Ultrasound-modulated optical tomography

Biological tissues to light are much like a glass of milk, where one cannot see a sugar cube in the center of the glass because milk scatters light. Optical imaging of biological tissues has to overcome this problem by recovering imaging information from the scattered light although light at selected wavelengths is able to penetrate 5-10 cm thick biological tissues and provide detectable optical signal. The Optical Imaging Laboratory has pioneered a technique called ultrasound-modulated optical tomography, in which the optical sensitivity is combined with the spatial resolution of ultrasonic imaging.

The goal of this research is to develop a novel non-ionizing non-invasive imaging modality for biomedical applications. Ultrasonic modulation of scattered laser light has been used to image objects buried in tissue-simulating turbid media. The ultrasonic wave that was focused into the turbid media modulated the laser light passing through the ultrasonic field. The modulated laser light reflected primarily the local mechanical and optical properties in the focal zone. A raster scanning over the turbid medium yielded an image of the medium based on the ultrasound-modulated optical signal. Buried objects in 5-cm thick tissue phantoms were located with millimeter resolution (see the following figure). Although this imaging modality has generic applications in biomedicine, we will first test the technique for breast cancer detection.

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