High-resolution ultrasound-modulated optical tomography in biological tissues

Abstract

We present a novel implementation of high-resolution ultrasound-modulated optical tomography that, based on optical contrast, can image several millimeters deep into soft biological tissues. A long-cavity confocal Fabry -Perot interferometer, which provides a large etendue and a short response time, was used to detect the ultrasound-modulated coherent light that traversed the scattering biological tissue. Using 15-MHz ultrasound, we imaged with high-contrast light-absorbing structures placed .3 mm below the surface of chicken breast tissue. The resolution along the axial and the lateral directions with respect to the ultrasound propagation direction was better than 70 and 120 mm, respectively. The resolution can be scaled down further by use of higher ultrasound frequencies. This technology is complementary to other imaging technologies, such as confocal microscopy and optical-coherence tomography, and has the potential for broad biomedical applications.

Correlation Transfer and Diffusion of Ultrasound-Modulated Multiply Scattered Light

“…At present, the development of effective detection systems is the subject of intense research. [3][4][5][6][7][8][9][10] Also, the exact nature of the ultrasound-modulation of light in a highly optically scattering medium is still not totally understood due to the complicated light-ultrasound interaction in the presence of optical scatterers. Similarly to dynamic light scattering by scatterers undergoing Brownian motion, 11 dynamic scattering by optical scatterers oscillating in an ultrasound field causes optical frequency shifts.…”

Fast acousto-optic tissue sensing with tandem nanosecond pulses

“…The disadvantage of this technique is the great loss of signal photons due to the small etendue (the product of the solid angle and area of an aperture) when pinholes are used to select a parallel light beam with a certain frequency. However long-cavity [50] confocal Fabry-Perot interferometers are used which have a high etendue.…”

“…A third method to increase the axial resolution uses short US pulses [50,54,57,74]. These pulses consist of a few US cycles and thus modulate the light only locally in the axial direction.…”

“…Another example of what could be seen as synthetic focusing is used by Li et al [78]. Sakadžić et al [50] used tomography to achieve very high resolutions in the order of 100 µm.…”

“…While this is not a problem for PA, for AO tissue dynamics has impeded practical in vivo application based on spatial speckle analysis. AO detection is based on either analysis of dynamic laser speckles or narrow band spectral filters like spectral hole burning [69] and Fabry Perot etalons [50]. The speckle based techniques are widely used but suffer from speckle decorrelation, leading to long measurement times and low signal-to-noise ratios.…”