Multimodal Optical Medical Imaging Concepts Based on Optical Coherence Tomography

Optical medical imaging techniques in general exhibit outstanding resolution and molecule-specific contrast. They come however with a limited penetration in depth and small field of view. Multimodal concepts help to combine complementary strengths of different imaging technologies. The present article reviews the advantages of optical multimodal imaging concepts using optical coherence tomography (OCT) as core technology. In particular we first discuss polarization sensitive OCT, Doppler OCT and OCT angiography, OCT elastography, and spectroscopic OCT as intramodal concepts. To highlight intermodal imaging concepts, we then chose the combination of OCT with photoacoustics, and with non-linear optical microscopy. The selected multimodal concepts and their particular complementary strengths and applications are discussed in detail. The article concludes with notes on standardization of OCT imaging and multimodal extensions

Endoscopic optical coherence tomography with a flexible fiber bundle

We demonstrate in vivo endoscopic optical coherence tomography (OCT) imaging in the forward direction using a flexible fiber bundle. In comparison to current conventional forward looking probe schemes, our approach simplifies the endoscope design by avoiding the integration of any beam steering components in the distal probe end due to 2D scanning of a focused light beam over the proximal fiber bundle surface. We describe the challenges that arise when OCT imaging with a fiber bundle is performed, such as multimoding or cross-coupling. The performance of different fiber bundles with varying parameters such as numerical aperture, core size and core structure was consequently compared and artifacts that degrade the image quality were described in detail. Based on our findings, we propose an optimal fiber bundle design for endoscopic OCT imaging

Logarithmic transformation technique for exact signal recovery in frequency-domain optical-coherence tomography

AN APPEAL FROM A JUDGMENT AND DECREE OF DIVORCE OF THE THIRD JUDICIAL DISTRICT, SALT LAKE COUNTY, UTAH THE HONORABLE JOHN A. ROKICH JUDGE PRESIDING

Coherent transfer functions and extended depth of field

To preserve the speed advantage of Fourier Domain detection in Optical Coherence Microscopy (OCM), extended depth of field is needed. With a narrow probing volume that extends over a long axial range, tissue could be measured in vivo and at cellular resolution. To assess and improve the DOF and the lateral resolution, we analyzed the coherent transfer function (CTF) of OCM. Both the illumination and detection optics contribute equally to the overall imaging performance. In the Fourier domain detection, each pixel of the spectrometer has its specific CTF, sampling a different region of the object’s spatial frequency spectrum. For classical optics and increasing numerical apertures these regions start to overlap and bend, which limits the depth of field. Annular apertures, created with Bessel-like beams produced by axicon lenses or phase filters, circumvent these detrimental effects, but introduce strong side lobes. Decoupling the detection and the illumination apertures is needed to provide the flexibility in engineering a CTF that optimizes the lateral resolution and the DOF at the same time all while reducing these side lobes. We evaluated different combinations of Gaussian and Bessel-like illumination and detection optics, both theoretically and experimentally. Using Bessel-like beams as well in the illumination as in the detection paths, but with annular apertures of different lobe radii, we obtained a lateral resolution of 1.3 μm and an extended depth of field of more than 300 μm, which was completely decoupled from the numerical aperture and scalable to high lateral resolution

Optical coherence tomography angiography for chronic venous insufficiency and venous leg ulcer

Chronic venous insufficiency (CVI) ranks among the most common health care issues worldwide. The current diagnosis of CVI is done by clinical examination and duplex ultrasound, which can only detect visible physical changes and deeper vascular structures whereas the superficial cutaneous vasculature cannot be resolved. There is indeed a lack of information that can potentially be extracted from the cutaneous microvasculature of patients affected by CVI. In this work, we designed and applied an optical coherence tomography angiography (OCTA) system, which is customized for lower extremity imaging of patients. Featuring fast imaging speed, large field of view, high spatial resolution, and most importantly non-invasiveness, this OCTA system was successfully applied in CVI and venous leg ulcer patient imaging. Using the OCTA results acquired from a cohort of 27 human subjects, we can clearly distinguish the vascular patterns uniquely associated with various stages of CVI. The findings of this study give an unexplored indicator to the disease of CVI and venous leg ulcer. With more patients to be recruited, we believe that OCTA imaging results for CVI can be used as a powerful tool in CVI screening and diagnosis

Multimodal imaging of the mouse eye using visible light photoacoustic ophthalmoscopy and near-infrared-II optical coherence tomography

Non-invasive imaging plays a crucial role in diagnosing and studying eye diseases. However, existing photoacoustic ophthalmoscopy (PAOM) techniques in mice have limitations due to handling restrictions, suboptimal optical properties, limited availability of light sources and permissible light fluence at the retina. This study introduces an innovative approach that utilizes Rose Bengal, a contrast agent, to enhance PAOM contrast. This enables visualization of deeper structures like the choroidal microvasculature and sclera in the mouse eye using visible light. The integration of near-infrared-II optical coherence tomography (NIR-II OCT) provides additional tissue contrast and insights into potential NIR-II PAOM capabilities. To optimize imaging, we developed a cost-effective 3D printable mouse eye phantom and a fully 3D printable tip/tilt mouse platform. This solution elevates PAOM to a user-friendly technology, which can be used to address pressing research questions concerning several ocular diseases such as myopia, glaucoma and/or age-related macular degeneration in the future.Comment: 14 pages, 4 figure