Neurosurgical training is performed on human cadavers and simulation models, such as VR platforms, which have several drawbacks. Head phantoms could solve most of the issues related to these trainings. The aim of this study was to design a realistic and CT-compatible head phantom, with a specific focus on endo-nasal skull-base surgery and brain biopsy. A head phantom was created by segmenting an image dataset from a cadaver. The skull, which includes a complete structure of the nasal cavity and detailed skull-base anatomy, is 3D printed using PLA with calcium, while the brain is produced using a PVA mixture. The radiodensity and mechanical properties of the phantom were tested and adjusted in material choice to mimic real-life conditions. Surgeons find the skull, the structures at the skull-base and the brain realistically reproduced. The head phantom can be employed for neurosurgical education, training and surgical planning, and can be successfully used for simulating surgeries.
Surgery is a crucial treatment for malignant brain tumors where gross total resection improves the prognosis. Tissue samples taken during surgery are either subject to a preliminary intraoperative histological analysis, or sent for a full pathological evaluation which can take days or weeks. Whereas a lengthy complete pathological analysis includes an array of techniques to be executed, a preliminary tissue analysis on frozen tissue is performed as quickly as possible (30-45 minutes on average) to provide fast feedback to the surgeon during the surgery. The surgeon uses the information to confirm that the resected tissue is indeed tumor and may, at least in theory, initiate repeated biopsies to help achieve gross total resection. However, due to the total turn-around time of the tissue inspection for repeated analyses, this approach may not be feasible during a single surgery. In this context, intraoperative image-guided techniques can improve the clinical workflow for tumor resection and improve outcome by aiding in the identification and removal of the malignant lesion. Hyperspectral imaging (HSI) is an optical imaging technique with the potential to extract combined spectral-spatial information. By exploiting HSI for human brain-tissue classification in 13 in-vivo hyperspectral images from 9 patients, a brain-tissue classifier is developed. The framework consists of a hybrid 3D-2D CNN-based approach and a band-selection step to enhance the capability of extracting both spectral and spatial information from the hyperspectral images. An overall accuracy of 77% was found when tumor, normal and hyper-vascularized tissue are classified, which clearly outperforms the state-of-the-art approaches (SVM, 2D-CNN). These results may open an attractive future perspective for intraoperative brain-tumor classification using HSI.
In neurosurgery, technical solutions for visualizing the border between healthy brain and tumor tissue is of great value, since they enable the surgeon to achieve gross total resection while minimizing the risk of damage to eloquent areas. By using real-time non-ionizing imaging techniques, such as hyperspectral imaging (HSI), the spectral signature of the tissue is analyzed allowing tissue classification, thereby improving tumor boundary discrimination during surgery. More particularly, since infrared penetrates deeper in the tissue than visible light, the use of an imaging sensor sensitive to the near-infrared wavelength range would also allow the visualization of structures slightly beneath the tissue surface. This enables the visualization of tumors and vessel boundaries prior to surgery, thereby preventing the damaging of tissue structures. In this study, we investigate the use of Diffuse Reflectance Spectroscopy (DRS) and HSI for brain tissue classification, by extracting spectral features from the near infra-red range. The applied method for classification is the linear Support Vector Machine (SVM). The study is conducted on ex-vivo porcine brain tissue, which is analyzed and classified as either white or gray matter. The DRS combined with the proposed classification reaches a sensitivity and specificity of 96%, while HSI reaches a sensitivity of 95% and specificity of 93%. This feasibility study shows the potential of DRS and HSI for automated tissue classification, and serves as a fjrst step towards clinical use for tumor detection deeper inside the tissue.
Safe and accurate placement of spinal screws remains a critical step during open and minimally invasive spinal fusion surgery. We investigated the application of diffuse reflectance spectroscopy (DRS) for real-time instrument guidance during a spinal screw placement procedure. A custom-built screw probe with integrated optical fibers was inserted into a vertebra under image guidance in an ex vivo human setting. We found that fat content derived from the spectra gradually changed as the probe approached the cortical bone boundary. The results indicate that DRS integrated into surgical instruments has the potential to improve the safety and accuracy of spinal screw placement procedures.
The use of pre-operative CT and MR images for navigation during endo-nasal skull-base endoscopic surgery is a well-established procedure in clinical practice. Fusion of CT and MR images on the endoscopic view can offer an additional advantage by directly overlaying surgical-planning information in the surgical view. Fusion of intraoperative images, such as cone beam computed tomography (CBCT), represents a step forward since these images can also account for intra-operative anatomical changes. In this work, we present a method for intra-operative CBCT image fusion on the endoscopic view for endo-nasal skull-base surgery, implemented on the Philips surgical navigation system. This is the first study which utilizes an optical tracking system (OTS) embedded in the flat-panel detector of the C-arm for endoscopic-image augmentation. In our method the OTS, co-registered in the same CBCT coordinate system, is used for tracking the endoscope. Accuracy in CBCT image registration in the endoscopic view is studied using a calibration board. Image fusion is tested in a realistic surgical scenario by using a skull phantom and inserts that mimic critical structures at the skull base. Overall performances tested on the skull phantom show a high accuracy in tracking the endoscope and registration of CBCT on endoscopic view. It can be concluded that the implemented system show potential for usage in endo-nasal skull-base surgery.
Safe and accurate placement of screws remains a critical issue in open and minimally invasive spine surgery. We propose to use diffuse reflectance (DR) spectroscopy as a sensing technology at the tip of a surgical instrument to ensure a safe path of the instrument through the cancellous bone of the vertebrae. This approach could potentially reduce the rate of cortical bone breaches, thereby resulting in fewer neural and vascular injuries during spinal fusion surgery. In our study, DR spectra in the wavelength ranges of 400 to 1600 nm were acquired from cancellous and cortical bone from three human cadavers. First, it was investigated whether these spectra can be used to distinguish between the two bone types based on fat, water, and blood content along with photon scattering. Subsequently, the penetration of the bone by an optical probe was simulated using the Monte-Carlo (MC) method, to study if the changes in fat content along the probe path would still enable distinction between the bone types. Finally, the simulation findings were validated via an experimental insertion of an optical screw probe into the vertebra aided by x-ray image guidance. The DR spectra indicate that the amount of fat, blood, and photon scattering is significantly higher in cancellous bone than in cortical bone (p < 0.01), which allows distinction between the bone types. The MC simulations showed a change in fat content more than 1 mm before the optical probe came in contact with the cortical bone. The experimental insertion of the optical screw probe gave similar results. This study shows that spectral tissue sensing, based on DR spectroscopy at the instrument tip, is a promising technology to identify the transition zone from cancellous to cortical vertebral bone. The technology therefore has the potential to improve the safety and accuracy of spinal screw placement procedures.
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