We have designed a multimodality system that combines optical coherence tomography (OCT) and laser-induced fluorescence (LIF) in a 2.0-mm-diameter endoscopic package. OCT provides approximately 18-microm resolution cross-sectional structural information over a 6-mm field. LIF spectra are collected sequentially at submillimeter resolution across the same field and provide histochemical information about the tissue. We present the use of a rod prism to reduce the asymmetry in the OCT beam caused by a cylindrical window. The endoscope has been applied to investigate mouse colon cancer in vivo.
Frequency domain optical coherence tomography (FD-OCT) allows interferometer topologies with simplified system construction and handling. Problems of dispersion and polarization matching between the sample and reference arms, as well as beamsplitter spectral non-uniformity, are mitigated when the interferometer is wholly contained in the endoscope tip. A common path set-up, using a reference reflection originating from the inside surface of the glass envelope at the distal end of the endoscope, and an alternative approach with more efficient collection of the reference light using a novel beamsplitter design have been developed. High speed (20,000 A-lines/s) ultrahigh axial resolution (2.4 mum) tomograms of mouse colon have been acquired using a 2 mm outer diameter endoscope in vivo. The FD-OCT system uses a compact mode-locked Ti:Al(2)O(3) laser emitting a broad spectrum (160 nm full-width-half-maximum) centered at 800 nm in combination with a CCD based, spectrally sensitive detector.
: Recent substantial developments in light source and detector technology have initiated a paradigm shift in retinal optical coherence tomography (OCT) performance. Broad bandwidth light sources in the 800 nm and 1060 nm wavelength region enable axial OCT resolutions of 2-3 mum and 5-7 mum, respectively. Novel high speed silicon based CMOS cameras at 800 nm and InGaAs based CCD cameras in combination with frequency domain OCT technology enable data acquisition speeds of up to 47,000 A-scans/s at 1060 nm and up to 312,500 A-scans/s at 800 nm. Combining ultrahigh axial resolution, ultrahigh speed OCT at 800 nm with pancorrected adaptive optics allows volumetric in vivo cellular resolution retinal imaging. Commercially available three-dimensional (3D) retinal OCT at 800 nm (20,000 A-scans/s, 6 mum axial resolution) is compared to ultrahigh speed 3D retinal imaging at 800 nm (160,000 A-scans/s, 2-3 mum axial resolution), high speed 3D choroidal imaging at 1060 nm (47,000 Ascan/ second, 6-7 mum axial resolution) and cellular resolution retinal imaging at 800 nm using adaptive optics OCT at 160,000 A-scans/second with isotropic resolution of ~2 mum. Analysis of the performance of these four imaging modalities applied in normal and pathologic eyes focusing on motion artifact free volumetric retinal imaging and revealing novel, complementary morphological information due to enhanced resolution, speed and penetration is presented.
Endoscopic ultrahigh-resolution optical coherence tomography (OCT) enables collection of minimally invasive cross-sectional images in vivo, which may be used to facilitate rapid development of reliable mouse models of colon disease as well as assess chemopreventive and therapeutic agents. The small physical scale of mouse colon makes light penetration less problematic than in other tissues and high resolution acutely necessary. In our 2-mm diameter endoscopic time domain OCT system, isotropic ultrahigh-resolution is supported by a center wavelength of 800 nm and full-width-at-half-maximum bandwidth of 150 nm (mode-locked titanium:sapphire laser) combined with 1:1 conjugate imaging of a small core fiber. A pair of KZFSN5/SFPL53 doublets provides excellent color correction to support wide bandwidth throughout the imaging depth. A slight deviation from normal beam exit angle suppresses collection of the strong back reflection at the exit window surface. Our system achieves axial resolution of 3.2 microm in air and 4.4-microm lateral spot diameter with 101-dB sensitivity. Microscopic features too small to see in mouse tissue with conventional resolution systems, including colonic crypts, are clearly resolved. Resolution near the cellular level is potentially capable of identifying abnormal crypt formation and dysplastic cellular organization.
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