A dual modality fluorescence confocal and optical coherence tomography microendoscope

We demonstrate the implementation of a Fourier domain optical coherence tomography (OCT) imaging system incorporated into the optical train of a fluorescence confocal microendoscope. The slit-scanning confocal system has been presented previously and achieves 3μm lateral resolution and 25μm axial resolution over a field of view of 430μm. Its multi-spectral mode of operation captures images with 6nm average spectral resolution. To incorporate OCT imaging, a common-path interferometer is made with a super luminescent diode and a reference coverslip located at the distal end of the fiber bundle catheter. The infrared diode spectral width allows a theoretical OCT axial resolution of 12.9μm. Light from the reference and sample combine, and a diffraction grating produces a spectral interferogram on the same 2D CCD camera used for confocal microendoscopic imaging. OCT depth information is recovered by a Fourier transform along the spectral dispersion direction. Proper operation of the system scan mirrors allows rapid switching between confocal and OCT imaging modes. The OCT extension takes advantage of the slit geometry, so that a 2D image is acquired without scanning. Combining confocal and OCT imaging modalities provides a more comprehensive view of tissue and the potential to improve disease diagnosis. A preliminary bench-top system design and imaging results are presented.