Probe for evaluating the absorbing and transport scattering properties of turbid fluids using low-cost time-of-flight technology

A probe is described that when immersed into a highly scattering fluid provides a measurement of its scattering and absorbing properties at a single optical wavelength. It uses recently available low-cost proximity sensor modules to estimate the mean flight times of photons diffusely transmitted between near-infrared sources and detectors at two different separations. The probe has been designed with a specific application for enabling the rapid and efficient production of fluids, which mimic the optical properties of biological tissues. The potential of the device is demonstrated using precalibrated solutions of intralipid, an intravenous nutrient, and absorbing dye. It is shown that a combination of time-of-flight measurements at two source–detector separations can uniquely specify the absorption coefficient and the transport scattering coefficient

Derivation of chromophore concentrations in turbid media using the rate of change of optical attenuation with respect to wavelength

A spectroscopic method is investigated for estimating the concentrations of absorbers in highly scattering media using measurements of the rate of change of optical attenuation with wavelength. Such measurements are independent of absolute intensity and thus may be significantly less influenced by changes in coupling which often cause artefacts in medical applications of near-infrared spectroscopy. The method has been explored using a combination of stochastic (Monte Carlo) and analytical (diffusion-based) models and experiments on samples of turbid fluids. Results suggest that the method is highly tolerant of changes in the measurement geometry. The accuracy of the derived concentrations of absorbers can be strongly influenced by the wavelength dependence of scattering, and an ad-hoc, empirically-derived correction for this dependency has been investigated and implemented with some success

A spread spectrum approach to time-domain near-infrared diffuse optical imaging using inexpensive optical transceiver modules

We introduce a compact time-domain system for near-infrared spectroscopy using a spread spectrum technique. The proof-of-concept single channel instrument utilises a low-cost commercially available optical transceiver module as a light source, controlled by a Kintex 7 field programmable gate array (FPGA). The FPGA modulates the optical transceiver with maximum-length sequences at line rates up to 10Gb/s, allowing us to achieve an instrument response function with full width at half maximum under 600ps. The instrument is characterised through a set of detailed phantom measurements as well as proof-of-concept in vivo measurements, demonstrating performance comparable with conventional pulsed time-domain near-infrared spectroscopy systems

Sleep State Modulates Resting-State Functional Connectivity in Neonates.

The spontaneous cerebral activity that gives rise to resting-state networks (RSNs) has been extensively studied in infants in recent years. However, the influence of sleep state on the presence of observable RSNs has yet to be formally investigated in the infant population, despite evidence that sleep modulates resting-state functional connectivity in adults. This effect could be extremely important, as most infant neuroimaging studies rely on the neonate to remain asleep throughout data acquisition. In this study, we combine functional near-infrared spectroscopy with electroencephalography to simultaneously monitor sleep state and investigate RSNs in a cohort of healthy term born neonates. During active sleep (AS) and quiet sleep (QS) our newborn neonates show functional connectivity patterns spatially consistent with previously reported RSN structures. Our three independent functional connectivity analyses revealed stronger interhemispheric connectivity during AS than during QS. In turn, within hemisphere short-range functional connectivity seems to be enhanced during QS. These findings underline the importance of sleep state monitoring in the investigation of RSNs

Assessment of an in situ temporal calibration method for time-resolved optical tomography

A 32-channel time-resolved optical imaging device is de- veloped at University College London to produce functional images of the neonatal brain and the female breast. Reconstruction of images using time-resolved measurements of transmitted light requires careful calibration of the temporal characteristics of the measurement system. Since they can often vary over a period of time, it is desirable to evaluate these characteristics immediately after, or prior to, the acqui- sition of image data. A calibration technique is investigated that is based on the measurement of light back-reflected from the surface of the object being imaged. This is facilitated by coupling each detector channel with an individual source fiber. A Monte Carlo model is em- ployed to investigate the influence of the optical properties of the object on the back-reflected signal. The results of simulations indicate that their influence may be small enough to be ignored in some cases, or could be largely accounted for by a small adjustment to the cali- brated data. The effectiveness of the method is briefly demonstrated by imaging a solid object with tissue-equivalent optical properties

Mapping cortical haemodynamics during neonatal seizures using diffuse optical tomography: A case study

AbstractSeizures in the newborn brain represent a major challenge to neonatal medicine. Neonatal seizures are poorly classified, under-diagnosed, difficult to treat and are associated with poor neurodevelopmental outcome. Video-EEG is the current gold-standard approach for seizure detection and monitoring. Interpreting neonatal EEG requires expertise and the impact of seizures on the developing brain remains poorly understood. In this case study we present the first ever images of the haemodynamic impact of seizures on the human infant brain, obtained using simultaneous diffuse optical tomography (DOT) and video-EEG with whole-scalp coverage. Seven discrete periods of ictal electrographic activity were observed during a 60 minute recording of an infant with hypoxic–ischaemic encephalopathy. The resulting DOT images show a remarkably consistent, high-amplitude, biphasic pattern of changes in cortical blood volume and oxygenation in response to each electrographic event. While there is spatial variation across the cortex, the dominant haemodynamic response to seizure activity consists of an initial increase in cortical blood volume prior to a large and extended decrease typically lasting several minutes. This case study demonstrates the wealth of physiologically and clinically relevant information that DOT–EEG techniques can yield. The consistency and scale of the haemodynamic responses observed here also suggest that DOT–EEG has the potential to provide improved detection of neonatal seizures

Dual wavelength spread-spectrum time-resolved diffuse optical instrument for the measurement of human brain functional responses

Near-infrared spectroscopy has proven to be a valuable method to monitor tissue oxygenation and haemodynamics non-invasively and in real-time. Quantification of such parameters requires measurements of the time-of-flight of light through tissue, typically achieved using picosecond pulsed lasers, with their associated cost, complexity, and size. In this work, we present an alternative approach that employs spread-spectrum excitation to enable the development of a small, low-cost, dual-wavelength system using vertical-cavity surface-emitting lasers. Since the optimal wavelengths and drive parameters for optical spectroscopy are not served by commercially available modules as used in our previous single-wavelength demonstration platform, we detail the design of a custom instrument and demonstrate its performance in resolving haemodynamic changes in human subjects during apnoea and cognitive task experiments

Performance assessment of time-domain optical brain imagers, part 1: basic instrumental performance protocol

open21siAbstract.  Performance assessment of instruments devised for clinical applications is of key importance for validation and quality assurance. Two new protocols were developed and applied to facilitate the design and optimization of instruments for time-domain optical brain imaging within the European project nEUROPt. Here, we present the “Basic Instrumental Performance” protocol for direct measurement of relevant characteristics. Two tests are discussed in detail. First, the responsivity of the detection system is a measure of the overall efficiency to detect light emerging from tissue. For the related test, dedicated solid slab phantoms were developed and quantitatively spectrally characterized to provide sources of known radiance with nearly Lambertian angular characteristics. The responsivity of four time-domain optical brain imagers was found to be of the order of 0.1  m2 sr. The relevance of the responsivity measure is demonstrated by simulations of diffuse reflectance as a function of source-detector separation and optical properties. Second, the temporal instrument response function (IRF) is a critically important factor in determining the performance of time-domain systems. Measurements of the IRF for various instruments were combined with simulations to illustrate the impact of the width and shape of the IRF on contrast for a deep absorption change mimicking brain activation.H. Wabnitz; D. R. Taubert; M. Mazurenka; O. Steinkellner; A. Jelzow;R. Macdonald;D. Milej;P. Sawosz;M. Kacprzak;A. Liebert;R. Cooper;J. Hebden;A. Pifferi;A. Farina;I. Bargigia;D. Contini;M. Caffini;L. Zucchelli;L. Spinelli;R. Cubeddu;A. TorricelliH., Wabnitz; D. R., Taubert; M., Mazurenka; O., Steinkellner; A., Jelzow; R., Macdonald; D., Milej; P., Sawosz; M., Kacprzak; A., Liebert; R., Cooper; J., Hebden; Pifferi, ANTONIO GIOVANNI; Farina, Andrea; Bargigia, Ilaria; Contini, Davide; Caffini, Matteo; Zucchelli, LUCIA MARIA GRAZIA; Spinelli, Lorenzo; Cubeddu, Rinaldo; Torricelli, Alessandr

Correction to: Cluster identification, selection, and description in Cluster randomized crossover trials: the PREP-IT trials

An amendment to this paper has been published and can be accessed via the original article