroadenoma were treated surgically via transsphenoidal approach using a neuronavigation system in Beijing Tiantan Hospital. Image data for computed tomography or magnetic resonance were obtained and analyzed by the navigation system to make a three-dmensional reconstruction. During the operation, the tumor and its surrounding structures of the sellar region could be located accurately at any time. Among these cases, the tumors were removed totally in 26 cases (41.3%), subtotally in 36 cases (57.1%) and partially in one case (1.6%). Postoperative neurological complications occurred in 15 cases (23.8%). One patient died, the operative mortality was 1.6%. During the operation, the accuracy of the neuronavigation system was 2.3±1.1 mm. The neuronavigation system is quite helpful for transsphenoidal surgery of pituitary macroadenoma. Its accuracy of location is very useful and important in determining anatomical structure and protecting normal tissues and vessels. Moreover, fluoroscopy was not required during the surgery.     

Accuracy evaluation of surface-based registration methods in a computer navigation system for hip surgery performed through a posterolateral approach.

OBJECTIVE: Many computer navigation systems have recently been developed for brain surgery, and the use of such systems in orthopedic surgery is increasing. Intraoperative registration of preoperative images is one of the most important steps in controlling the overall accuracy of computer navigation systems. Various parameters, such as CT-scan slice thickness, reconstruction pitch, intraoperative data sampling area, and data sampling volume, may affect the accuracy of registration. The purpose of this study was to evaluate the effect of the aforementioned parameters on the accuracy of registration for hip surgery performed through a posterolateral approach, and to find a clinically suitable trade-off between accuracy and surgical invasiveness. MATERIALS AND METHODS: One cadaveric pelvis and one cadaveric femur were used for this study. Four alumina ceramic balls with a diameter of 28 mm and within 1 micrometer of sphericity were attached to the pelvis, and three similar balls attached to the femur, to determine relative position. CT-scan images of the pelvis and femur were obtained with a helical scanner. Three sets of slice thickness and slice pitch were chosen for data acquisition, and two additional sets of reconstructed data were made. Bone contours were extracted by cutting out the surrounding substrate at a given CT number threshold, and surface models of the bone were made from the resultant data. The positions of the pelvis and femur were tracked by LED markers attached to the bone using an optical three-dimensional position sensor (OPTOTRAK). Registration of the computer models to the real objects was performed by measuring the position of a certain number of surface points on each object with an OPTOTRAK pen-probe. RESULTS AND CONCLUSION: Slice thickness and reconstruction pitch affected the accuracy of registration. As the sampling area was expanded from the periarticular area to the distant peripheral area, accuracy increased slightly. Accuracy did not increase when the whole area was used, but in fact decreased, especially in the femur. The positive effect of increasing the number of sampling points was saturated at 30 points when the surface of the periarticular area was sampled. The following trade-off between accuracy and invasiveness, in terms of various parameters of preoperative and intraoperative data, is proposed as clinically optimal: perform the CT scan with 3-mm slice thickness and 1-mm reconstruction pitch, and sample the periarticular area with 30 sampling points. With these parameters, the accuracy of registration was 1.2 mm and 0.9 degrees of bias with 0.7 mm and 0.3 degrees of RMS in the pelvis, and 1.4 mm and 0.6 degrees of bias with 1.3 mm and 0.3 degrees of RMS in the femur.     

Adolescent idiopathic scoliosis treated with posteromedial translation: radiologic evaluation with a 3D low-dose system

Purpose

Computed tomography can be used for three-dimensional (3D) evaluation of adolescent idiopathic scoliosis (AIS) patients, but at the expense of high radiation exposure, and with the limitation of being performed in the supine position. These drawbacks can now be avoided with low-dose stereoradiography, even in routine clinical use. The purpose of this study was to determine the 3D postoperative correction of AIS patients treated by posteromedial translation.

Methods

Forty-nine consecutive patients operated for AIS (Lenke 1–4) using posteromedial translation were included. Corrections were evaluated preoperatively, postoperatively and after at least 2 years using the EOS imaging system. 3D angles were measured in the plane of maximum deformity.

Results

Mean number of levels fused and operative time were 13.5 ± 1 and 215 ± 25 min, respectively. Main thoracic, proximal thoracic, and lumbar curves corrections averaged 64.4 ± 18, 31 ± 10 and 69 ± 20 %, respectively. Mean T4–T12 kyphosis increased 18.8° ± 9° in the subgroup of hypokyphotic patients. Mean apical vertebral rotation reduction was 48.3 ± 20 %. Trunk height gain averaged 27.8 ± 14 mm. There was no pseudarthrosis or significant loss of correction in any plane during follow-up. Two patients (4 %) developed asymptomatic proximal junctional kyphosis, despite having normal thoracic kyphosis. Their sagittal balance was shifted posteriorly by 36 and 47 mm, respectively, by the operation, but revision surgery was not performed.

Conclusions

Low-dose stereoradiography provided 3D reconstructions of the fused and unfused spine in routine clinical use. Postoperative 3D analysis showed that posteromedial translation enhanced sagittal balance correction, without sacrificing frontal or axial correction of the deformity.     

Accuracy evaluation of a shape-based registration method for a computer navigation system for total knee arthroplasty

This study evaluated the effect of computed tomography (CT) slice thickness, reconstruction pitch, intraoperative data sampling area, and data sampling volume on the accuracy of registration and determined a clinically acceptable trade-off between accuracy and surgical invasiveness. One cadaveric femur and one cadaveric tibia were used. Computed tomography of the femur and tibia were obtained using a helical scanner. Three sets of slice thickness and slice pitch were chosen for data acquisition, and two additional sets of reconstructed data were made. Bone contours were extracted by removing surrounding substrate. Surface models of bones were made from the resulting data. Registration of surface models to real objects was performed by measuring the position of various surface points on various areas of each object using an OPTOTRAK pen-probe (Northern Digital Inc, Ontario, Canada). The following trade-off is proposed as clinically optimal: perform CT with 3-mm slice thickness and 1-mm reconstruction pitch, and sample a periarticular area of 30 sampling points. The accuracy of registration in terms of position and angle was 0.8 mm and 0.6 degrees of bias with 0.2 mm and 0.3 degrees of root-mean-square in the femur, and 0.5 mm and 0.4 degrees of bias with 0.2 mm and 0.3 degrees of root-mean-square in the tibia.     

O型臂联合CT三维导航系统辅助颈椎椎弓根螺钉置入的准确性研究

目的:探讨O型臂联合CT三维导航系统辅助颈椎椎弓根螺钉置钉的准确性,并与侧块螺钉置钉进行比较.方法:回顾性分析2017年3月～2021年2月在我院分别使用O型臂联合CT三维导航系统辅助置入椎弓根螺钉与徒手置入侧块螺钉行颈椎后路内固定术的54例患者,其中男44例,女10例,年龄42～79岁(58.3±9.3岁).根据置钉...     

3D腹腔镜胃癌根治术

胃癌在中国是发病率最高的恶性肿瘤之一。但是,由于腹腔镜胃癌手术解剖层面多、淋巴清扫范围广泛、消化道重建多样,故在普外科领域腹腔镜下胃癌根治术为难度较高的手术。随着科技与设备的发展,3D腹腔镜逐步踏入普外科手术领域,提供了三维立体图像,使手术变得更加精细,降低操作难度,弥补了传统2D腹腔镜缺乏纵深感、立体解剖描述不足的劣势。立体视野能为主刀提供更加清晰的手术视野,协助术者完成精细操作,在胃癌根治术中使淋巴清扫、系膜解剖等变得更加流畅、精准。     

标杆型3D打印导板辅助寰枢椎椎弓根置钉准确度分析

目的探讨标杆型3D打印导板辅助寰枢椎椎弓根置钉的可行性,并进行置钉准确度分析。方法 2014年6月—2015年8月,本院收治寰枢椎脱位患者21例,男12例,女9例;年龄12~54岁,平均42.6岁。术前使用Mimics 17.0软件和3-matic 9.0软件为每例患者制作标杆型3D打印导板,术中使用标杆型3D打印导板辅助寰枢椎椎弓根置钉,术后患者行颈椎CT平扫。在Mimics 17.0软件中,将手术前后的寰枢椎模型及螺钉配对拟合,调整空间坐标轴,测量并比较术前预设钉道与术后实际钉道的内倾角、头倾角、进钉点坐标。结果 21例患者手术顺利,手术时间(193±51)min,术中出血量(384±127)m L。共置入寰椎椎弓根螺钉30枚,枢椎椎弓根螺钉42枚。除2枚寰椎椎弓根螺钉侵入椎管≤2 mm外,其他螺钉均位于椎弓根骨皮质内。寰椎左右侧预设最佳钉道内倾角度分别为9.4°±1.8°、9.8°±1.6°,实际钉道内倾角度分别为8.7°±1.6°、10.6°±2.2°;左右侧预设最佳钉道头倾角度分别为8.9°±2.5°、8.8°±2.3°,实际钉道头倾角度分别为9.3°±2.9°、9.4°±3.5°。枢椎左右侧预设最佳钉道内倾角度分别为21.9°±6.6°、22.4°±6.9°,左右侧实际钉道内倾角度分别为24.1°±6.3°、20.8°±6.4°;左右侧预设最佳钉道头倾角度分别为23.7°±7.3°、24.2°±7.2°,左右侧实际钉道头倾角度分别为22.1°±7.9°、22.3°±7.6°。寰枢椎术后实际钉道与术前预设最佳钉道的内倾角、头倾角、进钉点坐标差异均无统计学意义(P0.05)。结论标杆型3D打印导板辅助寰枢椎椎弓根置钉方向可调整性好,置钉准确度较高,为临床寰枢椎置钉提供了一种新的方法。     

Real-time integration of ultrasound into neuronavigation: technical accuracy using a light-emitting-diode-based navigation system

Summary. Background. In brain surgery, intraoperative brain deformation is the major source of postimaging inaccuracy of neuronavigation. For intraoperative imaging of brain deformation, we developed a platform for the integration of ultrasound imaging into a navigation system.Method. A commercially available ultrasound system was linked to a light-emitting-diode- (LED) based neuronavigation system via rigid fixation of a position localiser to the ultrasound probe and ultrasound image transfer into the navigation system via a S-VHS port. Since the position of the ultrasound image co-ordinate system is not readily defined within the navigation reference co-ordinate system (REF CS), a transformation which links both co-ordinate systems has to be defined by a calibration procedure. Calibration of the ultrasound probe within the REF CS was performed via a cross-wire phantom. The phantom target was defined within the navigation co-ordinate system (by pointer under microscopic control) and imaged by ultrasound. Ultrasound presets were optimised (digital beam focusing, gain intensity) to attain a small echoic target for manual target definition. The transformation was derived from 150 ultrasound measures and iteration. Accuracy was calculated as mean linear error (LE; in X_REF, Y_REF, or Z_REF direction), overall mean LE (linear errors of all axes X_REF to Z_REF) and Euclidean error (EE; vectorial distance from the physical target).Findings. Optimised ultrasound presets (8MHz frequency, digital beam focusing, 20% gain intensity) enabled a low interobserver error (mean: 0.5mm, SD: 0.28) for target definition within the 2-D ultrasound image. Mean accuracy of pointer-based physical target definition in the REF CS was 0.7mm (RMSE; SD: 0.23mm). For navigated ultrasound, the overall mean LE was 0.43mm (SD: 1.36mm; 95%CL: 3.13mm) with a mean EE of 2.26mm (SD: 0.97mm; 95%CL: 4.21mm).Interpretation. Using a single target cross-wire phantom, a highly accurate integration of ultrasound imaging into neuronavigation was achieved. The phantom accuracy of integration lies within the range of application accuracy of navigation systems and warrants clinical studies.