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3 pages, 176 KiB

Open AccessEditorial

Special Issue on Diffuse Optical Spectroscopy: Advances towards Widespread Applications

by Alberto Dalla Mora

Appl. Sci. 2021, 11(23), 11548; https://doi.org/10.3390/app112311548 - 06 Dec 2021

Viewed by 1385

Abstract

Light is a powerful tool for the non-invasive and non-destructive analysis of several organic and inorganic materials [...] Full article

(This article belongs to the Special Issue Diffuse Optical Spectroscopy: Advances Towards Widespread Applications)

Research

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11 pages, 1178 KiB

Open AccessArticle

Diffuse Optical Tomography Using Bayesian Filtering in the Human Brain

by Estefania Hernandez-Martin and Jose Luis Gonzalez-Mora

Appl. Sci. 2020, 10(10), 3399; https://doi.org/10.3390/app10103399 - 14 May 2020

Cited by 7 | Viewed by 2325

Abstract

The present work describes noninvasive diffuse optical tomography (DOT), a technology for measuring hemodynamic changes in the brain. These changes provide relevant information that helps us to understand the basis of neurophysiology in the human brain. Advantages, such as portability, direct measurements of [...] Read more.

The present work describes noninvasive diffuse optical tomography (DOT), a technology for measuring hemodynamic changes in the brain. These changes provide relevant information that helps us to understand the basis of neurophysiology in the human brain. Advantages, such as portability, direct measurements of hemoglobin state, temporal resolution, and the lack of need to restrict movements, as is necessary in magnetic resonance imaging (MRI) devices, means that DOT technology can be used both in research and clinically. Here, we describe the use of Bayesian methods to filter raw DOT data as an alternative to the linear filters widely used in signal processing. Common problems, such as filter selection or a false interpretation of the results, which is sometimes caused by the interference of background physiological noise with neural activity, can be avoided with this new method. Full article

(This article belongs to the Special Issue Diffuse Optical Spectroscopy: Advances Towards Widespread Applications)

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18 pages, 3551 KiB

Open AccessArticle

Method for Quantitative Broadband Diffuse Optical Spectroscopy of Tumor-Like Inclusions

by Sandhya Vasudevan, Farnoush Forghani, Chris Campbell, Savannah Bedford and Thomas D. O’Sullivan

Appl. Sci. 2020, 10(4), 1419; https://doi.org/10.3390/app10041419 - 20 Feb 2020

Cited by 9 | Viewed by 2450

Abstract

A hybrid reflectance-based diffuse optical imaging (DOI) technique combining discrete wavelength frequency-domain (FD) near-infrared spectroscopy (NIRS) with broadband continuous wave NIRS measurements was developed to quantify the broadband optical properties of deep tumor-like inclusions. This method was developed to more accurately measure the [...] Read more.

A hybrid reflectance-based diffuse optical imaging (DOI) technique combining discrete wavelength frequency-domain (FD) near-infrared spectroscopy (NIRS) with broadband continuous wave NIRS measurements was developed to quantify the broadband optical properties of deep tumor-like inclusions. This method was developed to more accurately measure the broadband optical properties of human tumors using a compact handheld imaging probe and without requiring a priori spectral constraints. We simulated the reconstruction of absorption and scattering spectra (650–1000 nm) of human breast tumors in a homogeneous background at depths of 0 to 10 mm. The hybrid DOI technique demonstrated enhanced performance in reconstruction of optical absorption with a mean accuracy over all 71 wavelengths of 8.39% versus 32.26% for a 10 mm deep tumor with the topographic DOI method. The new hybrid technique was also tested and validated on two heterogeneous tissue-simulating phantoms with inclusion depths of 2, 7, and 9 mm. The mean optical absorption accuracy over all wavelengths was similarly improved up to 5x for the hybrid DOI method versus topographic DOI for the deepest inclusions. Full article

(This article belongs to the Special Issue Diffuse Optical Spectroscopy: Advances Towards Widespread Applications)

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14 pages, 6547 KiB

Open AccessArticle

Imaging System Based on Silicon Photomultipliers and Light Emitting Diodes for Functional Near-Infrared Spectroscopy

by Giovanni Maira, Antonio M. Chiarelli, Stefano Brafa, Sebania Libertino, Giorgio Fallica, Arcangelo Merla and Salvatore Lombardo

Appl. Sci. 2020, 10(3), 1068; https://doi.org/10.3390/app10031068 - 05 Feb 2020

Cited by 9 | Viewed by 2571

Abstract

We built a fiber-less prototype of an optical system with 156 channels each one consisting of an optode made of a silicon photomultiplier (SiPM) and a pair of light emitting diodes (LEDs) operating at 700 nm and 830 nm. The system uses functional [...] Read more.

We built a fiber-less prototype of an optical system with 156 channels each one consisting of an optode made of a silicon photomultiplier (SiPM) and a pair of light emitting diodes (LEDs) operating at 700 nm and 830 nm. The system uses functional near-infrared spectroscopy (fNIRS) and diffuse optical tomography (DOT) imaging of the cortical activity of the human brain at frequencies above 1 Hz. In this paper, we discuss testing and system optimization performed through measurements on a multi-layered optical phantom with mechanically movable parts that simulate near-infrared light scattering inhomogeneities. The baseline optical characteristics of the phantom are carefully characterized and compared to those of human tissues. Here we discuss several technical aspects of the system development, such as LED light output drift and its possible compensation, SiPM linearity, corrections of channel signal differences, and signal-to-noise ratio (SNR). We implement an imaging algorithm that investigates large phantom regions. Thanks to the use of SiPMs, very large source-to-detector distances are acquired with a high SNR and 2 Hz time resolution. The overall results demonstrate the high potentialities of a system based on SiPMs for fNIRS/DOT human brain imaging applications. Full article

(This article belongs to the Special Issue Diffuse Optical Spectroscopy: Advances Towards Widespread Applications)

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15 pages, 2265 KiB

Open AccessArticle

Determining Whether Tennis Benefits the Updating Function in Young Children: A Functional Near-Infrared Spectroscopy Study

by Yinghui Lai, Zhipeng Wang, Guang H. Yue and Changhao Jiang

Appl. Sci. 2020, 10(1), 407; https://doi.org/10.3390/app10010407 - 06 Jan 2020

Cited by 13 | Viewed by 2949

Abstract

This study aimed at investigating the behavioral and neuro-electrical impacts of a coordinative exercise intervention on the updating function of the working memory (WM) in young children. Children in the experimental group was tested on the 1-back working memory task before and after [...] Read more.

This study aimed at investigating the behavioral and neuro-electrical impacts of a coordinative exercise intervention on the updating function of the working memory (WM) in young children. Children in the experimental group was tested on the 1-back working memory task before and after a coordinative exercise program that involved a 60 min session twice per week for eight weeks (totally 16 sessions), while the control group underwent routine classroom activities with the same WM tests. The results showed that the hit rates of performing the 1-back task increased significantly in the experimental group compared with that of the control group. The experimental group demonstrated a larger decrease in both reaction time and false alarm rates from pre-test to post-test than the control group. Physical fitness improved after exercise intervention in the experimental group. Neural adaptations due to the exercise training were evaluated using functional near-infrared spectroscopy (fNIRS) and the results indicated that the experimental group experienced a greater cortical oxygenated hemoglobin (Oxy-Hb) increase in the prefrontal area after the intervention than the control group. These results suggest that coordinative exercises are beneficial for improving WM as well as reaction time and physical fitness in young children. Full article

(This article belongs to the Special Issue Diffuse Optical Spectroscopy: Advances Towards Widespread Applications)

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36 pages, 10898 KiB

Open AccessArticle

Absorption and Remission Characterization of Pure, Dielectric (Nano-)Powders Using Diffuse Reflectance Spectroscopy: An End-To-End Instruction

by Sergej Bock, Christian Kijatkin, Dirk Berben and Mirco Imlau

Appl. Sci. 2019, 9(22), 4933; https://doi.org/10.3390/app9224933 - 16 Nov 2019

Cited by 36 | Viewed by 8134

Abstract

This paper addresses the challenging task of optical characterization of pure, dielectric (nano-)powders with the aim to provide an end-to-end instruction from appropriate sample preparation up to the determination of material remission and absorption spectra. We succeeded in establishing an innovative preparation procedure [...] Read more.

This paper addresses the challenging task of optical characterization of pure, dielectric (nano-)powders with the aim to provide an end-to-end instruction from appropriate sample preparation up to the determination of material remission and absorption spectra. We succeeded in establishing an innovative preparation procedure to reproducibly obtain powder pellet samples with an ideal Lambertian scattering behavior. As a result, a procedure based on diffuse reflectance spectroscopy was developed that allows for (i) performing reproducible and artifact-free, high-quality measurements as well as (ii) a thorough optical analysis using Monte Carlo and Mie scattering simulations yielding the absorption spectrum in the visible spectral range. The procedure is valid for the particular case of powders that can be compressed into thick, non-translucent pellets and neither requires embedding of the dielectric (nano-)powders within an appropriate host matrix for measurements nor the use of integrating spheres. The reduced spectroscopic procedure minimizes the large number of sources for errors, enables an in-depth understanding of non-avoidable artifacts and is of particular advantage in the field of material sciences, i.e., for getting first insights to the optical features of a newly synthesized, pure dielectric powder, but also as an inline inspection tool for massively parallelised material characterization. Full article

(This article belongs to the Special Issue Diffuse Optical Spectroscopy: Advances Towards Widespread Applications)

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21 pages, 6949 KiB

Open AccessArticle

Diffuse Correlation Spectroscopy at Short Source-Detector Separations: Simulations, Experiments and Theoretical Modeling

by Karthik Vishwanath and Sara Zanfardino

Appl. Sci. 2019, 9(15), 3047; https://doi.org/10.3390/app9153047 - 28 Jul 2019

Cited by 5 | Viewed by 3738

Abstract

Diffuse correlation spectroscopy (DCS) has widely been used as a non-invasive optical technique to measure tissue perfusion in vivo. DCS measurements are quantified to yield information about moving scatterers using photon diffusion theory and are therefore obtained at long source-detector separations (SDS). However, [...] Read more.

Diffuse correlation spectroscopy (DCS) has widely been used as a non-invasive optical technique to measure tissue perfusion in vivo. DCS measurements are quantified to yield information about moving scatterers using photon diffusion theory and are therefore obtained at long source-detector separations (SDS). However, short SDS DCS could be used for measuring perfusion in small animal models or endoscopically in clinical studies. Here, we investigate the errors in analytically retrieved flow coefficients from simulated and experimental data acquired at short SDS. Monte Carlo (MC) simulations of photon correlation transport was programmed to simulate DCS measurements and used to (a) examine the accuracy and validity of theoretical analyses, and (b) model experimental measurements made on phantoms at short SDS. Experiments consisted of measurements from a series of optical phantoms containing an embedded flow channel. Both the fluid flow rate and depth of the flow channel from the liquid surface were varied. Inputs to MC simulations required to model experiments were obtained from corrected theoretical analyses. Results show that the widely used theoretical DCS model is robust for quantifying relative changes in flow. We also show that retrieved flow coefficients at short SDS can be scaled to retrieve absolute values via MC simulations. Full article

(This article belongs to the Special Issue Diffuse Optical Spectroscopy: Advances Towards Widespread Applications)

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15 pages, 4348 KiB

Open AccessArticle

Multi Simulation Platform for Time Domain Diffuse Optical Tomography: An Application to a Compact Hand-Held Reflectance Probe

by Edoardo Ferocino, Antonio Pifferi, Simon Arridge, Fabrizio Martelli, Paola Taroni and Andrea Farina

Appl. Sci. 2019, 9(14), 2849; https://doi.org/10.3390/app9142849 - 17 Jul 2019

Cited by 4 | Viewed by 2539

Abstract

Time Domain Diffuse Optical Tomography (TD-DOT) enables a full 3D reconstruction of the optical properties of tissue, and could be used for non-invasive and cost-effective in-depth body exploration (e.g., thyroid and breast imaging). Performance quantification is crucial for comparing results coming from different [...] Read more.

Time Domain Diffuse Optical Tomography (TD-DOT) enables a full 3D reconstruction of the optical properties of tissue, and could be used for non-invasive and cost-effective in-depth body exploration (e.g., thyroid and breast imaging). Performance quantification is crucial for comparing results coming from different implementations of this technique. A general-purpose simulation platform for TD-DOT clinical systems was developed with a focus on performance assessment through meaningful figures of merit. The platform was employed for assessing the feasibility and characterizing a compact hand-held probe for breast imaging and characterization in reflectance geometry. Important parameters such as hardware gating of the detector, photon count rate and inclusion position were investigated. Results indicate a reduced error (<10%) on the absorption coefficient quantification of a simulated inclusion up to 2-cm depth if a photon count rate ≥ 10⁶ counts per second is used along with a good localization (error < 1 mm down to 25 mm-depth). Full article

(This article belongs to the Special Issue Diffuse Optical Spectroscopy: Advances Towards Widespread Applications)

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16 pages, 4670 KiB

Open AccessArticle

Hyper-spectral Recovery of Cerebral and Extra-Cerebral Tissue Properties Using Continuous Wave Near-Infrared Spectroscopic Data

by Joshua Deepak Veesa and Hamid Dehghani

Appl. Sci. 2019, 9(14), 2836; https://doi.org/10.3390/app9142836 - 16 Jul 2019

Cited by 7 | Viewed by 2181

Abstract

Near-infrared spectroscopy (NIRS) is widely used as a non-invasive method to monitor the hemodynamics of biological tissue. A common approach of NIRS relies on continuous wave (CW) methodology, i.e. utilizing intensity-only measurements, and, in general, assumes homogeneity in the optical properties of the [...] Read more.

Near-infrared spectroscopy (NIRS) is widely used as a non-invasive method to monitor the hemodynamics of biological tissue. A common approach of NIRS relies on continuous wave (CW) methodology, i.e. utilizing intensity-only measurements, and, in general, assumes homogeneity in the optical properties of the biological tissue. However, in monitoring cerebral hemodynamics within humans, this assumption is not valid due to complex layered structure of the head. The NIRS signal that contains information about cerebral blood hemoglobin levels is also contaminated with extra-cerebral tissue hemodynamics, and any recovery method based on such a priori homogenous approximation would lead to erroneous results. In this work, utilization of hyper-spectral intensity only measurements (i.e., CW) at multiple distances are presented and are shown to recover two-layered tissue properties along with the thickness of top layer, using an analytical solution for a two-layered semi-infinite geometry. It is demonstrated that the recovery of tissue oxygenation index (TOI) of both layers can be achieved with an error of 4.4%, with the recovered tissue thickness of 4% error. When the data is measured on a complex tissue such as the human head, it is shown that the semi-infinite recovery model can lead to uncertain results, whereas, when using an appropriate model accounting for the tissue-boundary structure, the tissue oxygenation levels are recovered with an error of 4.2%, and the extra-cerebral tissue thickness with an error of 11.8%. The algorithm is finally used together with human subject data, demonstrating robustness in application and repeatability in the recovered parameters that adhere well to expected published parameters. Full article

(This article belongs to the Special Issue Diffuse Optical Spectroscopy: Advances Towards Widespread Applications)

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15 pages, 1592 KiB

Open AccessArticle

Cultivar Classification of Single Sweet Corn Seed Using Fourier Transform Near-Infrared Spectroscopy Combined with Discriminant Analysis

by Guangjun Qiu, Enli Lü, Ning Wang, Huazhong Lu, Feiren Wang and Fanguo Zeng

Appl. Sci. 2019, 9(8), 1530; https://doi.org/10.3390/app9081530 - 12 Apr 2019

Cited by 35 | Viewed by 3957

Abstract

Seed purity is a key indicator of crop seed quality. The conventional methods for cultivar identification are time-consuming, expensive, and destructive. Fourier transform near-infrared (FT-NIR) spectroscopy combined with discriminant analyses, was studied as a rapid and nondestructive technique to classify the cultivars of [...] Read more.

Seed purity is a key indicator of crop seed quality. The conventional methods for cultivar identification are time-consuming, expensive, and destructive. Fourier transform near-infrared (FT-NIR) spectroscopy combined with discriminant analyses, was studied as a rapid and nondestructive technique to classify the cultivars of sweet corn seeds. Spectra with a range of 1000–2500 nm collected from 760 seeds of two cultivars were used for the discriminant analyses. Thereafter, 126 feature wavelengths were identified from 1557 wavelengths using a genetic algorithm (GA) to build simplified classification models. Four classification algorithms, namely K-nearest neighbor (KNN), soft independent method of class analogy (SIMCA), partial least-squares discriminant analysis (PLS-DA), and support vector machine discriminant analysis (SVM-DA) were tested on full-range wavelengths and feature wavelengths, respectively. With the full-range wavelengths, all four algorithms achieved a high classification accuracy range from 97.56% to 99.59%, and the SVM-DA worked better than other models. From the feature wavelengths, no significant decline in accuracies was observed in most of the models and a high accuracy of 99.19% was still obtained by the PLS-DA model. This study demonstrated that using the FT-NIR technique with discriminant analyses could be a feasible way to classify sweet corn seed cultivars and the proper classification model could be embedded in seed sorting machinery to select high-purity seeds. Full article

(This article belongs to the Special Issue Diffuse Optical Spectroscopy: Advances Towards Widespread Applications)

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Review

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30 pages, 7685 KiB

Open AccessReview

Time-Gated Single-Photon Detection in Time-Domain Diffuse Optics: A Review

by Alberto Dalla Mora, Laura Di Sieno, Rebecca Re, Antonio Pifferi and Davide Contini

Appl. Sci. 2020, 10(3), 1101; https://doi.org/10.3390/app10031101 - 06 Feb 2020

Cited by 20 | Viewed by 6114

Abstract

This work reviews physical concepts, technologies and applications of time-domain diffuse optics based on time-gated single-photon detection. This particular photon detection strategy is of the utmost importance in the diffuse optics field as it unleashes the full power of the time-domain approach by [...] Read more.

This work reviews physical concepts, technologies and applications of time-domain diffuse optics based on time-gated single-photon detection. This particular photon detection strategy is of the utmost importance in the diffuse optics field as it unleashes the full power of the time-domain approach by maximizing performances in terms of contrast produced by a localized perturbation inside the scattering medium, signal-to-noise ratio, measurement time and dynamic range, penetration depth and spatial resolution. The review covers 15 years of theoretical studies, technological progresses, proof of concepts and design of laboratory systems based on time-gated single-photon detection with also few hints on other fields where the time-gated detection strategy produced and will produce further impact. Full article

(This article belongs to the Special Issue Diffuse Optical Spectroscopy: Advances Towards Widespread Applications)

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38 pages, 10414 KiB

Open AccessFeature PaperReview

Broadband Time Domain Diffuse Optical Reflectance Spectroscopy: A Review of Systems, Methods, and Applications

by Sanathana Konugolu Venkata Sekar, Pranav Lanka, Andrea Farina, Alberto Dalla Mora, Stefan Andersson-Engels, Paola Taroni and Antonio Pifferi

Appl. Sci. 2019, 9(24), 5465; https://doi.org/10.3390/app9245465 - 12 Dec 2019

Cited by 19 | Viewed by 4788

Abstract

This review presents recent developments and a wide overview of broadband time domain diffuse optical spectroscopy (TD-DOS). Various topics including physics of photon migration, advanced instrumentation, methods of analysis, applications covering multiple domains (tissue chromophore, in vivo studies, food, wood, pharmaceutical industry) are [...] Read more.

This review presents recent developments and a wide overview of broadband time domain diffuse optical spectroscopy (TD-DOS). Various topics including physics of photon migration, advanced instrumentation, methods of analysis, applications covering multiple domains (tissue chromophore, in vivo studies, food, wood, pharmaceutical industry) are elaborated. The key role of standardization and recent studies in that direction are discussed. Towards the end, a brief outlook is presented on the current status and future trends in broadband TD-DOS. Full article

(This article belongs to the Special Issue Diffuse Optical Spectroscopy: Advances Towards Widespread Applications)

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