With the onset of clinically available spectral domain (SD-OCT) and swept source (SS-OCT) systems, clinicians are now easily able to recognize sub retinal microstructure and vascularization in the choroidal and scleral regions. As the bloodrich choroid supplies nutrients to the upper retinal layers, the ability to monitor choroid function accurately is of vital importance for clinical assessment of retinal health. However, the physical appearance of the choroid blood vessels (darker under a healthy Retinal Pigmented Epithelium (RPE) compared to regions displaying an RPE atrophic lesion) has led to confusion within the OCT ophthalmic community. The differences in appearance between each region in the OCT image may be interpreted as different vascular patterns when the vascular networks are in fact very similar. To explain this circumstance, we simulate light scattering phenomena in the RPE and Choroid complexes using the finite difference time domain (FDTD) method. The simulation results are then used to describe and validate imaging features in a controlled multi-layered tissue phantom designed to replicate human RPE, choroid, and whole blood microstructure. Essentially, the results indicate that the strength of the OCT signal from choroidal vasculature is dependent on the health and function of the RPE, and may not necessarily directly reflect the health and function of the choroidal vasculature.
We report a novel use of optical coherence tomography (OCT) based angiography to visualize and quantify dynamic response of cerebral capillary flow pattern in mice upon hindpaw electrical stimulation through the measurement of the capillary transit-time heterogeneity (CTH) and capillary mean transit time (MTT) in a wide dynamic range of a great number of vessels in vivo. The OCT system was developed to have a central wavelength of 1310 nm, a spatial resolution of ~8 µm and a system dynamic range of ~105 dB at an imaging rate of 92 kHz. The mapping of dynamic cerebral microcirculations was enabled by optical microangiography protocol. From the imaging results, the spatial homogenization of capillary velocity (decreased CTH) was observed in the region of interest (ROI) corresponding to the stimulation, along with an increase in the MTT in the ROI to maintain sufficient oxygen exchange within the brain tissue during functional activation. We validated the oxygen consumption due to an increase of the MTT through demonstrating an increase in the deoxygenated hemoglobin (HbR) during the stimulation by the use of laser speckle contrast imaging.
We propose an approach to measure heterogeneous velocities of red blood cells (RBCs) in capillary vessels using full-field time-varying dynamic speckle signals. The approach utilizes a low coherent laser speckle imaging system to record the instantaneous speckle pattern, followed by an eigen-decomposition-based filtering algorithm to extract dynamic speckle signal due to the moving RBCs. The velocity of heterogeneous RBC flows is determined by cross-correlating the temporal dynamic speckle signals obtained at adjacent locations. We verify the approach by imaging mouse pinna in vivo, demonstrating its capability for full-field RBC flow mapping and quantifying flow pattern with high resolution. It is expected to investigate the dynamic action of RBCs flow in capillaries under physiological changes.
Radiance is sensitive to the variations of tissue optical parameters, such as absorption coefficient μa, scattering coefficient μs, and anisotropy factor g. Therefore, similar to fluence, radiance can be used for tissue characterization. Compared with fluence, radiance has the advantage of offering the direction information of light intensity. Taking such advantage, the optical parameters can be determined by rotating the detector through 360 deg with only a single optode pair. Instead of the translation mode used in the fluence-based technologies, the Rotation mode has less invasiveness in the clinical diagnosis. This paper explores a new method to obtain the optical properties by measuring the distribution of light intensity in liquid phantom with only a single optode pair and the detector rotation through 360 deg. The angular radiance and distance-dependent radiance are verified by comparing experimental measurement data with Monte Carlo (MC) simulation for the short source-detector separations and diffusion approximation for the large source-detector separations. Detecting angular radiance with only a single optode pair under a certain source-detection separation will present a way for prostate diagnose and light dose calculation during the photon dynamic therapy (PDT).
In the research of optical diagnosis, such as noninvasive measurement of blood glucose by near-infrared
diffuse-reflectance spectroscopy, the fiber-optic probe are widely used to deliver light to the interested tissue site and
collect the light from the tissue. In order to minimize motion artifacts and specula reflectance, the fiber-optic probe
contact to tissue site with certain pressure. The spacing between tissue components decreased due to water displacement,
while the volumes of cells and elastic fibers are reduced which in turn increase the concentration of the scatter and
absorber inside the tissue. In our research a three-layer skin model is established and the Finite Element Method is
employed to simulate the deformation of skin tissue caused by fiber-optic probe with different pressure. The change of
water volume inside the tissue as well as the concentration and scattering cross section of scatters are considered. The
Monte Carlo simulation is utilized to establish the diffuse-reflectance spectroscopy of three-layer skin model before and
after compression. The result indicated that the pressure of fiber-optics probe should be controlled less the 50kpa to
reduce the influence on measurement.
The technologies of high sensitivity optical spectroscopy analysis on turbid media play an important part in scientific
research and biomedical applications. The optical path in which photons travel inside the turbid media generally brings
information of the components of the media. This paper introduces a novel method to study some of the properties of
turbid media by measuring and analyzing the differences of optic paths of wavelength modulated laser beams
experienced in the media. The operating principle to accomplish detecting media information in specified optical length
is theoretical analyzed. The Experiments and measurements on the multiple scattering properties in transparent media
(water, and air) and turbid media (simulation tissue fluid) are reported in the paper as well.
The estimate of tissue optical properties is an important challenge in biomedical science. In the research of
precancerous diagnosis and glucose concentration detection, the accuracy of chromospheres concentrations
measurement depends on the measurement of absorption coefficient. So determining the absorption coefficient
accurately is crucial both in vivo and in vitro. The
Double-Integrating-Spheres (DIS) system is widely used in
measuring optical properties of tissue. As there are light losses, sphere alters and cross talk in the measurement with
DIS system, the estimating error of the optical properties increases, especially for absorption coefficient. Based on the
DIS setup, the Monte Carlo simulation and principle of the integrating sphere are applied to investigate the effects of
light loss and cross talk with various parameters of sample. According to the investigation, a fast correcting method is
introduced to modify the measuring results. After a calibration dataset was employed, the algorithm based on artificial
neutral network is applied to modify the measurement with DIS system. The modified results indicate that the
reconstruction accuracy of absorption coefficient is fully improved compared with the uncorrected ones.
Measurement of optical properties in near infrared is very important for the applications of diffuse optical tomography
(DOT) and near infrared spectroscopy (NIRS), such as the in vivo detection of glucose concentration and oxygen
saturation of tissue. In some wavelength, the optical properties of tissue are also applied in cancer diagnostics and
therapy. Integrating sphere system is a widely adopted tool for in vitro measurement of tissue optical properties, but to
our knowledge, most of the systems are only based on He-Ne laser or a spectrometer. A multi-wavelength optical
property measurement system based on LDs in near infrared,
double-integrating-spheres, and lock-in detection is
introduced in this paper. Laser Diodes in 1300-1600nm are sinusoidal modulated in 30 KHz and an optical switch is
adopted for wavelength selection. Studied on the theory of double integrated spheres, there are two main factors
affecting the measurement accuracy: (1) light loss from the samples; (2) the inaccurate knowledge of the reflectance
index of the under detecting sample. Based on the investigation of these factors and the results of Monte Carlo
simulation, the system was carefully designed and fully improved. For evaluating the system, the optical properties of
intralipid-10% solution and a mixture of intralipid /CuSO4 solution were measured in 1310nm and compared with those
reported in literatures or measured with other tools. From the results of the phantoms measurements, it is concluded that
the system can get the reduced scattering coefficient and absorption coefficient with a relative error of less than 5% and
10%, respectively. Then the system is used to measure the optical properties of cervical tissues in vitro, for the
wavelength between 600-1600nm.
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