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

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.

Extended depth of focus for coherence-based cellular imaging

“…Such passive methods require unconventional optical elements (e.g., axicon) that are difficult to reliably manufacture [11] or phase/ amplitude modification of the imaging system’s pupil [12], similarly suffering from complexity, and challenging the alignment and fabrication [13]. Recently, we observed nearly an order of magnitude DOF extension [resolution characterized in terms of full width-at half-maximum (FWHM) of the point spread function (PSF)] in a scattering phantom image using a very simple optical system comprising a cylindrical waveguide in front of a lens that retains the small size and simplicity of conventional endoscopic OCT imaging probes [14]. This self-imaging wavefront division optical system generates a coaxially focused multimode (CAFM) beam to acquire a cross-sectional image.…”

Visualization and tissue classification of human breast cancer images using ultrahigh‐resolution OCT

“…A recent study [33] demonstrated that UHR OCT may enable high resolution 3D visualization of a variety of tissue types in fresh excised breast tissue to aid in differentiation of malignancy with an appreciable imaging depth. Moreover, UHR OCT was also demonstrated in small diameter catheters [34,35], which would benefit not only surgical margin guidance during lumpectomy but also local biopsy of early cancerous sites during ductoscopy [36].…”

Flexible, high-resolution micro-optical coherence tomography endobronchial probe toward in vivo imaging of cilia

“…However, the clinical utility of this probe was limited by its relatively large diameter and the fact that it was rigid. We also reported another μOCT probe design featuring a significantly reduced diameter and increased flexibility [16]. However, the longer working distance required for airway imaging creates a large optical path difference between the sample position and the glass reflection that acts as the reference, which would require an extremely high-resolution spectrometer to capture the resultant high-frequency fringes.…”

“…We performed ex vivo μOCT imaging of mouse trachea using both the benchtop μOCT instrument we utilized in previous studies [16] and the flexible probe attached to a typical SD-OCT platform (Fig. 1).…”