Evaluation of portable CT scanners for otologic image-guided surgery

Are 3D Image Guidance Systems Ready for Use? A Comparative Analysis of 3D Image Guidance Implementations in Minimally Invasive Partial Nephrectomy

Introduction: Three-dimensional image-guided surgical (3D-IGS) systems for minimally invasive partial nephrectomy (MIPN) can potentially improve the efficiency and accuracy of intraoperative anatomical localization and tumor resection. This review seeks to analyze the current state of research regarding 3D-IGS, including the evaluation of clinical outcomes, system functionality, and qualitative insights regarding 3D-IGS's impact on surgical procedures. Methods: We have systematically reviewed the clinical literature pertaining to 3D-IGS deployed for MIPN. For inclusion, studies must produce a patient-specific 3D anatomical model from two-dimensional imaging. Data extracted from the studies include clinical results, registration (alignment of the 3D model to the surgical scene) method used, limitations, and data types reported. A subset of studies was qualitatively analyzed through an inductive coding approach to identify major themes and subthemes across the studies. Results: Twenty-five studies were included in the review. Eight (32%) studies reported clinical results that point to 3D-IGS improving multiple surgical outcomes. Manual registration was the most utilized (48%). Soft tissue deformation was the most cited limitation among the included studies. Many studies reported qualitative statements regarding surgeon accuracy improvement, but quantitative surgeon accuracy data were not reported. During the qualitative analysis, six major themes emerged across the nine applicable studies. They are as follows: 3D-IGS is necessary, 3D-IGS improved surgical outcomes, researcher/surgeon confidence in 3D-IGS system, enhanced surgeon ability/accuracy, anatomical explanation for qualitative assessment, and claims without data or reference to support. Conclusions: Currently, clinical outcomes are the main source of quantitative data available to point to 3D-IGS's efficacy. However, the literature qualitatively suggests the benefit of accurate 3D-IGS for robotic partial nephrectomy.

Bringing CT Scanners to the Skies: Design of a CT Scanner for an Air Mobile Stroke Unit

Stroke is the second most common cause of death and remains a persistent health challenge globally. Due to its highly time-sensitive nature, earlier stroke treatments should be enforced for improved patient outcome. The mobile stroke unit (MSU) was conceptualized and implemented to deliver the diagnosis and treatment to a stroke patient in the ultra-early time window (<1 h) in the pre-hospital setting and has shown to be clinically effective. However, due to geographical challenges, most rural communities are still unable to receive timely stroke intervention, as access to specialized stroke facilities for optimal stroke treatment poses a challenge. Therefore, the aircraft counterpart (Air-MSU) of the conventional road MSU offers a plausible solution to this shortcoming by expanding the catchment area for regional locations in Australia. The implementation of Air-MSU is currently hindered by several technical limitations, where current commercially available CT scanners are still oversized and too heavy to be integrated into a conventional helicopter emergency medical service (HEMS). In collaboration with the Australian Stroke Alliance and Melbourne Brain Centre, this article aims to explore the possibilities and methodologies in reducing the weight and, effectively, the size of an existing CT scanner, such that it can be retrofitted into the proposed search and rescue helicopter—Agusta Westland AW189. The result will be Australia’s first-ever customized CT scanner structure designed to fit in a search-and-rescue helicopter used for Air-MSU.

Use of intraoperative CT scanning for quality control assessment of cochlear implant electrode array placement

Background: Imaging of cochlear implant (CI) electrode arrays (EAs) consists of intraoperative fluoroscopy to rule out tip fold-over and/or post-operative computerized tomography (CT) if concern exists regarding extrusion or misplacement of the EA. Intraoperative CT (iCT) can satisfy these current needs and enables specification of final intracochlear position.Aims/objectives: To describe iCT scanning of CI recipients at an academic medical center.Materials and methods: iCT was used to scan CI recipients within the operating room before recovering from general anesthesia.Results: In fiscal year 2019, 301 CI were placed (83 children, 218 adult). One hundred, seventy-five iCTs were performed (58% of total CIs) of which 52 were children (63% of pediatric CIs) and 123 were adult (57% of adult CIs). Of 7 CI surgeons, use of iCT ranged from 14% to 100% (mean 60%). Four tip fold-overs were identified and corrected intraoperatively. Surgeons reported using the images to improve technique (i.e. pulling back precurved EAs to improve perimodiolar positioning).Conclusion and significance: The current standard of care for CI is to insert EAs without feedback as to final location. iCT provides surgeons with rapid post-insertion feedback which allows detection and correction of suboptimally placed EAs as well as refinement of surgical technique.

Clinical Micro-CT Empowered by Interior Tomography, Robotic Scanning, and Deep Learning

While micro-CT systems are instrumental in preclinical research, clinical micro-CT imaging has long been desired with cochlear implantation as a primary application. The structural details of the cochlear implant and the temporal bone require a significantly higher image resolution than that (about 0.2 mm) provided by current medical CT scanners. In this paper, we propose a clinical micro-CT (CMCT) system design integrating conventional spiral cone-beam CT, contemporary interior tomography, deep learning techniques, and the technologies of a micro-focus X-ray source, a photon-counting detector (PCD), and robotic arms for ultrahigh-resolution localized tomography of a freely-selected volume of interest (VOI) at a minimized radiation dose level. The whole system consists of a standard CT scanner for a clinical CT exam and VOI specification, and a robotic micro-CT scanner for a local scan of high spatial and spectral resolution at minimized radiation dose. The prior information from the global scan is also fully utilized for background compensation of the local scan data for accurate and stable VOI reconstruction. Our results and analysis show that the proposed hybrid reconstruction algorithm delivers accurate high-resolution local reconstruction, and is insensitive to the misalignment of the isocenter position, initial view angle and scale mismatch in the data/image registration. These findings demonstrate the feasibility of our system design. We envision that deep learning techniques can be leveraged for optimized imaging performance. With high-resolution imaging, high dose efficiency and low system cost synergistically, our proposed CMCT system has great promise in temporal bone imaging as well as various other clinical applications.

The future of partial nephrectomy

Innovation in recent times has accelerated due to factors such as the globalization of communication; but there are also more barriers/safeguards in place than ever before as we strive to streamline this process. From the first planned partial nephrectomy completed in 1887, it took over a century to become recommended practice for small renal tumours. At present, identified areas for improvement/innovation are 1) to preserve renal parenchyma, 2) to optimise pre-operative eGFR and 3) to reduce global warm ischaemia time. All 3 of these, are statistically significant predictors of post-operative renal function. Urologists, have a proud history of embracing innovation & have experimented with different clamping techniques of the renal vasculature, image guidance in robotics, renal hypothermia, lasers and new robots under development. The DaVinci model may soon no longer have a monopoly on this market, as it loses its stranglehold with novel technology emerging including added features, such as haptic feedback with reduced costs. As ever, our predictions of the future may well fall wide of the mark, but in order to progress, one must open the mind to the possibilities that already exist, as evolution of existing technology often appears to be a revolution in hindsight.

3D Rapid Prototyping for Otolaryngology-Head and Neck Surgery: Applications in Image-Guidance, Surgical Simulation and Patient-Specific Modeling

The aim of this study was to demonstrate the role of advanced fabrication technology across a broad spectrum of head and neck surgical procedures, including applications in endoscopic sinus surgery, skull base surgery, and maxillofacial reconstruction. The initial case studies demonstrated three applications of rapid prototyping technology are in head and neck surgery: i) a mono-material paranasal sinus phantom for endoscopy training ii) a multi-material skull base simulator and iii) 3D patient-specific mandible templates. Digital processing of these phantoms is based on real patient or cadaveric 3D images such as CT or MRI data. Three endoscopic sinus surgeons examined the realism of the endoscopist training phantom. One experienced endoscopic skull base surgeon conducted advanced sinus procedures on the high-fidelity multi-material skull base simulator. Ten patients participated in a prospective clinical study examining patient-specific modeling for mandibular reconstructive surgery. Qualitative feedback to assess the realism of the endoscopy training phantom and high-fidelity multi-material phantom was acquired. Conformance comparisons using assessments from the blinded reconstructive surgeons measured the geometric performance between intra-operative and pre-operative reconstruction mandible plates. Both the endoscopy training phantom and the high-fidelity multi-material phantom received positive feedback on the realistic structure of the phantom models. Results suggested further improvement on the soft tissue structure of the phantom models is necessary. In the patient-specific mandible template study, the pre-operative plates were judged by two blinded surgeons as providing optimal conformance in 7 out of 10 cases. No statistical differences were found in plate fabrication time and conformance, with pre-operative plating providing the advantage of reducing time spent in the operation room. The applicability of common model design and fabrication techniques across a variety of otolaryngological sub-specialties suggests an emerging role for rapid prototyping technology in surgical education, procedure simulation, and clinical practice.

Minimally invasive image-guided access for drainage of petrous apex lesions: a case report

OBJECTIVE

In this case report, we present a novel, minimally invasive image-guided approach to drainage of a petrous apex lesion.

PATIENT(S)

A 34-year-old man diagnosed with a petrous apex lesion consistent with cholesterol granuloma. The granuloma was large and caused mild compression of the brainstem with associated neurologic symptoms and seizure-like activity.

INTERVENTIONS

Based on the anatomic location of the lesion, it was determined that the treatment plan would be to surgically drain the lesion via 2 linear paths-one after an infralabyrinthine approach and the other a subarcuate approach. Customized microstereotactic frames that mount on bone-implanted markers and constrain the drill along the desired path were used to accurately drill these desired paths and avoid damage to surrounding critical structures. After a simple mastoidectomy, the petrous apex was successfully reached without damage to vital adjacent structures by drilling the 2 linear channels using 2 custom microstereotactic frames.

MAIN OUTCOME MEASURES

Viscous brown liquid and debris was recovered by irrigating through one of the channels and suctioning through the other.

RESULTS

Drainage of the petrous apex was successfully performed via 2 linear channels without any complications. Custom microstereotactic frames were used to accurately drill those linear channels. Postoperative CT ensured no complications. Postoperative course of the patient was remarkable with normal hearing and normal facial nerve function.

CONCLUSION

We presented a successful implementation of an image-guided approach to drain petrous apex.

Forces and trauma associated with minimally invasive image-guided cochlear implantation

OBJECTIVE

Minimally invasive image-guided cochlear implantation (CI) utilizes a patient-customized microstereotactic frame to access the cochlea via a single drill-pass. We investigate the average force and trauma associated with the insertion of lateral wall CI electrodes using this technique.

STUDY DESIGN

Assessment using cadaveric temporal bones.

SETTING

Laboratory setup.

SUBJECTS AND METHODS

Microstereotactic frames for 6 fresh cadaveric temporal bones were built using CT scans to determine an optimal drill path following which drilling was performed. CI electrodes were inserted using surgical forceps to manually advance the CI electrode array, via the drilled tunnel, into the cochlea. Forces were recorded using a 6-axis load sensor placed under the temporal bone during the insertion of lateral wall electrode arrays (2 each of Nucleus CI422, MED-EL standard, and modified MED-EL electrodes with stiffeners). Tissue histology was performed by microdissection of the otic capsule and apical photo documentation of electrode position and intracochlear tissue.

RESULTS

After drilling, CT scanning demonstrated successful access to cochlea in all 6 bones. Average insertion forces ranged from 0.009 to 0.078 N. Peak forces were in the range of 0.056 to 0.469 N. Tissue histology showed complete scala tympani insertion in 5 specimens and scala vestibuli insertion in the remaining specimen with depth of insertion ranging from 360° to 600°. No intracochlear trauma was identified.

CONCLUSION

The use of lateral wall electrodes with the minimally invasive image-guided CI approach was associated with insertion forces comparable to traditional CI surgery. Deep insertions were obtained without identifiable trauma.

Minimally invasive image-guided cochlear implantation for pediatric patients: clinical feasibility study

OBJECTIVE

Minimally invasive image-guided cochlear implantation (CI) involves accessing the cochlea via a linear path from the lateral skull to the cochlea avoiding vital structures including the facial nerve. Herein, we describe and demonstrate the feasibility of the technique for pediatric patients.

STUDY DESIGN

Prospective.

SETTING

Children's Hospital.

SUBJECTS AND METHODS

Thirteen pediatric patients (1.5 to 8 years) undergoing traditional CI participated in this Institutional Review Board-approved study. Three fiducial markers were bone-implanted surrounding the ear, and a CT scan was acquired. The CT scan was processed to identify the marker locations and critical structures of the temporal bone. A safe linear path was determined to target the cochlea avoiding damage to vital structures. A custom microstereotactic frame was fabricated that would mount on the fiducial markers and constrain a tool to the desired trajectory. After traditional mastoidectomy and prior to cochleostomy, the custom microstereotactic frame was mounted on the bone-implanted markers to confirm that the achieved trajectory was safe and accurately accessed the cochlea.

RESULTS

For all the 13 patients, it was possible to determine a safe trajectory to the cochlea. Custom microstereotactic frames were validated successfully on 9 patients. Two of these patients had inner ear malformations, and this technique helped the surgeon confirm ideal location for cochleostomy. For patients with normal anatomy, the mean and standard deviation of the closest distance of the trajectory to facial nerve and chorda tympani were 1.1 ± 0.3 mm and 1.2 ± 0.5 mm, respectively.

CONCLUSION

Minimally invasive image-guided CI is feasible for pediatric patients.

Extra-dimensional Demons: a method for incorporating missing tissue in deformable image registration

PURPOSE

A deformable registration method capable of accounting for missing tissue (e.g., excision) is reported for application in cone-beam CT (CBCT)-guided surgical procedures. Excisions are identified by a segmentation step performed simultaneous to the registration process. Tissue excision is explicitly modeled by increasing the dimensionality of the deformation field to allow motion beyond the dimensionality of the image. The accuracy of the model is tested in phantom, simulations, and cadaver models.

METHODS

A variant of the Demons deformable registration algorithm is modified to include excision segmentation and modeling. Segmentation is performed iteratively during the registration process, with initial implementation using a threshold-based approach to identify voxels corresponding to "tissue" in the moving image and "air" in the fixed image. With each iteration of the Demons process, every voxel is assigned a probability of excision. Excisions are modeled explicitly during registration by increasing the dimensionality of the deformation field so that both deformations and excisions can be accounted for by in- and out-of-volume deformations, respectively. The out-of-volume (i.e., fourth) component of the deformation field at each voxel carries a magnitude proportional to the excision probability computed in the excision segmentation step. The registration accuracy of the proposed "extra-dimensional" Demons (XDD) and conventional Demons methods was tested in the presence of missing tissue in phantom models, simulations investigating the effect of excision size on registration accuracy, and cadaver studies emulating realistic deformations and tissue excisions imparted in CBCT-guided endoscopic skull base surgery.

RESULTS

Phantom experiments showed the normalized mutual information (NMI) in regions local to the excision to improve from 1.10 for the conventional Demons approach to 1.16 for XDD, and qualitative examination of the resulting images revealed major differences: the conventional Demons approach imparted unrealistic distortions in areas around tissue excision, whereas XDD provided accurate "ejection" of voxels within the excision site and maintained the registration accuracy throughout the rest of the image. Registration accuracy in areas far from the excision site (e.g., > ∼5 mm) was identical for the two approaches. Quantitation of the effect was consistent in analysis of NMI, normalized cross-correlation (NCC), target registration error (TRE), and accuracy of voxels ejected from the volume (true-positive and false-positive analysis). The registration accuracy for conventional Demons was found to degrade steeply as a function of excision size, whereas XDD was robust in this regard. Cadaver studies involving realistic excision of the clivus, vidian canal, and ethmoid sinuses demonstrated similar results, with unrealistic distortion of anatomy imparted by conventional Demons and accurate ejection and deformation for XDD.

CONCLUSIONS

Adaptation of the Demons deformable registration process to include segmentation (i.e., identification of excised tissue) and an extra dimension in the deformation field provided a means to accurately accommodate missing tissue between image acquisitions. The extra-dimensional approach yielded accurate "ejection" of voxels local to the excision site while preserving the registration accuracy (typically subvoxel) of the conventional Demons approach throughout the rest of the image. The ability to accommodate missing tissue volumes is important to application of CBCT for surgical guidance (e.g., skull base drillout) and may have application in other areas of CBCT guidance.