Nonlinear interferometric vibrational imaging

A method of examining a sample, which includes: exposing a reference to a first set of electromagnetic radiation, to form a second set of electromagnetic radiation scattered from the reference; exposing a sample to a third set of electromagnetic radiation to form a fourth set of electromagnetic radiation scattered from the sample; and interfering the second set of electromagnetic radiation and the fourth set of electromagnetic radiation. The first set and the third set of electromagnetic radiation are generated from a source; at least a portion of the second set of electromagnetic radiation is of a frequency different from that of the first set of electromagnetic radiation; and at least a portion of the fourth set of electromagnetic radiation is of a frequency different from that of the third set of electromagnetic radiation

Contrast enhanced spectroscopic optical coherence tomography

A method of forming an image of a sample includes performing SOCT on a sample. The sample may include a contrast agent, which may include an absorbing agent and/or a scattering agent. A method of forming an image of tissue may include selecting a contrast agent, delivering the contrast agent to the tissue, acquiring SOCT data from the tissue, and converting the SOCT data into an image. The contributions to the SOCT data of an absorbing agent and a scattering agent in a sample may be quantified separately

Distinguishing non-resonant four-wave-mixing noise in coherent stokes and anti-stokes Raman scattering

A method of examining a sample comprises exposing the sample to a pump pulse of electromagnetic radiation for a first period of time, exposing the sample to a stimulant pulse of electromagnetic radiation for a second period of time which overlaps in time with at least a portion of the first exposing, to produce a signal pulse of electromagnetic radiation for a third period of time, and interfering the signal pulse with a reference pulse of electromagnetic radiation, to determine which portions of the signal pulse were produced during the exposing of the sample to the stimulant pulse. The first and third periods of time are each greater than the second period of time

Structural and Functional Biomedical Imaging Using Polarization-Based Optical Coherence Tomography

University of Minnesota Ph.D. dissertation. August 2015. Major: Biomedical Engineering. Advisor: Taner Akkin. 1 computer file (PDF); x, 103 pages.Biomedical imaging has had an enormous impact in medicine and research. There are numerous imaging modalities covering a large range of spatial and temporal scales, penetration depths, along with indicators for function and disease. As these imaging technologies mature, the quality of the images they produce increases to resolve finer details with greater contrast at higher speeds which aids in a faster, more accurate diagnosis in the clinic. In this dissertation, polarization-based optical coherence tomography (OCT) systems are used and developed to image biological structure and function with greater speeds, signal-to-noise (SNR) and stability. OCT can image with spatial and temporal resolutions in the micro range. When imaging any sample, feedback is very important to verify the fidelity and desired location on the sample being imaged. To increase frame rates for display as well as data throughput, field-programmable gate arrays (FPGAs) were used with custom algorithms to realize real-time display and streaming output for continuous acquisition of large datasets of swept-source OCT systems. For spectral domain (SD) OCT systems, significant increases in signal-to-noise ratios were achieved from a custom balanced detection (BD) OCT system. The BD system doubled measured signals while reducing common term. For functional imaging, a real-time directed scanner was introduced to visualize the 3D image of a sample to identify regions of interest prior to recording. Elucidating the characteristics of functional OCT signals with the aid of simulations, novel processing methods were also developed to stabilize samples being imaged and identify possible origins of functional signals being measured. Polarization-sensitive OCT was used to image cardiac tissue before and after clearing to identify the regions of vascular perfusion from a coronary artery. The resulting 3D image provides a visualization of the perfusion boundaries for the tissue that would be damaged from a myocardial infarction to possibly identity features that lead to fatal cardiac arrhythmias. 3D functional imaging was used to measure functional retinal activity from a light stimulus. In some cases, single trial responses were possible; measured at the outer segment of the photoreceptor layer. The morphology and time-course of these signals are similar to the intrinsic optical signals reported from phototransduction. Assessing function in the retina could aid in early detection of degenerative diseases of the retina, such as glaucoma and macular degeneration

Characterization of flow dynamics in vessels with complex geometry using Doppler optical coherence tomography

The study of flow dynamics in complex geometry vessels is highly important in many biomedical applications where the knowledge of the mechanic interactions between the moving fluid and the housing media plays a key role for the determination of the parameters of interest, including the effect of blood flow on the possible rupture of atherosclerotic plaques. Doppler Optical Coherence Tomography (DOCT) is an optic, non-contact, non-invasive technique able to achieve detailed analysis of the flow/vessel interactions, allowing simultaneously high resolution imaging of the morphology and composition of the vessel and of the flow velocity distribution along the measured cross-section. DOCT system was developed to image high-resolution one-dimensional and multi-dimensional velocity distribution profiles of Newtonian and non-Newtonian fluids flowing in vessels with complex geometry, including Y-shaped and T-shaped vessels, vessels with aneurism, bifurcated vessels with deployed stent and scaffolds. The phantoms were built to study the interaction of the flow dynamics with different channel geometries and to map the related velocity profiles at several inlet volume flow rates. Feasibility studies for quantitative observation of the turbulence of flows arising within the complex geometry vessels are discussed. In addition, optical clearing of skin tissues has been utilized to achieve DOCT imaging of human blood vessels in vivo, at a depth up to 1.7 mm. Two-dimensional OCT images of complex flow velocity profiles in blood vessel phantom and in vivo subcutaneous human skin tissues are presented. The effect of optical clearing on in vivo images is demonstrated and discussed. DOCT was also applied for imaging scaffold structures and for mapping flow distributions within the scaffold.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

HIGH-SPEED ENDOSCOPIC OPTICAL COHERENCE TOMOGRAPHY AND ITS APPLICATIONS

Optical coherence tomography (OCT) is a real-time high-resolution imaging technology providing cross-sectional images of biological structures at a resolution of <1 to 20 µm and a penetration depth of 1 to 3 mm in most highly scattering tissues. OCT is in general non-invasive and can perform real-time ‘optical biopsy’ with a resolution approaching standard low magnification histopathology but without tissue removal. Conventional OCT requires a bulky imaging probe, which limits most of the in vivo applications to ophthalmology and dermatology. The development of miniature OCT imaging probe has greatly expanded the scope of the applications (e.g., cardiology, gastroenterology, etc.). Recent technical advances in OCT has extended the imaging speed from a few kHz to a few hundreds kHz, enabling in vivo three-dimensional (3D) imaging. This dissertation describes the development of a high-speed endoscopic OCT imaging system. The system employs the Fourier domain mode locking laser technology at a wavelength range of 1300 nm to reach an axial resolution of 9.7 µm and an A-scan rate of 220 kHz. A Mach-Zehnder interferometer setup is used to achieve shot-noise limited detection. A generic OCT software platform is developed for data acquisition, processing, display, storage, and 3D visualization. Miniature OCT imaging probes are designed and fabricated for in vivo 3D OCT imaging. The utility of the high-speed endoscopic OCT system is demonstrated for clinical and basic researches in pulmonology and gastroenterology. In addition, an ultrahigh-resolution endoscopic OCT system is developed at a wavelength range of 800 nm to reach an axial resolution of 3.0 µm and an A-scan rate of up to 20 kHz. Furthermore, a novel type of OCT contrast agents, scattering dominant gold nanocages, is developed with the aid of a cross-reference OCT imaging method. Finally, a multimodal endoscopic imaging system combines 1300 nm en face OCT and 1550 nm two photon fluorescence is developed. Compared with most of other imaging modalities, high-speed endoscopic OCT has unmatched advantages including high spatial resolution, imaging speed, and non-invasiveness / minimal invasiveness. The results in this dissertation suggest that high-speed endoscopic OCT may has a great impact on healthcare as well as basic research