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Published September 2008 | Published
Journal Article Open

Ultrasound-modulated optical microscopy

Abstract

We demonstrate that microscopic imaging is feasible in ultrasound-modulated optical tomography (UOT) of soft biological tissues, using a high-frequency focused ultrasound transducer with a 75-MHz central frequency. Our experiments in tissue mimicking phantoms show that at an imaging depth of about 2mm, an axial resolution better than 30μm can be achieved, whereas the lateral resolution is 38μm. A long-cavity scanning confocal Fabry-Perot interferometer (CFPI) is used for real-time detection of multiply scattered light modulated by high-frequency ultrasound pulses propagating in an optically scattering medium. We also compare the performances of various high-frequency focused ultrasound transducers with central frequencies of 15MHz, 30MHz, 50MHz, and 75MHz. The comparison is based on two-dimensional (2-D) images of optically absorbing objects positioned at a few millimeters depth below the surface of both optically scattering phantoms and soft biological tissue samples. Our experimental results show that modulation depth and image contrast decrease with an increase in ultrasound frequency. In addition, we use analytical calculations to show that modulation depth decreases with increasing ultrasound frequency.

Additional Information

© 2008 SPIE. Paper 08118R received Apr. 8, 2008; revised manuscript received Jun. 24, 2008; accepted for publication Jul. 8, 2008; published online Oct. 9, 2008. We thank Dr. S. Sakadzic for fruitful scientific and technical discussions and Dr. K. Maslov for preparing acoustic lenses for all four transducers used in our experiments. This research was supported by the National Institutes of Health through Grant Nos. R33 CA094267 and R01 CA106728.

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