In vivo optical mapping of the tympanic membrane impulse response.

The wide frequency range of the human hearing could be narrowed by various pathologies in the middle ear and in the tympanic membrane that lead to conductive hearing loss. Diagnosing such hearing problems is challenging, however, often relying on subjective hearing tests supported by functional tympanometry. Here we present a method for in vivo 2D mapping of the impulse response of the tympanic membrane, and demonstrate its potential on a healthy human volunteer. The imaging technique is based on interferometric spectrally encoded endoscopy, with a handheld probe designed to scan the human tympanic membrane within less than a second. The system obtains high-resolution 2D maps of key functional parameters including peak response, rise and decay times, oscillation bandwidth and resonance frequency. We also show that the system can identify abnormal regions in the membrane by detecting differences in the local mechanical parameters of the tissue. We believe that by offering a full 2D mapping of broad-bandwidth dynamics of the tympanic membrane, the presented imaging modality would be useful for effective diagnosis of conductive hearing loss in patients.

Measuring the red blood cell shape in capillary flow using spectrally encoded flow cytometry.

Red blood cells in small capillaries exhibit a wide variety of deformations that reflect their true physiological conditions at these important locations. By applying a technique for the high-speed microscopy of flowing cells, termed spectrally encoded flow cytometry (SEFC), we image the light reflected from the red blood cells in human capillaries, and propose an analytical slipper-like model for the cell morphology that can reproduce the experimental in vivo images. The results of this work would be useful for studying the unique flow conditions in these vessels, and for extracting useful clinical parameters that reflect the true physiology of the blood cells in situ.

Pinhole shifting for reducing speckle contrast in reflectance confocal microscopy.

The high speckle contrast in reflectance confocal microscopy is perhaps the most limiting factor on this imaging modality, particularly in high scattering samples such as biological tissues. In this Letter, we propose and numerically analyze a method for speckle reduction that uses simple lateral shifting of the confocal pinhole in several directions, which results in reduced speckle contrast and only a moderate penalty in both lateral and axial resolutions. By simulating free-space electromagnetic wave propagation through a high-numerical-aperture (NA) confocal imaging system, and assuming only single-scattering events, we characterize the 3D point-spread function (PSF) that results from full-aperture pinhole shifting. Simple summation of four different pinhole-shifted images resulted in a 36% reduction in speckle contrast, with reductions of only 17% and 60% in the lateral and axial resolutions, respectively. This method could be particularly useful in noninvasive microscopy for clinical diagnosis, where fluorescence labeling is impractical and high image quality is imperative for achieving accurate diagnosis.