This paper reports initial experimentation of a dual beam flow velocity estimation setup based on optical coherence
tomography (OCT) for biomedical applications. The proposed work incorporates a low cost switching mechanism
(rotating galvanometer mirror) for optical signal discrimination between adjacent fiber channels enabling quasisimultaneous
multiple specimen scanning. A cascaded interferometric design is used with two sample output arms
orientated in parallel to eachother. A cross-correlation computation between these two parallel sample beams yields a
relative time delay, enabling assessment and quantification of flow velocities.
The microcirculation plays a critical role is maintaining organ health and function by serving as a vascular are where
trophic metabolism exchanges between blood and tissue takes place. To facilitate regular assessment in vivo, noninvasive
microcirculation imagers are required in clinics. Among this group of clinical devices, are those that render
microcirculation morphology such as nailfold capillaroscopy, a common device for early diagnosis and monitoring of
microangiopathies. However, depth ambiguity disqualify this and other similar techniques in medical tomography where
due to the 3-D nature of biological organs, imagers that support depth-resolved 2-D imaging and 3-D image
reconstruction are required. Here, we introduce correlation map OCT (cmOCT), a promising technique for
microcirculation morphology imaging that combines standard optical coherence tomography and an agile imaging
analysis software based on correlation statistic. Promising results are presented of the microcirculation morphology
images of the brain region of a small animal model as well as measurements of vessel geometry at bifurcations, such as
vessel diameters, branch angles. These data will be useful for obtaining cardiovascular related characteristics such as
volumetric flow, velocity profile and vessel-wall shear stress for circulatory and respiratory system.
Light scattering in blood caused by refractive index mismatch between erythrocyte cytoplasm and blood plasma leads to
a reduction in imaging spatial resolution, imaging depth and contrast of optical imaging techniques. A possible solution
to this problem is of the addition of biocompatible clearing agents, such as glucose, fructose, glycerol, dextrans etc. The
basic principle of the optical clearing technique is refractive index matching between erythrocyte cytoplasm and blood
plasma. Optical clearing, a technique that has been successfully demonstrated with biologic tissue, represents a
promising approach to increasing the imaging depth for various techniques, for example optical coherence tomography
(OCT).
OCT is based on low-coherence interferometry to produce cross-sectional tomographic imaging of the internal
microstructure in materials and biological tissues by measuring the echo time delay and magnitude of backscattered
light. One of the main advantages of this technique is the ability to investigate turbid and highly scattering media, such as
whole blood.
To determine the optimal concentration of clearing agents required for blood optical clearing in order to improve light
penetration depth for optical coherence tomography, clearing agents such as glucose and fructose, with various
concentrations were added to blood and investigated by OCT. Changes in light attenuation and sedimentation and
aggregation properties of blood depending on particular agent and its concentration were studied.
Collagen and elastin fibers are generally arranged in parallel bundles within the dermis. These bundles are oriented such
that they can most efficiently resist the stress and strain that normally occurs on the skin during movement. The pattern
of these fiber bundles establishes the lines of cleavage of the skin. Knowledge of the orientation of these is of key
importance for surgical procedures. When incisions are cut parallel to the cleavage line orientation the incision will heal
better and produce less scaring.
In this work we report a novel application of Optical coherence tomography for the determination of cleavage line
orientation in in-vivo human skin. The technique operates by pressing a small circular indenter onto the skin to deform
the skin. This is then imaged using optical coherence tomography. Analysis of the resulting deformation can be seen to
have an ellipsoidal shape which is related to the cleavage line orientation. We demonstrate that the technique can be used
to map the cleavage line orientation in-vivo.
There exist numerous planar imaging methods for mapping the human microvasculature. In medical diagnostics,
tomography is preferred over surface imaging for the simple reason that biological organs are 3-dimensional in nature.
The aim of this work is to create a novel technique to non-invasively map the concentration of red blood cells in the
human microcirculation allowing 3-dimensional image reconstruction. We propose a tomographic system which is based
on absorption contrast imaging. A Michelson interferometry method is employed using a broadband, white light source.
This work details preliminary results of the calibration procedure of a 'bulk' system. A mirror, reflectance standards,
glass-mirror arrangement, and color filter arrangement were used as samples. The resultant interference patterns from
each were imaged and analyzed.
The use of microneedles as a method of circumventing the barrier properties of the stratum corneum is receiving much attention. Although skin disruption technologies and subsequent transdermal diffusion rates are being extensively studied, no accurate data on depth and closure kinetics of microneedle-induced skin pores are available, primarily due to the cumbersome techniques currently required for skin analysis. We report on the first use of optical coherence tomography technology to image microneedle penetration in real time and in vivo. We show that optical coherence tomography (OCT) can be used to painlessly measure stratum corneum and epidermis thickness, as well as microneedle penetration depth after microneedle insertion. Since OCT is a real-time, in-vivo, nondestructive technique, we also analyze skin healing characteristics and present quantitative data on micropore closure rate. Two locations (the volar forearm and dorsal aspect of the fingertip) have been assessed as suitable candidates for microneedle administration. The results illustrate the applicability of OCT analysis as a tool for microneedle-related skin characterization.
Since its discovery in 1842 by Christian Johann Doppler, the Doppler Effect has had many applications in the scientific
world. In recent years, the phenomenon has been integrated with Optical Coherence Tomography (OCT) yielding
Doppler Optical Coherence Tomography (DOCT), a technique that is useful for high-resolution imaging of the skin
microcirculation. However, interpretation of DOCT images is rather challenging. Thus, our study aims to aid
understanding of DOCT images with respect to parameters of microcirculation components such as blood vessel size,
depth and angular position. To this end, we have constructed a gel-based tissue and blood-flow model for performing
DOCT studies under well controlled conditions. We present results from a pilot study using a gel-based tissue and blood
flow model. Human blood was pumped through the model at various velocities from a commercial calibrated syringe
pump, serving as a standard reference point for all velocity measurements. The range of velocity values was chosen to
coincide with that found in the human vasculature. Simultaneous DOCT imaging at different flow rates contributed to
establishing the capabilities and limitations of the DOCT system under investigation. We present preliminary results as
first step to developing a robust validation protocol with which to aid future research in this area.
An optics laboratory plays a critical role in optics education. A major challenge for optics educators in Africa is the shortage or non-availability of laboratory teaching equipment. Optics teaching equipment is beyond the budget of most universities in the developing world such as the new National University of Science and Technology in Zimbabwe.
The paper details a successful strategy - local fabrication/assembling of optics laboratory teaching aids - adopted by the Applied Physics Department at Zimbabwe's National University of Science and Technology. Students and technical staff under the guidance of an academic member of staff do equipment fabrication and assembling.
The paper describes some of the project-type set-ups for performing experiments on (1) laser light scattering and impurity determination; (2) industrial imaging inspection (3) light transmission and reflection and (4) refractive index measurement.
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