Abstract
We demonstrate high speed, swept source optical coherence microscopy (OCM) using a MEMS tunable vertical cavity surface-emitting laser (VCSEL) light source. The light source had a sweep rate of 280 kHz, providing a bidirectional axial scan rate of 560 kHz. The sweep bandwidth was 117 nm centered at 1310 nm, corresponding to an axial resolution of 13.1 µm in air, corresponding to 8.1 µm (9.6 µm spectrally shaped) in tissue. Dispersion mismatch from different objectives was compensated numerically, enabling magnification and field of view to be easily changed. OCM images were acquired with transverse resolutions between 0.86 µm - 3.42 µm using interchangeable 40X, 20X and 10X objectives with ~600 µm x 600 µm, ~1 mm x 1 mm and ~2 mm x 2 mm field-of-view (FOV), respectively. Parasitic variations in path length with beam scanning were corrected numerically. These features enable swept source OCM to be integrated with a wide range of existing scanning microscopes. Large FOV mosaics were generated by serially acquiring adjacent overlapping microscopic fields and combining them in post-processing. Fresh human colon, thyroid and kidney specimens were imaged ex vivo and compared to matching histology sections, demonstrating the ability of OCM to image tissue specimens.
Highlights
Optical coherence microscopy (OCM) uses coherence-gated detection to remove out-of-focus light and improves contrast and imaging depth over conventional reflectance confocal microscopy for imaging scattering tissues [1, 2]
We demonstrate Swept source OCM (SS-OCM) using a high speed, prototype vertical cavity surface-emitting laser (VCSEL) light source operating at 1310 nm with a 280 kHz sinusoidal sweep frequency and bidirectional A-scan rate of 560 kHz (Thorlabs, Inc. and Praevium Research, Inc.)
The specimens were stored in chilled Dulbecco's Modified Eagle Medium (DMEM) and imaged within several hours after removal from the body
Summary
Optical coherence microscopy (OCM) uses coherence-gated detection to remove out-of-focus light and improves contrast and imaging depth over conventional reflectance confocal microscopy for imaging scattering tissues [1, 2]. The utility of OCM to identify pathologies has been demonstrated in ex vivo studies using human breast, thyroid and renal tissue [3,4,5,6]. Lung, thyroid, and head and neck cancers would benefit from an imaging modality that enables real time assessment of surgical specimens and could reduce the rates of second surgeries from positive or close surgical margins [7,8,9]. OCM has a broad range of applications for research and biological microscopy, ranging from cellular level imaging of the cortex in small animals, to in vivo imaging of developmental biology specimens [10,11,12,13,14]
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