Ramya Balachandran

Clinical Validation of Percutaneous Cochlear Implant Surgery: Initial Report

Objective: Percutaneous cochlear implant surgery consists of a single drill path from the lateral mastoid cortex to the cochlea via the facial recess. We sought to clinically validate this technique in patients undergoing traditional cochlear implant surgery.

Percutaneous cochlear access using bone-mounted, customized drill guides: demonstration of concept in vitro.

Hypothesis: Percutaneous cochlear access can be performed using bone-mounted drill guides that are custom made on the basis of preintervention computed tomographic scans. Background: We have previously demonstrated the ability to use image guidance based on fiducial markers to obtain percutaneous cochlear access in vitro. A simpler approach that has far less room for application error is to constrict the path of the drill to pass in a predetermined trajectory using a drill guide. Methods: Cadaveric temporal bone specimens (n = 8) were affixed with three bone-implanted fiducial markers. The temporal bone computed tomographic scans were obtained and used in planning a straight trajectory from the mastoid surface to the cochlea without violating the boundaries of the facial recess, namely, the chorda tympani, the incus buttress, and the facial nerve. These surgical plans were used to manufacture a customized drill guide by means of rapid prototyping (MicroTargeting Platform; FHC Inc.; Bowdoinham, ME, U.S.A.) that mounts onto anchor pins previously used to mount fiducial markers. The specimens then underwent traditional mastoidectomy with facial recess. The drill guide was mounted, and a 1-mm drill bit was passed through the guide across the mastoid and the facial recess. The course of the drill bit and its relationship to the boundaries of the facial recess were photographed and measured. Results: Eight cadaveric specimens were subjected to the study protocol. In seven of eight specimens, the drill bit trajectory was accurate; it passed from the lateral cortex to the lateral wall of the cochlea without compromise of any critical structures. In one specimen, the access to the middle ear was achieved, but the incus was hit by the drill. The average shortest distance ± standard deviation from the edge of the drill bit to the boundaries of the facial recess was 0.78 ± 0.56 mm (chorda tympani), 2.00 ± 1.06 mm (incus buttress), and 1.27 ± 0.54 mm (facial nerve). Conclusion: Our study demonstrates the ability to obtain percutaneous cochlear access in vitro using customized drill guides manufactured on the basis of preintervention radiographic studies.

Minimally invasive, image-guided, facial-recess approach to the middle ear: demonstration of the concept of percutaneous cochlear access in vitro.

Hypothesis: Image-guided surgery will permit accurate access to the middle ear via the facial recess using a single drill hole from the lateral aspect of the mastoid cortex. Background: The widespread use of image-guided methods in otologic surgery has been limited by the need for a system that achieves the necessary level of accuracy with an easy-to-use, noninvasive fiducial marker system. We have developed and recently reported such a system (accuracy within the temporal bone = 0.76 ± 0.23 mm; n = 234 measurements). With this system, image-guided otologic surgery is feasible. Methods: Skulls (n = 2) were fitted with a dental bite-block affixed fiducial frame and scanned by computed tomography using standard temporal-bone algorithms. The frame was removed and replaced with an infrared emitter used to track the skull during dissection. Tracking was accomplished using an infrared tracker and commercially available software. Using this system in conjunction with a tracked otologic drill, the middle ear was approached via the facial recess using a single drill hole from the lateral aspect of the mastoid cortex. The path of the drill was verified by subsequently performing a traditional temporal bone dissection, preserving the tunnel of bone through which the drill pass had been made. Results: An accurate approach to the middle ear via the facial recess was achieved without violating the canal of the facial nerve, the horizontal semicircular canal, or the external auditory canal. Conclusions: Image-guided otologic surgery provides access to the cochlea via the facial recess in a minimally invasive, percutaneous fashion. While the present study was confined to in vitro demonstration, these exciting results warrant in vivo testing, which may lead to clinically applicable access.

Percutaneous Cochlear Implant Drilling via Customized Frames: an in vitro study

Objective: Percutaneous cochlear implantation (PCI) surgery uses patient-specific customized microstereotactic frames to achieve a single drill-pass from the lateral skull to the cochlea, avoiding vital anatomy. We demonstrate the use of a specific microstereotactic frame, called a “microtable,” to perform PCI surgery on cadaveric temporal bone specimens. Study Design: Feasibility study using cadaveric temporal bones. Subjects and Methods: PCI drilling was performed on six cadaveric temporal bone specimens. The main steps involved were 1) placing three bone-implanted markers surrounding the ear, 2) obtaining a CT scan, 3) planning a safe surgical path to the cochlea avoiding vital anatomy, 4) constructing a microstereotactic frame to constrain the drill to the planned path, and 5) affixing the frame to the markers and using it to drill to the cochlea. The specimens were CT scanned after drilling to show the achieved path. Deviation of the drilled path from the desired path was computed, and the closest distance of the mid-axis of the drilled path from critical structures was measured. Results: In all six specimens, we drilled successfully to the cochlea, preserving the facial nerve and ossicles. In four of six specimens, the chorda tympani was preserved, and in two of six specimens, it was sacrificed. The mean ± standard deviation error at the target was found to be 0.31 ± 0.10 mm. The closest distances of the mid-axis of the drilled path to structures were 1.28 ± 0.17 mm to the facial nerve, 1.31 ± 0.36 mm to the chorda tympani, and 1.59 ± 0.43 mm to the ossicles. Conclusion: In a cadaveric model, PCI drilling is safe and effective.

Design of a Bone-Attached Parallel Robot for Percutaneous Cochlear Implantation

Access to the cochlea requires drilling in close proximity to bone-embedded nerves, blood vessels, and other structures, the violation of which can result in complications for the patient. It has recently been shown that microstereotactic frames can enable an image-guided percutaneous approach, removing reliance on human experience and hand-eye coordination, and reducing trauma. However, constructing current microstereotactic frames disrupts the clinical workflow, requiring multiday intrasurgical manufacturing delays, or an on-call machine shop in or near the hospital. In this paper, we describe a new kind of microsterotactic frame that obviates these delay and infrastructure issues by being repositionable. Inspired by the prior success of bone-attached parallel robots in knee and spinal procedures, we present an automated image-guided microstereotactic frame. Experiments demonstrate a mean accuracy at the cochlea of 0.20 ± 0.07 mm in phantom testing with trajectories taken from a human clinical dataset. We also describe a cadaver experiment evaluating the entire image-guided surgery pipeline, where we achieved an accuracy of 0.38 mm at the cochlea.

Percutaneous inner-ear access via an image-guided industrial robot system

Abstract Image-guided robots have been widely used for bone shaping and percutaneous access to interventional sites. However, due to high-accuracy requirements and proximity to sensitive nerves and brain tissues, the adoption of robots in inner-ear surgery has been slower. In this paper the authors present their recent work towards developing two image-guided industrial robot systems for accessing challenging inner-ear targets. Features of the systems include optical tracking of the robot base and tool relative to the patient and Kalman filter-based data fusion of redundant sensory information (from encoders and optical tracking systems) for enhanced patient safety. The approach enables control of differential robot positions rather than absolute positions, permitting simplified calibration procedures and reducing the reliance of the system on robot calibration in order to ensure overall accuracy. Lastly, the authors present the results of two phantom validation experiments simulating the use of image-guided robots in inner-ear surgeries such as cochlear implantation and petrous apex access.

Minimally invasive image-guided cochlear implantation surgery: First report of clinical implementation

Minimally invasive image‐guided approach to cochlear implantation (CI) involves drilling a narrow, linear tunnel to the cochlea. Reported herein is the first clinical implementation of this approach.

Accuracy Evaluation of microTargeting Platforms for Deep-Brain Stimulation Using Virtual Targets

Deep-brain-stimulation (DBS) surgery requires implanting stimulators at target positions with sub millimetric accuracy. Traditional stereotactic frames can provide such accuracy, but a recent innovation called the micro Targeting Platform (FHC, Inc.) replaces this large, universal frame with a single-use, miniature, and custom-designed platform. Both single-target and dual-target platforms are available for unilateral and bilateral procedures, respectively. In this paper, their targeting accuracies are evaluated in vitro. Our approach employs ldquovirtual targets,rdquo which eliminates the problem of collision of the implant with the target. We implement virtual targets by mounting fiducial markers, which are not used in platform targeting, on an artificial skull and defining targets relative to the skull via that fiducial system. The fiducial system is designed to surround the targets, thereby reducing the overall effect of fiducial localization inaccuracies on the evaluation. It also provides the geometrical transformation from image to physical space. Target selection is based on an atlas of stimulation targets from a set of 31 DBS patients. The measured targeting error is the displacement between the phantom implant and the virtual target. Our results show that the micro Targeting Platform exhibits sub millimetric in vitro accuracy with a mean of 0.42 mm and a 99.9% level of 0.90 mm.

Percutaneous access to the petrous apex in vitro using customized micro-stereotactic frames based on image-guided surgical technology

Abstract Conclusion. Our study demonstrates (in cadavers) the ability to obtain a minimally invasive approach to access the petrous apex using patient-customized micro-stereotactic frames based on pre-intervention radiographic studies. Objective. To conduct in vitro studies to demonstrate the feasibility of percutaneous petrous apex access using customized, bone-mounted, micro-stereotactic frames. Methods. Cadaveric temporal bone specimens (n = 10) were affixed with three bone-implanted fiducial markers. CT scans were obtained and used in planning, in reference to the fiducial markers, a straight transmastoid infralabyrinthine trajectory from the mastoid surface to the petrous apex without violating the basal turn of the cochlea or the carotid artery. A drill press was mounted on the customized frame and used to guide a 2 mm drill bit on the desired trajectory. The course of the drill bit and its relationship to surrounding vital anatomy (cochlea, carotid artery, facial nerve, and internal jugular vein) were determined by repeat CT scanning. Results. In 10 of 10 specimens, the drill bit trajectory was accurate with clearance (mean ± standard deviation in mm) from the cochlea, facial nerve, carotid artery, and jugular vein of 3.43 ± 1.57, 3.14 ± 1.15, 4.57 ± 1.52, and 6.05 ± 2.98, respectively.

Iterative Solution for Rigid-Body Point-Based Registration with Anisotropic Weighting

Rigid-body, point-based registration is commonly used for image-guided systems. Fiducial markers that can be localized in image and physical space are attached to patient anatomy. The fiducial marker locations in the two spaces are used to obtain the physical-to-image registration. It is a common practice to obtain physical positions via optical systems, whose localization error is anisotropic. Furthermore, the positions are often reckoned relative to a coordinate reference frame (CRF) that is rigidly attached to the patient. The use of a CRF enables patient movement relative to the tracking system, but it tends to exacerbate the anisotropy. It is common practice to ignore the localization anisotropy and employ a closed-form solution, which is available for isotropic weighting but not for anisotropic weighting. Iterative methods are available for anisotropic weighting but are quite complex. We present a new iterative algorithm for anisotropic weighting that is simple, intuitive, and has only one adjustable parameter. We show using simulations that our algorithm is more accurate than the isotropic solution for anisotropic localization error. In particular, we show that the new algorithm reduces target registration error when anisotropic localization error is present. When all the localization errors are isotropic, the new algorithm performs as well as the closed-form solution.