This review describes the diffusion model for light transport in tissues and the medical applications of diffuse light. Diffuse optics is particularly useful for measurement of tissue hemodynamics, wherein quantitative assessment of oxy- and deoxy-hemoglobin concentrations and blood flow are desired. The theoretical basis for near-infrared or diffuse optical spectroscopy is developed, and the basic elements of diffuse optical tomography are outlined. We also discuss diffuse correlation spectroscopy, a technique whereby temporal correlation functions of diffusing light are transported through tissue and are used to measure blood flow. Essential instrumentation is described, and representative brain and breast functional imaging and monitoring results illustrate the workings of these new tissue diagnostics.

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Diffuse optics for tissue monitoring and tomography

This review celebrates the 30th anniversary of the first in vivo near-infrared (NIR) spectroscopy (NIRS) publication, which was authored by Professor Frans Jobsis. At first, NIRS was utilized to experimentally and clinically investigate cerebral oxygenation. Later it was applied to study muscle oxidative metabolism. Since 1993, the discovery that the functional activation of the human cerebral cortex can be explored by NIRS has added a new dimension to the research. To obtain simultaneous multiple and localized information, a further major step forward was achieved by introducing NIR imaging (NIRI) and tomography. This review reports on the progress of the NIRS and NIRI instrumentation for brain and muscle clinical applications 30 years after the discovery of in vivo NIRS. The review summarizes the measurable parameters in relation to the different techniques, the main characteristics of the prototypes under development, and the present commercially available NIRS and NIRI instrumentation. Moreover, it discusses strengths and limitations and gives an outlook into the "bright" future.

https://www.spiedigitallibrary.org/journals/Journal-of-Biomedical-Optics/volume-12/issue-06/062104/Progress-of-near-infrared-spectroscopy-and-topography-for-brain-and/10.1117/1.2804899.pdf

Progress of near-infrared spectroscopy and topography for brain and muscle clinical applications

Near-Infrared Spectroscopy NIRS and diffuse optical im- aging DOI are increasingly used to detect hemodynamic changes in the cerebral cortex induced by brain activity. Until recently, the small number of optodes in NIRS instruments has hampered measurement of optical signals from diverse brain regions. Our new DOI system has 32 detectors and 32 sources; by arranging them in a specific pattern, we can cover most of the adult head. With the increased number of optodes, we can collect optical data from prefrontal, sensorimotor, and visual cortices in both hemispheres simultaneously. We describe the system and report system characterization measurements on phan- toms as well as on human subjects at rest and during visual, motor, and cognitive stimulation. Taking advantage of the system's larger number of sources and detectors, we explored the spatiotemporal pat- terns of physiological signals during rest. These physiological signals, arising from cardiac, respiratory, and blood-pressure modulations, in- terfere with measurement of the hemodynamic response to brain stimulation. Whole-head optical measurements, in addition to provid- ing maps of multiple brain regions' responses to brain activation, will enable better understandings of the physiological signals, ultimately leading to better signal processing algorithms to distinguish physi- ological signal clutter from brain activation signals. © 2006 Society of

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Diffuse optical imaging of the whole head.

We present a regularized Gauss-Newton method for solving the inverse problem of parameter reconstruction from boundary data in frequency-domain diffuse optical tomography. To avoid the explicit formation and inversion of the Hessian which is often prohibitively expensive in terms of memory resources and runtime for large-scale problems, we propose to solve the normal equation at each Newton step by means of an iterative Krylov method, which accesses the Hessian only in the form of matrix-vector products. This allows us to represent the Hessian implicitly by the Jacobian and regularization term. Further we introduce transformation strategies for data and parameter space to improve the reconstruction performance. We present simultaneous reconstructions of absorption and scattering distributions using this method for a simulated test case and experimental phantom data.

https://iopscience.iop.org/article/10.1088/0031-9155/50/10/013/pdf

Gauss-Newton method for image reconstruction in diffuse optical tomography

We used near-infrared spectroscopy (NIRS) to study responses to speech and music on the auditory cortices of 13 healthy full-term newborn infants during natural sleep. The purpose of the study was to investigate the lateralization of speech and music responses at this stage of development. NIRS data was recorded from eight positions on both hemispheres simultaneously with electroencephalography, electrooculography, electrocardiography, pulse oximetry, and inclinometry. In 11 subjects, statistically significant (P < 0.02) oxygenated (HbO2) and total hemoglobin (HbT) responses were recorded. Both stimulus types elicited significant HbO2 and HbT responses on both hemispheres in five subjects. Six of the 11 subjects had positive HbO2 and HbT responses to both stimulus types, whereas one subject had negative responses. Mixed positive and negative responses were observed in four neonates. On both hemispheres, speech and music responses were significantly correlated (r = 0.64; P = 0.018 on the left hemisphere (LH) and r = 0.60; P = 0.029 on the right hemisphere (RH)). On the group level, the average response to the speech stimuli was statistically significantly greater than zero in the LH, whereas responses on the RH or to the music stimuli did not differ significantly from zero. This suggests a more coherent response to speech on the LH. However, significant differences in lateralization of the responses or mean response amplitudes of the two stimulus types were not observed on the group level.

/pdf/hemodynamic-responses-to-speech-and-music-in-newborn-infants-1dttxwfq9v.pdf

Hemodynamic responses to speech and music in newborn infants

In this article, we describe the multichannel implementation of an intensity modulated optical tomography system developed at Helsinki University of Technology. The system has two time-multiplexed wavelengths, 16 time-multiplexed source fibers and 16 parallel detection channels. The gain of the photomultiplier tubes (PMTs) is individually adjusted during the measurement sequence to increase the dynamic range of the system by 104. The PMT used has a high quantum efficiency in the near infrared (8% at 800nm), a fast settling time, and low hysteresis. The gain of the PMT is set so that the dc anode current is below 80nA, which allows the measurement of phase independently of the intensity. The system allows measurements of amplitude at detected intensities down to 1fW, which is sufficient for transmittance measurements of the female breast, the forearm, and the brain of early pre-term infants. The mean repeatability of phase and the logarithm of amplitude (lnA) at 100MHz were found to be 0.08° and 0.004, res...

Toivo Katila

Papers

Instrumentation and calibration methods for the multichannel measurement of phase and amplitude in optical tomography