Frame-based Technique Research Articles

Review of the targeting accuracy of frameless and frame-based robot-assisted deep brain stimulation electrode implantation in pediatric patients using the Neurolocate module.

The Neurolocate module is a 3D frameless patient registration module that is designed for use with the Neuromate stereotactic robot. Long-term electrical stimulation of the globus pallidus internus (GPi) and subthalamic nucleus (STN) via deep brain electrode implantation is particularly successful in a select group of movement disorders in pediatric patients. This study aimed to review the targeting accuracy of deep brain stimulation (DBS) electrode implantation in a single center, comparing standard frame-based techniques to the frameless Neurolocate module. Twenty-four pediatric patients underwent implantation of bilateral DBS electrodes under general anesthesia during the period of August 2018-August 2022. All patients underwent robot-assisted stereotactic implantation of DBS electrodes using an intraoperative O-arm 3D scanner to confirm the final electrode position. These coordinates were compared with the planned entry and target, with attention to depth, radial, directional, and absolute errors, in addition to Euclidean distance (ED). The primary outcome evaluated the accuracy and safety of the Neurolocate frameless technology compared with standard frame-based techniques. Of the 24 bilateral DBS electrode implantations performed, 62.5% used Neurolocate technology: 87.5% were delivered to the GPi and the remaining 12.5% to the STN. The mean patient age was 11.0 (range 4-18) years and 70.8% were male. The median absolute errors in x-, y-, and z-axes were 0.35, 0.75, and 0.9 mm, respectively, using the Neurolocate module compared with 0.30, 0.95, and 1.1 mm using the standard frame-based technique. The median ED from the planned target to the actual electrode position with the Neurolocate module was 1.28 mm versus 1.69 mm using standard frame-based techniques. No major perioperative complications occurred. Stereotactic robot-assisted DBS implantation with the frameless Neurolocate module is safe for use in the pediatric population, showing good surgical accuracy and no inferiority to standard frame-based techniques. The Neurolocate module for robotic DBS surgery has the potential to improve surgical targeting accuracy, surgical time, patient comfort, and safety.

Anesthetic Concerns during Gamma-Knife Radiosurgery.

Gamma-knife radiosurgery (GKRS) has emerged as one of the mainstream modalities in the treatment of many neurosurgical conditions. The indications for Gamma knife are ever-increasing and presently more than 1.2 million patients have been treated with Gamma knife worldwide. A neurosurgeon usually leads the team of radiation oncologists, medical physicists, nursing staff, and radiation technologists. Seldom, help from anesthetist colleagues is required in managing patients, who either require sedation or anesthesia. In this article, we try to elucidate anesthetic considerations in Gamma-knife treatment for different age groups. With the collective experience of authors involved in Gamma-Knife Radiosurgery of 2526 patients in 11 years with a frame-based technique, authors have tried to elucidate an effective and operational management strategy. For pediatric patient (n = 76) population and mentally challenged adult patients (n = 12), GKRS merits special attention given its noninvasive nature but problems of frame fixation, imaging, and claustrophobia during radiation delivery become an issue. Even among adults, many patients have anxiety, fear, or claustrophobia, who require medications either to sedate or anesthetize during the procedure. A major goal in treatment would be a painless frame fixation, avoid inadvertent movement during dose delivery, and a fully wake, painless, and smooth course after frame removal. The role of anesthesia is to ensure patient immobilization during image acquisition and radiation delivery while ensuring an awake, neurologically accessible patient at the end of the radiosurgery.

Deep brain stimulation for Parkinson's disease in practice: results of the survey by the Italian Neurosurgery Society.

Deep brain stimulation (DBS) is a safe and effective treatment for patients with advanced Parkinson's disease (PD) and many neurosurgical centers in Italy have a DBS program. Considering the prevalence of PD and criteria for DBS implantation, about 3200-10,350 PD patients may benefit from DBS in Italy. The global management of patients underwent DBS is complex and it can be supposed that many differences exist between centers in clinical practice. The Italian Neurosurgery Society (SINch) designed this survey to investigate the state of the art of DBS for PD in Italy. A 26-item closed-ended question survey was designed and sanded by email at all Italian Neurosurgery centers. The main topic investigated was DBS teams, anatomical target selection, surgical procedure, neuroimaging, intraoperative target localization, DBS device and patients' follow-up. A total of 23 neurosurgery centers completed the survey. There are mainly low-to medium-volume centers (<20 annual DBS procedures) with dedicated DBS teams. The principal anatomical target used is subthalamic nucleus (STN) and, relative to the surgical technique, it emerges that in Italy DBS are bilaterally implanted in a single-step session with awake anesthesia and with frame-based technique. Final leads positioning is defined by microelectrode recordings (MER) and microstimulation (MS), with limited role of intraoperative neuroimaging (MRI and O-Arm). The stimulation is started at 15 or 30 days from procedure. Many centers of neurosurgery in Italy have a well-established DBS program for patients with advanced PD and some practical differences in technique between centers exist. Further investigation is needed to investigate specific criteria for selecting one technique over another.

Techniques of Frameless Robot-Assisted Deep Brain Stimulation and Accuracy Compared with the Frame-Based Technique.

sBackground: Frameless robot-assisted deep brain stimulation (DBS) is an innovative technique for leads implantation. This study aimed to evaluate the accuracy and precision of this technique using the Sinovation SR1 robot. Methods: 35 patients with Parkinson’s disease who accepted conventional frame-based DBS surgery (n = 18) and frameless robot-assisted DBS surgery (n = 17) by the same group of neurosurgeons were analyzed. The coordinate of the tip of the intended trajectory was recorded as xi, yi, and zi. The actual position of lead implantation was recorded as xa, ya, and za. The vector error was calculated by the formula of √(xi − xa)2 + (yi − ya)2 + (zi − za)2 to evaluate the accuracy. Results: The vector error was 1.52 ± 0.53 mm (range: 0.20–2.39 mm) in the robot-assisted group and was 1.77 ± 0.67 mm (0.59–2.98 mm) in the frame-based group with no significant difference between two groups (p = 0.1301). In 10.7% (n = 3) frameless robot-assisted implanted leads, the vector error was greater than 2.00 mm with a maximum offset of 2.39 mm, and in 35.5% (n = 11) frame-based implanted leads, the vector error was larger than 2.00 mm with a maximum offset of 2.98 mm. Leads were more posterior than planned trajectories in the robot-assisted group and more medial and posterior in the conventional frame-based group. Conclusions: Awake frameless robot-assisted DBS surgery was comparable to the conventional frame-based technique in the accuracy and precision for leads implantation.

Intraoperative Computed Tomography for Registration of Stereotactic Frame in Frame-Based Deep Brain Stimulation.

Deep brain stimulation (DBS) electrode placement utilizing a frame-based technique requires registration of the stereotactic frame with computed tomography (CT) or magnetic resonance (MR) imaging. This traditionally has been accomplished with a conventional CT scanner. In recent years, intraoperative CT has become more prevalent. To compare the coordinates obtained with intraoperative CT and conventional CT for registration of the stereotactic frame for DBS. Patients undergoing DBS electrode placement between 2015 and 2017, who underwent both conventional and intraoperative CT for registration of the stereotactic frame, were included for analysis. The coordinates for the stereotactic target, anterior commissure, and posterior commissure for each CT method were recorded. The mean, maximum, minimum, and standard deviation of the absolute difference for each of the paired coordinates was calculated. Paired t-tests were performed to test for statistical significance of the difference. The directional difference as well as the vector error between the paired coordinates was also calculated. The mean absolute difference between conventional and intraoperative CT for the coordinate pairs was less than 0.279 mm or 0.211 degrees for all coordinate pairs analyzed. This was not statistically significant for any of the coordinate pairs. Moreover, the maximum absolute difference between all coordinate pairs was 1.04 mm. Intraoperative CT imaging provides stereotactic frame registration coordinates that are similar to those obtained by a standard CT scanner. This may save time and hospital resources by obviating the need for the patient to go to the radiology department for a CT scan.

An Outcomes Comparison of Patients Treated for Arteriovenous Malformation with LINAC-based Stereotactic Radiosurgery by a Standard Frame-Based Technique or a Frameless Technique Utilizing 3-Dimensional Rotational Angiography

An Outcomes Comparison of Patients Treated for Arteriovenous Malformation with LINAC-based Stereotactic Radiosurgery by a Standard Frame-Based Technique or a Frameless Technique Utilizing 3-Dimensional Rotational Angiography

Web-based adaptive presentation techniques to enhance learning outcomes in higher education

The purpose of this study is to develop and compare two different techniques of adaptive presentation techniques (adaptive multimedia/ frames). Moreover, this study aimed at investigating the effect of both treatments on improving learning outcomes. The participants are two experimental groups: Group A (n = 35) were taught content through the multimedia-based technique, and group B (n = 35) were taught content through the frame-based technique. The results showed that the adaptive presentation techniques have an effect on enhancing students’ learning outcomes. Also, the comparison of the techniques showed a significant difference between the mean scores of the two groups in favor of group A. The study concluded that the adaptive multimedia-based technique showed higher impact relatively than the frame-based technique. In light of these results, it is recommended that an expansion of the use of web-based adaptive presentation techniques WAPT for enhancing students’ learning in higher education is needed.

Frameless stereotaxy in subthalamic deep brain stimulation: 3-year clinical outcome

BackgroundIn most centers, the surgery of deep brain stimulation (DBS) is performed using a stereotactic frame. Compared with frame-based technique, frameless stereotaxy reduces the duration of surgical procedure and patient’s discomfort, with lead placing accuracy equivalent after the learning curve. Although several studies have investigated the targeting accuracy of this technique, only a few studies reported clinical outcomes, with data of short-term follow-up.ObjectiveTo assess clinical efficacy and safety of frameless bilateral subthalamic nucleus (STN) DBS in Parkinson’s disease (PD) patients at 1- and 3-year follow-up.MethodsConsecutive PD patients who underwent bilateral STN-DBS with a manual adjustable frameless system were included in the study. The data were collected retrospectively.ResultsEighteen PD patients underwent bilateral STN-DBS implant and were included in the study. All patients completed 1-year observation and ten of them completed 3-year observation. At 1-year follow-up, motor efficacy of STN stimulation in off-med condition was of 30.1% (P = 0.003) and at 3-year follow-up was of 36.3%, compared with off-stim condition at 3-year follow-up (P = 0.005). Dopaminergic drugs were significantly reduced by 31.2% 1 year after the intervention (P = 0.003) and 31.7% 3 years after the intervention (P = 0.04). No serious adverse events occurred during surgery.ConclusionsFrameless stereotaxy is an effective and safe technique for DBS surgery at 1- and 3-year follow-up, with great advantages for patients’ discomfort during surgery.

Superior accuracy and precision of SEEG electrode insertion with frame-based vs. frameless stereotaxy methods

Stereotactic electroencephalography (SEEG) has largely become the preferred method for intracranial seizure localization in epileptic patients due to its low morbidity and minimally invasive approach. While robotic placement is gaining popularity, many centers continue to use manual frame-based and frameless methods for electrode insertion. However, it is unclear how these methods compare in regard to accuracy, precision, and safety. Here, we aim to compare frame-based insertion using a CRW frame (Integra®) and frameless insertion using the StealthStation™ S7 (Medtronic®) navigation system for common temporal SEEG targets. We retrospectively examined electrode targets in SEEG patients that were implanted with either frame-based or frameless methods at a level 4 epilepsy center. We focused on two commonly used targets: amygdala and hippocampal head. Stealth station software was used to merge pre-operative MR with post-operative CT images for each patient, and coordinates for each electrode tip were calculated in relation to the midcommissural point. These were compared to predetermined ideal coordinates in regard to error and directional bias. A total of 81 SEEG electrodes were identified in 23 patients (40 amygdala and 41 hippocampal head). Eight of 45 electrodes (18%) placed with the frameless technique and 0 of 36 electrodes (0%) placed with the frame-based technique missed their target and were not clinically useful. The average Euclidean distance comparing actual to ideal electrode tip coordinates for frameless vs. frame-based techniques was 11.0mm vs. 7.1mm (p< 0.001) for the amygdala and 12.4mm vs. 8.5mm (p< 0.001) for the hippocampal head, respectively. There were no hemorrhages or clinical complications in either group. Based on this series, frame-based SEEG insertion is significantly more accurate and precise and results in more clinically useful electrode contacts, compared to frameless insertion using a navigation guidance system. This has important implications for centers not currently using robotic insertion.

A comparative outcomes analysis of patients treated for arteriovenous malformation with LINAC-based stereotactic radiosurgery by a standard frame-based technique or a frameless technique utilizing 3-dimensional rotational angiography

Previous work at our institution treating arteriovenous malformation (AVM) with radiosurgery (RS) demonstrated superior nidus visualization and geometric accuracy with use of 3-dimensional rotational angiography (3DRA) compared to biplanar digital subtraction angiography. We have since adopted a unique radiosurgical protocol that utilizes 3DRA in the planning of linear accelerator (LINAC)-based RS delivered in a frameless manner. This study seeks to compare clinical outcomes between patients treated by this novel approach and those treated by our historic frame-based protocol. Clinical data were queried for all patients treated for AVM by single-fraction RS from 2003 to 2017. RICs were identified and classified as radiologic, symptomatic, or permanent. Excellent outcome was defined as nidus obliteration without intracranial hemorrhage (ICH) or symptomatic RIC. Clinical predictors of study outcomes were identified through univariate and multivariate logistic regression using backwards elimination to optimize a predictive model. 131 AVMs in 124 patients were included with a median follow-up of 88 months. 59 AVMs received frame-based RS and 72 AVMs received frameless RS. Rate of obliteration was 64% for frame-based RS and 61% for frameless RS (p = 0.70). Radiologic, symptomatic, and permanent RICs rates were 68%, 17%, and 8%, respectively, for frame-based cases, versus 40% (p < 0.01), 8% (p = 0.13), and 3% (p = 0.15), respectively, for frameless cases. Excellent outcome was achieved in 49% of frame-based cases and 53% of frameless cases (p = 0.68). These results illustrate the safety and effectiveness of frameless LINAC-based AVM RS utilizing 3DRA.

Incorporating New Technology Into a Surgical Technique: The Learning Curve of a Single Surgeon's Stereo-Electroencephalography Experience.

Technological improvements frequently outpace the publication of randomized, controlled trials in surgical patients. This makes the application of new surgical techniques difficult as surgeons solely use clinical experience to guide changes in their practice. To quantitatively examine the learning curve of incorporating new technology into a surgical technique and discuss the clinical significance of incorporating this new technology into daily practice. To identify areas of improvement for operative efficiency and safety. A retrospective observational study examining quantitative measures of operative efficiency and safety from 2009 to 2017 in 454 consecutive patients undergoing stereo-electroencephalography depth electrode implantations. The transition to a new robotic technique significantly improved operative times (196 min [95% CI 173-219] vs 115 min [95% CI 111-118], P<.0001). Cumulative sum (CUSUM) analysis demonstrated that mastery of the robotic technique took much longer than the frame-based technique (operative time peak at case 75 vs case 25, plateau of 150 vs 10 cases). Although hemorrhage rates using different vascular imaging techniques did not appear to differ using traditional statistical analysis (magnetic resonance imaging, MRI 22.3%, computed tomography angiography, CTA 17.9%, angiogram 18.1%, likelihood ratio χ2=4.84, P=.30), CUSUM analysis suggested MRI as the vascular imaging modality leading to higher hemorrhage and symptomatic hemorrhage rates at our center. This experience demonstrates an improvement in operative efficiency through a series of changes made using clinical experience and intuition while transitioning to a completely new paradigm. CUSUM analysis identified potential areas for improvement in both operative efficiency and safety if used in a prospective manner.

Frameless Deep Brain Stimulation Surgery: A Single-Center Experience and Retrospective Analysis of Placement Accuracy of 220 Electrodes in a Series of 110 Patients

Background: Proper lead placement is considered one of the key factors in achieving a good clinical outcome in deep brain stimulation (DBS), but there is still considerable controversy surrounding the accuracy of the frameless in comparison to the frame-based technique. Objective: We report our single-center experience with DBS electrode placement to evaluate the accuracy of the frameless stereotactic system. Methods: We prospectively analyzed the data of 110 patients who underwent DBS surgery for Parkinson disease, dystonia, essential tremor, or refractory epilepsy. The final targets (FTs) of the 220 leads were: subthalamic nucleus, globus pallidus pars interna, ventralis intermedius nucleus, and anterior nuclei of thalamus in thalamus. A bilateral stereotactic approach using a combined identification of target based on preoperative images (MRI and CT scan fusion) and intra-operative micro-electrode recording (MER) were done. We collected and compared the coordinates of planned target (PT), the definitive expected target (ET) during MER, and the effective final location (FT) of the lead using the postoperative CT. Accuracy was assessed by both vector error (VE) and deviation from the PT. Results: The mean and SD from PTs was 0.78 ± 0.43 mm in the x direction, 0.68 ± 0.41 mm in the y direction, and 0.76 ± 0.41 mm in the z direction. Global VE was 1.43 ± 0.37. Conclusion: Frameless systems appear to be a reliable and accurate technique.

RTHP-03. FRAME-BASED AND MASKED STEREOTACTIC RADIOSURGERY: A PATIENT EXPERIENCE COMPARISON WITH THE GAMMA KNIFE ICON

Abstract INTRODUCTION Patients undergoing stereotactic radiosurgery (SRS) for intracranial pathology have two treatment options: frame-based (FB) versus masked (MB). There is sparse information on a patient’s experience between the two types and to what extent a patient’s diagnosis will predict their SRS experience. METHODS A retrospective analysis of patients who completed a questionnaire of their experience after SRS using the Gamma Knife Icon was completed. RESULTS Fifty-eight patients completed the questionnaire, 60% were FB and 40% MB. The average age was 63.3 + 15.3 years, 40% were male. Of the patients treated with a FB technique, 51% didn’t find SRS to be uncomfortable. Comparatively, 91% of MB patients didn’t find SRS to be uncomfortable. Patients who underwent FB treatment rated their pain of frame placement on a visual analog scale (VAS) 1–3, 24%, VAS 4–6, 46%, VAS 7–10, 30%. Eight patients answered that they didn’t tolerate the procedure as expected, most of which were treated using a FB method (87%). Compared to previous surgery or SRS, five patients found their experience of SRS wasn’t tolerable, while 93% of patients would consider repeat SRS. All patients treated felt adequately informed about the procedure. The patient experience of discomfort during SRS and their evaluation of pain during frame placement between patients treated for benign versus malignant lesions (discomfort: 59% vs. 22%, respectively and median VAS pain: 6 + 2.67, 4.5 + 1.99, respectively) determined a benign diagnosis had more discomfort during SRS compared to a malignant diagnosis. Pain during frame placement was similar for both diagnoses. CONCLUSION Patients experienced frame-based SRS as more uncomfortable than mask-based treatment. Benign pathologies appeared to have more discomfort compared to malignant pathologies. All patients of both techniques felt adequately informed about their procedure.

Accuracy of SEEG Electrodes Implanted in Lateral Position Versus Supine Position

Abstract INTRODUCTION Accuracy during SEEG implantations is critical as several electrodes will cross narrow corridors between cerebral blood vessels. Previous studies have compared the accuracy of different techniques such as frame-based, frameless, and robot-assisted implantations and overall SEEG has been reported to be quite safe, with a major complication incidence of less than 1%. Typically, the supine position is utilized for implantation; however, the lateral position may be more comfortable and ergonomic for trajectories with a posterior entry point (eg, posterior approach to the insula). To our knowledge, this is the first study to compare the accuracy of SEEG electrodes implanted in supine position vs lateral position. METHODS About 22 patients who underwent SEEG electrode implantation using Leksell frame fixation and Neuromate robot were included in this study and clustered according to the supine (n = 11) or lateral (n = 11) position. A total of 284 electrodes (Supine: n = 139; Lateral: n = 145) were analyzed. Postoperative Oarm images were co-registered with the preoperative plan on Voxim software. Cartesian coordinates of the entry point (EP) and target point (TP) were obtained from the planned trajectory and the implanted electrode. Three-dimensional error (Euclidian distance) and radial error for EP and TP were calculated. Wilcoxon rank sum test was used to compare lateral versus supine group. RESULTS Radial errors were similar between both groups. EP three-dimensional error was higher in the lateral position group (1.3 mm vs 1.7 mm, P = .004), whereas TP three-dimensional error was higher in the supine position group (2.9 mm vs 1.8 mm, P &lt; .001). CONCLUSION SEEG electrode implantation using frame-based fixation and robot-assisted technique in the lateral position has similar accuracy compared to implantation in the supine position.

Finite Element Analysis of Shell-First and Longitudinally Reinforced Frame-Based Wooden Ships

During the period between the 5th century BC and the 6th century AD, two ship construction technologies were prevalent around the Mediterranean Sea: shell-first and frame-based. The shell-first concept was of a strong rigid hull, comprising edge-joined strakes reinforced by transverse frames which were not joined to the keel. In the frame-based technique, transverse frames were connected to the keel to form the skeleton, and the strakes were then nailed to the frames. The hull was strengthened with longitudinal reinforcements. These concepts did not exist in isolation, and at times both techniques were combined. An initial global finite element study (FEA) which analyzed the two technologies, the shell-first Maʻagan Mikhael (400 BC), and the frame-based Dor 2001/1 (6th century AD), revealed that the ships were on a structural par. In that same study, a controlled FEA experiment on generic models was constructed to simulate shell-first and frame-based ships, showing, however, that the shell-first technique exhibited significantly higher structural integrity than the frame-based method. These results prompted a secondary study to explore the mechanical-structural contribution of longitudinal reinforcements to frame-based constructs. Using the same frame-based generic model as in the previous study, longitudinal reinforcements were added in various configurations. The FEA results from this study demonstrated that three critical interdependent factors determined the relative strengths of shell-first and frame-based techniques: the number of transverse frames, the number of longitudinal reinforcements, and their relative locations.

Application of intracranial electrode implantation using stereotactic frame in identification of epileptogenic zone

Objective To explore the safety and reliability of intracranial electrode implantation based on stereotactic frame. Methods Sixty patients with refractory epilepsy were retrospectively included from June 2015 to June 2016 in Beijing Tiantan-Fengtai Epilepsy Center. We analyzed relevant indexes which might influence the SEEG (stereo-electroencephalograhy) electrode implantation target deviations and complications related to the implantation. Video-EEG monitoring was conducted after the electrode implantation before operation was performed to remove the seizure focus according to the preoperative evaluation. Outcomes were followed-up. Results Sixty patients underwent a total of 474 intracranial electrodes implantation with an average electrode number of 8.0 ± 2.5 and an average application time of 13.5 ± 3.1 min per electrode. The entrance point deviation, target deviation, electrode-skull angle and electrode length in the brain were 0.0-8.3 mm (median: 1.1 mm), 0-12 mm (median: 1.4 mm), 44.0-90.0° (median: 67.5°) and 15-97 mm (median: 43 mm), respectively. The target deviation was positively correlated with the deviation of entry point (r=0.426, P<0.01). The target deviation was negatively correlated with the electrode skull angle (r=-0.247, P<0.01). The target deviation was positively correlated with the length of electrode in the brain (r=0.145, P<0.01). There are totally 6(10%) cases developing complications including small amount of cerebral hematoma in 3(5%), brain abscess in 1(2%) and electrode bending in 2(3%). Fifty-three patients were followed up for 1-2 (1.5±0.5) years post resection surgery. There was 72%(38/53) of the patients achieving seizure free (Engel Ⅰ). Meanwhile, seizures remained in the other 28%(15/53) of the patients (Engel Ⅱ-Ⅳ). Conclusion The stereotactic frame-based intracranial electrode implantation technique seems safe and reliable. Combined with postoperative video-EEG analysis, it could be applied for localization of epileptogenic zone. Key words: Epilepsy; Neurosurgical procedures; Stereoelectroencephalogram; Prognosis

Cloud and Shadow Detection using Sequential Characteristics on Multi-Spectral Satellite Images

For land and sea surface monitoring applications that rely on optical Earth Observation satellite images, it is required that cloud and cloud shadow areas in the images are detected and removed. As a consequence, the frequency of obtaining new images can be increased and short-term changes can be studied more effectively. In this paper, an algorithm is designed that is able to automatically detect clouds and shadows in medium-resolution optical multi-spectral images. The developed system is a frame-based image processing technique utilizing multiple spectral bands for feeding a cloud and shadow detector, where possible cloud contamination is recursively removed from the input images. The cloud detector utilizes Brightness Temperature Differences in the spectral regions of Far IR (FIR) and Thermal IR (TIR). After careful considerations, the reflective band FIR was adopted for usage in this Difference Image. The shadow detector uses Background Subtraction, which iteratively constructs its Reference Image automatically. This iterative nature is exploited to utilize time-sequential characteristics among the input images. After experiments, 94.6% of the clouds are detected, with a precision of 86.5%, as determined using per-pixel ground-truth data. For shadows, these statistics are 77.1% and 75.8%, respectively and may be further improved in future work. Selected mid-resolution Landsat images have been used for the validation.

Editorial Issue 27.6

This issue contains four papers. In the first paper, Mingfei Wang, Jinyuan Jia, Ning Xie, and Chenxi Zhang, from Tongji University in Shanghai, China, aim to solve the challenging problems of choosing the data supplier for data-dispatching services in distributed virtual environments based on peer-to-peer networks. They propose a dynamic node-organizing mechanism that aims by applying the avatar's behavioral characteristics to the neighbor maintenance mechanism and scene data transmission. They have conducted extensive simulation experiments that simulate avatar behaviors in a popular online game. The results show that their proposed mechanism achieved a substantial alleviation of neighbor churn and reduced information exchange, which improves the transmission efficiency in DVEs. In the second paper, Masaki Oshita, from the Kyushu Institute of Technology, Japan, proposes an interactive character motion control interface that uses hands. Using their hands and fingers, the user can control a large number of degrees of freedom (DOFs) at the same time. The author applied principal component analysis (PCA) to a set of sample poses and assigned the extracted principal components to each DOF of the hands (such as the hand positions and finger bending/extending angles). The author developed methods for computing the feature vector, for applying PCA, and for pose and action synthesis. In addition, he introduced a pose transition method for performing a step motion when necessary to prevent foot sliding. He presents his experimental results and demonstrates the effectiveness of his interface. In the third paper, Wenwu Yang, Xun Wang, Wangbin Kou, Bailin Yang, and Guozheng Wang, from Zhejiang Gongshang University, Hangzhou, China, present a topology-aware method based on moving least squares (MLS) deformation approach for 2D characters. First, a Laplace equation is solved to obtain a set of weights, which are called as harmonic weights. Then, the MLS deformation is performed by using the harmonic weights as the deformation influence of the user-specified controls. Finally, the possible distortion in the traditional MLS deformation can be effectively avoided, since the harmonic weights spread the deformation of the controls in a localized and topology-aware way. In addition, a simple but effective area-preserving variant of MLS deformation is proposed, which is suitable for the editing of incompressible objects. Mohammadali Hajizadeh and Hossein Ebrahimnezhad, from Sahand University of Technology, Islamic Republic of Iran, propose a key frame-based technique for 3D dynamic mesh compression. First, key frames are extracted from the animated sequence. Extracted key frames are then linearly combined using blending weights to predict the vertex locations of the other frames. These blending weights play a key role in the proposed algorithm since the prediction performance and the required number of key frames are greatly dependent on these weights. They present a novel method in order to compute the optimum blending weight, which makes it possible to predict location of the vertices of the non-key frames with the minimum number of key frames. The residual prediction errors are finally quantized and encoded using Huffman coding and another heuristic method. Experimental results on different test sequences with various sizes, topologies, and geometries demonstrate the privileged performance of the proposed method compared to the previous techniques.

Analysis of translational errors in frame-based and frameless cranial radiosurgery using an anthropomorphic phantom.

ObjectiveTo evaluate three-dimensional translational setup errors and residual errors in image-guided radiosurgery, comparing frameless and frame-based techniques, using an anthropomorphic phantom.Materials and MethodsWe initially used specific phantoms for the calibration and quality control of the image-guided system. For the hidden target test, we used an Alderson Radiation Therapy (ART)-210 anthropomorphic head phantom, into which we inserted four 5mm metal balls to simulate target treatment volumes. Computed tomography images were the taken with the head phantom properly positioned for frameless and frame-based radiosurgery.ResultsFor the frameless technique, the mean error magnitude was 0.22 ± 0.04 mm for setup errors and 0.14 ± 0.02 mm for residual errors, the combined uncertainty being 0.28 mm and 0.16 mm, respectively. For the frame-based technique, the mean error magnitude was 0.73 ± 0.14 mm for setup errors and 0.31 ± 0.04 mm for residual errors, the combined uncertainty being 1.15 mm and 0.63 mm, respectively.ConclusionThe mean values, standard deviations, and combined uncertainties showed no evidence of a significant differences between the two techniques when the head phantom ART-210 was used.

Frameless Stereotactic Ommaya Reservoir Placement: Efficacy and Complication Comparison with Frame-Based Technique

Background: Ommaya reservoirs are ventricular access devices used primarily for the administration of intrathecal antineoplastic chemotherapy. In patients with low or normal ventricular volume, stereotaxy can improve accuracy of catheter placement with minimal morbidity. Frameless stereotaxy has become an increasingly popular alternative to frame-based stereotaxy. Relative rates of successful catheter placement between these two techniques are not described in the literature. Objectives: To compare a large series of frameless to frame-based stereotactic catheter placements for Ommaya reservoirs, with an aim to compare accuracy and complication rate between the two procedures. Methods: A consecutive series of 41 frame-based and 68 frameless Ommaya reservoir placement procedures performed at our institution from 1998 to 2013 was reviewed. Patient demographics, operative accuracy and complication rates for the two techniques were compared. Results: Characteristics of the two groups were similar in diagnoses, age and other related factors. Comparison of frameless to frame-based stereotactic Ommaya catheter placement did not show significant differences in accuracy of placement, overall morbidity or mortality, or in any subcategory of complications. Conclusions: These findings suggest that frameless stereotactic Ommaya reservoir placement is as safe and accurate as the frame-based technique.