Non-invasive imaging modalities, especially optical coherence tomography (OCT) are capable of providing high resolution structural and functional imaging capabilities for ophthalmic applications. Apart from functional imaging, OCT has also been used to extract functional dynamics within the microvasculature in response to changes in local environment. In mammals, various physiological processes, such as energy metabolisms, cardiovascular functions and circadian rhythms exhibit fluctuations in response to change in the local and external environment. These rhythmic oscillations within the body have been observed within the neurons, microvasculature, muscles and heart and play a vital role in modulating the biological processes and associated physiological response by an organism. Cornea is the transparent, avascular layer of the eye that controls the entry of light into the eye and also helps to refract the light onto the retina. Corneal injuries caused by various chemical, physical, and pathological stimuli damages the corneal epithelium, the stroma and the endothelium, thereby hindering its proper functioning. The maintenance of corneal transparency is vital for optimum vision, and this is ensured by the avascular cornea evenly spaced collagen fibrils of uniform diameter within the stroma, and also the level of hydration within the stromal layer. Recently, nano-sensitive OCT (nsOCT) technique has been proposed by our group that retains the high spatial frequency information in an OCT image, thereby enabling the detection of nanoscale structural alterations in in vivo imaging of tissues. In this paper, we describe nsOCT based approach to detect the dynamic/temporal structural changes within the cornea following an alkali injury using a high speed swept source OCT.
Optical coherence tomography (OCT), a non-invasive label-free depth resolved imaging technique, facilitates cellular level structural and functional imaging of living animal and human tissues, but the structural sensitivity and resolution are fundamentally limited to microscale. Detection of structural changes in biological samples at nanoscale poses a significant challenge to both researchers and healthcare professionals. Furthermore, when considering physiological processes, it is desirable to be able to resolve these structural changes both spatially and temporally. Here, we present a novel method for detecting nanoscale structural changes non-invasively. This technique is based on adaptation of the correlation mapping approach to nano-sensitive optical coherence tomography (nsOCT). Our work describes the principles of this technique and demonstrates the feasibility of correlation mapping nano-sensitive optical coherence tomography (cm-nsOCT) by monitoring internal structural changes within different objects, including human skin in vivo. Structural changes can be visualized at each point in the sample over space or time. The experimental results show new possibilities for the study of structural changes, without the need for biomarkers or labels. Thus, cm-nsOCT could potentially offer exciting and far-reaching opportunities for early disease diagnosis, as well as myriad applications for researchers.
Optical Coherence Tomography (OCT) is a non-invasive 3 dimensional optical imaging modality that enables high
resolution cross sectional imaging in biological tissues and materials. Its high axial and lateral resolution combined with
high sensitivity, imaging depth and wide field of view makes it suitable for wide variety of high resolution medical imaging
applications at clinically relevant speed. With the advent of swept source lasers, the imaging speed of OCT has increased
considerably in recent years. OCT has been used in ophthalmology to study dynamic changes occurring in the cornea and
iris, thereby providing physiological and pathological changes that occur within the anterior segment structures such as in
glaucoma, during refractive surgery, lamellar keratoplasty and corneal diseases. In this study, we assess the changes in
corneal thickness in the anterior segment of the eye during wound healing process in a rat corneal burn model following
stem cell therapy using high speed swept source OCT.
Optical Coherence Tomography (OCT) is a non-invasive 3 dimensional optical imaging modality that enables high
resolution cross sectional imaging in biological tissues and materials. Unlike other 3 D medical imaging modalities, OCT
provides high axial and lateral resolution combined with high sensitivity, imaging depth and wide field of view which
makes it suitable for wide variety of medical imaging applications1. Apart from analysing the morphological characteristics
of the biological organs with micron scale axial and lateral resolution, OCT also provides functional information from the
biological sample. Among the various functional extensions of OCT, angiographic OCT that enables visualization of
lumens of blood vessels from the acquired OCT B scan images has been of high research interest in the recent past.
Blood flow velocity and red blood cell concentration are of vital importance in assessing tissue microcirculation. Laser speckle contrast analysis is being considered as a promising tool in the qualitative assessment of flow velocity as well as scatterer concentration in different body fluids, though the quantification part still remains challenging. The fractal-based spatial correlation analysis of speckle flow images along with the corresponding contrast analysis for the quantitative assessment of flow and scatterer concentration is investigated. In this study, phantom body fluid solution (intralipid 20%) of different concentrations is pumped at different flow rates through the designed flow channel using a syringe pump and the corresponding speckle images are acquired. The fractality of the acquired speckle images in response to the changes in concentration of the fluid as well as the variations in fluid flow is analyzed along with the corresponding contrast-based analysis. Following this qualitative analysis, an experimental model is attempted toward quantification of these parameters from a single acquired speckle image by considering the contrast and fractality changes together.
Laser based techniques offer non invasive means of imaging and optical signal acquisition in the biomedical field.
Laser Doppler flowmetry and laser speckle imaging are important laser based methods in current research and have
been explored for the analysis of blood flow. Doppler flow meters as well as laser speckle imagers use tissue backscattered
light to non-invasively assess the blood flow rate. While because of large spatial variability and the temporal
heterogeneity in tissue microvasculature, the measured blood flow rate is expressed in relative units in laser
Doppler, laser speckle methods offers a whole field imaging resulting in absolute measurements of flow velocity.
Measurement of and analysis of blood flow is vital in evaluating normal as well as differently diseased conditions of
the human body. Several parameters related to flow along with flow velocity are important in characterizing tissues
based on blood flow. Complexity of the flow is one of such important parameters which could be explored by looking
at the fractality of the acquired Doppler signals / speckle images. In this paper, we are comparing the results of
blood flow complexities assessed through fractal dimensions of Doppler signals and speckle images acquired from
different parts of the body. The method adopted is expected to serve as a helping tool in characterizing normal and
malignant tissues with associated variation in blood flow complexities based on the values of obtained fractal dimensions
in such cases.
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