Esteban F. Carbajal

Differential permeability rate and percent clearing of glucose in different regions in rabbit sclera

Imaging of biological tissues with optical coherence tomography (OCT) poses a great interest for its capability to noninvasively outline subsurface microstructures within tissues. However, a major limitation for many optical imaging techniques is inadequate depth penetration of light in turbid media, which is bounded to just a few millimeters. There have been several attempts to improve light penetration depth in biological tissues, including application of different tissue optical clearing methods. In this study, an aqueous solution of glucose (40%) is added to rabbit sclera in vitro, where depth-resolved permeability coefficients and optical clearing are calculated with OCT. The permeability rate in regions in the upper 80- to 100-microm region is found to be different from that of regions in the deeper 100-microm region: (6.01+/-0.37)x10(-6) cmsec and (2.84+/-0.68)x10(-5) cmsec, respectively. A difference in percent clearing is also noted. Optical clearing of the upper region is about 10% and increased to 17 to 22% in the one beneath. These results demonstrate the capability of OCT-based methods to not only measure the diffusion rate and optical clearing of a tissue, but also its ability of functional differentiation between layers of epithelial tissues.

Permeability of hyperosmotic agent in normal and atherosclerotic vascular tissues

Noninvasive cardiovascular imaging could lead to the early detection and timely treatment of complex atherosclerotic lesions responsible for major cardiovascular events. Recent investigations have suggested that optical coherence tomography (OCT) is an ideal diagnostic tool due to the high resolution this technology achieves in discriminating the different features of atherosclerotic lesions based on structural imaging. We explore the capability of OCT for functional imaging of normal and atherosclerotic aortic tissues based on time- and depth-resolved quantification of the permeability of biomolecules through these tissues. The permeability coefficient of 20% aqueous solution of glucose was found to be (6.80+/-0.18)x10(-6) cms in normal aortas and (2.69+/-0.42)x10(-5) cms in aortas with atherosclerotic disease. The results suggest that this new OCT functional imaging method-the assessment of the permeability coefficients of various physiologically neutral biomolecules in vascular tissues-could assist in early diagnosing and detecting the different components of atherosclerotic lesions.

Revealing retroperitoneal liposarcoma morphology using optical coherence tomography

A new approach to distinguish normal fat, well-differentiated (WD), and dedifferentiated liposarcoma (LS) tumors is demonstrated, based on the use of optical coherence tomography (OCT). OCT images show the same structures seen with conventional histological methods. Our visual grading analysis is supported by numerical analysis of observed structures for normal fat and WDLS samples. Further development could apply the real-time and high resolution advantages of OCT for use in liposarcoma diagnosis and clinical procedures.

The effect of solution concentration on diffusion in scleral tissues

The calculation of permeability coefficient of analytes could potentially be used in a variety of basic science and clinical fields, as well as advanced diagnostic imaging. Before this can occur, a more thorough understanding of the diffusion rate of analytes in biological tissues is needed. For this task, we utilized Optical Coherence Tomography for the functional imaging of glucose diffusion through rabbit sclera tissues. The permeability coefficients were calculated for different concentrations of glucose solution as they diffused through the tissue. From the experiments performed it was noticed that the concentration of the analyte was inversely proportional to the permeability coefficient calculated. The permeability coefficient of glucose solution with lower concentration was faster when compared with higher concentration. The decrease in the permeability coefficient ranged from (1.67 ± 0.17) x 10-5 cm/sec with the 10% glucose solution to (5.08 ± 0.23) x 10-6cm/sec of 25% glucose solution. The results of this study could expand the use of the permeability coefficient into the field of diagnostic imaging.

Nonlinear diffusivity of analytes in tissues

Noninvasive assessments of optical clearing and permeability coefficients of tissues pose great possibilities in advanced diagnostics and medical applications. In order for both of these to become utilized in common practice, a greater understanding of molecular diffusivity in multi-layered tissues is required. In biological tissues, the different layers are comprised of differentiated cells and/or collagen fibrils which come together to form that specific layer. Therefore, a patchwork of layers is created each with its own set of properties. In our current study we analyze and describe the dynamics of matter diffusion and its underlying non-linear character in various epithelial tissues. For instance, the permeability coefficient (PC) of 20% concentrated mannitol in the rabbit eye sclera showed an increasing trend as it was measured deeper into the tissue. The PC was found to be 2.18 × 10-6 cm/sec at 50 μm away from the epithelial layer. It increased to about 7.33 × 10-6 cm/sec when it was computed at 210 μm from the epithelial layer. Different layers in the sclera showed different clearing response to glucose solution as well. The first 100 μm region from the epithelial layer cleared about 10% whereas the next 100 μm cleared about 17-22%. The importance of this study is that it may offer a novel explanation to how a layers composition affects optical clearing and the permeability coefficient of analytes and solutions.

Quantification of microbubbles in blood with phase-sensitive SSOCT

We have developed a phase stabilized swept source optical coherence tomography (PhS-SSOCT), that shows an axial resolution of 10 μm, phase sensitivity of 0.04 radians, imaging depth of up to 6 mm in air and a scanning speed of 20 kHz for a single A-line. In this paper, the PhS-SSOCT is applied to quantify gas microbubbles in blood in vitro. The results indicate that the system is able to detect bubbles of diameters greater than 10 μm using the structural image and the microbubbles of diameter less than 10 μm could be detected using the temporal phase response. Images of the bubbles of diameters 600 μm, 405 μm and 6 μm along with their phase responses are presented. Results indicate that the PhS-SSOCT could be potentially used for rapid assessment of blood microbubbles in vivo that cause diseases associated with decompression sickness, venous and arterial gas emboli and barotraumas. Eventually, PhS-SSOCT can be utilized as an early diagnostic tool for clinical purposes.

Noninvasive assessment of optical clearing of epithelial tissues with OCT

Selective translucence of epithelial tissues is key technique for imaging in highly scattering media. Here we demonstrate capability of OCT for noninvasive and depth-resolved quantification of tissue optical clearing by application of various hyperosmotic agents.

Quantifying permeability of glucose in normal and atherosclerotic pig aorta in vitro using optical coherence tomography

High in-depth resolution imaging, such as Optical Coherence Tomography, could be the next frontier in noninvasive quantification of diffusion in epithelial tissues. In this study we employed OCT in a method that could help differentiate various forms of atherosclerosis and distinguish between normal and diseased tissue. The diffusion of glucose solution in normal and diseased pig aorta in vitro was monitored and the permeability coefficient was calculated. The results suggest that this OCT method may have high potential for early detection of tissue abnormalities while used in diffusion studies.