arXiv subjects

Prabhakar Pradhan

Publications and source records attributed to Prabhakar Pradhan.

At least 37 records · Page 2Linked to original sources

arXiv2019

Numerical study of the degree of light scattering strength versus fractal dimension in optical fractal disordered media: Applications in strong to weak disordered media

Optical scattering strength of fractal optical disordered media with varying fractal dimension is reported. The diffusion limited aggregation (DLA) technique is used to generate fractal samples in 2D and 3D, and fractal dimensions are calculated using the box-counting method. The degree of structural disorder of these samples are calculated using their light localization strength, using the inverse participation ratio (IPR) analyses of the optical eigenfunctions. Results show non-monotonous behavior of the disorder-induced scattering strength with the fractal dimension, attributed to the competition between increasing structural disorder due to decrease in fractality versus decrease in scattering centers due to decreasing fractality.

physics.optics↗

arXiv2019

Nanoscale structural alterations in cancer cells to assess anti-cancerous drug effectiveness in cancer treatment using TEM imaging

Understanding the nanoscale structural changes can provide the physical state of cells/tissues. It has been now shown that increases in nanoscale structural alterations are associated with the progress of carcinogenesis in most of the cancer cases, including early carcinogenesis. Anti-cancerous therapies are intended for the growth inhibition of cancer cells; however, it is challenging to detect the efficacy of such drugs in early stages of treatment. A unique method to assess the impact of anti-cancerous drugs on cancerous cells/tissues is to probe the nanoscale structural alterations. In this paper, we study the effect of different anti-cancerous drugs on ovarian tumorigenic cells, using their nanoscale structural alterations as a biomarker. Transmission electron microscopy (TEM) imaging on thin cell sections is performed to obtain their nanoscale structures. The degree of nanoscale structural alterations of tumorigenic cells and anti-cancerous drug treated tumorigenic cells are quantified by using the recently developed inverse participation ratio (IPR) technique. Results show an increase in the degree of nanoscale fluctuations in tumorigenic cells relative to non-tumorigenic cells; then a nearly reverse of the degree of fluctuation of tumorigenic cells to that of non-tumorigenic cells, after the anti-cancerous drugs treatment. These results support that the effect of anti-cancerous drugs in cancer treatment can be quantified by using the degree of nanoscale fluctuations of the cells via TEM imaging. Potential applications of the technique for cancer treatment are also discussed.

physics.bio-ph↗

arXiv2019

Optical detection of structural properties of tumor tissues generated by xenografting of drug-sensitive and drug-resistant cancer cells using partial wave spectroscopy (PWS)

The quantitative measurement of structural alterations at the nanoscale level is important for understanding the physical state of biological samples. Studies have shown that the progression of cancer is associated with the rearrangements of building blocks of cells/tissues such as DNA, RNA, lipids, etc. Partial wave spectroscopy is a recently developed mesoscopic physics-based spectroscopic imaging technique which can detect such nanoscale changes in cells/tissues. At present, chemotherapy drug treatment is the only effective form of treatment; however, the development of drug-resistant cancer cells is a major challenge for this treatment. Earlier PWS analyses of prostate cancer cells, a 2D structure, have shown that drug-resistant cancer cells have a higher degree of structural disorder compared to drug-sensitive cancer cells. At the same time, structural properties of the metastasize tumor grown to 3D structure from drug-resistant and drug-sensitive cancer cells within the body is not well studied. In this paper, the structural properties of tissues from grown 3D tumors, generated from docetaxel drug-sensitive and drug-resistant prostate cancer cells xenografted into a mouse model, are studied. The results show that xenografted tumor tissues from drug-resistant cells have higher disorder strength than the tumor generated from drug-sensitive prostate cancer cells. Potential applications of the technique to assess chemotherapy effectiveness in cancer treatment are discussed.

physics.med-ph↗

arXiv2018

Optical detection of fractal dimensions of MUC13 stained pancreatic tissues for cancer diagnostics

Transmission intensity of a thin tissue sample produce intensity distribution that is proportional to the refractive index pattern in the thin slice, in turn reflects mass density pattern, and using the intensity pattern, fractal dimension can be calculated. In this paper, we report fractal dimension analyses of MUC13 stained pancreatic cancer tissues. Pancreatic cancer is deadliest due to its physical orientation, and no prominent chemical change till the late stages of cancer. The presence of pancreatic cancer can be detected using MUC13, however this fails to explain about the stages of cancer. Here we studied MUC13 expressed cancer tissues and observe their cancer stages by fractal dimension of light transmission intensity. Our results show that an early stage of pancreatic cancer for MUC13 expressed tissue is accurately distinguished by fractal dimension analysis. Further, their application to cancer diagnostics is also discussed in detail.

physics.med-ph↗

arXiv2018

Derivation of statistics of real delay time from statistics of imaginary delay time using spectroscopic technique in weakly disordered optical media

Delay time is defined as a time that a wave spent in a scattering medium before it escapes, and this can be derived by the energy derivative of the phase of the scattering wave. Considering the complex reflection amplitude R=|R|exp(iθ) of a light wave, real delay time τ_r (i.e., sojourn or Wigner delay time), which is the energy derivative of the real phase (τ_r =dθ/cdk), and complex delay time τ_i , which is the energy derivative of the reflection coefficient (τ_i=dθ_i/cdk, |R|=r^1/2=exp(-θ_i)), have the same statistical form and a mirror image with a shift in time in weak disorder and short length regime. Real delay time statistics obtained from the reflection coefficient can be attributed to the strong correlation between the reflection coefficient and its phase in this regime. The range of the scattering parameters for this validation, as well as application of this method in characterization of weakly disordered media is also discussed.

physics.optics↗

arXiv2018

Photonic localization probe of molecular specific intranuclear structural alterations in brain cells due to fetal alcoholism via confocal microscopy

Molecular specific photonic localization is a sensitive technique to probe the structural alterations or abnormalities in a cell such as abnormalities due to alcohol or other drugs. Alcohol consumption during pregnancy by mother, or fetal alcoholism, is one of the major factors of mental retardation in children. Fetal alcohol syndrome and alcohol related neurodevelopmental disorder are awful outcomes of the maternal alcohol consumption linked with notable cognitive and behavioral defects. Alcohol consumed by the pregnant mother, being teratogenic, interferes with the fetal health resulting brain damage and other birth defects. This might affect the brain cells at the very nanolevel which cannot be predicted by the present histopathological procedures. We perform quantification of nanoscale spatial structural alterations in two different spatial molecular components, DNA and histone molecular mass densities, in brain cell nuclei of fetal alcohol effected (FAE) pups at postnatal day 60. Confocal images of the brain cells are collected and the degree of morphological alterations in DNA and histone, in terms of mass density fluctuations are obtained using the recently developed molecular specific light or photonic localization analysis technique. The results show an increase in degree of spatial structural disorder in DNA and a reduced histone modification. Increase in spatial disorder in DNA may suggest DNA unwinding and possibly responsible for increase in gene expression. Reduced histone modification may suggest its release from the DNA and help in the unwinding of DNA and gene expression. The probable cause for structural disorder as well as opposite rearrangements for DNA and histone molecules in fetal alcohol effects is also discussed.

physics.bio-ph↗

arXiv2017

Optical study of stress hormone-induced nanoscale structural alteration in brain using partial wave spectroscopic (PWS) microscopy

Chronic stress affects nano to microscale structures of the brain cells/tissues due the suppression of neural growths and reconnections, hence the neuronal activities. This results in depression, memory loss and even the death of the brain cells. Our recently developed novel optical technique, partial wave spectroscopic (PWS) microscopy has nanoscale sensitivity, and hence, can detect nanoscale changes in brain tissues due to stress. In this study, we applied this technique to quantify the stress related structural changes in the corticosterone-treated mouse model of stress. Our results show that brains from corticosterone-treated mice showed higher nanoscale structural disorder in the hippocampal region as compared to the brain from normal (vehicle) mice. The increase in structural alteration correlates with the duration of the stress. We further quantified the relative changes and the spatial localization of these changes in this mouse model and found out that the maximum changes occurred nearly symmetrically in both regions of the hippocampus. The mRNA for stress-related genes, BDNF and TrkB were also significantly reduced in the hippocampus of corticosterone-treated mice compared to that in control mice. These results indicate that chronic corticosterone treatment induces nanoscale structural alterations in mouse brain that corresponds to the changes in stress-related gene expression.

physics.bio-ph↗

arXiv2017

Optical study of chemotherapy efficiency in cancer treatment via intracellular structural disorder analysis using partial wave spectroscopy

With the progress of cancer, the macromolecules such as DNA, RNA, lipids, etc. inside cells undergo spatial structural rearrangements and alterations. Mesoscopic physics based optical partial wave spectroscopy (PWS) was recently introduced to quantify changes in the nanoscale structural disorder in biological cells. The measurement is done in a parameter termed as disorder strength ( Ld) which represents the degree of nanoscale structural disorder inside the cells. It was shown that cancerous cells have higher disorder strength than the normal cells. In this work, using the PWS technique, we analyzed the hierarchy of different types of prostate cancer cells by quantifying their average disorder strengths. The results showed that increase in the tumorigenicity level of prostate cancer is correlated with the increase in the disorder strength Ld. Furthermore, using the Ld parameter we also analyzed docetaxel chemo-resistance attribute of these prostate cancer cells, in comparison to docetaxel chemo-sensitive cancer cells. Our results show that chemo drug resistive cancer cells have mutations to more aggressive, or increased in Ld values relative to the chemo sensitive cancer cells. Potential applications of the Ld parameter for determining the effectiveness of the chemotherapy drug on cancer cells are discussed.

physics.bio-ph↗

arXiv2017

Detection of Cancer Stages via Fractal Dimension Analysis of Optical Transmission Imaging of Tissue Micro Arrays (TMA)

Cancer is an epidemic worldwide. At present one in four persons has cancer and this statistic will change to one in a two person in the near future. It is now known that war against cancer is the early, curable detection and treatment. Affordable, quick and easy detection methods are, therefore, essential. Standard pathologist way of detecting cancer is looking at the stained biopsy tissue samples under microscope, brings lots of human error. A tissue is a spatial heterogeneous medium and it has fractal properties due to its self-similarity in mass distribution. It is now known that with the progress of cancer the tissue heterogeneity changes due to more mass accumulations and rearrangement of intracellular macromolecules such as DNA and lipids etc. Furthermore, there are tissue micro array (TMA) samples available that provides array of hundred samples in one glass slides. In this study, using reflectance microscopy we have analyzed the fractal dimension of 5μm colon TMA samples to correctly distinguish between normal, adjacent to cancer, benign, stage-1 and stage-2 colon cancers. This fractal property of the tissues is also supported by entropy and spatial correlation calculations. The application of this method for diagnostic applications is also discussed.

q-bio.TO↗

arXiv2016

Deriving real delay time statistics from the complex delay time statistics in weakly disordered optical media

Considering the complex reflection amplitude R=|R|exp(iθ) of a light wave, real delay time τ_r (i.e., sojourn or Wigner delay time), which is the energy derivative of the real phase (τ_r =dθ/cdk), and complex delay time τ_i , which is the energy derivative of the reflection coefficient (τ_i=dθ_i/cdk, |R|=r^1/2=exp(-θ_i)), have the same statistical form and a mirror image with a shift in time in weak disorder and short length regime. Real delay time statistics obtained from the reflection coefficient can be attributed to the strong correlation between the reflection coefficient and its phase in this regime.

physics.optics↗

arXiv2015

Enhancing the sensitivity of mesoscopic light reflection statistics in weakly disordered media by interface reflections

Reflection statistics have not been well studied for optical random media whose mean refractive indices do not match with the refractive indices of their surrounding media. Here, we theoretically study how this refractive index mismatch between a one dimensional (1D) optical sample and its surrounding medium affects the reflection statistics in the weak disorder limit, when the fluctuation part of the refractive index (dn) is much smaller than the mismatch as well as the mean refractive index of the sample (dn << ). In the theoretical derivation, we perform a detailed calculation that results in the analytical forms of mean and standard deviation (STD) of the reflectance in terms of disorder parameters (dn and lc) in an index mismatched backscattering system. Particularly, the orders of disorder parameters in STD of the reflectance for index mismatched systems is shown to be lower ( ( lc )^1/2 ) than that of the matched systems ( lc). By comparing STDs of the reflection coefficient of index matched and mismatched systems, we show that reflectance at the sample boundaries in index mismatched systems can enhance the signal of the STD to the disorder parameters of the reflectance. In terms of biophotonics applications, this result can lead to potential techniques that effectively extract the sample disorder parameters by manipulating the index mismatch conditions. Potential applications of the technique for enhancement in sensitivity of cancer detection at single cell level are also discussed.

physics.optics↗

arXiv2015

Probing intracellular mass density fluctuation through confocal microscopy: application in cancer diagnostics as a case study

Intracellular structural alterations are hallmark of several disease conditions and treatment modalities. However, robust methods to quantify these changes are scarce. In view of this, we introduce a new method to quantify structural alterations in biological cells through the widely used confocal microscopy. This novel method employs optical eigenfunctions localization properties of cells and quantifies the degree of structural alterations, in terms of nano- to micron scale intracellular mass density fluctuations, in one single parameter. Such approach allows a powerful way to compare changing structures in heterogeneous cellular media irrespective of the origin of the cause. As a case study, we demonstrate its applicability in cancer detection with breast and prostate cancer cases of different tumorigenicity levels. Adding new dimensions to the confocal based studies, this technique has potentially significant applications in areas ranging from disease diagnostics to therapeutic studies, such as patient prognosis and assessing survival potential.

physics.bio-ph↗

arXiv2015

Quantitative analysis of the nanoscale intra-nuclear structural alterations in hippocampal cells in chronic alcoholism via transmission electron microscopy study

Chronic alcoholism is known to alter morphology of hippocampal, an important region of cognitive function in the brain. We performed quantification of nanoscale structural alterations in nuclei of hippocampal neuron cells due to chronic alcoholism, in mice model. Transmission electron microscopy images of the neuron cells were obtained and the degrees of structural alteration, in terms of mass density fluctuations, were determined using the recently developed light localization analysis technique. The results, obtained at the length scales ranging from 33 to 195 nm, show that the 4-week alcohol fed mice have higher degree of structural alteration in comparison to the control mice. The degree of structural alterations starts becoming significantly distinguishable around 100 nm sample length, which is the typical length scale of the building blocks of cells, such as DNA, RNA, etc. Different degrees of structural alterations at such length scales suggest possible structural rearrangement of chromatin inside the nuclei.

physics.bio-ph↗

arXiv2015

Nanoscale intracellular mass-density alteration as a signature of the effect of alcohol on early carcinogenesis: A transmission electron microscopy (TEM) study

Alcohol consumption interferes with the functioning of multiple organ systems, causing changes in the chemistry, physiology and pathology of tissues and cellular organelles. Although epigenetic modifications underlie the development of cancer, exposure to carcinogenic chemicals, such as alcohol, can also contribute to disease development. However, the effects of chronic alcoholism on normal or pre-carcinogenic cells/tissues in different organelles are not well understood. Therefore, we herein study the effect of alcohol consumption on colonic nucleus using control and azoxymethane (AOM) and dextran sulfate sodium (DSS) treated carcinogenic mice. Previous studies showed that progression of carcinogenesis is associated with increase in the degree of intranuclear nanoscale structural disorder. In the present work, we quantify the degree of nanostructural disorder as a measure of carcinogenesis. To accomplish this, transmission electron microscopy (TEM) imaging of respective colonic epithelial cell nuclei are used to construct disordered optical lattices, and the properties of nanoscale disorder are then studied by analyzing the inverse participation ratio (IPR) of the spatially localized eigenfunctions of these optical lattices. Nanoscale structural disorder strength, as a marker of cancer progression, is measured in the length scale of 10 to 75 nm. Results show no significant visible effect in nanoscale structural changes on colon cell nuclei from alcohol exposure. However, alcohol was found to act as an enhancer of nanoscale disorder in precancerous cells and, hence, carcinogenic processes. To the best of our knowledge, this is the first study to quantify the effect of alcohol on early carcinogenic biological cells, using mesoscopic condensed matter physics.

physics.bio-ph↗

arXiv2015

Phase statistics of light wave reflected from one-dimensional optical disordered media and its effects on light transport properties

Light wave reflection from optical disordered media is always associate with its phase, and the phase statistics influence the reflection statistics. We report a detailed numerical study of the statistics of the reflection coefficient RR* and its associated phase(theta) for plane electromagnetic waves reflected from one dimensional (1D) Gaussian white-noise optical disordered media, ranging from weak to strong disordered regimes. We solve numerically the full Fokker-Planck (FP) equation for the joint probability distribution in the RR* - phase(theta) space for different lengths of the sample with different disorder strengths. The statistical optical transport properties of 1D optical disordered media are calculated using the full FP equation numerically. This constitutes a complete solution for the reflection phase statistics and its effects on light transport properties in a 1D Gaussian white-noise disordered optical potentials. Our results show the regime of the validation of the random phase approximations (RPA) or uniform phase distribution, within the Born approximation, as well as the contribution of the phase statistics to the different reflection averages for strong disorder regimes. Results of the previous work reported in the literature relative to the present work also been reviewed and discussed

physics.optics↗

arXiv2015

Reflection statistics of weakly disordered optical medium when its mean refractive index is different from an outside medium

Based on the difference between mean background of an optical sample refractive index n_0 and an outside medium, n_out, different than n_0, we study the reflection statistics of a one-dimensional weakly disordered optical medium with refractive index n(x)=n_0+dn(x). Considering dn(x) as color noise with the exponential spatial correlation decay length l_c and k as the incident wave vector, our results show that for the small correlation length limit, i.e. k*l_c<1, the average value of reflectance, r, follows a form that is similar to that of the matched refractive-index case n_0=n_out, i.e., proportional to l_c. However, the standard deviation of r is proven to be std(r(dn,l_c)) proportional to sqrt( l_c), which is different from the matched case. Applications to light scattering from layered media and biological cells are discussed

physics.optics↗

arXiv2007

Penetration depth of low-coherence enhanced backscattered light in sub-diffusion regime

The mechanisms of photon propagation in random media in the diffusive multiple scattering regime have been previously studied using diffusion approximation. However, similar understanding in the low-order (sub-diffusion) scattering regime is not complete due to difficulties in tracking photons that undergo very few scatterings events. Recent developments in low-coherence enhanced backscattering (LEBS) overcome these difficulties and enable probing photons that travel very short distances and undergo only a few scattering events. In LEBS, enhanced backscattering is observed under illumination with spatial coherence length L_sc less than the scattering mean free path l_s. In order to understand the mechanisms of photon propagation in LEBS in the subdiffusion regime, it is imperative to develop analytical and numerical models that describe the statistical properties of photon trajectories. Here we derive the probability distribution of penetration depth of LEBS photons and report Monte Carlo numerical simulations to support our analytical results. Our results demonstrate that, surprisingly, the transport of photons that undergo low-order scattering events has only weak dependence on the optical properties of the medium (l_s and anisotropy factor g) and strong dependence on the spatial coherence length of illumination, L_sc, relative to those in the diffusion regime. More importantly, these low order scattering photons typically penetrate less than l_s into the medium due to low spatial coherence length of illumination and their penetration depth is proportional to the one-third power of the coherence volume (i.e. [l_s πL_sc^2 ]^1/3).

cond-mat.mes-hall↗

arXiv2006

Circular polarization memory effect in enhanced backscattering of light under partially coherent illumination

We experimentally study the propagation of circularly polarized light in the sub-diffusion regime by exploiting enhanced backscattering (EBS, also known as coherent backscattering) of light under low spatial coherence illumination. We demonstrate for the first time that circular polarization memory effect exists in EBS over a large range of scatterers' sizes in this regime. We show that EBS measurements under low spatial coherence illumination from the helicity preserving and orthogonal helicity channels cross over as the mean free pathlength of light in media varies, and that the cross point indicates the transition from multiple to double scattering in EBS of light.

cond-mat.mes-hall↗