Publications

2009
Sota Oguro, Junichi Tokuda, Haytham Elhawary, Steven Haker, Ron Kikinis, Clare MC Tempany, and Nobuhiko Hata. 2009. “MRI signal intensity based B-spline nonrigid registration for pre- and intraoperative imaging during prostate brachytherapy.” J Magn Reson Imaging, 30, 5, Pp. 1052-8.Abstract
PURPOSE: To apply an intensity-based nonrigid registration algorithm to MRI-guided prostate brachytherapy clinical data and to assess its accuracy. MATERIALS AND METHODS: A nonrigid registration of preoperative MRI to intraoperative MRI images was carried out in 16 cases using a Basis-Spline algorithm in a retrospective manner. The registration was assessed qualitatively by experts' visual inspection and quantitatively by measuring the Dice similarity coefficient (DSC) for total gland (TG), central gland (CG), and peripheral zone (PZ), the mutual information (MI) metric, and the fiducial registration error (FRE) between corresponding anatomical landmarks for both the nonrigid and a rigid registration method. RESULTS: All 16 cases were successfully registered in less than 5 min. After the nonrigid registration, DSC values for TG, CG, PZ were 0.91, 0.89, 0.79, respectively, the MI metric was -0.19 +/- 0.07 and FRE presented a value of 2.3 +/- 1.8 mm. All the metrics were significantly better than in the case of rigid registration, as determined by one-sided t-tests. CONCLUSION: The intensity-based nonrigid registration method using clinical data was demonstrated to be feasible and showed statistically improved metrics when compare to only rigid registration. The method is a valuable tool to integrate pre- and intraoperative images for brachytherapy.
Junichi Tokuda, Gregory S Fischer, Xenophon Papademetris, Ziv Yaniv, Luis Ibanez, Patrick Cheng, Haiying Liu, Jack Blevins, Jumpei Arata, Alexandra J Golby, Tina Kapur, Steve Pieper, Everette C Burdette, Gabor Fichtinger, Clare M Tempany, and Nobuhiko Hata. 2009. “OpenIGTLink: an open network protocol for image-guided therapy environment.” Int J Med Robot, 5, 4, Pp. 423-34.Abstract
BACKGROUND: With increasing research on system integration for image-guided therapy (IGT), there has been a strong demand for standardized communication among devices and software to share data such as target positions, images and device status. METHOD: We propose a new, open, simple and extensible network communication protocol for IGT, named OpenIGTLink, to transfer transform, image and status messages. We conducted performance tests and use-case evaluations in five clinical and engineering scenarios. RESULTS: The protocol was able to transfer position data with submillisecond latency up to 1024 fps and images with latency of <10 ms at 32 fps. The use-case tests demonstrated that the protocol is feasible for integrating devices and software. CONCLUSION: The protocol proved capable of handling data required in the IGT setting with sufficient time resolution and latency. The protocol not only improves the interoperability of devices and software but also promotes transitions of research prototypes to clinical applications.
Shigehiro Morikawa, Shigeyuki Naka, Koichiro Murakami, Yoshimasa Kurumi, Hisanori Shiomi, Tohru Tani, Hasnine A Haque, Junichi Tokuda, Nobuhiko Hata, and Toshiro Inubushi. 2009. “Preliminary clinical experiences of a motorized manipulator for magnetic resonance image-guided microwave coagulation therapy of liver tumors.” Am J Surg, 198, 3, Pp. 340-7.Abstract
BACKGROUND: In magnetic resonance (MR) image-guided microwave thermocoagulation of liver tumors, the choice of the optimal puncture route is an important and time-consuming process. To assist this process, we have developed a motorized MR-compatible manipulator. METHODS: The manipulator consists of a passive end effecter with 2 degrees-of-freedom (DOF) rotation and active base stages with 3 ultrasonic motors. It automatically chases the preset target point with synergetic remote-center-of-motion (RCM) control. A mechanical torque limiter and an electrical shutdown switch were added for patient safety. RESULTS: The manipulator was used for this procedure in 15 cases and successfully utilized to treat liver tumors in various locations. Thoracoscopic assistance was combined with the manipulator in 6 cases. No complications were experienced. CONCLUSIONS: The manipulator was found to be very effective for assisting MR-guided microwave coagulation of liver tumors.
2008
Polina Golland, Nobuhiko Hata, Sebastien Ourselin, and Nicholas Ayache. 2008. “Advances in radiological image analysis from MICCAI 2007.” Acad Radiol, 15, 11, Pp. 1345-6.
Peter Kazanzides, Tian Xia, Clint Baird, George Jallo, Kathryn Hayes, Nobuyuki Nakajima, and Nobuhiko Hata. 2008. “A cooperatively-controlled image guided robot system for skull base surgery.” Stud Health Technol Inform, 132, Pp. 198-203.Abstract
We created an image-guided robot system to assist with skull base drilling by integrating a robot, a commercial navigation system, and an open source visualization platform. The objective of this procedure is to create a cavity in the skull base to allow access for neurosurgical interventions. The motivation for introducing an image-guided robot is to improve safety by preventing the surgeon from accidentally damaging critical structures during the drilling procedure. Our approach is to attach the cutting tool to the robot end-effector and operate the robot in a cooperative control mode, where robot motion is determined from the forces and torques applied by the surgeon. We employ "virtual fixtures" to constrain the motion of the cutting tool so that it remains in the safe zone that was defined on a preoperative CT scan. This paper presents the system design and the results of phantom and cadaveric experiments. Both experiments have demonstrated the feasibility of the system, with average overcut error at about 1 mm and maximum errors at 2.5 mm.
Tian Xia, Clint Baird, George Jallo, Kathryn Hayes, Nobuyuki Nakajima, Nobuhiko Hata, and Peter Kazanzides. 2008. “An integrated system for planning, navigation and robotic assistance for skull base surgery.” Int J Med Robot, 4, 4, Pp. 321-30.Abstract
BACKGROUND: We developed an image-guided robot system to provide mechanical assistance for skull base drilling, which is performed to gain access for some neurosurgical interventions, such as tumour resection. The motivation for introducing this robot was to improve safety by preventing the surgeon from accidentally damaging critical neurovascular structures during the drilling procedure. METHODS: We integrated a Stealthstation navigation system, a NeuroMate robotic arm with a six-degree-of-freedom force sensor, and the 3D Slicer visualization software to allow the robotic arm to be used in a navigated, cooperatively-controlled fashion by the surgeon. We employed virtual fixtures to constrain the motion of the robot-held cutting tool, so that it remained in the safe zone that was defined on a preoperative CT scan. RESULTS: We performed experiments on both foam skull and cadaver heads. The results for foam blocks cut using different registrations yielded an average placement error of 0.6 mm and an average dimensional error of 0.6 mm. We drilled the posterior porus acusticus in three cadaver heads and concluded that the robot-assisted procedure is clinically feasible and provides some ergonomic benefits, such as stabilizing the drill. We obtained postoperative CT scans of the cadaver heads to assess the accuracy and found that some bone outside the virtual fixture boundary was cut. The typical overcut was 1-2 mm, with a maximum overcut of about 3 mm. CONCLUSIONS: The image-guided cooperatively-controlled robot system can improve the safety and ergonomics of skull base drilling by stabilizing the drill and enforcing virtual fixtures to protect critical neurovascular structures. The next step is to improve the accuracy so that the overcut can be reduced to a more clinically acceptable value of about 1 mm.
Clare Tempany, Sarah Straus, Nobuhiko Hata, and Steven Haker. 2008. “MR-guided prostate interventions.” J Magn Reson Imaging, 27, 2, Pp. 356-67.Abstract
In this article the current issues of diagnosis and detection of prostate cancer are reviewed. The limitations for current techniques are highlighted and some possible solutions with MR imaging and MR-guided biopsy approaches are reviewed. There are several different biopsy approaches under investigation. These include transperineal open magnet approaches to closed-bore 1.5T transrectal biopsies. The imaging, image processing, and tracking methods are also discussed. In the arena of therapy, MR guidance has been used in conjunction with radiation methods, either brachytherapy or external delivery. The principles of the radiation treatment, the toxicities, and use of images are outlined. The future role of imaging and image-guided interventions lie with providing a noninvasive surrogate for cancer surveillance or monitoring treatment response. The shift to minimally invasive focal therapies has already begun and will be very exciting when MR-guided focused ultrasound surgery reaches its full potential.
Nobuhiko Hata, Junichi Tokuda, Shelley Hurwitz, and Shigehiro Morikawa. 2008. “MRI-compatible manipulator with remote-center-of-motion control.” J Magn Reson Imaging, 27, 5, Pp. 1130-8.Abstract
PURPOSE: To develop and assess a needle-guiding manipulator for MRI-guided therapy that allows a physician to freely select the needle insertion path while maintaining remote center of motion (RCM) at the tumor site. MATERIALS AND METHODS: The manipulator consists of a three-degrees-of-freedom (DOF) base stage and passive needle holder with unconstrained two-DOF rotation. The synergistic control keeps the Virtual RCM at the preplanned target using encoder outputs from the needle holder as input to motorize the base stage. RESULTS: The manipulator assists in searching for an optimal needle insertion path which is a complex and time-consuming task in MRI-guided ablation therapy for liver tumors. The assessment study showed that accuracy of keeping the virtual RCM to predefined position is 3.0 mm. In a phantom test, the physicians found the needle insertion path faster with than without the manipulator (number of physicians = 3, P = 0.001). However, the alignment time with the virtual RCM was not shorter when imaging time for planning were considered. CONCLUSION: The study indicated that the robot holds promise as a tool for accurately and interactively selecting the optimal needle insertion path in liver ablation therapy guided by open-configuration MRI.
Gregory S Fischer, Iulian Iordachita, Csaba Csoma, Junichi Tokuda, Simon P Dimaio, Clare M Tempany, Nobuhiko Hata, and Gabor Fichtinger. 2008. “MRI-Compatible Pneumatic Robot for Transperineal Prostate Needle Placement.” IEEE ASME Trans Mechatron, 13, 3, Pp. 295-305.Abstract
Magnetic resonance imaging (MRI) can provide high-quality 3-D visualization of prostate and surrounding tissue, thus granting potential to be a superior medical imaging modality for guiding and monitoring prostatic interventions. However, the benefits cannot be readily harnessed for interventional procedures due to difficulties that surround the use of high-field (1.5T or greater) MRI. The inability to use conventional mechatronics and the confined physical space makes it extremely challenging to access the patient. We have designed a robotic assistant system that overcomes these difficulties and promises safe and reliable intraprostatic needle placement inside closed high-field MRI scanners. MRI compatibility of the robot has been evaluated under 3T MRI using standard prostate imaging sequences and average SNR loss is limited to 5%. Needle alignment accuracy of the robot under servo pneumatic control is better than 0.94 mm rms per axis. The complete system workflow has been evaluated in phantom studies with accurate visualization and targeting of five out of five 1 cm targets. The paper explains the robot mechanism and controller design, the system integration, and presents results of preliminary evaluation of the system.
Gregory S Fischer, Iulian Iordachita, Csaba Csoma, Junichi Tokuda, Philip W Mewes, Clare M Tempany, Nobuhiko Hata, and Gabor Fichtinger. 2008. “Pneumatically Operated MRI-Compatible Needle Placement Robot for Prostate Interventions.” IEEE Int Conf Robot Autom, 2008, Pp. 2489-2495.Abstract
Magnetic Resonance Imaging (MRI) has potential to be a superior medical imaging modality for guiding and monitoring prostatic interventions. The strong magnetic field prevents the use of conventional mechatronics and the confined physical space makes it extremely challenging to access the patient. We have designed a robotic assistant system that overcomes these difficulties and promises safe and reliable intra-prostatic needle placement inside closed high-field MRI scanners. The robot performs needle insertion under real-time 3T MR image guidance; workspace requirements, MR compatibility, and workflow have been evaluated on phantoms. The paper explains the robot mechanism and controller design and presents results of preliminary evaluation of the system.
Jens A Richolt, Nobuhiko Hata, Ron Kikinis, Detlef Scale, and Michael B Millis. 2008. “Quantitative evaluation of angular measurements on plain radiographs in patients with slipped capital femoral epiphysis: a 3-dimensional analysis of computed tomography-based computer models of 46 femora.” J Pediatr Orthop, 28, 3, Pp. 291-6.Abstract
BACKGROUND: In cases of slipped capital femoral epiphyses (SCFE) findings on plain radiographs help to determine the further necessary course of action. In severe cases possible surgical procedures are commonly indicated and planned using angular measurements on plain radiographs to describe the extent and direction of the slip. The aim of this study was to quantify the amount of angular errors deriving from this method. METHODS: Data and imaging of 23 consecutive patients with SCFE (31 affected and 15 unaffected femora) were included in this study. We determined shaft-neck/shaft-physis angles on antero-posterior and torsional angles on lateral radiographs in a clinical setting. As a reference we enabled similar angular measurements on CT-based three-dimensional computer models of the same femora bearing no projectional errors and malpositioning problems. RESULTS: In average, shaft-neck- and shaft-physis-angles were overestimated (6.5 degrees and 10.1 degrees ) on plain radiographs and neck torsion underestimated (-15.7 degrees ). In general the variability was high, especially for neck and physeal torsional measurements with standard deviations of +/-11.8 degrees and +/-16.7 degrees . Three out of four torsional measurements on affected femora were outside a +/-10 degrees window of error, about every third outside a +/-20 degrees window. CONCLUSION: Our results suggest to be careful when using plain radiographs as a source to determine the slippage extent in SCFE. Before using a plain radiograph to reject or indicate and plan a correction osteotomy in an individual case of SCFE the surgeon should reassure that radiographic method and patient positioning provide a reproducible and accurate depiction of the femoral geometry. LEVEL OF EVIDENCE: Level II; 23 consecutive patients with SCFE in the senior authors practice; evaluation of the reliability of angular measurements on plain radiographs; CT based 3D computer models of the same femora as a reference.
Jaesung Hong, Nobuhiko Hata, Kozo Konishi, and Makoto Hashizume. 2008. “Real-time magnetic resonance imaging driven by electromagnetic locator for interventional procedure and endoscopic therapy.” Surg Endosc, 22, 2, Pp. 552-6.Abstract
BACKGROUND: Surgical navigation systems using an optical position sensor have the occlusion problem due to a person or instrument in the line of sight of the camera. In this study, occlusion-free real-time magnetic resonance (MR) scanning with a passive electromagnetic locator is proposed. METHODS: A newly developed converter transforms the data of an electromagnetic locator into that of an optical sensor. Registration between the two different coordinate systems is performed for the electromagnetic locator to substitute the optical sensor without modifying the MRI system. RESULTS: An oil marker attached to the electromagnetic locator was identified in real-time MR images. Preliminary results demonstrated the high usability of the electromagnetic locator as an alternative position tracking method in the MR gantry. CONCLUSIONS: The occlusion problem of optical sensors is resolved by the proposed method.
Junichi Tokuda, Gregory S Fischer, Csaba Csoma, Simon P Dimaio, David G Gobbi, Gabor Fichtinger, Clare M Tempany, and Nobuhiko Hata. 2008. “Software strategy for robotic transperineal prostate therapy in closed-bore MRI.” Med Image Comput Comput Assist Interv, 11, Pt 2, Pp. 701-9.Abstract
A software strategy to provide intuitive navigation for MRI-guided robotic transperineal prostate therapy is presented. In the system, the robot control unit, the MRI scanner, and open-source navigation software are connected to one another via Ethernet to exchange commands, coordinates, and images. Six states of the system called "workphases" are defined based on the clinical scenario to synchronize behaviors of all components. The wizard-style user interface allows easy following of the clinical workflow. On top of this framework, the software provides features for intuitive needle guidance: interactive target planning; 3D image visualization with current needle position; treatment monitoring through real-time MRI. These features are supported by calibration of robot and image coordinates by the fiducial-based registration. The performance test shows that the registration error of the system was 2.6 mm in the prostate area, and it displayed real-time 2D image 1.7 s after the completion of image acquisition.
2007
Nobuhiko Hata, Steve Piper, Ferenc A Jolesz, Clare MC Tempany, Peter McL Black, Shigehiro Morikawa, Horoshi Iseki, Makoto Hashizume, and Ron Kikinis. 2007. “Application of open source image guided therapy software in MR-guided therapies.” Med Image Comput Comput Assist Interv, 10, Pt 1, Pp. 491-8.Abstract
We present software engineering methods to provide free open-source software for MR-guided therapy. We report that graphical representation of the surgical tools, interconnectively with the tracking device, patient-to-image registration, and MRI-based thermal mapping are crucial components of MR-guided therapy in sharing such software. Software process includes a network-based distribution mechanism by multi-platform compiling tool CMake, CVS, quality assurance software DART. We developed six procedures in four separate clinical sites using proposed software engineering and process, and found the proposed method is feasible to facilitate multicenter clinical trial of MR-guided therapies. Our future studies include use of the software in non-MR-guided therapies.
Simon DiMaio, Tina Kapur, Kevin Cleary, Stephen Aylward, Peter Kazanzides, Kirby Vosburgh, Randy Ellis, James Duncan, Keyvan Farahani, Heinz Lemke, Terry Peters, William Bill Lorensen, David Gobbi, John Haller, Laurence Larry Clarke, Stephen Pizer, Russell Taylor, Robert Galloway, Gabor Fichtinger, Nobuhiko Hata, Kimberly Lawson, Clare Tempany, Ron Kikinis, and Ferenc Jolesz. 2007. “Challenges in image-guided therapy system design.” Neuroimage, 37 Suppl 1, Pp. S144-51.Abstract
System development for image-guided therapy (IGT), or image-guided interventions (IGI), continues to be an area of active interest across academic and industry groups. This is an emerging field that is growing rapidly: major academic institutions and medical device manufacturers have produced IGT technologies that are in routine clinical use, dozens of high-impact publications are published in well regarded journals each year, and several small companies have successfully commercialized sophisticated IGT systems. In meetings between IGT investigators over the last two years, a consensus has emerged that several key areas must be addressed collaboratively by the community to reach the next level of impact and efficiency in IGT research and development to improve patient care. These meetings culminated in a two-day workshop that brought together several academic and industrial leaders in the field today. The goals of the workshop were to identify gaps in the engineering infrastructure available to IGT researchers, develop the role of research funding agencies and the recently established US-based National Center for Image Guided Therapy (NCIGT), and ultimately to facilitate the transfer of technology among research centers that are sponsored by the National Institutes of Health (NIH). Workshop discussions spanned many of the current challenges in the development and deployment of new IGT systems. Key challenges were identified in a number of areas, including: validation standards; workflows, use-cases, and application requirements; component reusability; and device interface standards. This report elaborates on these key points and proposes research challenges that are to be addressed by a joint effort between academic, industry, and NIH participants.
Jan Lesniak, Junichi Tokuda, Ron Kikinis, Catherina Burghart, and Nobuhiko Hata. 2007. “A device guidance method for organ motion compensation in MRI-guided therapy.” Phys Med Biol, 52, 21, Pp. 6427-38.Abstract
Organ motion compensation in image-guided therapy is an active area of research. However, there has been little research on motion tracking and compensation in magnetic resonance imaging (MRI)-guided therapy. In this paper, we present a method to track a moving organ in MRI and control an active mechanical device for motion compensation. The method proposed is based on MRI navigator echo tracking enhanced by Kalman filtering for noise robustness. We also developed an extrapolation scheme to resolve any discrepancies between tracking and device control sampling rates. The algorithm was tested in a simulation study using a phantom and an active mechanical tool holder. We found that the method is feasible to use in a clinical MRI scanner with sufficient accuracy (0.36 mm to 1.51 mm depending on the range of phantom motion) and is robust to noise. The method proposed may be useful in MRI-guided targeted therapy, such as focused ultrasound therapy for a moving organ.
Yasutoshi Honda and Nobuhiko Hata. 2007. “Dynamic imaging of swallowing in a seated position using open-configuration MRI.” J Magn Reson Imaging, 26, 1, Pp. 172-6.Abstract
PURPOSE: To assess the feasibility of dynamic MRI of swallowing in a seated position using an open-configuration MRI scanner, and to compare its capacity for motion analysis around the pharyngeal wall with that of videofluorography. MATERIALS AND METHODS: Six healthy individuals (four women and two men, mean age = 31.4 +/- 7.5 years) were examined with an open-configuration MRI system using a fast spoiled gradient-recalled echo (SPGR) sequence. Dynamic imaging was performed while the subjects were in a seated position after they swallowed oral contrast medium from a cup. An oral and maxillofacial radiologist measured the motion of six structures: the hyoid bone (HB), larynx (LX), upper oropharynx (UOP), lower oropharynx (LOP), pharyngoesophageal segment (PES) behind the vocal folds, and upper esophagus (ESO). The measured motions were compared with reported values from videofluorography-based observations. RESULTS: Open-configuration MRI depicted the anatomic structures related to swallowing (lip, tongue, soft palate, mandible, pharynx, HB, LX, and PES), and the course of the mylohyoid muscle (MM). The vertical and anteroposterior displacements of these structures did not differ significantly from those measured by videofluorography. CONCLUSION: Dynamic imaging of swallowing using open-configuration MRI provides image information comparable to that obtained from videofluorography.
Nobuyuki Nakajima, Jun Wada, Tamotsu Miki, Jo Haraoka, and Nobuhiko Hata. 2007. “Surface rendering-based virtual intraventricular endoscopy: retrospective feasibility study and comparison to volume rendering-based approach.” Neuroimage, 37 Suppl 1, Pp. S89-99.Abstract
OBJECTIVE: Virtual endoscopic simulations using volume rendering (VR) have been proposed as a tool for training and understanding intraventricular anatomy. It is not known whether surface rendering (SR), an alternative to VR, can visualize intraventricular and subependymal structures better and thus making the virtual endoscope more useful for simulating the intraventricular endoscopy. We sought to develop SR-virtual endoscopy and compared the visibility of anatomical structures in SR and VR using retrospective cases. MATERIALS AND METHODS: Fourteen patients who underwent endoscopic intraventricular surgery of third ventricle enrolled the study. SR-virtual endoscopy module was developed in open-source software 3D Slicer and virtual endoscopic scenes from the retrospective cases were created. VR virtual endoscopy of the same cases was prepared in commercial software. Three neurosurgeons scored the visibility of substructures in lateral and third ventricle, arteries, cranial nerves, and other lesions Results: We found that VR and SR-virtual endoscopy performed similarly in visualization of substructures in lateral and third ventricle (not significant statistically). However, the SR was statistically significantly better in visualizing subependymal arteries, cranial nerves, and other lesions (p<0.05, respectively). CONCLUSIONS: We concluded that SR-virtual endoscopy is a promising tool to visualize critical anatomical structures in simulated endoscopic intraventricular surgery. The results lead us to propose a hybrid technique of volume and surface rendering to balance the strength of surface rendering alone in visualizing arteries, nerves and lesions, with fast volume rendering of third and lateral ventricles.
Philip Blumenfeld, Nobuhiko Hata, Simon DiMaio, Kelly Zou, Steven Haker, Gabor Fichtinger, and Clare MC Tempany. 2007. “Transperineal prostate biopsy under magnetic resonance image guidance: a needle placement accuracy study.” J Magn Reson Imaging, 26, 3, Pp. 688-94.Abstract
PURPOSE: To quantify needle placement accuracy of magnetic resonance image (MRI)-guided core needle biopsy of the prostate. MATERIALS AND METHODS: A total of 10 biopsies were performed with 18-gauge (G) core biopsy needle via a percutaneous transperineal approach. Needle placement error was assessed by comparing the coordinates of preplanned targets with the needle tip measured from the intraprocedural coherent gradient echo images. The source of these errors was subsequently investigated by measuring displacement caused by needle deflection and needle susceptibility artifact shift in controlled phantom studies. Needle placement error due to misalignment of the needle template guide was also evaluated. RESULTS: The mean and standard deviation (SD) of errors in targeted biopsies was 6.5 +/- 3.5 mm. Phantom experiments showed significant placement error due to needle deflection with a needle with an asymmetrically beveled tip (3.2-8.7 mm depending on tissue type) but significantly smaller error with a symmetrical bevel (0.6-1.1 mm). Needle susceptibility artifacts observed a shift of 1.6 +/- 0.4 mm from the true needle axis. Misalignment of the needle template guide contributed an error of 1.5 +/- 0.3 mm. CONCLUSION: Needle placement error was clinically significant in MRI-guided biopsy for diagnosis of prostate cancer. Needle placement error due to needle deflection was the most significant cause of error, especially for needles with an asymmetrical bevel.
2006
Simon P Dimaio, Neculai Archip, Nobuhiko Hata, Ion-Florin Talos, Simon K Warfield, Amit Majumdar, Nathan McDannold, Kullervo Hynynen, Paul R Morrison, William M Wells, Daniel F Kacher, Randy E Ellis, Alexandra J Golby, Peter M Black, Ferenc A Jolesz, and Ron Kikinis. 2006. “Image-guided neurosurgery at Brigham and Women's Hospital.” IEEE Eng Med Biol Mag, 25, 5, Pp. 67-73.

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