Inhomogeneity in optical properties of rat brain: a study for LLLT dosimetry (original) (raw)
Related papers
Near-infrared light penetration profile in the rodent brain
Journal of Biomedical Optics, 2013
Near-infrared (NIR) lasers find applications in neuro-medicine both for diagnostic and treatment purposes. Penetration depth and profile into neural tissue are critical parameters to be considered in these applications. Published data on the optical properties of rodent neural tissue are rare, despite the frequent use of rats as an animal model. The aim of this study was to measure the light intensity profile inside the rat brain using a direct method, while the medium is being illuminated by an NIR laser beam, and compare the results with in vitro measurements of transmittance in the rat brain slices. The intensity profile along the vertical axis had an exponential decline with multiple regions that could be approximated with different coefficients. The Monte Carlo method that was used to simulate light-tissue interactions and predict the scattering coefficient of brain tissue from the measurements suggested that more scattering occurred in deeper layers of the cortex. A single scattering coefficient of 125 cm −1 was estimated for cortical layers from 300 to 1500 μm and a gradually increasing value from 125 to 370 cm −1 for depths of 1500 to 3000 μm. The deviations of in vivo results from the in vitro transmittance measurements, as well as the postmortem in vivo results from the alive measurements were significant.
Laser scattering by transcranial rat brain illumination
Biophotonics: Photonic Solutions for Better Health Care III, 2012
Due to the great number of applications of Low-Level-Laser-Therapy (LLLT) in Central Nervous System (CNS), the study of light penetration through skull and distribution in the brain becomes extremely important. The aim is to analyze the possibility of precise illumination of deep regions of the rat brain, measure the penetration and distribution of red (λ = 660 nm) and Near Infra-Red (NIR) (λ = 808 nm) diode laser light and compare optical properties of brain structures. The head of the animal (Rattus Novergicus) was epilated and divided by a sagittal cut, 2.3 mm away from mid plane. This section of rat's head was illuminated with red and NIR lasers in points above three anatomical structures: hippocampus, cerebellum and frontal cortex. A high resolution camera, perpendicularly positioned, was used to obtain images of the brain structures. Profiles of scattered intensities in the laser direction were obtained from the images. There is a peak in the scattered light profile corresponding to the skin layer. The bone layer gives rise to a valley in the profile indicating low scattering coefficient, or frontal scattering. Another peak in the region related to the brain is an indication of high scattering coefficient ( s ) for this tissue. This work corroborates the use of transcranial LLLT in studies with rats which are subjected to models of CNS diseases. The outcomes of this study point to the possibility of transcranial LLLT in humans for a large number of diseases.
In Vivo Local Determination of Tissue Optical Properties: Applications to Human Brain
Applied Optics, 1999
Local and superficial near-infrared ͑NIR͒ optical-property characterization of turbid biological tissues can be achieved by measurement of spatially resolved diffuse reflectance at small source-detector separations ͑Ͻ1.4 mm͒. However, in these conditions the inverse problem, i.e., calculation of localized absorption and the reduced scattering coefficients, is necessarily sensitive to the scattering phase function. This effect can be minimized if a new parameter of the phase function ␥, which depends on the first and the second moments of the phase function, is known. If ␥ is unknown, an estimation of this parameter can be obtained by the measurement, but the uncertainty of the absorption coefficient is increased. A spatially resolved reflectance probe employing multiple detector fibers ͑0.3-1.4 mm from the source͒ is described. Monte Carlo simulations are used to determine ␥, the reduced scattering and absorption coefficients from reflectance data. Probe performance is assessed by measurements on phantoms, the optical properties of which were measured by other techniques ͓frequency domain photon migration ͑FDPM͒ and spatially resolved transmittance͔. Our results show that changes in the absorption coefficient, the reduced scattering coefficient, and ␥ can be measured to within Ϯ0.005 mm Ϫ1 , Ϯ0.05 mm Ϫ1 , and Ϯ0.2, respectively. In vivo measurements performed intraoperatively on a human skull and brain are reported for four NIR wavelengths ͑674, 811, 849, 956 nm͒ when the spatially resolved probe and FDPM are used. The spatially resolved probe shows optimum measurement sensitivity in the measurement volume immediately beneath the probe ͑typically 1 mm 3 in tissues͒, whereas FDPM typically samples larger regions of tissues. Optical-property values for human skull, white matter, scar tissue, optic nerve, and tumors are reported that show distinct absorption and scattering differences between structures and a dependence on the phase-function parameter ␥.
Red and NIR light dosimetry in the human deep brain
Physics in medicine and biology, 2015
Photobiomodulation (PBM) appears promising to treat the hallmarks of Parkinson's Disease (PD) in cellular or animal models. We measured light propagation in different areas of PD-relevant deep brain tissue during transcranial, transsphenoidal illumination (at 671 and 808 nm) of a cadaver head and modeled optical parameters of human brain tissue using Monte-Carlo simulations. Gray matter, white matter, cerebrospinal fluid, ventricles, thalamus, pons, cerebellum and skull bone were processed into a mesh of the skull (158 × 201 × 211 voxels; voxel side length: 1 mm). Optical parameters were optimized from simulated and measured fluence rate distributions. The estimated μeff for the different tissues was in all cases larger at 671 than at 808 nm, making latter a better choice for light delivery in the deep brain. Absolute values were comparable to those found in the literature or slightly smaller. The effective attenuation in the ventricles was considerably larger than literature va...
Light Scattering Properties Vary across Different Regions of the Adult Mouse Brain
PLoS ONE, 2013
Recently developed optogenetic tools provide powerful approaches to optically excite or inhibit neural activity. In a typical in-vivo experiment, light is delivered to deep nuclei via an implanted optical fiber. Light intensity attenuates with increasing distance from the fiber tip, determining the volume of tissue in which optogenetic proteins can successfully be activated. However, whether and how this volume of effective light intensity varies as a function of brain region or wavelength has not been systematically studied. The goal of this study was to measure and compare how light scatters in different areas of the mouse brain. We delivered different wavelengths of light via optical fibers to acute slices of mouse brainstem, midbrain and forebrain tissue. We measured light intensity as a function of distance from the fiber tip, and used the data to model the spread of light in specific regions of the mouse brain. We found substantial differences in effective attenuation coefficients among different brain areas, which lead to substantial differences in light intensity demands for optogenetic experiments. The use of light of different wavelengths additionally changes how light illuminates a given brain area. We created a brain atlas of effective attenuation coefficients of the adult mouse brain, and integrated our data into an application that can be used to estimate light scattering as well as required light intensity for optogenetic manipulation within a given volume of tissue. Citation: Al-Juboori SI, Dondzillo A, Stubblefield EA, Felsen G, Lei TC, et al. (2013) Light Scattering Properties Vary across Different Regions of the Adult Mouse Brain. PLoS ONE 8(7): e67626.
Journal of Biophotonics, 2022
Neuro-oncology surgery would benefit from detailed intraoperative tissue characterization provided by noncontact, contrast-agent-free, noninvasive optical imaging methods. In-depth knowledge of target tissue optical properties across a wide-wavelength spectrum could inform the design of optical imaging and computational methods to enable robust tissue analysis during surgery. We adapted a dual-beam integrating sphere to analyse small tissue samples and investigated ex vivo optical properties of five types of human brain tumour (meningioma, pituitary adenoma, schwannoma, lowand high-grade glioma) and nine different types of healthy brain tissue across a wavelength spectrum of 400 to 1800 nm. Fresh and frozen tissue samples were analysed. All tissue types demonstrated similar absorption spectra, but the reduced scattering coefficients of tumours show visible differences in the Jonathan Shapey and Yijing Xie have contributed equally to this study.
NIR Light Penetration Depth in the Rat Peripheral Nerve and Brain Cortex
2007
Near infrared (NIR) light energy has been used in medical applications both for diagnostic and treatment purposes. A priory knowledge of optical tissue properties is necessary in these applications; not only of human but also in animals for testing of devices. However, published data on the optical properties of neural tissue in rodents are rare. The aim of this study was to measure the penetration depth of light into the rat peripheral nerve and brain cortex at NIR wavelengths. Penetration depth was calculated from measurements of transmitted light for various thicknesses of the neural tissue. We found the penetration depth in the rat sciatic nerve to be 0.35 ± 0.023 mm and in the white matter 0.35 ± 0.026 mm. The penetration depth of the gray matter was 0.41 ± 0.029 mm. Compared to the data reported in literature for the human brain, the rat peripheral and the brain cortex attenuate the NIR light much more strongly.
Characterization of light penetration through brain tissue, for optogenetic stimulation
2021
The recent development of optogenetic tools, to manipulate neuronal activity using light, provides opportunities for novel brain-machine interface (BMI) control systems for treating neurological conditions. An issue of critical importance, therefore, is how well light penetrates through brain tissue. We took two different approaches to estimate light penetration through rodent brain tissue. The first employed so-called “nucleated patches” from cells expressing the light-activated membrane channel, channelrhodopsin (ChR2). By recording light-activated currents, we used these nucleated patches as extremely sensitive, microscopic, biological light-meters, to measure light penetration through 300-700µm thick slices of rodent neocortical tissue. The nucleated patch method indicates that the effective illumination drops off with increasing tissue thickness, corresponding to a space constant of 317µm (95% confidence interval between 248-441µm). We compared this with measurements taken from...
Modern studies of the penetration of light into biological tissues is becoming very important in various medical applications. This is an important factor for determining the optical dose in many diagnostic and therapeutic procedures. The absorption and scattering properties of the tissue under study determine how deeply the light will penetrate into the tissue. However, these optical properties are highly dependent on the wavelength of the light source and tissue condition. This overview paper analyzes the transmission of light through different areas of human and animal head tissues, and the optimal laser wavelength and power density required to reach different parts of the brain are determined using lasers with different wavelengths by comparing the distribution of fluence, penetration depth and the mechanism of interaction between laser light and head tissues. The power variation in different regions of the head is presented, as estimated using Monte Carlo (MC) simulations. Data are analyzed for the absorption and scattering coefficients of the head tissue layers (scalp, skull, brain), calculated using integrating sphere measurements and inverse problem solving algorithms such as inverse MC (IMC) and adding-doubling (IAD). This study not only offered a quantitative comparison between wavelengths in terms of light transmission efficiency, but also anticipated the exciting opportunity for online, accurate and visible optimization of LLLT lighting parameters.
2020
Abstract. Optical clearing, in combination with recently developed optical imaging techniques, enables visualization and acquisition of high-resolution, three-dimensional images of biological structures deep within the tissue. Many different approaches can be used to reduce light absorption and scattering within the tissue, but there is a paucity of research on the quantification of clearing efficacy. With the use of a custom-made spectroscopy system, we developed a way to quantify the quality of clearing in biological tissue and applied it to the mouse brain. Three clearing techniques were compared: BABB (1:2 mixture of benzyl alcohol and benzyl benzoate, also known as Murray's clear), pBABB (peroxide BABB, a modification of BABB which includes the use of hydrogen peroxide), and passive CLARITY. We found that BABB and pBABB produced the highest degree of optical clearing. Furthermore, the approach allows regional measurement of light attenuation to be performed, and our result...