Recently we developed the open-source FlexNIRS: a battery-operated, wireless, wearable oximeter whose self-calibrating geometry allows measurements of oxygen saturation in tissue. The first implementation of the device operating at 100 Hz has been validated and is enrolled in several measurement campaigns across different research laboratories. A recent firmware upgrade provides 266 Hz sampling rate, and hardware modifications provide improved form factor, wearability, and multi-modal acquisition. The new version is currently adopted in multiple clinical measurement campaigns focusing on pulsatile component analysis. We will present the instrument performance, its recent and future upgrades, and the applications where the device is currently in use.
Diffuse correlation spectroscopy (DCS) is an optical technique which is used to estimate blood flow in tissue through the analysis of the temporal fluctuations in light intensity. Recently, the development of interferometric techniques (iDCS/iDWS), have allowed for drastic improvement in measurement SNR. In this work, we build upon the iDCS technique by combining it with another advanced DCS modality, time-domain DCS (TD-DCS). This combination allows for the application of pathlength specific coherent gain, which has the potential to further improve the performance of DCS in the non-invasive measurement of deep tissue blood flow.
Peripheral edema, also known as leg swelling, is observed frequently because of various causes such as sitting or standing for a long time, inflammation, injury or diseases in venous circulation system, lymphatic system, kidney and heart. It is also a side effect of chemotherapy or hormonal therapy. But to our knowledge, there is no wearable optical monitor that can quantify changes in the tissue water content related to edema. We have conducted simulations on the minimal number of light source-detector pairs and the wavelengths of the sources that can measure changes in the water fraction in superficial tissues within a compact form factor wearable optical sensor using continuous wave near-infrared spectroscopy (CW NIRS). The wavelength range we have investigated is from 800 to 1100 nm. We will present the results of simulations under various device configurations.
Functional near-infrared spectroscopy (fNIRS) and diffuse correlation spectroscopy (DCS) have shown promise as non-invasive optical methods for cerebral functional imaging. Both approaches currently have limits to sensitivity in adults. Sensitivity can be improved using temporal discrimination, where the laser excitation is of short (~400ps) duration and the detector rejects early photons that have not penetrated into the brain while maintain high sensitivity to those that have. We report here further demonstration of a high-speed Read-Out Integrated Circuit (ROIC) that integrates with a 32x32 Single-Photon Avalanche photo-Detector (SPAD) array that can be either silicon (Si, for visible to infra-red) in indium-phosphide (InP, to allow operation at 1064nm). Data is exfiltrated serially directly to an FPGA where it can be processed in real time. This presentation will include results of recent detector performance tests and phantom demonstrations using this powerful new tool.
Speckle contrast optical spectroscopy (SCOS) is an emerging camera-based technique that can measure human cerebral blood flow (CBF) noninvasively with high signal-to-noise ratio (SNR). A noise correction procedure has previously been developed to improve SCOS measurement accuracy, which requires precise characterization of camera properties. Here, we provide guidance on choosing and characterizing a camera for SCOS, considering factors such as linearity, read noise, and gain. We then validate a noise-corrected SCOS measurement of flow changes in a liquid phantom against diffuse correlation spectroscopy (DCS).
KEYWORDS: Speckle, Monte Carlo methods, Sensors, Cameras, Pulsed laser operation, Light sources and illumination, Neurophotonics, Tissues, Signal to noise ratio, Cerebral blood flow
SignificanceThe non-invasive measurement of cerebral blood flow based on diffuse optical techniques has seen increased interest as a research tool for cerebral perfusion monitoring in critical care and functional brain imaging. Diffuse correlation spectroscopy (DCS) and speckle contrast optical spectroscopy (SCOS) are two such techniques that measure complementary aspects of the fluctuating intensity signal, with DCS quantifying the temporal fluctuations of the signal and SCOS quantifying the spatial blurring of a speckle pattern. With the increasing interest in the use of these techniques, a thorough comparison would inform new adopters of the benefits of each technique.AimWe systematically evaluate the performance of DCS and SCOS for the measurement of cerebral blood flow.ApproachMonte Carlo simulations of dynamic light scattering in an MRI-derived head model were performed. For both DCS and SCOS, estimates of sensitivity to cerebral blood flow changes, coefficient of variation of the measured blood flow, and the contrast-to-noise ratio of the measurement to the cerebral perfusion signal were calculated. By varying complementary aspects of data collection between the two methods, we investigated the performance benefits of different measurement strategies, including altering the number of modes per optical detector, the integration time/fitting time of the speckle measurement, and the laser source delivery strategy.ResultsThrough comparison across these metrics with simulated detectors having realistic noise properties, we determine several guiding principles for the optimization of these techniques and report the performance comparison between the two over a range of measurement properties and tissue geometries. We find that SCOS outperforms DCS in terms of contrast-to-noise ratio for the cerebral blood flow signal in the ideal case simulated here but note that SCOS requires careful experimental calibrations to ensure accurate measurements of cerebral blood flow.ConclusionWe provide design principles by which to evaluate the development of DCS and SCOS systems for their use in the measurement of cerebral blood flow.
SignificanceCombining near-infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS) allows for quantifying cerebral blood volume, flow, and oxygenation changes continuously and non-invasively. As recently shown, the DCS pulsatile cerebral blood flow index (pCBFi) can be used to quantify critical closing pressure (CrCP) and cerebrovascular resistance (CVRi).AimAlthough current DCS technology allows for reliable monitoring of the slow hemodynamic changes, resolving pulsatile blood flow at large source–detector separations, which is needed to ensure cerebral sensitivity, is challenging because of its low signal-to-noise ratio (SNR). Cardiac-gated averaging of several arterial pulse cycles is required to obtain a meaningful waveform.ApproachTaking advantage of the high SNR of NIRS, we demonstrate a method that uses the NIRS photoplethysmography (NIRS-PPG) pulsatile signal to model DCS pCBFi, reducing the coefficient of variation of the recovered pulsatile waveform (pCBFi-fit) and allowing for an unprecedented temporal resolution (266 Hz) at a large source-detector separation (>3 cm).ResultsIn 10 healthy subjects, we verified the quality of the NIRS-PPG pCBFi-fit during common tasks, showing high fidelity against pCBFi (R2 0.98 ± 0.01). We recovered CrCP and CVRi at 0.25 Hz, >10 times faster than previously achieved with DCS.ConclusionsNIRS-PPG improves DCS pCBFi SNR, reducing the number of gate-averaged heartbeats required to recover CrCP and CVRi.
Functional near-infrared spectroscopy (fNIRS) and diffuse correlation spectroscopy (DCS) have shown promise as non-invasive optical methods for cerebral functional imaging. DCS approaches currently have limited sensitivity in adults. fNIRS sensitivity is also limited, particularly in high-detector-density applications. Sensitivity can be improved using temporal discrimination (TD), where the laser excitation is of short (~400ps) duration and the detector rejects early photons that have not penetrated into the brain while maintain high sensitivity to those that have. We report here on the development of a novel 32x32 Single-Photon Avalanche photo-Detector (SPAD) array and Read-Out Integrated Circuit (ROIC) that can operate in either the visible or NIR enabling high-channel-count TD-fNIRS or TD-DCS systems.
We present a novel system based on a four-stage fiber delay network designed for multistate time-domain diffuse correlation spectroscopy, providing three output fibers per each delay state. The fiber delay network is coupled to a custom pulsed laser at 1064 nm and four SNSPDs, allowing to measure up to 12 independent source-detector pairs simultaneously. The system delivers 300ps optical pulses, 100 mW average optical power per fiber output, operates at 62.5 MHz and each cycle provides 4 laser pulses displaced of 4 ns. The instrument has been validated on healthy human subject during functional tasks, proving state-of-the-art performance.
Infants born at an extremely low gestational age are at an increased risk of intraventricular hemorrhaging during the first three postnatal days. We have built a standalone easy-to-use multi-wavelength multi-distance diffuse correlation spectroscopy system, which utilizes three time-multiplexed long coherence lasers at 785, 808, and 853 nm, single photon detectors, and photon time-tagging electronics to simultaneously quantify cerebral blood flow, tissue optical properties, and blood oxygen saturation. The system has been designed specifically for use on preterm infants. The device shows good agreement with a commercially available NIRS-DCS system. We are currently monitoring preterm infants and will show results.
Significance: Multi-laboratory initiatives are essential in performance assessment and standardization—crucial for bringing biophotonics to mature clinical use—to establish protocols and develop reference tissue phantoms that all will allow universal instrument comparison.
Aim: The largest multi-laboratory comparison of performance assessment in near-infrared diffuse optics is presented, involving 28 instruments and 12 institutions on a total of eight experiments based on three consolidated protocols (BIP, MEDPHOT, and NEUROPT) as implemented on three kits of tissue phantoms. A total of 20 synthetic indicators were extracted from the dataset, some of them defined here anew.
Approach: The exercise stems from the Innovative Training Network BitMap funded by the European Commission and expanded to include other European laboratories. A large variety of diffuse optics instruments were considered, based on different approaches (time domain/frequency domain/continuous wave), at various stages of maturity and designed for different applications (e.g., oximetry, spectroscopy, and imaging).
Results: This study highlights a substantial difference in hardware performances (e.g., nine decades in responsivity, four decades in dark count rate, and one decade in temporal resolution). Agreement in the estimates of homogeneous optical properties was within 12% of the median value for half of the systems, with a temporal stability of <5 % over 1 h, and day-to-day reproducibility of <3 % . Other tests encompassed linearity, crosstalk, uncertainty, and detection of optical inhomogeneities.
Conclusions: This extensive multi-laboratory exercise provides a detailed assessment of near-infrared Diffuse optical instruments and can be used for reference grading. The dataset—available soon in an open data repository—can be evaluated in multiple ways, for instance, to compare different analysis tools or study the impact of hardware implementations.
Diffuse correlation spectroscopy (DCS) is an emerging near infrared spectroscopy modality able to measure cerebral blood flow (CBF) non-invasively and continuously in humans. We have reported a limited applicability in adults due to the significant extracerebral tissue thickness and the low signal-to-noise ratio (SNR) of the measurements. Improvements to DCS brain sensitivity and SNR can be achieved by operating DCS at 1064 and using superconducting nanowire single-photon detectors (SNSPDs). Initial human results show a 16-fold improvement in SNR and 20% improvement in depth sensitivity. This allows us to resolve changes in CBF in adult subjects more robustly and accurately than was previously achievable.
We present the design of an innovative time-gated 32×32 InP/InGaAs-based Single Photon Avalanche Diode (SPAD) array with sub-nanosecond gating capabilities operating up to 10MHz repetition rate specifically designed for time-domain diffuse correlation spectroscopy at 1064nm. We present the detector design, experimental characterization and preliminary validations on a liquid phantom. This testing is informing us for a revision of the photodetector which will allow to reach up to 192 optical channels towards functional blood flow changes measurements with full head coverage with improved brain sensitivity thanks to early-photons rejection.
Standard techniques for detection of thyroid cancer (ultrasound screening and fine-needle aspiration biopsy) have limited sensitivity and specificity, leading to a very large number of unnecessary thyroid extraction surgeries. With the aim of improving diagnosis, hybrid diffuse optics and ultrasound were used on nodules patients to obtain tissue hemodynamic information. Nodules rated 4A or 4B in the thyroid imaging reporting and data system (TI-RADS) are of clinical relevance and were classified using a logistic regression model built on our results. Fourteen benign and four malignant nodules were classified with a sensitivity of 100% and specificity of 77%.
We present the design of an innovative instrument for time-gated diffuse correlation spectroscopy. It features a 1064nm pulsed sub-ns long coherence-length laser operating up to 75MHz, a 100-channel in-FPGA correlator and a novel time-gated 32×32 InP/InGaAs-based Single Photon Avalanche Diode (SPAD) array with sub-nanosecond gating capabilities operating up to 10MHz repetition rate. We present components experimental characterization and preliminary validations on a liquid phantom. This testing is informing us for a revision of the photodetector which will allow to reach up to 192 optical channels towards functional blood flow changes measurements with full head coverage.
LUCA platform combines clinical ultrasound with near-infrared time-domain and correlation spectroscopies to improve thyroid cancer screening. We characterized its precision and classified thyroid nodules in a clinical campaign on 45 subjects.
When monitoring patients with a skin contact sensor it is important to ensure that this is properly attached to the skin. This is important both for patient safety and data quality. We have developed a skin-contact sensitive technology that exploits the capacitive coupling of the sensor to detect the quality of the attachment to the subject’s skin and ensure galvanic isolation between patient and sensor. The developed technology can be easily embedded in any optical probe design without adding weight of bulkiness to the probe and provides the capability to detect optical probe displacements and alert user/operators/ hospital staff.
Performance assessment and standardization are indispensable for instruments of clinical relevance in general and clinical instrumentation based on photon migration/diffuse optics in particular. In this direction, a multi-laboratory exercise was initiated with the aim of assessing and comparing their performances. 29 diffuse optical instruments belonging to 11 partner institutions of a European level Marie Curie Consortium BitMap1 were considered for this exercise. The enrolled instruments covered different approaches (continuous wave, CW; frequency domain, FD; time domain, TD and spatial frequency domain imaging, SFDI) and applications (e.g. mammography, oximetry, functional imaging, tissue spectroscopy). 10 different tests from 3 well-accepted protocols, namely, the MEDPHOT2 , the BIP3 , and the nEUROPt4 protocols were chosen for the exercise and the necessary phantoms kits were circulated across labs and institutions enrolled in the study. A brief outline of the methodology of the exercise is presented here. Mainly, the design of some of the synthetic descriptors, (single numeric values used to summarize the result of a test and facilitate comparison between instruments) for some of the tests will be discussed.. Future actions of the exercise aim at deploying these measurements onto an open data repository and investigating common analysis tools for the whole dataset.
The LUCA device combines clinical ultrasound, time-domain near infrared and diffuse correlation spectroscopies with the aim of improving thyroid cancer screening sensitivity and specificity. The preliminary clinical campaign on patients (n=31) with thyroid nodules and healthy controls (n=11) allowed the characterization of the precision of the instrument and demonstrated that using a couple of biomarkers the muscle-to-nodule contrast allows an area under the curve of 0.92 for single-nodule patients and 0.77 for all patients in differentiating benign and malignant nodules in a receiver operating characteristic curve. We will present the updated results from the ongoing study.
We present a lightweight TD-NIRS system, two-wavelength, one detection channel that can be battery operated and worn as a backpack for freely-moving cerebral and muscle hemodynamic monitoring. Oxy- and deoxy-genated hemoglobin absolute concentration can be retrieved in real time even in outdoor measurements thanks to the rugged feature of the device.
KEYWORDS: Near infrared spectroscopy, Hemodynamics, Brain, Absorption, Scattering, Single photon detectors, Electronics, Control systems, Solids, In vivo imaging
We present a wearable TD-NIRS system (two wavelengths, one channel). The system is battery operated, can be remotely controlled and is able to perform measurements on brain and muscle on freely-moving subjects.
In this paper we present the ex-vivo characterization of a full-custom made multi-wavelength, two channel Time-Resolved Spectroscopy (TRS) module developed with the aim of being integrated in to a multi-modal spectroscopic device. This module overcomes all the main drawbacks of systems based on time-domain techniques such as high complexity and bulkiness while guaranteeing performances comparable to expensive state-of-the-art available devices. Each subcomponent of the module has been tailored and optimized to meet all the above-mentioned requirements. In order to assess and translate the performances of these tools for effective clinical use, we characterized the system following the guidelines of common standardization protocols. By following MEDPHOT guidelines, the linearity and accuracy in retrieving absolute values of absorption and scattering coefficients were determined by means of measurements on homogeneous phantoms. Finally, by means of a mechanically switchable solid inhomogeneous phantom (developed under the nEUROPT project) we simulated the clinical problem of detecting and localizing an absorption perturbation in a homogeneous background with broad applications such as detection of cancer lesions, thyroid, etc.
We present the current status of the LUCA project whose aim is to develop an innovative device combining ultrasound and diffuse optics for an improved screening of the thyroid cancer.
Time gating for SPADs is exploited either for increasing their maximum count rate or for detecting faint signals hidden by strong unwanted light pulses. Here we describe two short-gate techniques for high-speed photon counting with InGaAs/InP SPADs: i) a sinusoidal gating system at about 1.3 GHz, with very low afterpulsing and high count rate; ii) a SiGe integrated circuit for sub-nanosecond gating with < 200 ps rising/falling edges.
We present a new full-custom instrument for time-domain diffuse optical spectroscopy developed within Horizon 2020 LUCA (Laser and Ultrasound Co-Analyzer for thyroid nodules) project. It features eight different picosecond diode lasers (in the 635 - 1050 nm range), two 1.3 × 1.3 mm2 active-area SiPMs (Silicon PhotoMultipliers) working in single-photon mode and two 10 ps resolution time-to-digital converters. A custom FPGA-based control board manages the instrument and communicates with an external computer via USB connection. The instrument proved state-of-the-art performance: an instrument response function narrower than 160 ps (fullwidth at half-maximum), a long-term measurement stability better than 1%, and an output average optical power higher than 1 mW at 40 MHz. The instrument has been validated with phantom measurements.
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