We present an implementation of ultrasound-modulated optical tomography that has the potential to provide high resolution images of tissue structures at a penetration depth of several millimeters. Light and pulsed ultrasound are focused on an approximately 100 μm wide area below the sample surface. With this configuration, the length of the ultrasonic pulses determines the axial resolution,
and the lateral resolution results from the width of the ultrasonic beam at the focus. Diffuse light reflected from the sample is collected into a fiber and the modulated component is separated from the background by a confocal Fabry-Perot interferometer. Using this setup, high contrast images are obtained of 100 μm wide pieces of hair that are buried one millimeter below the surface of the
tissue-mimicking sample. It is the first time, to the authors' knowledge, that images with such high resolution have been obtained using ultrasound-modulated optical tomography in the reflection mode.
We present an image reconstruction technique for ultrasound-modulated optical tomography. It is the first time, to the authors' knowledge, that a reconstruction technique is developed for such tomography. In analogy to X-ray computed tomography, an ultrasonic beam is scanned linearly and angularly across a biological-tissue sample. Ultrasound-modulated optical signals, reflecting the optical properties of the sample inside the ultrasonic column, are detected and taken as the projection data for the reconstruction, where a filtered back-projection algorithm is implemented. With the technique, two-dimensional images of biological tissues in cross-sections containing the scanned ultrasonic axis are obtained. The image resolution is determined by the diameter of the ultrasonic focal zone. The technique can be implemented with any standard signal-detection scheme for ultrasonic modulation of coherent light in scattering media and can be applied directly to achieve three-dimensional images of biological tissues.
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