Surgical Guidance for Removal of Cholesteatoma Using a Multispectral 3D-Endoscope

We develop a stereo-multispectral endoscopic prototype in which a filter-wheel is used for surgical guidance to remove cholesteatoma tissue in the middle ear. Cholesteatoma is a destructive proliferating tissue. The only treatment for this disease is surgery. Removal is a very demanding task, even for experienced surgeons. It is very difficult to distinguish between bone and cholesteatoma. In addition, it can even reoccur if not all tissue particles of the cholesteatoma are removed, which leads to undesirable follow-up operations. Therefore, we propose an image-based method that combines multispectral tissue classification and 3D reconstruction to identify all parts of the removed tissue and determine their metric dimensions intraoperatively. The designed multispectral filter-wheel 3D-endoscope prototype can switch between narrow-band spectral and broad-band white illumination, which is technically evaluated in terms of optical system properties. Further, it is tested and evaluated on three patients. The wavelengths 400 nm and 420 nm are identified as most suitable for the differentiation task. The stereoscopic image acquisition allows accurate 3D surface reconstruction of the enhanced image information. The first results are promising, as the cholesteatoma can be easily highlighted, correctly identified, and visualized as a true-to-scale 3D model showing the patient-specific anatomy.Peer Reviewe

Doctor of Philosophy

dissertationFor many with severe-to-profound hearing loss, a condition in which the cochlea is unable to convert sound vibration into neural information to the brain, the cochlear implant has become the standard treatment. The goal of a cochlear-implant system is to bypass the malfunctioned cochlea and directly stimulate the nerves responsible for hearing through an array of electrodes on a silicone-elastomer carrier. However, the insertion of the electrode arrays can often cause intracochlear damage and eliminate residual hearing. With increased focus on hearing preservation in cochlear implantation, methods to minimize intracochlear damage have become a priority in electrode-array insertions. This dissertation explores the application of magnetic manipulation toward improved cochlear-implant electrode-array insertions. We start with initial 3-to-1 proof-of-concept experiments to demonstrate the feasibility of this approach. Then, to achieve relevancy at clinical scale, lateral-wall-type electrode-array models, used in the clinic, are slightly modified at the tip to include a tiny magnet. Next, a scala-tympani phantom is designed with both simulated cochleostomy and round-window openings to mimic both classes of insertions typically conducted. In particular, this is the first phantom to model a round-window opening and can be used reliably to simulate insertion forces in cadaver cochleae. Electrode arrays are then magnetically guided through these phantoms with a statistically significant (p < 0.05) reduction in insertion forces, and by as much as 50% for some electrode-array models. In particular, guiding the electrode-array tip through the cochlear hook and the basal turn, in the same insertion, was demonstrated for the first time using this technology. All existing methods to guide the electrode array can only be accomplished for the basal turn. Analysis is conducted to determine the optimal size and placement of a magnetic dipole-field source for use in the clinic. Its placement is determined to be consistently lateral to and anterior to the patient’s cochlea. Its size depends on numerous factors including the patient, torque requirements, and registration error. Sensitivity curves summarizing these factors are provided. The volume of the magnetic dipole-field source can be reduced by a factor of 5, on average, by moving it from the modiolar configuration originally proposed to this optimal configuration. We verify that magnetic forces do not pose any appreciable risk to the basilar membrane at the optimal configuration. Although patient-specific optimal configurations are characterized, a one-size-fits-all version is described that may be more practical and carries the benefit of substantial robustness to registration error

Image Quality, Modeling, and Design for High-Performance Cone-Beam CT of the Head

Diagnosis and treatment of neurological and otolaryngological diseases rely heavily on visualization of fine, subtle anatomical structures in the head. In particular, high-quality head imaging at the point of care mitigates patient risk associated with transport and decreases time to diagnosis for time-sensitive diseases. Cone-beam computed tomography (CBCT) systems have found widespread adoption in diagnostic and image-guided procedures. Such systems exhibit potential for adaptation as point-of-care systems due to relatively low cost, mechanical simplicity, and inherently high spatial resolution, but are generally challenged by low contrast imaging tasks (e.g., visualization of tumors or hemorrhages). This thesis details the development and design of a CBCT imaging system with performance sufficient for high-quality imaging of the head and suitable to deployment at the point of care. The performance of a commercially available head-and-neck CBCT scanner was assessed to determine the potential of such systems for high-quality head imaging. Results indicated low-contrast visualization was challenged by high detector noise and scatter. Photon counting x-ray detectors (PCDs) were identified as a potential technology that could improve the low-contrast visualization, and an imaging performance model was developed to quantify their imaging performance. The model revealed important implications for energy resolution, noise, and spatial resolution as a function of energy threshold and charge sharing rejection. A new CBCT system dedicated to detection of low-contrast contrast intracranial hemorrhage was designed with guidance from an imaging chain model to optimize the system configuration (geometry, detector, x-ray source, etc.). The results indicated flat panel detectors (FPDs) were favorable due to a large field of view, but benefited from detector readout gain adjustments. Dual-gain detector readout was compared with use of bowtie filter in high-gain readout mode to investigate potential improvements to noise performance in FPDs. Finally, technical assessment of the prototype CBCT head scanner (with design based on guidance from the image quality model) indicated performance suitable for translation to clinical studies in the neurosciences critical care unit

Minimally invasive tubular retraction and transtubular approaches in neurosurgery

Minimally invasive surgical approaches have revolutionized surgical care and are becoming increasingly common and sought after in neurosurgery. Despite significant advancements in these techniques and associated technologies, the use of spatulas, that remain essentially unchanged since the late 1800s, for brain retraction endures as a mainstay of neurosurgical practice. In the last decade, tubular retractors have been successfully used in the management of deep-seated intraparenchymal and intraventricular lesions but have yet to be used to minimize brain retraction in skull base surgery. In order to determine the full applicability of transtubular techniques in neurosurgery, we compare brain retraction pressures between tubular retractors and brain spatulas in common neurosurgical approaches, assess the feasibility of performing minimally invasive transtubular skull base and general neurosurgical approaches, and introduce a novel technique for closure of transtubular minicraniectomies with maintenance of anatomic integrity. In all approaches assessed, tubular retraction resulted in average brain retraction pressures that were 57% less collectively than those resulting from spatula retraction. Tubular retractors demonstrated more consistent average retraction pressures between approaches and required 50% less mean retraction distance compared to spatula retractors, while cortical tearing was observed microscopically in 39% of cases following spatula retraction. Transtubular supraorbital, anterior transpetrosal, interhemispheric transcallosal, retrosigmoid, and supracerebellar infratentorial approaches are safe and effective surgical corridors to their respective intracranial targets, with ample surgical exposure, freedom, and maneuverability and minimal retraction of brain tissue. The tubular retractor provided sufficient working space for standard bimanual surgical technique without obstruction of the visual field and permitted sufficient surgical freedom while allowing for constant monitoring of retracted tissues. Adequate preoperative planning of the surgical trajectory was critical for facilitating a safe, direct, and practicable surgical corridor. Closure of transtubular minicraniectomies could be accomplished by rapid on-demand 3D printing of patient-specific cranioprostheses which was found to be a novel, feasible, and inexpensive option that was accomplished with minimal technical difficulty. Tubular retraction in neurosurgery provides a safe and effective conduit for the application of percutaneous minimally invasive approaches while inducing substantially reduced brain retraction pressures than conventional spatula retractors. Advances in neuronavigation and surgical robotics will continue to expand the indications for tubular retraction in neurosurgery