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Papers - Okada, Eiji

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Monte Carlo modeling of photoacoustic guided technique in scattering media

Arisu J., Yamamura N., Nakagawa K., Takagi S., Okada E.

Proceedings of SPIE - The International Society for Optical Engineering 12628 2023

ISSN 0277786X

The photoacoustic guided (PAG) technique can noninvasively increase light penetration and localization in deep tissue. The mechanism of the PAG technique is considered to be a pressure dependent refractive index change caused by acoustic wave that produces a virtual waveguide, but it is still a highly controversial issue. In this study, light propagation in the models with the PAG region was calculated by a Monte Carlo simulation. We assumed that the change in the refractive index or anisotropy factor of scattering in the PAG region contributes to the light guiding effect. Both the refractive index and anisotropy factor heterogeneities increase the photon density in the PAG region of the deep tissue part. The effect of localization of the photon density in the PAG region with the anisotropy factor heterogeneity is less significant compared to that with the refractive index heterogeneity.

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Influence of the heterogeneity of extracerebral tissues on scalp-cortex correlation of fNIRS for infants

Tachikawa R., Okada E.

Proceedings of SPIE - The International Society for Optical Engineering 12628 2023

ISSN 0277786X

For the prediction of the scalp-cortex correlation (SCC), it is important to consider the influence of the extracerebral tissues on light propagation in the brain. The three-layered infant head models in which the scalp, skull, and cerebrospinal fluid (CSF) are combined as a homogeneous tissue are constructed in order to investigate the influence of the heterogeneity of the thin extracerebral tissues on the prediction of the SCC of infants. The spatial sensitivity profile in the brain calculated by the three-layered model is less broadened than that by the ordinary five-layered model due to the lack of the low scattering CSF layer. However, the influence of the heterogeneity of the extracerebral tissues on the SCC of infants is less significant than that of an adult. The three-layered head model is practically useful to predict the acceptable SCC of the functional near infrared spectroscopy measurements of infants.

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3D-printed head surface model of a standard brain template for scalp-cortex correlation of fNIRS

Kaneko T., Okada E.

Proceedings of SPIE - The International Society for Optical Engineering 12608 2023

ISSN 0277786X

The scalp-cortex correlation (SCC) is important for the brain activity measurements by functional near-infrared spectroscopy. A physical head surface model was manufactured to accurately determine the probe positions mounted on the probe holder attached to the head. The coordinates of the probe positions measured in the physical space were mapped to the surface of the virtual head model. The light propagation in the virtual head model was calculated to obtain the spatial sensitivity profile and normalized partial optical path length for the evaluation of the SCC.

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Monte Carlo simulation of photon transport in a scattering-dominated medium with a refractive index gradient for acoustic light-guiding

YAMAMURA N. A. O. T. O., OKADA E. I. J. I., NAKAGAWA K. E. I. I. C. H. I., TAKAGI S. H. U.

OPTICS CONTINUUM 1 ( 4 ) 846 - 859 2022.04

Acoustic light waveguides use a technology that employs acoustic waves to create pressure-dependent refractive index distribution and guide light deep into biological tissue similar to an optical fiber. The method by which acoustic optical waveguides increase light transmission in biological tissues occurring inside scattering-dominated medium has not been clarified. To understand the phenomena occurring inside the scattering-dominated medium, we performed Monte Carlo simulations of photon transport in acoustic optical waveguides. The findings indicate that the larger the change in the refractive index in the scattering-dominated media, the greater the effect of photon confinement. In addition, as the refractive index gradient was increased, the near-field internal fluence was found to be greatly enhanced. The transition depth, which indicates the region where the internal fluence is enhanced by the refractive index gradient, was determined as a function of the radius at which the refractive index change is given.

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Targeting brain regions of interest in functional near-infrared spectroscopy—Scalp-cortex correlation using subject-specific light propagation models

Cai L., Nitta T., Yokota S., Obata T., Okada E., Kawaguchi H.

Human Brain Mapping (Human Brain Mapping) 42 ( 7 ) 1969 - 1986 2021.05

ISSN 10659471

Targeting specific brain regions of interest by the accurate positioning of optodes (emission and detection probes) on the scalp remains a challenge for functional near-infrared spectroscopy (fNIRS). Since fNIRS data does not provide any anatomical information on the brain cortex, establishing the scalp-cortex correlation (SCC) between emission-detection probe pairs on the scalp and the underlying brain regions in fNIRS measurements is extremely important. A conventional SCC is obtained by a geometrical point-to-point manner and ignores the effect of light scattering in the head tissue that occurs in actual fNIRS measurements. Here, we developed a sensitivity-based matching (SBM) method that incorporated the broad spatial sensitivity of the probe pair due to light scattering into the SCC for fNIRS. The SCC was analyzed between head surface fiducial points determined by the international 10–10 system and automated anatomical labeling brain regions for 45 subject-specific head models. The performance of the SBM method was compared with that of three conventional geometrical matching (GM) methods. We reveal that the light scattering and individual anatomical differences in the head affect the SCC, which indicates that the SBM method is compulsory to obtain the precise SCC. The SBM method enables us to evaluate the activity of cortical regions that are overlooked in the SCC obtained by conventional GM methods. Together, the SBM method could be a promising approach to guide fNIRS users in designing their probe arrangements and in explaining their measurement data.

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Experimental tests of indicators for the degree of validness of the diffusion approximation

Capart A., Ikegaya S., Okada E., Machida M., Hoshi Y.

Journal of Physics Communications (Journal of Physics Communications) 5 ( 2 ) 1 - 17 2021

ISSN 2399-6528

The diffusion approximation has been one of the central topics in near-infrared spectroscopy (NIRS). When NIRS measurements are analyzed by the diffusion theory, the measurements must be performed in the diffusive regime. However, since most of past researches have focused on theoretical or qualitative nature of the diffusion approximation, it is not easy to know if each measurement is designed in the diffusive regime. In this paper, we consider the diffusion approximation quantitatively and propose indicators that quantify the degree of validness of the diffusion approximation. The difference between the measurement and diffusion theory can be evaluated with the χ value, ℓ and ℓ norms, and Kullback-Leibler divergence. We conduct a liquid phantom experiment to test the proposed χ value. Moreover, the χ value is further investigated by Monte Carlo simulations. We find the χ value becomes significantly large when measurements are performed in the nondiffusive or transport regime. The proposed indicators similarly work. In particular, the χ value is shown to work as an indicator which evaluates the degree of validness of the diffusion approximation. These indicators are general and can be used for different numerical, experimental, and clinical measurements in NIRS. 2 1 2 2 2 2 2

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Correlating functional near-infrared spectroscopy with underlying cortical regions of 0-, 1-, and 2-year-olds using theoretical light propagation analysis

Cai Lin, Okada Eiji, Minagawa Yasuyo, Kawaguchi Hiroshi

NEUROPHOTONICS 8 ( 2 ) 025009 2021

ISSN 2329-423X

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Non-contact acquisition of brain function using a time-extracted compact camera

Ando T., Nakamura T., Fujii T., Shiono T., Nakamura T., Suzuki M., Anzue-Satoi N., Narumi K., Watanabe H., Korenaga T., Okada E., Inoue Y.

Scientific Reports (Scientific Reports) 9 ( 1 ) 17854 2019.12

ISSN 2045-2322

A revolution in functional brain imaging techniques is in progress in the field of neurosciences. Optical imaging techniques, such as high-density diffuse optical tomography (HD-DOT), in which source-detector pairs of probes are placed on subjects’ heads, provide better portability than conventional functional magnetic resonance imaging (fMRI) equipment. However, these techniques remain costly and can only acquire images at up to a few measurements per square centimetre, even when multiple detector probes are employed. In this study, we demonstrate functional brain imaging using a compact and affordable setup that employs nanosecond-order pulsed ordinary laser diodes and a time-extracted image sensor with superimposition capture of scattered components. Our technique can simply and easily attain a high density of measurement points without requiring probes to be attached, and can directly capture two-dimensional functional brain images. We have demonstrated brain activity imaging using a phantom that mimics the optical properties of an adult human head, and with a human subject, have measured cognitive brain activation while the subject is solving simple arithmetical tasks.

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In situ estimation of optical properties of rat and monkey brains using femtosecond time-resolved measurements

Hoshi Y., Tanikawa Y., Okada E., Kawaguchi H., Nemoto M., Shimizu K., Kodama T., Watanabe M.

Scientific Reports (Scientific Reports) 9 ( 1 ) 9165 2019.12

ISSN 2045-2322

An accurate knowledge of tissue optical properties (absorption coefficients, μ , and reduced scattering coefficients, μ ’) is critical for precise modeling of light propagation in biological tissue, essential for developing diagnostic and therapeutic optical techniques that utilize diffusive photons. A great number of studies have explored the optical properties of various tissue, and these values are not known in detail due to difficulties in the experimental determination and significant variations in tissue constitution. Especially, in situ estimates of the optical properties of brain tissue, a common measurement target in optical imaging, is a challenge because of its layer structure (where the thin gray matter covers the white matter). Here, we report an approach to in situ estimates of the μ and μ ’ of the gray and white matter in living rat and monkey brains by using femtosecond time-resolved measurements and Monte Carlo simulation. The results demonstrate that the μ of the gray matter is larger than that of the white matter, while there was no significant difference in the μ ’ between the gray and white matter. The optical properties of the rat brain were very similar to those of the monkey brain except for the μ of the gray matter here. a s a s a s a

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Time-domain diffuse optical tomography with l<inf>p</inf> sparsity regularization for thyroid cancer imaging

Okawa S., Mimura T., Fujii H., Kawaguchi H., Tanikawa Y., Machida M., Okada E., Hoshi Y.

Optics InfoBase Conference Papers (Optics InfoBase Conference Papers) Part F142-ECBO 2019 2019

ISSN 9781557528209

Diffuse optical tomography (DOT) images the distribution of the optical properties, such as the absorption and scattering coefficients, via the image reconstruction from the light intensities measured at the surface of the biological medium. The changes in the optical properties reflect the conditions of the tissues. Therefore, DOT image can provide the information which is not obtained from the other modalities and is useful for medical diagnoses. In this study, the application of the DOT to thyroid cancer diagnosis was investigated. The ultrasound technique is usually carried out for the thyroid cancer diagnosis. It is, however, difficult to distinguish follicular carcinoma from adenoma of thyroid. The optical properties may be helpful for the diagnosis. The image reconstruction algorithm employing the regularization minimizing l -norm (0 < p < 2) of the reconstructed image was developed. The image was reconstructed from the time-resolved measurement data. The numerical simulations of the image reconstruction were tried. The numerical simulation demonstrated that the developed algorithm was able to image the changes in the optical properties in the medium. Additionally, the image reconstruction of the numerical neck phantom was simulated. The thyroid cancer region was reconstructed successfully. It was demonstrated that the developed algorithm had the possibility to image thyroid cancer. p

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Time-domain diffuse optical tomography with l<inf>p</inf> sparsity regularization for thyroid cancer imaging

Okawa S., Mimura T., Fujii H., Kawaguchi H., Tanikawa Y., MacHida M., Okada E., Hoshi Y.

Progress in Biomedical Optics and Imaging - Proceedings of SPIE (Progress in Biomedical Optics and Imaging - Proceedings of SPIE) 11074 2019

ISSN 9781510628410

Diffuse optical tomography (DOT) images the distribution of the optical properties, such as the absorption and scattering coefficients, via the image reconstruction from the light intensities measured at the surface of the biological medium. The changes in the optical properties reflect the conditions of the tissues. Therefore, DOT image can provide the information which is not obtained from the other modalities and is useful for medical diagnoses. In this study, the application of the DOT to thyroid cancer diagnosis was investigated. The ultrasound technique is usually carried out for the thyroid cancer diagnosis. It is, however, difficult to distinguish follicular carcinoma from adenoma of thyroid. The optical properties may be helpful for the diagnosis. The image reconstruction algorithm employing the regularization minimizing l -norm (0 < p < 2) of the reconstructed image was developed. The image was reconstructed from the timeresolved measurement data. The numerical simulations of the image reconstruction were tried. The numerical simulation demonstrated that the developed algorithm was able to image the changes in the optical properties in the medium. Additionally, the image reconstruction of the numerical neck phantom was simulated. The thyroid cancer region was reconstructed successfully. It was demonstrated that the developed algorithm had the possibility to image thyroid cancer. p

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Theoretical analysis of hemodynamic signal from the scalp in time-gated NIRS imaging using null source-detector separation

Nakamura G., Okada E.

Optics InfoBase Conference Papers (Optics InfoBase Conference Papers) Part F142-ECBO 2019 2019

ISSN 9781557528209

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Theoretical analysis of hemodynamic signal from the scalp in time-gated NIRS imaging using null source-detector separation

Nakamura G., Okada E.

Progress in Biomedical Optics and Imaging - Proceedings of SPIE (Progress in Biomedical Optics and Imaging - Proceedings of SPIE) 11074 2019

ISSN 9781510628410

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Influence of optical path length on multi-wavelength measurement of oxy- And deoxy-hemoglobins in the skin

Shirai T., Okada E.

Optics InfoBase Conference Papers (Optics InfoBase Conference Papers) Part F142-ECBO 2019 2019

ISSN 9781557528209

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Influence of optical path length on multi-wavelength measurement of oxy- A nd deoxy-hemoglobins in the skin

Shirai T., Okada E.

Progress in Biomedical Optics and Imaging - Proceedings of SPIE (Progress in Biomedical Optics and Imaging - Proceedings of SPIE) 11074 2019

ISSN 9781510628410

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Ex vivo assessment of various histological differentiation in human carotid plaque with near-infrared spectroscopy using multiple wavelengths

Munemitsu T., Ishii A., Okada E., Chihara H., Yoshida K., Takahashi J.C., Takagi Y., Miyamoto S.

Neurologia Medico-Chirurgica (Neurologia Medico-Chirurgica) 59 ( 5 ) 163 - 171 2019

ISSN 04708105

We previously reported that near-infrared hyperspectral imaging enabled the localization of atherosclerotic plaques from outside the vessels, but not the optical characteristics of each histological component. Therefore, the near-infrared spectrum of each component was collected from the sliced section of the human carotid plaque obtained with endarterectomy and the optical characteristics were confirmed in several wavelengths. Based on this information, we assessed the diagnostic accuracy for ex vivo chemogram in each plaque component created with near-infrared spectroscopy (NIRS), using multiple wavelengths. The chemogram projected on the actual image of plaque was created based on light intensity and transmittance change at three wavelengths. The wavelengths that were mainly were 1440, 1620, 1730, and 1930 nm. We evaluated the accuracy of histological diagnosis in chemogram compared with pathological findings, analyzing interobserver agreement with k-statistics. The chemograms that we created depicted the components of fibrous tissue, smooth muscle, lipid tissue, intraplaque hemorrhage, and calcification. Diagnostic odds ratio in each component was as follows: 259.6 in fibrous tissue, 144 in smooth muscle, 1123.5 in lipid tissue, 29.3 in intraplaque hemorrhage, and 136.3 in calcification. The κ-statistics revealed that four components, excluding intraplaque hemorrhage, had substantial or almost perfect agreement. Thus, this study demonstrated the feasibility of using chemogram focused on specific component during the histological assessment of atherosclerotic plaques, highlighting its potential diagnostic ability. Chemograms of various target components can be created by combining multiple wavelengths. This technology may prove to be useful in improving the histological assessment of plaque using NIRS.

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Partial optical path length in the scalp in subject-specific head models for multi-distance probe configuration of near infrared spectroscopy

Yanagisawa T., Kawaguchi H., Obata T., Okada E.

Proceedings of SPIE - The International Society for Optical Engineering (Proceedings of SPIE - The International Society for Optical Engineering) 10711 2018

ISSN 9781510619791

© 2018 SPIE. In the brain function measurement by near infrared spectroscopy using a multi-distance probe configuration, the ratio of the partial optical path length in the scalp for the long spacing probe pair to that for the short spacing probe pair is important for the calculation to eliminate the scalp component in the signal. Light propagation in the subject specific head models of 45 volunteers was calculated to predict the dependence of the partial optical path length in the scalp and the weighting factor for the multi-distance probe configuration. The weighting factor ranges from 1.0 to 2.3 and increases with the scalp thickness when the scalp thickness is less than 15 mm.

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Measurement of head phantom by functional near infrared imaging using multi-distance probe configuration

Hayabusa K., Okada E.

Proceedings of SPIE - The International Society for Optical Engineering (Proceedings of SPIE - The International Society for Optical Engineering) 10711 2018

ISSN 9781510619791

© 2018 SPIE. The contamination of the signal corresponding to the blood volume change in the scalp is one of the serious problems in functional near infrared imaging and the multi-distance probe configuration has been used to reduce the contamination of the scalp signal. The head phantom mimicking the local absorption change in the gray matter and global absorption change in the scalp was measured by a functional near infrared spectroscopy system using the multi-distance probe configuration to obtain the topographic image of the absorption change in the phantom. The measurement using the multi-distance probe configuration can effectively reduce the contamination of the scalp signal during the functional near infrared imaging.

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Evaluation of improvement of diffuse optical imaging of brain function by high-density probe arrangements and imaging algorithms

Yusuke Sakakibara, Kazuki Kurihara, and OKADA EIJI

Optical Reivew (Springer) 23 ( 2 ) 323 - 331 2016.04

Research paper (scientific journal), Accepted

Estimation of partial optical path length in the brain in subject-specific head models for near-infrared spectroscopy

Kotaro Nakamura, Kazuki Kurihara, Hiroshi Kawaguchi, Takayuki Obata, Hiroshi Ito, and OKADA EIJI

Optical Review (Springer) 23 ( 2 ) 316 - 322 2016.04

Research paper (scientific journal), Joint Work, Accepted

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