Research Of The Ultrasound-modulated Optical Imaging Technique

Optical tomography of biological tissue has become an active research field because of the advantages of noninvasive, sensitive and functional imaging for biomedical diagnosis. It is very helpful to find cancerous tumor of parenchyma organs in the initial stage, but the biological tissue is optically turbid and a strong scattering media, which results in a limited penetration depth of several millimeters with high resolution. On the other hand, some noncoherent measurement methods can be applied to image the tissue at several centimeters depth, while the image resolution is not satisfied.Therefore, focused ultrasound-modulated optical tomography has been developed and shows a promising prospect for imaging tissue in depth with better resolution. It combines the advantages of ultrasound and optical technology. Ultrasonic wave scatters much less in biological tissue than light wave and can be used as a localizer in tissue. The diffused photons tagged by the ultrasound in the focal zone will be collected and used for image. The possible mechanisms are based on ultrasound-induced variations of the optical properties of the media and displacements of scattering media variations.However, this acousto-optical tomography doesn't realize the clinical application, which needs a deep research. In this work, a new experimental configuration was proposed and demonstrated, which can improve its practicability.First, a new method of ultrasound-modulated optical tomography with real-time fast Fourier transformation (FFT) is reported to improve the detection sensitivity and SNR. By discriminating ultrasound modulated information carried by scattering photons, the tomographic images of the biological tissue simulating media and a buried object are reconstructed with FFT spectral intensity. With this method, the image quality and the detecting depth have been increased.Second, we have proposed a reflective and coaxial configuration, in which theultrasound beam and the incident laser are kept in the same axis direction. Then a 1MHz ultrasound beam is focused into the simulating media to modulate and tag the scattering laser light passing through the ultrasonic focused zone. The scattering photons that come from the focused zone carry the modulated information. After analyze the spectral intensity of the modulation frequency, we obtained, for the first time, a tomographic image of a buried object in a biological tissue-simulating media with a detecting depth of 20mm in this novel configuration.This coaxial method is more convenient in practical application than those existing method, and it is easy to reconstruct high-resolution image in both x and y direction simultaneously. The ultrasound transducer, incident laser fiber and probe fiber can be integrated into a compounded detector, which can be implemented in clinic application.