Distributed fiber optic shape sensing with simultaneous interrogation of multiple fibers based on Rayleigh-signature domain multiplexing.

We propose a method for shape sensing that employs Rayleigh-signature domain multiplexing to simultaneously probe the fibers or cores of a shape sensing setup with a single optical frequency-domain reflectometry scan. The technique enables incrementing the measurement speed by a factor equal to the number of multiplexed fibers at the expense of an increased noise floor in accordance with the Cramér-Rao lower bound. Nonetheless, we verify that the shape reconstruction performance of the proposed method is in very good agreement with that of conventional sequential core interrogation.

Green-Synthesized Silver Nanoparticle-Assisted Radiofrequency Ablation for Improved Thermal Treatment Distribution.

Thermal ablation therapy is known as an advantageous alternative to surgery allowing the treatment of multiple tumors located in hard-to-reach locations or treating patients with medical conditions that are not compatible with surgery. Appropriate heat propagation and precise control over the heat propagation is considered a weak point of thermal ablation therapy. In this work, silver nanoparticles (AgNPs) are used to improve the heat propagation properties during the thermal ablation procedure. Green-synthesized silver nanoparticles offer several attractive features, such as excellent thermal conductivity, biocompatibility, and antimicrobial activity. A distributed multiplexed fiber optic sensing system is used to monitor precisely the temperature change during nanoparticle-assisted radiofrequency ablation. An array of six MgO-based nanoparticles doped optical fibers spliced to single-mode fibers allowed us to obtain the two-dimensional thermal maps in a real time employing optical backscattering reflectometry at 2 mm resolution and 120 sensing points. The silver nanoparticles at 5, 10, and 20 mg/mL were employed to investigate their heating effects at several positions on the tissue regarding the active electrode. In addition, the pristine tissue and tissue treated with agarose solution were also tested for reference purposes. The results demonstrated that silver nanoparticles could increase the temperature during thermal therapies by propagating the heat. The highest temperature increase was obtained for 5 mg/mL silver nanoparticles introduced to the area close to the electrode with a 102% increase of the ablated area compared to the pristine tissue.

Machine Learning Estimation of the Phase at the Fading Points of an OFDR-Based Distributed Sensor.

The paper reports a machine learning approach for estimating the phase in a distributed acoustic sensor implemented using optical frequency domain reflectometry, with enhanced robustness at the fading points. A neural network configuration was trained using a simulated set of optical signals that were modeled after the Rayleigh scattering pattern of a perturbed fiber. Firstly, the performance of the network was verified using another set of numerically generated scattering profiles to compare the achieved accuracy levels with the standard homodyne detection method. Then, the proposed method was tested on real experimental measurements, which indicated a detection improvement of at least 5.1 dB with respect to the standard approach.

Distributed Sensing Network Enabled by High-Scattering MgO-Doped Optical Fibers for 3D Temperature Monitoring of Thermal Ablation in Liver Phantom.

Thermal ablation is achieved by delivering heat directly to tissue through a minimally invasive applicator. The therapy requires a temperature control between 50-100 °C since the mortality of the tumor is directly connected with the thermal dosimetry. Existing temperature monitoring techniques have limitations such as single-point monitoring, require costly equipment, and expose patients to X-ray radiation. Therefore, it is important to explore an alternative sensing solution, which can accurately monitor temperature over the whole ablated region. The work aims to propose a distributed fiber optic sensor as a potential candidate for this application due to the small size, high resolution, bio-compatibility, and temperature sensitivity of the optical fibers. The working principle is based on spatial multiplexing of optical fibers to achieve 3D temperature monitoring. The multiplexing is achieved by high-scattering, nanoparticle-doped fibers as sensing fibers, which are spatially separated by lower-scattering level of single-mode fibers. The setup, consisting of twelve sensing fibers, monitors tissue of 16 mm × 16 mm × 25 mm in size exposed to a gold nanoparticle-mediated microwave ablation. The results provide real-time 3D thermal maps of the whole ablated region with a high resolution. The setup allows for identification of the asymmetry in the temperature distribution over the tissue and adjustment of the applicator to follow the allowed temperature limits.

Reflector-less nanoparticles doped optical fiber biosensor for the detection of proteins: Case thrombin.

A miniature biosensing platform based on MgO-based nanoparticle doped optical fiber was developed for the biomolecule detection. The technology used a single mode fiber with MgO-based nanoparticles doped core. The detection was based on collecting the Rayleigh backscattering signatures with increased gain upon the etching of the fiber 1-2 mm away from the tip. The shift from the backscattered signal with the maximum value of the cross-correlation was used to report the results. The sensor exhibited a sensitivity range from 0.75 nm/refractive index unit up to 19.63 nm/refractive index unit for a refractive index range from 1.3329 up to 1.37649. The deposition of the thin gold layer increased the overall sensitivity of the biosensor by 3.7 times for the etched part of the fiber with diameter 8-9 µm. The proposed biosensor was tested for the detection of thrombin molecule concentrations ranging from 0.625 µg/ml to 20 µg/ml. Thiol modified DNA specific aptamers were used to functionalize the gold coated surface of the fiber for the detection. The sensor showed detectable sensitivity and specificity as compared to the other control proteins. The proposed biosensing platform could be multiplexed and can be used in vivo for the detection in clinical settings due to its miniature size, biocompatibility of silica glass and reflector less set up.

Distributed 2D temperature sensing during nanoparticles assisted laser ablation by means of high-scattering fiber sensors.

The high demand in effective and minimally invasive cancer treatments, namely thermal ablation, leads to the demand for real-time multi-dimensional thermometry to evaluate the treatment effectiveness, which can be also assisted by the use of nanoparticles. We report the results of 20-nm gold and magnetic iron oxide nanoparticles-assisted laser ablation on a porcine liver phantom. The experimental set-up consisting of high-scattering nanoparticle-doped fibers was operated by means of a scattering-level multiplexing arrangement and interrogated via optical backscattered reflectometry, together with a solid-state laser diode operating at 980 nm. The multiplexed 2-dimensional fiber arrangement based on nanoparticle-doped fibers allowed an accurate superficial thermal map detected in real-time.