Sensing using optical fibers is quite an established technology and is increasingly used in the field of bio-medical sensing applications owing to its small size, light weight, immunity towards electromagnetic interference, biocompatibility, sensitivity, and the ease with which it can be integrated with standard catheters leading to a designated point of inspection. Fiber Bragg gratings (FBGs), due to their ease of multiplexing, inherent sensitivity towards strain, and thereby pressure, can be suitably designed to make a novel pressure sensor for diagnosing and monitoring angiogenesis in brain tumors and for assessing vascular lesions inside coronary arteries. However, standard FBGs have a poor pressure sensitivity of 4pm/MPa (0.5fm/mmHg), which is insufficient to detect a few mmHg blood pressure changes. By utilizing the mechanical properties of modified FBGs with an elastomeric material coating, it is possible to improve the transduction mechanism of effectively translating pressure to strain and increase the resolution and sensitivity by two orders of magnitude (53.4 times) compared to standard FBGs. These modified FBGs could then be used to monitor respective pressure indices, i.e., Intracranial Pressure (ICP) and Instantaneous wave-free Ratio (iFR), by integrating them with catheters or endoscopes and using appropriate signal-processing algorithms. Moreover, a simulation of the modification of the blood vessel flow with respect to the secondary vessel formation is done to study the impact of different blood vessel formations during angiogenesis on pressure, thereby co-relating flow patterns to angiogenesis.
State-of-the-art optical fiber pressure sensors use displacement diaphragms and mechanical transducers to enhance pressure sensitivity, however, due to their bulkiness and large size they can’t be easily integrated inside pressure guide wire for intravital monitoring. Fiber Bragg Gratings (FBGs) due to their inherent advantages can be designed in a way that is suitable for monitoring Intracranial Pressure (ICP) and Instantaneous Wave-Free Ratio (iFR) pressure indices. The main disadvantage of FBG is that it has a low-pressure sensitivity of 3.04pm/MPa, which is insufficient for these applications and is made worse by the cross-sensitivity caused by temperature. We hereby present a two-pronged strategy to tackle this issue. The first step in improving sensitivity is to modify FBGs, and the second is to use signal processing methods to recover minor wavelength shifts. A frequency-selective detection technique can be used to measure sub-pm wavelength shifts for small modulated pressure signals. This technique was used to establish a test bench for measuring the pressure sensitivity of standard acrylate and polyimide coated FBGs as well as to confirm a linear relationship between the pressure range of interest and Bragg wavelength shift.
MR-guided high-intensity focused ultrasound (MR-HIFU) is a non-invasive therapeutic technology which has demonstrated clinical potential for tissue ablation. The application of this therapeutic approach facilitated to be a promising option to achieve faster pain palliation in patients with bone metastasis. However, its clinical adoption is still hampered by a lack of workflow integration. Currently, to ensure sufficient positioning, MR images have to be repeatedly acquired in between patient re-positioning tasks, leading to a time-consuming preparation phase of at least 30 minutes, involving extra costs and time to the available treatment time. Augmented reality (AR) is a promising technology that enables the fusion of medical images, such as MRI, with the view of an external camera. AR represents a valid tool for a faster localization and visualization of the lesion during positioning. The aim of this work is the implementation of a novel AR setup for accelerating the patient positioning during MRHIFU treatments by enabling adequate target positioning outside the MRI scanner. A marker-based approach was investigated for fusing the MR data with video data for providing an augmented view. Initial experiments on four volunteers show that MR images were overlaid on the camera views with an average re-projection error of 3.13 mm, which matches the clinical requirements for this specific application. It can be concluded that the implemented system is suitable for MR-HIFU procedures and supports its clinical adoption by improving the patient positioning, thereby offering potential for faster treatment time.
Peripheral Artery Diseases (PAD) are caused by the occlusions of arteries in the peripheral locations of the circulatory system. The severity of PAD is usually assessed using the Ankle Brachial Index (ABI) and the Ultrasound Doppler. Non-contact Photoplethysmography (PPG) imaging is a recent emerging technology capable of monitoring skin perfusion. Using an off-the-shelf camera and a light source, is possible to remotely detect the dynamic changes in blood volume in the skin and derive a map correlated to the blood perfusion. The aim of this study is the evaluation of a PPG imaging system (iPPG) for the assessment of Peripheral Arterial Diseases. Reduced blood flow is simulated on 21 volunteers by increasing the pressure in a pressure cuff. For each volunteer, measurements with iPPG, ultrasound, Laser Speckle Contrast Analysis (LASCA) and ABI were acquired. Our experiments show that iPPG can detect reduced perfusion levels, and correlates well with the other measurement systems.
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.
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.
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.
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