Research On High-Quality Photoacoustic Tomography Method Based On Magnetic Resonance Imaging Information

As an emerging biomedical molecular imaging modality,Photoacoustic Tomography(PAT)is capable of mapping tissue physiological metabolism and exogenous contrast agent information with the advantages of high spatial resolution of ultrasound imaging and high contrast of optical imaging.However,the angiographic anatomical reference provided by PAT is not enough to identify soft tissues.And with the increase of imaging depth,the image signal-to-noise ratio of PAT will be greatly reduced.The above reasons make it very difficult to accurately locate targeted lesions with PAT.Magnetic Resonance Imaging(MRI)is able to provide excellent anatomical definition and soft tissue contrast.This makes it possible to help improve target lesion positioning and analysis of PAT.Therefore,combining the two imaging modalities of PAT and MRI will simultaneously provide excellent structural,functional and molecular information.This thesis focuses on the combined imaging method of PAT and MRI,the PATMRI dual-modality imaging of mouse breast cancer,and the MRI structure information-based light fluence correction and image restoration of PAT:(1)The combined imaging method of PAT and MRI.The differences in animal fixation methods and imaging environments between the two modalities,PAT and MRI,make the image co-registration problem more challenging.In this study,we present a complete hardware-software solution for the successive acquisition and co-registration of PAT and MRI images in in vivo animal studies.Our solution includes a 3D-printed dual-modality animal imaging bed to ensure animal posture and position fixation during modality switching,and a spatial image co-registration algorithm with dualmodality markers.We successfully achieve precise image co-registration in healthy and tumor-bearing nude mice experiments,which demonstrate the feasibility of this PATMRI dual-modality imaging method for in vivo imaging.Our proposed dual-modality imaging method offers a unified,standardized,and convenient solution to implement successive acquisition of PAT and MRI images for in vivo preclinical animal research.(2)PAT-MRI dual-modality imaging of mouse breast cancer.Early detection and localization of tumors are of great significance for tumor treatment.We report on the utilization of a clinically commonly used nutritional medicine,the Intralipid,as a new contrast agent for PAT.In vivo imaging of different organs and tumor of nude mice demonstrate that the use of Intralipid can effectively enhance the imaging sensitivity of PAT.In addition,for precise localization and analysis of tumor,we employ coregistered hybrid-contrast PAT-MRI imaging to simultaneously display multi-scale anatomical,functional and molecular characteristics on cancerous living mice.Weeklong longitudinal dual-modality imaging of tumor development reveals information on size,border,vascular pattern,blood oxygenation,and molecular probe metabolism of the tumor micro-environment at the same time.(3)MRI structure information-based light fluence correction and image restoration of PAT.The presence of light fluence attenuation,artifacts,and noise makes PAT images of poor quality and cannot quantify the distribution of absorbers.To eliminate the effect of light fluence attenuation,we make use of the registered MRI images to assist organ segmentation and correct for the light fluence attenuation of PAT.The results show improved feature visibility and enhanced localization of endogenous and exogenous agents in the fluence corrected PAT images.Finally,to reduce image artifacts and noise,we incorporate the co-registered MRI images into the image restoration process of PAT using directional total variation(dTV).The experimental results demonstrate the improved anatomical landscape and soft-tissue contrast achieved by our method.