Epidural pressure measurement using a fiber-optic sensor (proof-of-principle in vivo animal trial)

BACKGROUND

An increase in epidural pressure around the stenosis has been observed in patients with lumbar spinal stenosis (LSS) with positive signs of sedimentation or redundant nerve roots. Further analysis of the pressure conditions in the stenotic area would be of great interest. We hypothesized that it would be possible to determine the physiological parameters of the epidural pulse wave and its course in pathological stenosis as a basis for objective identification of LSS based on pressure using a new measuring method with continuous spatial and temporal resolution.

METHODS

We performed a single-case proof-of-principle in vivo animal trial and used a newly developed hybrid pressure-measurement probe with a fiber-tip Fabry-Pérot interferometer and several fiber Bragg gratings (FBG).

RESULTS

With reproducible precision, we determined the mean epidural pressure to be 7.5 mmHg and the peak-to-peak value to be 4-5 mmHg. When analyzing the pressure measured by an FBG array, both the heart and respiratory rates can be precisely determined. This study was the first to measure the pulse wave velocity of the cerebrospinal fluid pressure wave as 0.97 m/s using the newly developed pressure probe. A simulated LSS was detected in real time and located exactly.

CONCLUSIONS

The developed fiber-optic pressure sensor probe enables a new objective measurement of epidural pressure. We confirmed our hypothesis that physiological parameters of the epidural pulse wave can be determined and that it is possible to identify an LSS.

Snake Robots for Surgical Applications: A Review

Although substantial advancements have been achieved in robot-assisted surgery, the blueprint to existing snake robotics predominantly focuses on the preliminary structural design, control, and human–robot interfaces, with features which have not been particularly explored in the literature. This paper aims to conduct a review of planning and operation concepts of hyper-redundant serpentine robots for surgical use, as well as any future challenges and solutions for better manipulation. Current researchers in the field of the manufacture and navigation of snake robots have faced issues, such as a low dexterity of the end-effectors around delicate organs, state estimation and the lack of depth perception on two-dimensional screens. A wide range of robots have been analysed, such as the i²Snake robot, inspiring the use of force and position feedback, visual servoing and augmented reality (AR). We present the types of actuation methods, robot kinematics, dynamics, sensing, and prospects of AR integration in snake robots, whilst addressing their shortcomings to facilitate the surgeon’s task. For a smoother gait control, validation and optimization algorithms such as deep learning databases are examined to mitigate redundancy in module linkage backlash and accidental self-collision. In essence, we aim to provide an outlook on robot configurations during motion by enhancing their material compositions within anatomical biocompatibility standards.

Temperature Monitoring in Hyperthermia Treatments of Bone Tumors: State-of-the-Art and Future Challenges

Bone metastases and osteoid osteoma (OO) have a high incidence in patients facing primary lesions in many organs. Radiotherapy has long been the standard choice for these patients, performed as stand-alone or in conjunction with surgery. However, the needs of these patients have never been fully met, especially in the ones with low life expectancy, where treatments devoted to pain reduction are pivotal. New techniques as hyperthermia treatments (HTs) are emerging to reduce the associated pain of bone metastases and OO. Temperature monitoring during HTs may significantly improve the clinical outcomes since the amount of thermal injury depends on the tissue temperature and the exposure time. This is particularly relevant in bone tumors due to the adjacent vulnerable structures (e.g., spinal cord and nerve roots). In this Review, we focus on the potential of temperature monitoring on HT of bone cancer. Preclinical and clinical studies have been proposed and are underway to investigate the use of different thermometric techniques in this scenario. We review these studies, the principle of work of the thermometric techniques used in HTs, their strengths, weaknesses, and pitfalls, as well as the strategies and the potential of improving the HTs outcomes.

Fiber optic probe with functional polymer composites for hyperthermia

We demonstrate a fiber optic probe incorporating functional polymer composites for controlled generation of photothermal effects. The probe combines carbon-based and rare-earth composites on the tip of standard multimode fibers, thus yielding a compact fiber optic photothermal probe (FOPP) whose temperature can be measured simultaneously through fluorescent thermometry. We evaluate the thermal features of the probe through experiments and numerical calculations showing that large thermal gradients are obtained within the vicinity of the heating zone. The temperatures achieved with the FOPP are within the ranges of interest for hyperthermia and can be attained using low optical powers (< 280 mW).

Quasi-distributed fiber optic sensor-based control system for interstitial laser ablation of tissue: theoretical and experimental investigations

This work proposes the quasi-distributed real-time monitoring and control of laser ablation (LA) of liver tissue. To confine the thermal damage, a pre-planning stage of the control strategy based on numerical simulations of the bioheat-transfer was developed to design the control parameters, then experimentally assessed. Fiber Bragg grating (FBG) sensors were employed to design the automatic thermometry system used for temperature feedback control for interstitial LA. The tissue temperature was maintained at a pre-set value, and the influence of different sensor locations (on the direction of the beam propagation and backward) on the thermal outcome was evaluated in comparison with the uncontrolled case. Results show that the implemented computational model was able to properly describe the temperature evolution of the irradiated tissue. Furthermore, the realized control strategy allowed for the accurate confinement of the laser-induced temperature increase, especially when the temperature control was actuated by sensors located in the direction of the beam propagation, as confirmed by the calculated fractions of necrotic tissues (e.g., 23 mm³ and 53 mm³ for the controlled and uncontrolled LA, respectively).

Techniques for Temperature Monitoring of Myocardial Tissue Undergoing Radiofrequency Ablation Treatments: An Overview

Cardiac radiofrequency ablation (RFA) has received substantial attention for the treatment of multiple arrhythmias. In this scenario, there is an ever-growing demand for monitoring the temperature trend inside the tissue as it may allow an accurate control of the treatment effects, with a consequent improvement of the clinical outcomes. There are many methods for monitoring temperature in tissues undergoing RFA, which can be divided into invasive and non-invasive. This paper aims to provide an overview of the currently available techniques for temperature detection in this clinical scenario. Firstly, we describe the heat generation during RFA, then we report the principle of work of the most popular thermometric techniques and their features. Finally, we introduce their main applications in the field of cardiac RFA to explore the applicability in clinical settings of each method.

Fiber Optic Sensors-Based Thermal Analysis of Perfusion-Mediated Tissue Cooling in Liver Undergoing Laser Ablation

The current challenge in the field of thermo-ablative treatments of tumors is to achieve a balance between complete destruction of malignant cells and safeguarding of the surrounding healthy tissue. Blood perfusion plays a key role for thermal ablation success, especially in the case of highly vascularized organs like liver. This work aims at monitoring the temperature within perfused swine liver undergoing laser ablation (LA). Temperature was measured through seven arrays of Fiber Bragg Grating sensors (FBGs) around the laser applicator. To mimic reality, blood perfusion within the ex-vivo liver was simulated using artificial vessels. The influence of blood perfusion on LA was carried out by comparing the temperature profiles in two different spatial configurations of vessels and fibers. The proposed setup permitted to accurately measure the heat propagation in real-time with a temperature resolution of 0.1 °C and to observe a relevant tissue cooling near to the vessel up to 65%.

Dynamic Characterisation of Fibre-Optic Temperature Sensors for Physiological Monitoring

Fast, miniature temperature sensors are required for various biomedical applications. Fibre-optics are particularly suited to minimally invasive procedures, and many types of fibre-optic temperature sensors have been demonstrated. In applications where rapidly varying temperatures are present, a fast and well-known response time is important; however, in many cases, the dynamic behaviour of the sensor is not well-known. In this article, we investigate the dynamic response of a polymer-based interferometric temperature sensor, using both an experimental technique employing optical heating with a pulsed laser, and a computational heat transfer model based on the finite element method. Our results show that the sensor has a time constant on the order of milliseconds and a -6 dB bandwidth of up to 178 Hz, indicating its suitability for applications such as flow measurement by thermal techniques, photothermal spectroscopy, and monitoring of thermal treatments.

Optical biosensors: an exhaustive and comprehensive review

Optical biosensors have exhibited worthwhile performance in detecting biological systems and promoting significant advances in clinical diagnostics, drug discovery, food process control, and environmental monitoring. Without complexity in their pretreatment and probable influence on the nature of target molecules, these biosensors have additional advantages such as high sensitivity, robustness, reliability, and potential to be integrated on a single chip. In this review, the state of the art optical biosensor technologies, including those based on surface plasmon resonance (SPR), optical waveguides, optical resonators, photonic crystals, and optical fibers, are presented. The principles for each type of biosensor are concisely introduced and particular emphasis has been placed on recent achievements. The strengths and weaknesses of each type of biosensor have been outlined as well. Concluding remarks regarding the perspectives of future developments are discussed.

Sensitivity enhanced temperature sensor with serial tapered two-mode fibers based on the Vernier effect

A sensitivity enhanced temperature sensor with cascaded tapered two-mode fibers (TTMFs) based on the Vernier effect is proposed and experimentally demonstrated. It is confirmed that series connection exhibits higher extinction ratio than parallel one both by theory and experiments, which provides guidance for related experiments. In experiments, two TTMFs have the same single-mode fiber-TTMF-single-mode fiber configuration, while the free spectral ranges (FSRs) are chosen with slightly difference by modifying the parameters in the tapering process. Experimental results show that the proposed temperature sensor possesses sensitivity of -3.348 nm/°C in temperature measurement range from 25 °C to 60°C, 11.3 times sensitivity enhancement in comparison with single TTMF. Benefiting from advantages of high temperature sensitivity, simplicity of manufacture and long distance sensing, this novel sensitivity enhanced temperature sensor can be applied to various particular fields, such as oil wells, coal mines and so on.

Development of hypothermia measurable fiber radiometric thermometer for thermotherapy

Temperature monitoring is extremely important during thermotherapy. Fiber-optic temperature sensors are preferred because of their flexibility and immunity to electromagnetic interference. Although many types of fiber-optic sensors have been developed, clinically adopting them remains challenging. Here, we report a silica fiber-based radiometric thermometer using a low-cost extended InGaAs detector to detect black body radiation between 1.7 and 2.4 μm. For the first time, this silica fiber-based thermometer is capable of measuring temperatures down to 35°C, making it suitable for monitoring hyperthermia during surgery. In particular, the thermometer has potential for seamless integration with current silica fiber catheters, which are widely used in laser interstitial thermotherapy. The feasibility, capability and sensitivity of tracking tissue temperature variation were proved through ex vivo tissue studies. After further improvement, the technology has the potential to be translated into clinics for monitoring tissue temperature.

Magnetic Resonance-compatible needle-like probe based on Bragg grating technology for measuring temperature during Laser Ablation

Temperature monitoring in tissue undergone Laser Ablation (LA) may be particularly beneficial to optimize treatment outcome. Among many techniques, fiber Bragg grating (FBG) sensors show valuable characteristics for temperature monitoring in this medical scenario: good sensitivity and accuracy, and immunity from electromagnetic interferences. Their main drawback is the sensitivity to strain, which can entail measurement error for respiratory and patient movements. The aims of this work are the design, the manufacturing and the characterization of a needle-like probe which houses 4 FBGs. Three FBGs have sensitive length of 1 mm and are used as temperature sensors; one FBG with length of 10 mm is used as reference and to sense eventual strain. The optical fiber housing the FBGs was encapsulated within a needle routinely used in clinical practice to perform MRI-guided biopsy. Two materials were used for the encapsulation: i) thermal paste for the 3 FBGs used for temperature monitoring, to maximize the thermal exchange with the needle; ii) epoxy resin for the reference FBG, to improve its sensitivity to strain. The static calibration of the needle-like probe was performed to estimate the thermal sensitivity of each FBG; the step response was investigated to estimate the response time. FBGs 1 mm long have thermal sensitivity of 0.01 nm·°C(-1), whereas the reference FBG presents 0.02 nm·°C(-1). For all FBGs, the response time was in the order of 100 ms. Lastly, experiments were performed on ex vivo swine liver undergoing LA to i) evaluate the possible presence of measurement artifact, due to the direct absorption of laser light by the needle and ii) assess the feasibility of the probe in a quasi clinical scenario.

Laser ablation of the biliary tree: in vivo proof of concept as potential treatment of unresectable cholangiocarcinoma

OBJECTIVES

The palliative treatment of cholangiocarcinoma is based on stent placement with well-known procedure-related complications. Consequently, alternative energy-based techniques were put forward with controversial long-term results. This study aims to evaluate the safety and effectiveness of biliary tree laser ablation (LA) in terms of: (i) absence of perforation, (ii) temperature increase, (iii) induced thermal damage in in vivo models.

MATERIALS AND METHODS

The common bile duct and cystic ducts of two pigs were ablated with a diode laser (circumferential irradiation pattern) for 6 and 3 min at 7 W. Laser settings were chosen from previous ex vivo experiments. Local temperature was monitored through a fibre Bragg grating (FBG) sensor embedded into the laser delivery probe. Histopathological analysis of the ablated specimen was performed through in situ endomicroscopy, haematoxylin and eosin (H&E) and nicotinamide adenine dinucleotide (NADH) stains.

RESULTS

Temperature reached a plateau of 53 °C with consequent thermal damage on the application area, regardless of laser settings and application sites. No perforation was detected macroscopically or microscopically. At the H&E stain, wall integrity was always preserved. The NADH stain allowed to evaluate damage extension. It turned out that the ablation spreading width depended on application time and duct diameter. In situ endomicroscopy revealed a clear distinction between ablated and non-ablated areas.

CONCLUSIONS

The temperature distribution obtained through LA proved to induce a safe and effective intraductal coagulative necrosis of biliary ducts. These results represent the basis for further experiments on tumour-bearing models for the treatment of obstructive cholangiocarcinoma.

Novel carbon fiber probe for temperature monitoring during thermal therapies

Thermal treatments are a valid clinical option in the management of several solid tumors. The difficulties to perform an accurate prediction improve the selectivity of the treatment effects represent the main hurdles in the spread of these techniques. Among other solutions, thermometric techniques are gaining acceptance in monitoring the effects of thermal treatments because they provide a clear end-point to obtain the complete removal of cancer without damaging the surrounding healthy tissue. This paper proposes a custom needle-like probe made of carbon fibers to embed seven fiber Bragg grating (FBG) sensors. This tool aims at a multiple points monitoring the tissue temperature during the thermal procedures, streamlining the FBG sensors insertion within the organ. After the description of the probe manufacturing, we reported the calibration of the seven sensors embedded within the probe, their step response, and the feasibility assessment of the probe for temperature monitoring during laser ablation on animal model (both in vivo and ex vivo). Results show that the proposed probe is easily maneuverable by the clinician, the sensors have a linear response with the temperature and a short step response; moreover, the probe allows measuring the temperature in seven points of the tissue; finally, it can be used during CTand MR-guided procedures without causing any artifact to the images. Thanks to these features the probe may be an useful solution to improve the safety and the outcomes of minimally invasive thermal ablation procedures, so to spread these procedures in the clinical field.

Laser Ablation for Cancer: Past, Present and Future

Laser ablation (LA) is gaining acceptance for the treatment of tumors as an alternative to surgical resection. This paper reviews the use of lasers for ablative and surgical applications. Also reviewed are solutions aimed at improving LA outcomes: hyperthermal treatment planning tools and thermometric techniques during LA, used to guide the surgeon in the choice and adjustment of the optimal laser settings, and the potential use of nanoparticles to allow biologic selectivity of ablative treatments. Promising technical solutions and a better knowledge of laser-tissue interaction should allow LA to be used in a safe and effective manner as a cancer treatment.

Multipoint temperature monitoring in liver undergoing computed tomography-guided radiofrequency ablation with fiber Bragg grating probes

In this work, we investigated the temperature increment experienced by biological tissue during radiofrequency ablation (RFA). The measurements were performed by using two custom-made thermal probes based on fiber optic sensors (fiber Bragg gratings, FBGs). The two probes embed a total of 9 FBGs. Experiments were performed during RFA of an ex vivo healthy porcine liver. The RFA heating module was equipped with 5 thermocouples. Results show that the temperature increment close to the applicator (i.e., 0.6 cm-0.7 cm) reaches the temperature which is set as a target on the RFA module (i.e., approximately 100 °C). The distance from the applicator also has an impact on the dynamics of the heating phenomenon: at short distances the tissue temperature reaches a steady state condition after a few minutes, on the other hand the sensors placed at a distance ≥2cm did not reach the steady-state conditions during the 14-minute procedure. The multipoint temperature monitoring, which uses sensors at several distances from the applicator, can provide useful information regarding the boundary of damaged volume. This approach can be combined with the monitoring temperature system embedded in the heating equipment, to better control the damaged volume, and to improve the treatment outcomes.

Temperature monitoring during radiofrequency ablation of liver: in vivo trials

Radiofrequency ablation (RFA) is a minimally invasive procedure used to treat tumors by means of hyperthermia, mostly through percutaneous approach. The tissue temperature plays a pivotal role in the achievement of the target volume heating, while sparing the surrounding healthy tissue from thermal damage. Several techniques for thermometry during RFA are investigated, most of them based on the use of single-point measurement system (e.g., thermocouples). The measurement of temperature map is crucial for the real-time control and fine adjustment of the treatment settings, to optimize the shape and size of the ablated volume. The recent interest about fiber optic sensors and, among them, fiber Bragg gratings (FBGs) for the monitoring of thermal effects motivated further investigation. In particular, the feature of FBGs to form an array of several elements, thus to be inscribed within the same fiber, allows the use of a single probe for the multi-points monitoring of the tissue temperature during RFA. Hence, the aim of this study is the development and characterization of a needle-like probe embedding an array of three FBGs, which was tested on pig liver during in vivo trials. The needle allows a safe and easy insertion of the fiber optic within the liver. It was inserted by ultrasound guidance into the liver, and monitored the change of tissue temperature during RFA controlled by the roll-off technique. Also the measurement error induced by breathing movements of the liver was assessed (less than 3 °C). Results encourage the use of the probe in clinical settings, as well as the improvement of some features, e.g., a higher number of FBGs for performing quasi-distributed measurement.

Fiber Optic Sensors for Temperature Monitoring during Thermal Treatments: An Overview

During recent decades, minimally invasive thermal treatments (i.e., Radiofrequency ablation, Laser ablation, Microwave ablation, High Intensity Focused Ultrasound ablation, and Cryo-ablation) have gained widespread recognition in the field of tumor removal. These techniques induce a localized temperature increase or decrease to remove the tumor while the surrounding healthy tissue remains intact. An accurate measurement of tissue temperature may be particularly beneficial to improve treatment outcomes, because it can be used as a clear end-point to achieve complete tumor ablation and minimize recurrence. Among the several thermometric techniques used in this field, fiber optic sensors (FOSs) have several attractive features: high flexibility and small size of both sensor and cabling, allowing insertion of FOSs within deep-seated tissue; metrological characteristics, such as accuracy (better than 1 °C), sensitivity (e.g., 10 pm·°C⁻¹ for Fiber Bragg Gratings), and frequency response (hundreds of kHz), are adequate for this application; immunity to electromagnetic interference allows the use of FOSs during Magnetic Resonance- or Computed Tomography-guided thermal procedures. In this review the current status of the most used FOSs for temperature monitoring during thermal procedure (e.g., fiber Bragg Grating sensors; fluoroptic sensors) is presented, with emphasis placed on their working principles and metrological characteristics. The essential physics of the common ablation techniques are included to explain the advantages of using FOSs during these procedures.