Abstract
Forward-viewing endoscopic optical coherence tomography (OCT) provides 3D imaging in vivo, and can be combined with widefield fluorescence imaging by use of a double-clad fiber. However, it is technically challenging to build a high-performance miniaturized 2D scanning system with a large field-of-view. In this paper we demonstrate how a 1D scanning probe, which produces cross-sectional OCT images (B-scans) and 1D fluorescence T-scans, can be transformed into a 2D scanning probe by manual scanning along the second axis. OCT volumes are assembled from the B-scans using speckle decorrelation measurements to estimate the out-of-plane motion along the manual scan direction. Motion within the plane of the B-scans is corrected using image registration by normalized cross correlation. En-face OCT slices and fluorescence images, corrected for probe motion in 3D, can be displayed in real-time during the scan. For a B-scan frame rate of 250 Hz, and an OCT lateral resolution of approximately , the approach can handle out-of-plane motion at speeds of up to 4 mm/s.
Highlights
Endoscopic optical coherence tomography (E-OCT) allows high-resolution imaging of tissue to a depth of 1-2 mm beneath the surface
The system, loosely based on a configuration reported by Scolaro et al [37], combines a swept-source OCT sub-system operating at a central wavelength λ0 = 1310 nm with a fluorescence imaging sub-system, with a λe = 488 nm solid-state laser providing the excitation
In the OCT sub-system, the output from a miniature beam-scanning element using a micro-electromechanical (MEMS) swept-source (Axsun Technologies, central wavelength λ0 = 1310 nm, tuning range ∆λ = 100 nm, sweep rate 100 kHz) is sent to a fused fiber coupler DC1, with a splitting ratio of 90/10. 10% of the optical power is routed to a custom-built optical delay line (ODL) forming the reference arm of the interferometer, and is afterwards reunited with the power returning from the object arm at DC2, which has a 50/50 split ratio to ensure balanced detection at the photo-detector BPD (Thorlabs, model PDB480C-AC)
Summary
Endoscopic optical coherence tomography (E-OCT) allows high-resolution imaging of tissue to a depth of 1-2 mm beneath the surface. Scanning can be achieved by rotating the fiber using a motor at the proximal end, outside of the patient [1,4,5]. The deflecting element may be fixed onto a micro-motor at the distal end of the probe, in which case the fiber and lens assembly itself does not need to rotate [6,7,8]. Different optical configurations in the distal end, such as those involving the use of a diffractive lens [5], can help to mitigate spectral losses when large spectral bandwidths are required for increased axial resolution. Different optical configurations in the distal end, such as those involving the use of a diffractive lens [5], can help to mitigate spectral losses when large spectral bandwidths are required for increased axial resolution. 3D imaging is achieved by moving the probe axially, obtaining ‘tunnel-like’
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