High-speed High-resolution Photoacoustic Computed Tomography:technology And Applications

Photoacoustic tomography is an emerging noninvasive imaging modality in biomedical imaging field in recent years.By acoustically detecting optical contrast,photoacoustic tomography is capable of imaging biological tissues with high contrast,high resolution,and deep penetration.Photoacoustic computed tomography(PACT)is one of the major implementations of photoacoustic tomography and has great potential for preclinical and clinical applications.However,existing PACT technologies and systems are variously limited by lacking of multimodality imaging,limited detector view angle and number of detector elements,insufficient spatial resolution,and lacking of programmability,which has slowed down their pace of preclinical and clinical translation.This thesis has studied and developed PACT technology and system with high imaging speed,high spatial resolution,and programmability which are available for preclinical and clinical research.The specific research contents are as follows:1,Two generations of PACT technology and system were studied and developed:the prototype PACT imaging system(1st generation)and the high-performance PACT imaging technology and system(2nd generation).The 1st generation PACT system is highly configurable,but the temporal resolution of which is limited by mechanical scanning,which makes it not capable of real-time imaging and is thus suitable for fundamental research.The 2nd generation PACT system integrates high imaging speed,high spatial resolution,programmability,and the ability of photoacoustic and ultrasound dual-modality imaging,and is thus available for preclinical and clinical research.More specifically,the 2nd generation PACT system equips with various types of ultrasonic transducer arrays with center frequency and number of elements up to 50 MHz and 512,respectively;in two-dimensional imaging,the spatial and temporal resolutions of which are up to 30 μm and 10 frames per second,respectively;in three-dimensional imaging,the elevational resolution and scanning speed of which are finer than 2 mm and faster than 5 mm per second,respectively.Based on the PACT systems developed,the impact of eight important system factors on imaging performance was analyzed and the negativity artifacts in photoacoustic images were investigated.This work is expected to provide practical guidelines on the design and development of advanced PACT systems and expedite the development of novel artifact-removal techniques and artifact-free image reconstruction algorithms.2,The concept of photoacoustic sentinel lymph node(SLN)identification and needle biopsy using clinically-approved carbon nanoparticles is proposed.The proposed technique is able to visualize the dynamic accumulation process of carbon nanoparticles in SLN and provide high-contrast image guidance for needle biopsy of the SLN.Histological analysis of the SLN reveals obvious accumulation of carbon nanoparticles in the SLN,which is consistent with imaging results.Further experimental results demonstrate that the proposed carbon nanoparticles possess much better performance over methylene blue and indocyanine green in terms of particle diameter,optical absorption,and photostability,and is thus more suitable for PACT based lymph node identification.The proposed technique for SLN identification and needle biopsy has good potential for clinical translation,and is of great significance to the early diagnosis of metastatic breast cancer.3,The concept of photoacoustic label-free finger angiography and recognition is proposed.The proposed technique is able to extract high-quality images of vasculatures in coronal and transverse planes of the finger and show the biodistribution of blood vessels and their relative positions with skin and bone.By mechanically scanning the ultrasonic transducer array,PACT is able to extract three-dimensional vasculature of the whole finger.In addition to structural information,PACT is also able to quantify the pulse rate of artery deep inside the finger,the result of which is consistent with physiological parameter of the subject.The proposed technique for structural and functional imaging of the vasculatures of human fingers has great potential to combine feature extraction,feature matching,and in vivo recognition and achieve high-accuracy and high-security recognition of personal identity.In summary,the technology and applications of high-speed and high-resolution PACT has been studied via simulations and experiments in this thesis.This work is of great significance to the design and development of advanced PACT systems and lay the theoretical and practical foundations for preclinical and clinical applications of PACT.