We present a multimodal approach using functional near-infrared spectroscopy (fNIRS) and optically pumped magnetometers (OPM) for imaging neurovascular coupling (NVC). The study aims to achieve high-density imaging by combining state-of-the-art implementation of the techniques. In-vivo studies during a motor cortex stimulation were carried out inside the 7-layer magnetically shielded room BMSR2 - the single most magnetically-shielded room on Earth. The study demonstrates the feasibility of the proposed approach and paves the way for future mapping and tomography reconstructions using magnetic and optical data.
Time domain diffuse correlation spectroscopy (td-DCS), has been proposed as a method that can increase the sensitivity of DCS for detecting blood flow index (BFI) in deep tissue. Several important parameters including the instrument response function (IRF), gate start time, gate width, and source-detector separation (SDS) must be taken into consideration. In our study, we characterized td-DCS system at three different SDS values and assessed each SDS's ability to detect dynamic changes of blood flow caused by moving red blood cells during cuff occlusion.
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%.
Time-domain diffuse correlation spectroscopy (TD-DCS) is a non-invasive optical technique, which measures tissue blood flow with path-length resolution. Ideally, this technique requires a pulsed laser with an adequate illumination power, a long coherence length, and a narrow instrument response function (IRF), while available laser modules cannot satisfy all these conditions. We systematically characterized three pulsed laser sources and compared their performances using phantom and in vivo measurements. We found that each laser has the potential to be used in TD-DCS applications. Also, the effects caused by the IRF are more significant than the effect of the limited coherence length.
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.
We show the hemodynamic response of a visual cortex on healthy volunteers under, hypoxia as registered with fNIRS system. Results show that amplitude of hemodynamic response to a visual stimulation correlates with the arterial oxygen saturation.
KEYWORDS: Visualization, Linear filtering, In vivo imaging, Signal detection, Sensors, Homodyne detection, Brain, Tissues, Hemodynamics, Electronic filtering
We introduce method of lock-in amplifying optical signals originating within brain. It requires 90-degree rotated source-detector pairs. In-vivo results suggest the proposed hardware and algorithm are brain-sensitive and real-time.
Diffuse correlation spectroscopy (DCS) is an emerging diffuse optical technique that quantifies microvascular blood flow. In spite of the wide range of clinical/research applications, DCS instrumentation is not yet standardized. In this study, we have analyzed the effect of experimental parameters as the measurement duration time and the number of detectors, at different photon count-rates, on the precision of a DCS experiment. This provides a recipe for finding device and experimental settings that optimize the precision while balancing cost and temporal resolution.
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 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.
A cloud-based NIRFAST server has been developed as a standalone tool for recovery of human thyroid hemodynamic parameters. The methodology utilize data from three complimentary diagnostic techniques: multi-spectral time-resolved spectroscopy (TRS) to measure concentrations of tissue constituents, diffuse correlation spectroscopy (DCS) to assess perfusion and ultrasound (US) images for optical probes guidance and building the tissue model. The recovery procedures benefit from using finite elements modelling and data processing based on highly massive parallel algorithms running on graphical processors with NVidia CUDA technology. The total execution time of thyroid hemodynamic parameters recovery is <120s. The server communication and calculation procedures are user-configurable through setting files. Therefore, the modular software architecture and remote access through a network interface make the server a universal tool applicable within a range of biomedical optics applications. The server can work as a post-processing box within an instrumental environment as shown in this work, a WWW-based software as a service or as a laboratory server. The NIRFAST server and methodology of analysing TRS/DCS/US data tuple were tested in-vivo on two thyroid malignant cancer patients showing differentiation in hemodynamic parameters (oxygenation and perfusion) between malignant and healthy tissue.
Parameter recovery in diffuse optical tomography is a computationally expensive algorithm, especially when used for large and complex volumes, as in the case of human brain functional imaging. The modeling of light propagation, also known as the forward problem, is the computational bottleneck of the recovery algorithm, whereby the lack of a real-time solution is impeding practical and clinical applications. The objective of this work is the acceleration of the forward model, within a diffusion approximation-based finite-element modeling framework, employing parallelization to expedite the calculation of light propagation in realistic adult head models. The proposed methodology is applicable for modeling both continuous wave and frequency-domain systems with the results demonstrating a 10-fold speed increase when GPU architectures are available, while maintaining high accuracy. It is shown that, for a very high-resolution finite-element model of the adult human head with ∼600,000 nodes, consisting of heterogeneous layers, light propagation can be calculated at ∼0.25 s/excitation source.
The aim of the study was to determine optimal measurement conditions for assessment of brain perfusion with the use of optical contrast agent and time-resolved diffuse reflectometry in the near-infrared wavelength range. The source-detector separation at which the distribution of time of flights (DTOF) of photons provided useful information on the inflow of the contrast agent to the intracerebral brain tissue compartments was determined. Series of Monte Carlo simulations was performed in which the inflow and washout of the dye in extra- and intracerebral tissue compartments was modeled and the DTOFs were obtained at different source-detector separations. Furthermore, tests on diffuse phantoms were carried out using a time-resolved setup allowing the measurement of DTOFs at 16 source-detector separations. Finally, the setup was applied in experiments carried out on the heads of adult volunteers during intravenous injection of indocyanine green. Analysis of statistical moments of the measured DTOFs showed that the source-detector separation of 6 cm is recommended for monitoring of inflow of optical contrast to the intracerebral brain tissue compartments with the use of continuous wave reflectometry, whereas the separation of 4 cm is enough when the higher-order moments of DTOFs are available.
An imaging system for brain oxygenation based on a time-gated, intensified charge-coupled device camera was developed. It allows one to image diffusely reflected light from an investigated medium at defined time windows delayed with respect to the laser pulse. Applying a fast optomechanical switch to deliver the light at a wavelength of 780 nm to nine source fibers allowed one to acquire images in times as short as 4 s. Thus, the system can be applied in in vivo studies. The system was validated in phantom experiments, in which absorbing inclusions were localized at different depths and different lateral positions. Then, the decrease in absorption of the brain tissue related to increase in oxygenation was visualized in the motor cortex area during finger tapping by a healthy volunteer.
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