Papers by Sergio Silvestri
Sensors, 2022
Heart rate (HR) and respiratory rate (fR) can be estimated by processing videos framing the upper... more Heart rate (HR) and respiratory rate (fR) can be estimated by processing videos framing the upper body and face regions without any physical contact with the subject. This paper proposed a technique for continuously monitoring HR and fR via a multi-ROI approach based on the spectral analysis of RGB video frames recorded with a mobile device (i.e., a smartphone’s camera). The respiratory signal was estimated by the motion of the chest, whereas the cardiac signal was retrieved from the pulsatile activity at the level of right and left cheeks and forehead. Videos were recorded from 18 healthy volunteers in four sessions with different user-camera distances (i.e., 0.5 m and 1.0 m) and illumination conditions (i.e., natural and artificial light). For HR estimation, three approaches were investigated based on single or multi-ROI approaches. A commercially available multiparametric device was used to record reference respiratory signals and electrocardiogram (ECG). The results demonstrated...
2020 IEEE International Workshop on Metrology for Industry 4.0 & IoT, 2020
Video photo-plethysmography (VPG) methods have been used over the years to monitor the heart rate... more Video photo-plethysmography (VPG) methods have been used over the years to monitor the heart rate. In this work, we report the usage of two different algorithms to extract cardiac signals from the recorded videos. Video recordings on six different subjects have been carried out at two different experimental setup conditions-front view and side view. Tests are also performed at three different Region of Interest (ROI)-forehead, cheek, and the carotid region. Results suggest that the carotid region offers the best performance in terms of accuracy. The accuracy rate remained consistently high on almost all the trials that underwent side view measurements. It is also noteworthy to mention that in many cases, the green channel exhibited much more accurate results than its counterpart sRGB color space.
2018 IEEE International Symposium on Medical Measurements and Applications (MeMeA), 2018
Gas flow measurements are pivotal in several medical applications. For instance, mechanical venti... more Gas flow measurements are pivotal in several medical applications. For instance, mechanical ventilators and applications for respiratory monitoring need flowmeters with strict requirements: they must be accurate, with adequate dynamic response, high sensitivity (especially if used for neonatal purposes), and they must be almost insensitive to the composition of the gas Only few types of flowmeters are may be used in these applications. Among differential pressure flowmeters, characterized by good static and dynamic responses, variable area orifice meters (VAOMs) are gaining large acceptance in applications related to respiratory monitoring, estimation of respiratory function, and mechanical ventilation. VAOMs consist of two main parts: a primary element (basically a restriction), and a secondary element (i.e., a differential pressure transducer). The installation of the primary and the secondary elements can strongly influence the input-output relationship of VAOMs and can introduce relevant bias error. The aim of this study was twofold: i) the experimental assessment of the influence of the lead lines length (LL) on the calibration curve of a variable orifice meter; ii) the experimental analysis of the influence of LL on the step response of the flowmeter in terms of settling time. Results show that the value of LL influences both the static response and the step response: regarding the static response, the sensor sensitivity significantly decreases with LL (e.g., the sensitivity decreases from 5.3 Pa/L·min-1 to 4.0 Pa/L·min-1, when LL increases from 4 cm to 182 cm); concerning the step response, the flowmeter increases the settling time from approximately 20 ms up to 60 ms using LL values of 4 cm and 182 cm, respectively. The findings of this study can be useful to figure out the impact of the LL value on the sensor response; in addition may provide useful information to correct the sensor response if it is used in condition of installation different from the one used during the calibration.
IEEE Sensors Journal, 2019
This paper investigates the performances of a headmounted wearable device for the breath-by-breat... more This paper investigates the performances of a headmounted wearable device for the breath-by-breath monitoring of respiratory frequency (fR) during exercise. The device exploits a new algorithm to estimate fR from the breathing-related pressure drops (P) recorded at the nostrils level. Performances of the wearable device in measuring breathby-breath and 30-s average fR values were evaluated during two high-intensity cycling exercise tests performed in laboratory. P signals were collected from 10 volunteers with the wearable device, and simultaneous measurements with a reference instrument were performed for validation purposes. Additionally, numerical simulations were carried out to reproduce the conditions expected in applied settings. Bland-Altman analysis, linear regression (r2) and percentage error (%E) were used for comparing the two instruments. Experimental tests demonstrate the robustness and validity of the proposed wearable device and related algorithm to measure breath-by-breath fR (overall %E = 4.03%) and 30-s average fR (overall %E = 2.38%) values. Biases obtained with the breathbybreath analysis (max.-0.06±6.27 breaths/min) were higher than those obtained in the 30-s window analysis (max.-0.03±1.60 breaths/min). In simulated conditions, %E increased up to 6.65%. The proposed wearable device is suitable for a wide variety of indoor applications where the fR monitoring during exercise at reduced invasiveness is of great value.
SPIE Proceedings, 2016
Optical fibre sensors have been applied to perform biophysical measurement in ex-vivo laser ablat... more Optical fibre sensors have been applied to perform biophysical measurement in ex-vivo laser ablation (LA), on pancreas animal phantom. Experiments have been performed using Fibre Bragg Grating (FBG) arrays for spatially resolved temperature detection, and an all-glass Extrinsic Fabry-Perot Interferometer (EFPI) for pressure measurement. Results using a Nd:YAG laser source as ablation device, are presented and discussed.
2015 37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), 2015
ABSTRACT
Proceedings of the 25th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (IEEE Cat. No.03CH37439)
A procedure to assist the switching from volume controlled to pressure controlled ventilation ass... more A procedure to assist the switching from volume controlled to pressure controlled ventilation assuring tidal volume is proposed. The method, based on a linear model of the dynamical behavior of the ventilatory system, identifies the main mechanical parameters of the system and is able to evaluate the pressure support value to set in pressure controlled ventilation in order to guarantee
Journal of Sensors, 2015
This work shows the development and characterization of a fiber optic tactile sensor based on Fib... more This work shows the development and characterization of a fiber optic tactile sensor based on Fiber Bragg Grating (FBG) technology. The sensor is a 3×3 array of FBGs encapsulated in a PDMS compliant polymer. The strain experienced by each FBG is transduced into a Bragg wavelength shift and the inverse characteristics of the sensor were computed by means of a feedforward neural network. A 21 mN RMSE error was achieved in estimating the force over the 8 N experimented load range while including all probing sites in the neural network training procedure, whereas the median force RMSE was 199 mN across the 200 instances of a Monte Carlo randomized selection of experimental sessions to evaluate the calibration under generalized probing conditions. The static metrological properties and the possibility to fabricate sensors with relatively high spatial resolution make the proposed design attractive for the sensorization of robotic hands. Furthermore, the proved MRI-compatibility of the sen...
2015 IEEE International Symposium on Medical Measurements and Applications (MeMeA) Proceedings, 2015
ABSTRACT Laser ablation (LA) is a minimally invasive procedure used to remove cancer by inducing ... more ABSTRACT Laser ablation (LA) is a minimally invasive procedure used to remove cancer by inducing hyperthermia. It is based on the interaction between laser light and tissue: the absorbed light is converted into heat causing a tissue temperature increase. The amount of damaged volume depends on temperature and time exposure of the tissue to the hyperthermia. As a consequence, the monitoring of tissue temperature during LA could be particularly beneficial to optimize treatment outcomes. Temperature can be measured by different transducers and techniques; thermocouples are one of the most employed. Their main drawback is related to the strong light absorption of the two metallic wires which constitute a thermocouple. The light absorption causes an overestimation of actual temperature, in literature known as artifact. This work aims at assessing this artifact on ex vivo swine pancreases undergoing LA. The artifacts have been estimated at the three laser powers (1.6 W, 2 W and 5 W) and at two distances from the optical applicator. In particular, the artifact decreases with the distance from the optical applicator and depends on P: at 1.6 W and 2 W it is negligible at 12 mm of distance, on the other hand at 5 W it is significant also at 15 mm (1.7 °C). Summing up: the artifact is strongly influenced by the distance between the thermocouple and the optical applicator, and by the laser power; also at high distance from the applicator it can cause error which are not acceptable for the application of interest (e.g., at 5 W and 10 mm the error is about 4 °C). Although the use of thermocouples entails the concern related to the artifact, it must be considered that proper model can be employed to correct the measurement error.
2015 IEEE International Symposium on Medical Measurements and Applications (MeMeA) Proceedings, 2015
ABSTRACT Minimally invasive thermal procedures are gaining acceptance in tumor treatment. Among o... more ABSTRACT Minimally invasive thermal procedures are gaining acceptance in tumor treatment. Among others, laser ablation (LA) is considered a valid alternative to surgical resection for inoperable patients. LA damages the tumor by increasing the tissue temperature. The temperature distribution within the tissue strongly influences the outcomes of the procedure. Hence, some thermometric techniques are employed in this scenario. Among them, MRI-based thermometry presents some advantages, such as the non-invasiveness. In this work, two sequences (EPI and FIESTA) have been used to monitor liver temperature. During the whole MRI procedure, the liver temperature has been monitored by MRI-compatible, fiber optic-based sensors. The temperature measured by these sensors has been used as reference in order to assess the sensitivity of MRI-thermometry. Moreover, the influence of Region of interests (ROIs) size on precision has been investigated. Results show that the absolute value of thermal sensitivity of FIESTA is double with respect to the sensitivity obtained with EPI (about -15 °C-1 vs -7 °C-1). Regarding the influence of ROI size, results show that the wider the extension the better the precision.
2015 IEEE International Symposium on Medical Measurements and Applications (MeMeA) Proceedings, 2015
Monitoring of local temperature in tissue undergoing Laser Ablation (LA) could be particularly be... more Monitoring of local temperature in tissue undergoing Laser Ablation (LA) could be particularly beneficial to optimize treatment outcomes. A number of both invasive and non-invasive thermometric techniques may be employed to perform this task. Among others, Fiber Bragg Grating (FBG) sensors show the following valuable characteristics for temperature monitoring during LA: good sensitivity and accuracy, and immunity from electromagnetic interferences. The main drawbacks are their intrinsic invasiveness and the sensitivity to strain, which can entail measurement error for respiratory and patient movements. The aim of this work is to experimental assess the characteristics of an FBG sensor, housed within a metallic needle, employed in temperature monitoring of tissue undergoing LA. The use of a metallic needle allows neglecting errors due to patient movements, but induces an increase in sensor response time and a temperature overestimation due to direct absorption of laser light by the needle. The proposed sensor is tested during LA of ex vivo swine livers, and the tissue temperature measured by the FBG housed within the needle is compared to the temperature measured by an FBG without needle. This comparison showed that the needle induces a temperature overestimation, strongly dependent on the distance between sensor and laser applicator (e.g., about 2 °C at 6 mm, 4.4 °C at 4 mm). Furthermore, the needle causes an increase of response time (about 140 ms vs 40 ms). Since this response time is sufficient for the particular application and the overestimation can be reduced by using different techniques of data processing, the use of a needle to protect FBG seems to be a feasible solution to overcome the concern related to patient movements.
2015 IEEE International Symposium on Medical Measurements and Applications (MeMeA) Proceedings, 2015
ABSTRACT Opto-electronic Plethysmography (OEP) is a motion analysis system used to measure chest ... more ABSTRACT Opto-electronic Plethysmography (OEP) is a motion analysis system used to measure chest wall kinematics and to indirectly evaluate respiratory volumes during breathing. Its working principle is based on the time-per-time computation of marker displacements placed on the thorax. This work aims at evaluating the metrological properties of a custom made chest wall simulator (CWS) developed to reproduce human chest wall kinematic. The CWS metrological properties have been estimated by the comparison of two different motion control strategies of the CWS: the first one is based on the script writing into each motion controller, the second one on macro command sent to the CWS. Three sets of experiments have been performed with the aim to: (i) evaluate precision and accuracy in reaching target displacements (i.e., ranging from 2 mm to 8 mm), (ii) evaluate the differences between set and simulated breathing period (i.e., from 10 to 30 breathing per minute), and (iii) assess the movement reproducibility. The precision error, expressed as the ratio between measurement uncertainty and the measured displacement, is always lower than 0.32% (27 µm) with script-based motion control and 0.25% (6 µm) with the macro one, for all the target displacements. The difference between the simulated breathing period and the set one is always lower than 0.30 s in both strategies of motion control (percentage error always lower than 15%). Standard deviation between measure, assumed as reproducibility index, showed values always lower than 37 µm. The observed performances allows considering both the strategies of control adoptable to be employed for CWS motion control during the OEP performance in further works.
Journal of Medical Devices, 2015
Temperature distribution monitoring in tissue undergoing laser ablation (LA) could be beneficial ... more Temperature distribution monitoring in tissue undergoing laser ablation (LA) could be beneficial for improving treatment outcomes. Among several thermometric techniques employed in LA, fiber Bragg grating (FBG) sensors show valuable characteristics, although their sensitivity to strain entails measurement error for patient respiratory movements. Our work describes a solution to overcome this issue by housing an FBG in a surgical needle. The metrological properties of the probes were assessed in terms of thermal sensitivity (0.027 nm °C−1 versus 0.010 nm °C−1 for epoxy liquid encapsulated probe and thermal paste one, respectively) and response time (about 100 ms) and compared with properties of nonencapsulated FBG (sensitivity of 0.010 nm °C−1, response time of 43 ms). The error due to the strain caused by liver movements, simulating a typical respiratory pattern, was assessed: the strain induces a probes output error less than 0.5 °C, which is negligible when compared to the respons...
2006 International Conference of the IEEE Engineering in Medicine and Biology Society, 2006
Lung protective ventilation utilizes low tidal volumes to ventilate patients with severe lung pat... more Lung protective ventilation utilizes low tidal volumes to ventilate patients with severe lung pathologies. The compensation of breathing circuit effects, i.e. those induced by compressible volume of the circuit, results particularly critical in the calculation of the actual tidal volume delivered to patient's respiratory system which in turns is responsible of the level of permissive hypercapnia. The present work analyzes the applicability of the equation for circuit compressible volume compensation in the case of pressure and volume controlled lung protective ventilation. Experimental tests conducted in-vitro show that the actual tidal volume can be reliably estimated if the compliance of the breathing circuit is measured with the same parameters and ventilation technique that will be utilized in lung protective ventilation. Differences between volume and pressure controlled ventilation are also quantitatively assessed showing that pressure controlled ventilation allows a more reliable compensation of breathing circuit compressible volume.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2014
In hemochromatosis an abnormal accumulation of iron is present in parenchymal organs and especial... more In hemochromatosis an abnormal accumulation of iron is present in parenchymal organs and especially in liver. Among the several techniques employed to diagnose the iron overload, magnetic resonance imaging (MRI) and Computed Tomography (CT) are the most promising non-invasive ones. MRI is largely used but shows limitation including an overestimation of iron and inability to quantify iron at very high concentrations. Therefore, some research groups are focusing on the estimation of iron concentration by CT images. Single X-ray CTs are not able to accurately perform this task in case of the presence of confounding factors (e.g., fat). A potential solution to overcome this concern is the employment of Dual-Energy CT (DECT). The aim of this work is to investigate influence of the kVp and mAs on CT number sensitivity to iron concentration. A phantom with test tubes filled with homogenized porcine liver at different iron concentrations, has been scanned with DECT at different mAs. The ima...
The open biomedical engineering journal, 2014
Instrumented gait analysis based on optoelectronic systems is an expensive technique used to obje... more Instrumented gait analysis based on optoelectronic systems is an expensive technique used to objectively measure the human movement features and it is generally considered as the gold standard. Opto-electronic plethysmography (OEP) is a particular motion analysis system able to: (i) determine chest wall kinematic via the evaluation of marker displacements placed on the thorax and (ii) compute respiratory volumes during breathing. The aim of this work is to describe the performances of a custom made, bio-inspired, mechatronic chest wall simulator (CWS), specifically designed to assess the metrological performances of the OEP system. The design of the simulator is based on the chest wall kinematic analysis of three healthy subjects previously determined. Two sets of experiments were carried out: (i) to investigate the CWS dynamic response using different target displacements (1 - 12 mm), and (ii) to assess the CWS accuracy and precision in simulating quite breathing, covering the phys...
Journal of Medical Engineering & Technology, 2006
Pulmonary ventilators for intensive care provide information on, among many other patient respira... more Pulmonary ventilators for intensive care provide information on, among many other patient respiratory parameters, patient resistance, compliance and 'work of breathing' values calculated from pressure and flow data patterns according to a widely utilized algorithm. The effects induced by the breathing circuit and analogue filtering of the ventilator measuring system are experimentally investigated during controlled ventilation. Three main phenomena are observed: (a) errors in calculation of resistance and compliance due to filtering of pressure and flow waveforms; (b) the presence of pressure oscillations at the beginning of inspiration and expiration phases; and (c) the phase shift between pressure and flow waveforms. The experimental evaluation of the measuring system of a neonatal ventilator is then conducted and: (a) a delay in pressure and flow measurement synchronization equal to 22 +/- 2 ms is evaluated; moreover, (b) a difference between the values provided by the ventilator and those measured by the reference experimental setup on respiratory parameters such as the compliance, resistance and work of breathing that lies in the range of 7-16% of reading is observed.
Journal of Clinical Monitoring and Computing, 2014
The gold standard methods to measure cardiac output (CO) are invasive and expose the patient to h... more The gold standard methods to measure cardiac output (CO) are invasive and expose the patient to high risks of various complications. The aim of this study is to assess an innovative non-invasive method for CO monitoring in mechanically ventilated patients after cardiac surgery and its agreement with values obtained by thermodilution technique. Continuous monitoring of respiratory gas concentrations and airflow allows the estimation of CO through a newly developed algorithm derived from a modified version of the Fick equation. It consists of two phases: the first involves measurements during steady breathing state, and the second starts when a sudden perturbation into the carbon dioxide elimination process is introduced by a prolonged expiration. This prospective clinical study involved thirty-five adult patients, undergone cardiac surgery. The measurements were performed in curarized and haemodynamically stable patients, during the post-surgery recovery in intensive care unit. The study protocol, which lasted 1 h for each patient, consisted of 20 measurements obtained by prolonged expiration-based method and 10 by thermodilution. The estimation of CO using the proposed method (CO K) agreed with the thermodilution (CO T) as demonstrated by: a low mean bias between CO K and CO T considering all patients (i.e.,-0.11 L min-1); a best fitting line having slope = 0.98, r = 0.81, p \ 0.0001; the lower and upper limits of agreement were-0.77 and ?0.54 L min-1 , respectively. CO K shows a mean percentage error of 34 %. In stable mechanically ventilated patients, undergone cardiac surgery, the proposed method is reliable if compared to the thermodilution. Considering the non-invasivity of the technique, further evaluations of its performances are encouraged.
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Papers by Sergio Silvestri