Fast Photoacoustic Imaging System And Its Application

At present,the biomedical imaging technologies such as ultrasound doppler imaging,X-ray,nuclear imaging and magnetic resonance imaging have their own defects due to their own technical mechanism.Although traditional optical imaging technology can carry out fast and non-invasive examination,high-resolution imaging in deep biological tissue cannot be achieved due to the strong scattering of tissues,so the advantages of optical imaging technology may not be fully applied.Therefore,the clinical application of optical imaging is still limited.In recent years,the development of photoacoustic imaging(PAI)has attracted the attention in biomedical imaging.This technology uses pulse laser to stimulate ultrasonic signal and obtains the light absorption distribution information of tissues.PAI is a hybrid imaging modality that combines the characteristics of optical imaging and ultrasonic imaging from the generation mechanism.It obtains the light absorption parameter distribution at a certain depth of biological tissue quickly and accurately.The image resolution is comparable to ultrasonic imaging.At present,the rapid development of software and hardware enables PAI to utilize the latest ultrasonic array detector,the high-speed data acquisition equipment and the solid-state lasers with significant technological advances in recent years to achieve realtime imaging.A rapid photoacoustic imaging system with high-resolution real-time imaging can greatly expand the application of PAI from laboratory research to pre-clinical research.At the same time,the development of multi-wavelength photoacoustic imaging can rapidly obtain the information of various components of biological tissue,making a big step of PAI to go out of the laboratory and become a clinical imaging modality.In this context,a new PAI system based on curved ultrasound array was designed and built based on previous researches in our laboratory.The new system was applied in photoacoustic brain imaging and human peripheral blood vessel imaging.The main contents of this paper include:1.Build a new PAI system.In this paper,a fast photoacoustic imaging system based on curved ultrasonic transducer array was designed and constructed.The imaging speed of the PAI system increased significantly so we can get images from multiple positions of human body easily.The disadvantages of single transducer PAI was emphasized here.Considering previous studies of other research groups,a numerical simulation for designing a new curved ultrasonic transducer array was carried out.A new imaging probe was developed with the combination of high-energy fiber bundle,ultrasonic transducer array and coupling liquid to achieve optimal light illumination and ultrasonic coupling.A multichannel pre-amplifier with multiplexing for PAI was built.High-speed data acquisition system was used to realize 64-channel parallel data acquisition and image reconstruction based on Labview platform.The onboard system achieved real-time photoacoustic imaging.The Matlab software was used for processing and analyzing photoacoustic data.2.Photoacoustic brain imaging.Cerebral hemodynamic changes during acupuncture were studied by using acoustic resolution photoacoustic microscope for the first time.The activation of some brain regions caused by acupuncture was observed.Then a coronalplane photoacoustic tomography system was designed and constructed.Multiple-layers PAI images of a mouse brain was realized by using near infrared laser.The development and recovery process of spontaneous cerebral hemorrhage in mice model were monitored and evaluated.Finally,the hemodynamic changes caused by neural activities in the resting state of mouse brain were observed after we developed the fast photoacoustic imaging system.For the first time,the brain network of mouse brain was observed and the functional connection in the single layer of the mouse brain was reconstructed by using the photoacoustic signals.3.Photoacoustic imaging of peripheral blood vessels in human.The fast photoacoustic imaging system was applied in a pre-clinical study to get images of human peripheral blood vessels.Since hemoglobin in human blood vessels is a natural contrast agent,it has higher light absorption than other tissues in the near infrared band.Using the near-infrared imaging window of biological tissue,the system was applied to monitor several important peripheral blood vessel landmarks and cross-verified by a commercial ultrasound platform.Multi-wavelength imaging was used to obtain the concentration distribution of different components in the blood.We introduced vessel stimulation test in PAI research for the first time to observe the hemodynamic changes before and after the occlusion on peripheral vessels.Healthy volunteers of different ages were recruited to participate in the experimental study.The differences in hemodynamic parameters between different groups were analyzed and compared,and the results with clinical value were obtained.The research carried out in this paper has completed the construction of a new experimental system,and demonstrated the potential of PAI in small animal brain imaging and in pre-clinical research,expanding the application field of this technology in clinical and scientific research.