μOCT imaging using depth of focus extension by self-imaging wavefront division in a common-path fiber optic probe.

Biwei Yin,Chia-Pin Liang,Kanwarpal Singh,Kengyeh K Chu,Rohith Reddy,Guillermo J Tearney

doi:10.1364/oe.24.005555

Biwei Yin, Chia-Pin Liang + Show 4 more

Open Access

https://doi.org/10.1364/oe.24.005555

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Abstract

Optical coherence tomography (OCT) is an attractive medical modality due to its ability to acquire high-resolution, cross-sectional images inside the body using flexible, small-diameter, scanning fiber optic probes. Conventional, cross-sectional OCT imaging technologies have approximately 10-μm axial resolution and 30-μm lateral resolution, specifications that enable the visualization of microscopic architectural morphology. While this resolution is useful for many clinical applications, it is insufficient for resolving individual cells that characterize many diseases. To address this gap, a supercontinuum-laser-based, μm-resolution OCT (μOCT) system and a 500 μm-diameter, extended depth of focus single fiber optic probe for endoscopic and intravascular imaging were designed and fabricated. At the distal tip of the fiber optic probe, a cylindrical waveguide was used to divide the wavefront to provide multiple circular propagation modes. Once transmitted through a relatively high NA lens (NA >0.1), these modes were projected as multiple coaxial foci (~3 μm full width at half maximum (FWHM)) over a greatly extended focal depth range. The distal tip of the probe also contained a common-path reference reflectance to minimize polarization and dispersion imbalances between sample and reference arm light. Measurements showed that the probe provides a 20-fold depth of focus extension, maintaining a 3-5 µm lateral resolution (FWHM of PSF) and a 2 μm axial resolution over a depth range of approximately 1 mm. These results suggest that this new optical configuration will be useful for achieving high-resolution, cross-sectional OCT imaging in catheter/endoscope-based medical imaging devices.

Highlights

Optical coherence tomography (OCT) [1, 2] is an interferometric coherence ranging-imaging modality that has significantly better resolution than other clinical imaging techniques such as ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI)
Key features of OCT include cross-sectional imaging, which is important clinically because many diseases manifest below the tissue surface, and its capability to image inside the body using flexible, small-diameter, fiber optic probes
These techniques require multiple image acquisitions, computationally intensive processing and phase stability during data acquisition. Most of these solutions either do not extend the focus sufficiently or are too large or complex to fit within the confines of small diameter scanning probes intended to be inserted inside the body. To address this technical barrier, we developed a single-fiber selfimaging wavefront division probe that has a diameter of 500 μm, less than 4-mm rigid length, and a 20-fold depth of focus (DOF) extension compared to a conventionally focused beam with comparable lateral resolution

Summary

Introduction

Optical coherence tomography (OCT) [1, 2] is an interferometric coherence ranging-imaging modality that has significantly better resolution than other clinical imaging techniques such as ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI). Key features of OCT include cross-sectional imaging, which is important clinically because many diseases manifest below the tissue surface, and its capability to image inside the body using flexible, small-diameter, fiber optic probes. With the introduction of single-mode-ultra-broad bandwidth supercontinuum light sources, significant progress has been made towards increasing the axial resolution of OCT, and recent studies using supercontinuum sources and common path interferometer configurations have shown μOCT axial resolutions ranging from 1 to 2 μm in tissue [4]. It has been difficult to improve lateral resolution beyond approximately 30 μm without sacrificing cross-sectional imaging because depth of focus (DOF) is proportional to the square of the lateral spot size

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