A geometric‐sensitivity‐difference based algorithm improves object depth‐localization for diffuse optical tomography in a circular‐array outward‐imaging geometry

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135030/1/mp1957.pd

On the stress-induced photon emission from organism: II, how will the stress-transfer kinetics affect the photo-genesis?

Much remains to be identified for the temporal course of stress-induced photon emission (PE) following stress of various types including but not limited to light. Induced PE often decays hyperbolically; yet, it is not uncommon for induced PE to manifest decay patterns that are various combinations of first-order responses. Induced PE also presented transient patterns characteristic of second-order responses. A soliton-based photon-storage model addressed the hyperbolic decay pattern of induced PE; however, there are questions regarding non-hyperbolic decay as well as the large range of delay-and-decay scales of induced PE. This work offers an alternative interpretation of the temporal course of induced PE when stressed upon an organism. It is proposed that the surface photon emission of induced PE due to a stress involves two causally sequential phases: a stress-transfer phase that transforms the stress to photo-genesis, and a photon-propagation phase that transmits the photons from the site of photo-genesis to surface emission. Part I has argued that a retarded or slow stress-transfer phase is necessary to explain induced PE occurring/lasting at a timescale several orders of magnitude later/longer than the photon propagation delay due to tissue scattering after stress-removal. Part II models the kinetics of the stress-transfer phase that sources the photo-genesis with a linear-system approach. The analysis illustrates how a single stress-transfer pathway may manifest various photo-genesis patterns in responding to the same stress-input, and why a single kinetic pattern of photo-genesis may arise from multiple paths of stress transfer. The theoretical insights may help devise stress-control strategies to enhance the yield of induced PE for more mechanistic discoveries and potentiating broader applications.Electrical and Computer Engineerin

New near-analytical path to the threshold size of spherical random lasing via geometric-distribution-probability weighting of the diffusive photon fluence rate

We demonstrate a new near-analytical path to the threshold-size of random-lasing for the case of a uniform and isotropic-scattering sphere. We assess a geometric-distribution-probability (GDP) weighted integration of the diffusion-equation derived time-dependent photon fluence-rate at a spherical boundary, in response to uniform, synchronous, and Delta-functional photon generations within the sphere. The GDP weights the contribution of the modeled Delta-functional photon sources to the temporal behavior of the photon fluence rate at the spherical boundary-domain based on the line-of-sight distance between the modeled-photon source and the same field point. The integral manifests a bi-phasic pattern versus time with a global minimum followed by an exponential growth. The line-of-sight length that corresponds to the time of global minimum decreases monotonically as the size of the sphere increases. The condition that this line-of-sight length equaling the radius of the sphere is hypothesized to indicate a threshold whereby the medium can sustain the growth of the photon fluence-rate at the boundary over time. This threshold line-of-sight length is assessed over a gain/scattering ratio of [0.001, 10000] covering the diffusive to quasi-ballistic regimes. The threshold line-of-sight length applied with a simple empirical gain/scattering ratio predicts the threshold size over the diffusive region and outperforms the threshold size given by the eigen-mode-decomposition in the semi-ballistic region, when compared to the radiative transfer approach. The method sheds new insights to amplified diffusion process in a scattering medium with gain.Electrical and Computer Engineerin

Phenomenological interpretations of some somatic temporal and spatial patterns of biophoton emission in humans

Biophoton emission remains controversial. The photo-genic origin of biophoton has been attributed to the oxidative stress or free radical production. However, there are considerable gaps in quantitative understanding of biophoton emission. I propose an analytical hypothesis for interpreting a few patterns of steady-state biophoton emission of human, including the dependency on age, the diurnal variation, and the geometric asymmetry associated with serious asymmetrical pathological conditions. The hypothesis is based on an alternative form of energy state, termed vivo-nergy, which is associated with only metabolically active organisms that are also under neuronal control. The hypothesis projects a decrease of the vivo-nergy in human during growth beyond puberty. The hypothesis also proposes a modification of the vivo-nergy by the phases of systematic or homeostatic physiology. The hypothesis further postulates that the deviation of the physiology-modified vivo-nergy from the pre-puberty level is deteriorated by acquired organ-specific pathological conditions. A temporal differential change of vivo-nergy is hypothesized to proportionally modulate oxidative stress that functions as the physical source of biophoton emission. The resulted steady-state diffusion of the photon emitted from a photo-genic source in a human geometry simplified as a homogeneous spherical domain is modeled by photon diffusion principles incorporating an extrapolated zero-boundary condition. The age and systematic physiology combined determines the intensity of the centered physiological steady-state photo-genic source. An acquired pathology sets both the intensity and the off-center position of the pathological steady-state photo-genic source. When the age-commemorated, physiology-commanded, and pathology-controlled modifications of the steady-state photo-genetic sources are implemented in the photon diffusion model, the photon fluence rate at the surface of the human-representing spherical domain reveals the patterns on age, the temporal variation corresponding to systematic physiology, and the geometric asymmetry associated with significant asymmetric pathological condition as reported for spontaneous biophoton emission. The hypothesis, as it provides conveniences for quantitative estimation of biophoton emission patterns, will be extended in future works towards interpreting the temporal characteristics of biophoton emission under stimulation.Electrical and Computer Engineerin

On the stress-induced photon emission from organism: I, will the scattering-limited delay affect the temporal course?

Much remains to be identified for the temporal course of stress-induced photon emission (PE) from organism following stress of various types including but not limited to light. Induced PE concerns surface light emission in excess of the baseline level of spontaneous ultraweak photon emission, in response to a localized or systematic stress via oxidative bursting. It is proposed that the surface emission of induced PE involves two causally sequential phases: a stress-transfer phase that transforms the stress to perturb photogenesis balanced at homeostasis and a photon-propagation phase that transmits the photons from the domain of perturbed photogenesis to surface emission. The traversing of induced PE photons from wherever the domains of photogenesis perturbation are in the organism following the stress to the surface must involve photon propagation of which the scattering will affect the photon lifetime. Induced PE is usually substantially retarded in occurrence or longer in duration with respect to the stress. In order to identify whether the time course of induced PE can be attributed entirely to the stress-perturbed photogenesis, Part I estimates the upper limit of the scattering-caused photon lifetime following photogenesis. The estimation of that upper limit is based on setting the photogenesis at the center of a spherical human-size tissue having an unrealistically strong tissue scattering. Time-resolved photon migration analysis reveals that the scattering-limited lifetime will not be greater than 100 ns at a human scale. The time course of induced PE reported thus suggests a much retarded and slower perturbation to photogenesis with respect to the time course of stress for manifesting the surface-observed induced PE. The theoretical insight, which may complement the soliton mechanism, also supports the exploration of entopic phenomena including phosphenes and negative afterimages via delayed PE. The subsequent Part II hypothesizes a few stress-transfer kinetic patterns feeding the photogenesis.Electrical and Computer Engineerin

Single-fiber reflectance spectroscopy of isotropic-scattering medium: An analytic perspective to the ratio-of-remission in steady-state measurements

Recent focused Monte Carlo and experimental studies on steady-state single-fiber reflectance spectroscopy (SfRS) from a biologically relevant scattering medium have revealed that, as the dimensionless reduced scattering of the medium increases, the SfRS intensity increases monotonically until reaching a plateau. The SfRS signal is semi-empirically decomposed to the product of three contributing factors, including a ratio-of-remission (RoR) term that refers to the ratio of photons remitting from the medium and crossing the fiber-medium interface over the total number of photons launched into the medium. The RoR is expressed with respect to the dimensionless reduced scattering parameter μ's dfib, where μ's is the reduced scattering coefficient of the medium and dfib is the diameter of the probing fiber. We develop in this work, under the assumption of an isotropic-scattering medium, a method of analytical treatment that will indicate the pattern of RoR as a function of the dimensionless reduced scattering of the medium. The RoR is derived in four cases, corresponding to in-medium (applied to interstitial probing of biological tissue) or surface-based (applied to contact-probing of biological tissue) SfRS measurements using straight-polished or angle-polished fiber. The analytically arrived surface-probing RoR corresponding to single-fiber probing using a 15° angle-polished fiber over the range of μ's dfib = (10-2 103) agrees with previously reported similarly configured experimental measurement from a scattering medium that has a Henyey-Greenstein scattering phase function with an anisotropy factor of 0.8. In cases of a medium scattering lightanisotropically, we propose how the treatment may be furthered to account for the scattering anisotropy using the result of a study of light scattering close to the point-of-entry by Vitkin et al.Electrical & Computer Engineerin

Self calibration iso-pathlength point in cylindrical tissue geometry: Solution of steady-state photon diffusion based on the extrapolated zero-boundary

Near-infrared optical techniques permit tissue diagnosis by surface measurement. However, the geometrical shape of this interface profiles the intensity of the surface measurement, which is found to have an iso-pathlength (IPL) point allowing for absorption identification independent of tissue scattering. The IPL point was projected in Monte Carlo (MC) simulation, validated experimentally in cylindrical tissues, but remains under-appreciated through analytical approaches. In this work, we present an analytical solution of an IPL point for steady-state diffusion based on the extrapolated zero-boundary condition. The same IPL points were found when comparing this solution to 3-D MC simulations for a tissue radius range of 5-8mm.Electrical and Computer Engineerin

The utility of direct-current as compared to frequency domain measurements in spectrally-constrained diffuse optical tomography toward cancer imaging

This work investigates, by means of analytical and simulation studies, the performance of spectrally-constrained image reconstruction in Continuous-Wave or Direct-Current (DC) and Frequency Domain (FD) near-infrared optical tomography. A recent analytic approach for estimating the accuracy of target recovery and the level of background artifact for optical tomography at single wavelength, based on the analysis of parametric reconstruction uncertainty level (PRUL), is extended to spectrally-constrained optical tomography. The analytical model is implemented to rank three sets of wavelengths that had been used as spectral prior in an independent experimental study. Subsequent simulation appraises the recovery of oxygenated hemoglobin (HbO), deoxygenated hemoglobin (Hb), water (H2O), scattering amplitude (A), and scattering power (b) using DC-only, DC-excluded FD, and DC-included FD, based on the three sets of wavelengths as the spectral prior. The simulation results support the analytic ranking of the performance of the three sets of spectral priors, and generally agree with the performance outcome of DC-only versus that of DC-excluded FD and DC-included FD. Specifically, this study indicate that: 1) the rank of overall quality of chromophore recovery is Hb, H2O, and HbO from the highest to lowest; and in the scattering part the A is always better recovered than b. This outcome does suggest that the DC-only information gives rise to unique solution to the image reconstruction routine under the given spectral prior. 2) DC-information is not-redundant in FD-reconstruction, as the artifact levels of DC-included FD reconstruction are always lower than those of DC-excluded FD. 3) The artifact level as represented by the noise-to-contrast-ratio is almost always the lowest in DC-only, leading to generally better resolution of multiple targets of identical contrasts over the background than in FD. However, the FD could outperform DC in the recovery of scattering properties including both A and b when the spectral prior is less optimal, implying the benefit of phase-information in scattering recovery in the context of spectrally-constrained optical tomography.Electrical and Computer Engineerin