Study On The Photoacoustic Imaging System Based On All-Opticl Detection

With the improvement of people's living standards and health concepts,higher requirements for early diagnosis and post-health monitoring of diseases are required,which requires more safe and efficient medical imaging technology.According to the characteristics of existing medical imaging technology and the direction of future demand,there is an urgent need for a non-invasive,low-cost,compact,human-safe imaging method capable of achieving micron-scale imaging at a depth of the order of centimeters,while being able to detect the information on structural morphology and compositional content within the organization.As a rapidly developing imaging technology,photoacoustic imaging technology has the characteristics of high contrast of optical imaging and high penetration of ultrasound imaging.Since photoacoustic imaging relies on the absorption properties of light by materials,it can not only achieve high-resolution imaging of biological tissue structures,but also identify and analyze the content of different biological tissue components to achieve functional imaging.At the same time,photoacoustic imaging uses low-energy laser as the excitation source,which has the advantages of safety,non-intrusion and low cost.It has broad application prospects in the field of biomedical imaging diagnosis and analysis.The photoacoustic signal is essentially ultrasonic.The use of a conventional piezoelectric ultrasonic probe to receive a photoacoustic signal has many disadvantages.The most important drawback is that it must transmit a photoacoustic signal by means of a coupling medium,which limits its application range.It also brings a lot of inconvenience to clinical applications.In addition,it is easy to block the excitation light source,has limited bandwidth,and is susceptible to electromagnetic interference.Therefore,a new detection method is needed to solve the problems caused by the conventional ultrasonic probe.Based on the previous research and analysis,this dissertation studies an optical interference method to detect photoacoustic signals.By solving the phase and polarization fading and optical energy loss problems in fiber interference,we have developed a kind of fiber optic interferometer sensing system that implements non-contact detection of photoacoustic signals.The Labview software platform is used to realize the unified control of data acquisition and scanning device.A point-by-point scanning imaging system based on two-dimensional displacement platform is developed.Combined with the fiber interferometer sensing system,we have built a photoacoustic imaging system based on all-optical detection.By testing and analyzing the sample,a high-resolution and high-contrast photoacoustic image was obtained,and the imaging system was measured to have a lateral resolution of ~205um and a longitudinal resolution of ~96um.The microcirculation structure and functional information of biological tissues were studied,and the structure imaging of biological tissue blood vessels was realized.At the same time,multi-wavelength measurement method was used to detect and image blood oxygen saturation in blood,which provided a non-contact non-destructive testing method for blood oxygen saturation.The innovations of this dissertation are as follows:1.A method for positive and negative phase feedback of phase feedback using a 3×3 fiber coupler is proposed.The method can automatically change the direction of the phase compensation according to the quadrant of the phase difference of the interferometer,and also reduce the influence of the interference intensity variation,so that the fiber interferometer can be quickly and accurately stabilized at the most sensitive position.2.A Faraday rotator-based sensing probe is designed,which not only solves the polarization fading problem of the fiber interferometer,but also realizes non-contact high-frequency point detection.3.In order to solve the problem of low sensitivity due to large energy loss after the reflected light is reflected on the surface of the measured object,we built a fiber-optic Mach-Zehnder interferometer based on fiber amplifier.