Photo Acoustic Imaging And Application To Endoscopy And Brain Research

Photo acoustic imaging technology has become a hot research, which reflects many outstanding advantages in the field of biomedical imaging applications. It uses a pulsed laser(typically a few nanoseconds bandwidth) irradiating biological soft tissue and causing local temperature change instantaneously due to different light absorption of the tissue, which can result in volume expansion generate ultrasound named photo acoustic signal. Photo acoustic signal generated within biological tissue reflect different optical absorption, metabolism and lesion characteristics in tissue, because the biological tissues with different physiological states have a different absorption of light. Photo acoustic imaging combines the advantages of ultrasonic high-resolution and optical high-contrast, so photo acoustic imaging system can obtain high quality images. In this paper, photo acoustic tomography imaging system was built based on photo acoustic imaging principle, and the system performance was verified by phantom and animal imaging. This paper developed piezoelectric ultrasonic transducer using AlN film based on MEMS technology, and applied the miniaturized MEMS sensor into photo acoustic imaging system innovatively, lay an important foundation for photo acoustic imaging technology in more areas of application. This paper carried out the experimental study of early colorectal cancer based on photo acoustic imaging technology and conducted brain imaging studies under acupuncture. Its main contents are summarized as follows:a)Built the first set of photo acoustic tomography system in laboratory, the stability and maneuverability of this system was verified by phantom, animal and human experiments. An Nd: YAG 532 nm laser(Brilliant, QUANTEL) was employed in this system to generate pulses of 6ns at 1-10 Hz. The control program of system was written based on Labview software for the timing control on laser, DAQ cards, stepper motor to ensure the normal operation of the system. The system needs about 2-3 minutes to complete a two-dimensional image now.b) This paper developed an photo acoustic endoscopic imaging system based on Polyvinylidene Fluoride(PVDF)piezoelectric film, and carried on the experimental study of early human colorectal cancer in vitro slices under the cooperation with West China Hospital. The PVDF four sensor array was firstly developed and integrated into the endoscopic probe, forming a complete photo acoustic endoscopic imaging system. Experimental research on human in vitro slice showed that photo acoustic endoscopy has some ability to distinguish the normal tissue and early cancerous tissue. This research provide a basis for the application of photo acoustic endoscopy in the early diagnosis of colorectal cancer in human clinical experiments.c) The paper developed a new micro machined piezoelectric ultrasonic transducer(pMUT) used in photoacoustic imaging system. pMUT chip was manufactured with AlN film as its piezoelectric layer and polyimide(PI) as the surface protective layer of the device. Pt was used as upper and lower electrodes and the center frequency of pMUT chip was approximately 2.9MHz. The coupling efficiency was measured to be 2.38%—3.71 %. Finally, the sensor was integrated into the photoacoustic imaging system, and successfully obtain a two-dimensional image of a human hair. This research lay an important foundation for application of p MUT array in photoacoustic imaging, which contribute to the real-time imaging and system miniaturization.d) This paper studied the brain hemodynamics during acupuncture based on photoacoustic tomography system. The results demonstrated that acupuncture and moxibustion on Yongquan point can increase the total hemoglobin(HbT) concentration in the brain. The photoacoustic tomography system was integrated with laser speckle imaging system to study the cerebral ischemia hemodynamics during acupuncture on Yanglingquan point(GB34). Experimental results showed that the cerebral blood flow(CBF) in ischemic region had a weaker response to the acupuncture compared to HbT concentration, while both of them had high response in the non-ischemic area. The findings revealed the mechanism of acupuncture of GB34 on cerebral ischemia,and laid the experimental basis for the application of acupuncture in cerebral ischemia diseases.