Surface matching for high-accuracy registration of the lateral skull base

PURPOSE The accuracy achievable when utilizing image guidance depends to a large extent on the accuracy with which the patient can be registered to preoperative image data. This work proposes a method for the registration of the temporal bone based on surface matching and investigates the achievable accuracy of the technique. METHODS Fourteen human temporal bones were utilized for evaluation; incisions were made, fiducial screws were implanted to act as a ground truth, and imaging was performed. The positions of the fiducials and surface of the mastoid were extracted from image data and reference positions defined at the round window and the mastoid surface. The surface of the bone was then digitized using a tracked pointer within the region exposed by the incisions and the physical and image point clouds registered, with the result compared to the fiducial-based registration. RESULTS Results of one case were excluded due to a problem with the ground truth registration. In the remaining cases an accuracy of [Formula: see text] and [Formula: see text] mm was observed relative to the ground truth at the surface of the mastoid and round window, respectively. CONCLUSIONS A technique for the registration of the temporal bone was proposed, based on surface matching after exposure of the mastoid surface, and evaluated on human temporal bone specimens. The results reveal that high-accuracy patient-to-image registration is possible without the use of fiducial screws

Accuracy and feasibility of a dedicated image guidance solution for endoscopic lateral skull base surgery.

OBJECTIVE We aimed to design, build and validate a surgical navigation system which fulfills the accuracy requirements for surgical procedures on the ear and the lateral skull base, and which integrates with the endoscopic workflow and operating room setup. MATERIALS AND METHODS The navigation system consists of portable tablet computer (iPad Pro, Apple Computer, USA) and an optical tracking system (Cambar B1, Axios3D, Germany), both connected via a wireless Bluetooth link and attached directly to the OR table. Active optical tracking references are rigidly fixed to both the patient and surgical tools. Software to support image import, registration and 2D/3D visualization has been developed. Two models were used for targeting accuracy assessment: a technical phantom model and an ex vivo temporal bone model. Additionally, workflow integration and usability of the navigation system during endoscopic lateral skull base procedures was investigated in ex vivo experiments on 12 sides of cadaver head specimens. RESULTS The accuracy experiments revealed a target registration error in the technical phantom model of 0.20 ± 0.10 mm (n = 36) and during the ex vivo assessment of 0.28 ± 0.10 mm (n = 21). Navigation was successfully carried out in n = 36 procedures (infracochlear, suprageniculate and transpromontorial approach), with navigated instruments usable without interference with the endoscope. The system aided in the successful and accurate identification of vital anatomical structures. CONCLUSIONS Useful surgical navigation is, to a large extent, a result of sufficiently accurate tracking technology. We have demonstrated sufficient accuracy and a potentially suitable integration for surgical application within endoscopic lateral skull base procedures

Three Dimensional Nonlinear Statistical Modeling Framework for Morphological Analysis

This dissertation describes a novel three-dimensional (3D) morphometric analysis framework for building statistical shape models and identifying shape differences between populations. This research generalizes the use of anatomical atlases on more complex anatomy as in case of irregular, flat bones, and bones with deformity and irregular bone growth. The foundations for this framework are: 1) Anatomical atlases which allow the creation of homologues anatomical models across populations; 2) Statistical representation for output models in a compact form to capture both local and global shape variation across populations; 3) Shape Analysis using automated 3D landmarking and surface matching. The proposed framework has various applications in clinical, forensic and physical anthropology fields. Extensive research has been published in peer-reviewed image processing, forensic anthropology, physical anthropology, biomedical engineering, and clinical orthopedics conferences and journals. The forthcoming discussion of existing methods for morphometric analysis, including manual and semi-automatic methods, addresses the need for automation of morphometric analysis and statistical atlases. Explanations of these existing methods for the construction of statistical shape models, including benefits and limitations of each method, provide evidence of the necessity for such a novel algorithm. A novel approach was taken to achieve accurate point correspondence in case of irregular and deformed anatomy. This was achieved using a scale space approach to detect prominent scale invariant features. These features were then matched and registered using a novel multi-scale method, utilizing both coordinate data as well as shape descriptors, followed by an overall surface deformation using a new constrained free-form deformation. Applications of output statistical atlases are discussed, including forensic applications for the skull sexing, as well as physical anthropology applications, such as asymmetry in clavicles. Clinical applications in pelvis reconstruction and studying of lumbar kinematics and studying thickness of bone and soft tissue are also discussed

Concept and Design of a Hand-held Mobile Robot System for Craniotomy

This work demonstrates a highly intuitive robot for Surgical Craniotomy Procedures. Utilising a wheeled hand-held robot, to navigate the Craniotomy Drill over a patient\u27s skull, the system does not remove the surgeons from the procedure, but supports them during this critical phase of the operation

The potential impact of CT-MRI matching on tumor volume delineation in advanced head and neck cancer

To study the potential impact of the combined use of CT and MRI scans on the Gross Tumor Volume (GTV) estimation and interobserver variation. Four observers outlined the GTV in six patients with advanced head and neck cancer on CT, axial MRI, and coronal or sagittal MRI. The MRI scans were subsequently matched to the CT scan. The interobserver and interscan set variation were assessed in three dimensions. The mean CT derived volume was a factor of 1.3 larger than the mean axial MRI volume. The range in volumes was larger for the CT than for the axial MRI volumes in five of the six cases. The ratio of the scan set common (i.e., the volume common to all GTVs) and the scan set encompassing volume (i.e., the smallest volume encompassing all GTVs) was closer to one in MRI (0.3-0.6) than in CT (0.1-0.5). The rest volumes (i.e., the volume defined by one observer as GTV in one data set but not in the other data set) were never zero for CT vs. MRI nor for MRI vs. CT. In two cases the craniocaudal border was poorly recognized on the axial MRI but could be delineated with a good agreement between the observers in the coronal/sagittal MRI. MRI-derived GTVs are smaller and have less interobserver variation than CT-derived GTVs. CT and MRI are complementary in delineating the GTV. A coronal or sagittal MRI adds to a better GTV definition in the craniocaudal directio

Design and clinical evaluation of an image-guided surgical microscope with an integrated tracking system

A new image-guided microscope system using augmented reality image overlays has been developed. With this system, CT cut-views and segmented objects such as tumors that have been previously extracted from preoperative tomographic images can be directly displayed as augmented reality overlays on the microscope image. The novelty of this design stems from the inclusion of a precise mini-tracker directly on the microscope. This device, which is rigidly mounted to the microscope, is used to track the movements of surgical tools and the patient. In addition to an accuracy gain, this setup offers improved ergonomics since it is much easier for the surgeon to keep an unobstructed line of sight to tracked objects. We describe the components of the system: microscope calibration, image registration, tracker assembly and registration, tool tracking, and augmented reality display. The accuracy of the system has been measured by validation on plastic skulls and cadaver heads, obtaining an overlay error of 0.7mm. In addition, a numerical simulation of the system has been done in order to complement the accuracy study, showing that the integration of the tracker onto the microscope could lead to an improvement of the accuracy to the order of 0.5mm. Finally, we describe our clinical experience using the system in the operation room, where three operations have been performed to dat