Polymer-coated fiber optic probe for the monitoring of breathing pattern and respiratory rate.

In recent years, no-invasive and small size systems are meeting the demand of the new healthcare system, in which the vital signs monitoring is gaining in importance. In this context, Fiber Bragg grating (FBG) sensors are becoming very popular and FBG-based systems could be used for monitoring vital signs. At the same time, FBG could be able to sense chemical parameters by the polymer functionalization. The aim of our study was investigating the ability of a polymer-coated FBG-based probe for monitoring breathing patterns and respiratory rates. We tested the proposed FBG-based probe on 9 healthy volunteers during spirometry, the most common pulmonary function test. Results showed the high accuracy of the proposed probe to detect respiratory rate. The comparison between the respiratory rates estimated by the probe with the ones by the spirometer showed the absolute value of the percentage errors lower than 2.07% (in the 78% of cases <.91%). Lastly, a Bland Altman analysis was performed to compare the instantaneous respiratory rate values gathered by the spirometer and the FBG probe showing the feasibility of breath-by-breath monitoring by the proposed probe. Results showed a bias of 0.06± 2.90 $\mathrm{breaths}\square {\mathrm {min}}^{-1}$. Additionally, our system was able to follow the breathing activities and monitoring the breathing patterns.

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.

A wearable textile for respiratory monitoring: Feasibility assessment and analysis of sensors position on system response.

The interest on wearable textiles to monitor vital signs is growing in the research field and clinical scenario related to the increasing demands of long-term monitoring. Despite several smart textile-based solutions have been proposed for assessing the respiratory status, only a limited number of devices allow the respiratory monitoring in a harsh environment or in different positions of the human body. In this paper, we investigated the performances of a smart textile for respiratory rate monitoring characterized by 12 fiber optic sensors (i.e., fiber Bragg grating) placed on specific landmarks for compartmental analysis of the chest wall movements during quiet breathing. We focused on the analysis of the influence of sensor position on both peak-to-peak amplitude of sensors output and accuracy of respiratory rate measurements. This analysis was performed on two participants, who wore the textile in two positions (i.e., standing and supine). Bland-Altman analysis on respiratory rate showed promising results (better than 0.3 breaths per minute). Referring to the peak-to-peak output amplitude, the abdomen compartment showed the highest excursions in both the enrolled participants and positions. Our findings open up new approaches to design and develop smart textile for respiratory rate monitoring.

Design and preliminary assessment of a smart textile for respiratory monitoring based on an array of Fiber Bragg Gratings.

Comfortable and easy to wear smart textiles have gained popularity for continuous respiratory monitoring. Among different emerging technologies, smart textiles based on fiber optic sensors (FOSs) have several advantages, like Magnetic Resonance (MR)-compatibility and good metrological properties. In this paper we report on the development and assessment of an MR-compatible smart textiles based on FOSs for respiratory monitoring. The system consists of six fiber Bragg grating (FBG) sensors glued on the textile to monitor six compartments of the chest wall (i.e., right and left upper thorax, right and left abdominal rib cage, and right and left abdomen). This solution allows monitoring both global respiratory parameters and each compartment volume change. The system converts thoracic movements into strain measured by the FBGs. The positioning of the FBGs was optimized by experiments performed using an optoelectronic system. The feasibility of the smart textile was assessed on 6 healthy volunteers. Experimental data were compared to the ones estimated by an optoelectronic plethysmography used as reference. Promising results were obtained on both breathing period (maximum percentage error is 1.14%), inspiratory and expiratory period, as well as on total volume change (mean percentage difference between the two systems was ~14%). The Bland-Altman analysis shows a satisfactory accuracy for the parameters under investigation. The proposed system is safe and non-invasive, MR-compatible, and allows monitoring compartmental volumes.

Magnetic resonance-based thermometry during laser ablation on ex-vivo swine pancreas and liver.

Laser Ablation (LA) is a minimally-invasive procedure for tumor treatment. LA outcomes depend on the heat distribution inside tissues and require accurate temperature measurement during the procedure. Magnetic resonance imaging (MRI) allows a non-invasive and three-dimensional thermometry of the organ undergoing LA. In this study, the temperature distribution within two swine pancreases and three swine livers undergoing LA (Nd:YAG, power: 2 W, treatment time: 4 min) was monitored by a 1.5-T MR scanner, utilizing two T1-weighted sequences (IRTF and SRTF). The signal intensity in four regions of interest, placed at different distances from the laser applicator, was related to temperature variations monitored in the same regions by twelve fiber Bragg grating sensors. The relationship between the signal intensity and temperature increase was calculated to obtain the calibration curve and to evaluate accuracy, sensibility and precision of each sequence. This is the first study of MR-based thermometry during LA on pancreas. More specifically, the IRTF sequence provides the highest temperature sensitivity in both liver (1.8 ± 0.2 °C(-1)) and pancreas (1.8 ± 0.5 °C(-1)) and the lowest precision and accuracy. SRTF sequence on pancreas presents the highest accuracy and precision (MODSFRT = -0.1 °C and LOASFRT = [-2.3; 2.1] °C).

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.

An MR-compatible force sensor based on FBG technology for biomedical application.

Fiber Bragg Grating (FBG) technology is very attractive to develop sensors for the measurement of thermal and mechanical parameters in biological applications, particularly in presence of electromagnetic interferences. This work presents the design, working principle and experimental characterization of a force sensor based on two FBGs, with the feature of being compatible with Magnetic Resonance. Two prototypes based on different designs are considered and characterized: 1) the fiber with the FBGs is encapsulated in a polydimethylsiloxane (PDMS) sheet; 2) the fiber with the FBGs is free without the employment of any polymeric layer. Results show that the prototype which adopts the polymeric sheet has a wider range of measurement (4200 mN vs 250 mN) and good linearity; although it has lower sensitivity (≈0.1 nm-N(1) vs 7 nm-N(1)). The sensor without polymeric layer is also characterized by employing a differential configuration which allows neglecting the influence of temperature. This solution improves the linearity of the sensor, on the other hand the sensitivity decreases. The resulting good metrological properties of the prototypes here tested make them attractive for the intended application and in general for force measurement during biomedical applications in presence of electromagnetic interferences.

Experimental assessment of CT-based thermometry during laser ablation of porcine pancreas.

Laser interstitial thermotherapy (LITT) is employed to destroy tumors in organs, and its outcome strongly depends on the temperature distribution inside the treated tissue. The recent introduction of computed tomography (CT) scan thermometry, based on the CT number dependence of the tissue with temperature, overcomes the invasiveness of other techniques used to monitor temperature during LITT. The averaged CT number (ROI = 0.02 cm(2)) of an ex vivo swine pancreas is monitored during LITT (Nd:YAG laser power of 3 W, treatment time: 120 s) at different distances from the applicator (from 4 to 30 mm). The averaged CT number shows a clear decrease during treatment: it is highest at 4 mm from the applicator (mean variation in the whole treatment of -0.256 HU s(-1)) and negligible at 30 mm, since the highest temperature increase is present close to the applicator (i.e., 45 °C at 4 mm and 25 °C at 6 mm). To obtain the relationship between CT numbers and pancreas temperature, the reference temperature was measured by 12 fiber Bragg grating sensors. The CT number decreases as a function of temperature, showing a nonlinear trend with a mean thermal sensitivity of -0.50 HU °C(-1). Results here reported are the first assessment of pancreatic CT number dependence on temperature, at the best of our knowledge. Findings can be useful to further investigate CT scan thermometry during LITT on the pancreas.