Research On Novel Medical Imaging Diagnosis Methods By Combining Optical And Acoustical Technology

Optical tomography in 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 tumors of parenchyma organs in the initial stages of growth. However, it is very difficult to image thick tissue by the pure optical method because biological tissue is optically turbid and a strong scattering media. Although it is possible to image to several centimeters depth with some noncoherent measurement methods, the image resolution is not satisfied. The coherent optical tomography can provide high-resolution image, but it is limited to a penetration depth of several millimeter into biological tissues.Recently, ultrasound-modulated optical tomography has been developed by combining the advantages of both ultrasound and optical technology for imaging tissue in depth. Because ultrasonic wave scatters much less in biological tissue than light wave, it can be used as a localizer in tissue. It is potential with this acousto-optical method to image in thick biological tissue with better resolution. For the ultrasonic modulation of light in scattering media, the possible mechanisms are based on ultrasound-induced variations of the optical properties of the media, and based on variations of the optical phase in response to both ultrasound-induced displacements of scatterers and ultrasonic modulation of the index of refraction. However, now this acousto-optical tomography has great distance from the clinical application due to both low signal-to-noise ratio (SNR) and impossibility to examine the patient in vivo. In this research work, we proposed and demonstrated several methods as following to improve the imaging quality, to image more depth and to apply easily.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, we havedetected and reconstructed the tomographic images of the buried object in simulating media, both the image quality and the detecting depth have been increased.Second, we report on a novel ultrasound-modulated optical tomographic technique applied in dense tissue-simulating turbid media. A 1MHz ultrasound beam is focused into the simulating media to modulate and tag the scattering laser light passing through the ultrasonic focused zone. A 10KHz sinusoidal wave, as a detection wave, is carried by the ultrasound beam through amplitude-modulation (AM). The scattering photons that come from the focused zone carry the modulated information. This method can be applied to image to tissue structures with different optical parameters. Both SNR and measurement accuracy are improved. For the first time, we obtained a series of tomographic images of a buried object in a biological tissue-simulating media with a detecting depth of 30mm.Third, we have proposed a new acousto-optical tomographic method, in which the incident laser, ultrasound and optical detector are coaxial to utilize the character of small lateral size of ultrasonic focused zone. Combing with frequency swept ultrasound technology, the tomographic images of different depth are obtained. This coaxial method is more convenient in practical application than vertical method, and it is easy to reconstructed high-resolution image in both x and y direction simultaneously. The ultrasound transducer, incident laser fiber interface and probe fiber can be integrated to a complex detecting head when using the method of detecting reflective model, which is practical to clinic application.At last, a new method of measuring photoacoustic (PA) waves in situ was proposed. We made a ultrasonic beam to pass through the thick biotissue sample as a probe beam. Its focus zone was used to limit...