Measurement of thermal properties of biological tissues and tissue-mimicking phantom with a dual-needle sensor

This work presents the measurement of the thermal properties of ex vivo biological tissues (i.e., porcine liver and kidney tissues) as a function of temperature, along with the thermal characterization of a tissue-mimicking agar-based phantom. The evaluation of the thermal properties was performed by the dual needle technique, adopting a sensor equipped with two needles, capable to deliver thermal energy to the biomaterial and monitor the related tissue thermal behavior. Measurements of thermal conductivity, thermal diffusivity, and volumetric heat capacity were conducted at room temperature and at temperatures relevant from a biological point of view, namely, body temperature and temperatures of similar to 60 degrees C- 65 degrees C, which are typically correlated to instantaneous thermal damage in tissue. Thermal properties of biological tissue remained rather constant at the investigated temperatures: average values of thermal conductivity ranged from 0.515 W/(m.K) to 0.575 W/(m.K), thermal diffusivity ranged from 0.144 mm(2)/s to 0.163 mm2/s, whilst the average volumetric heat capacity was from 3.48 MJ/(m(3).K) to 3.72 MJ/(m(3).K). Furthermore, the thermal properties of the realized agar phantom were comparable to the ones of biological tissues. The results of this study provide valuable information for the characterization of porcine liver and kidney tissues, in terms of their thermal properties, to be used in predictive mathematical models of thermal therapies and validate the usage of agar phantoms as tissue-mimicking materials

PID controlling approach based on FBG array measurements for laser ablation of pancreatic tissues

In this paper, we propose a temperature-based proportional–integral–derivative (PID) controlling algorithm using highly dense fiber Bragg grating (FBG) arrays for laser ablation (LA) of ex vivo pancreatic tissues. Custom-made highly dense FBG arrays with a spatial resolution of 1.2 mm were fabricated with the femtosecond point-by-point writing technology and optimized for LA applications. In order to obtain proper PID gain values, finite element method-based iterative simulation of different PID gains was performed. Then, the proposed algorithm, with numerically derived PID gains, was experimentally validated. In the experiments, the point temperature was controlled at different distances from the laser fiber tip (6.0 mm, 7.2 mm, 8.4 mm, and 10.8 mm). The obtained results report robust controlling and correlation between controlled distance and the resulting area of ablation. The results of the work encourage further investigation of FBG array application for LA control

Functionalized etched tilted fiber Bragg grating aptasensor for label-free protein detection

An aptasensor based on etched tilted fiber Bragg grating (eTFBG) is developed on a single-mode optical fiber targeting biomolecule detection. TFBGs were chemically etched using hydrofluoric acid (HF) to partially remove the fiber cladding. The sensor response was coarsely interrogated, resulting on a sensitivity increase from 1.25 nm/RIU (refractive index unit) at the beginning of the process, up to 23.38 nm/RIU at the end of the etching, for a RI range from 1.3418 to 1.4419 RIU. The proposed aptasensor showed improved RI sensitivity as compared to the unetched TFBG, without requiring metal depositions on the fiber surface or polarization control during the measurements. The proposed sensor was tested for the detection of thrombin-aptamer interactions based on silane-coupling surface chemistry, with thrombin concentrations ranging from 2.5 to 40 nM. Functionalized eTFBGs provided a competitive platform for biochemical interaction measurements, showing sensitivity values ranging from 2.3 to 3.3 p.m./nM for the particular case of thrombin detection

Analysis of hyperspectral camera settings for assessing liver tissue thermal damage

Hyperspectral imaging (HSI) is gaining, tremendous acceptance as an innovative non-invasive approach in the medical field. HSI is a sensing technique combining spectral and spatial information of the object of interest. Preliminary works have investigated the use of HSI for the intraoperative guidance of minimally invasive therapy such as thermal therapies. Data collected by the HSI system carry information of the tissue texture and may potentially track structural modifications caused by thermal treatment providing an alternative approach to the direct monitoring of the thermal outcome induced during the treatment. In this work, a commercial hyperspectral (HS) camera, working in the visible and near-infrared spectral range, has been tested for the estimation of thermal damage in the ex vivo liver. Firstly, the optimal experimental setup and settings to evaluate the optical response of tissues with the HSI were identified. Then, the reflectance of not-damaged tissue (room temperature) and tissue subjected to thermal damage was acquired and compared. Specifically, the damage was induced by homogeneously heating the tissue until reaching 50.0 degrees C and 70.0 degrees C. Inter-individual and intra-individual variability analysis was also computed using multiple samples and showed that by using the first derivative of reflectance the sources of variability are minimized. Furthermore, the first derivative shows variation in the shape mainly localized in the range [600-700] nm for the tissue subjected to 70.0 degrees C. The peak at 650 nm red-shifted and increased to reach 680 nm. A decrease at 945 nm is also visible for the damaged tissue with a preparation temperature of 70.0 degrees C as well as a slope variation in the range [800-900] nm. These results confirm the potential of using the hyperspectral camera to assess different levels of damage during thermal therapies encouraging additional studies to validate its use as a monitoring tool

Laser‐induced optothermal response of gold nanoparticles: From a physical viewpoint to cancer treatment application

Gold nanoparticles (GNPs)-based photothermal therapy (PTT) is a promising minimally invasive thermal therapy for the treatment of focal malignancies. Although GNPs-based PTT has been known for over two decades and GNPs possess unique properties as therapeutic agents, the delivery of a safe and effective therapy is still an open question. This review aims at providing relevant and recent information on the usage of GNPs in combination with the laser to treat cancers, pointing out the practical aspects that bear on the therapy outcome. Emphasis is given to the assessment of the GNPs' properties and the physical mechanisms underlying the laser-induced heat generation in GNPs-loaded tissues. The main techniques available for temperature measurement and the current theoretical simulation approaches predicting the therapeutic outcome are reviewed. Topical challenges in delivering safe thermal dosage are also presented with the aim to discuss the state-of-the-art and the future perspective in the field of GNPs-mediated PTT. This article is protected by copyright. All rights reserved