| Biomedical multimodal imaging approaches aim to improve the accuracy and effectiveness of current diagnosis by providing comprehensive disease information. With sharply increasing demands of functional imaging capability, several ultrasound-based state-of-the-art technologies have been developed to provide functional features of tissue, such as elastography to assess tissue mechanical property, thermal strain imaging to characterize tissue compositional property, and contrast-enhanced ultrasound imaging using microbubbles to assess blood perfusion, in addition to anatomical information provided by traditional grey-scale sonography. To further foster ultrasound imaging, in recent years photoacoustic imaging that detects optical contrast at relatively deep imaging depth has been developed. Photoacoustic imaging is capable providing non-invasive, real-time images of structural information with physiological features, such as oxygen saturation, representing hypoxia or the progression of cancer invasion and metastasis.;In this thesis, the combined ultrasound and photoacoustic imaging approach is innovatively engineered to provide both structural and functional information in high spatio-temporal resolution and contrast. First, the light illumination scheme in photoacoustic imaging is reinvented. With a conventional photoacoustic imaging system, approximately 30% energy of excited light would be lost due to reflection on the skin surface. A new light delivery scheme can collect and re-distribute reflected light to recover such energy loss, leading to improved signal amplitude. Second, optically-triggered phase-transition droplets as a highly efficient photoacoustic contrast agent are developed. Their vaporization and recondensation dynamics are investigated by an innovative approach of concurrent optical and acoustical measurements for better understanding of the underlying processes, which will eventually guide the design of repeatable phase-transition droplets. We also developed a novel photoacoustic dye with high photostability that allows for long time monitoring. Finally, in addition to photoacoustic imaging, deconvolution-based superresolution ultrasound imaging technology is developed to realize the spatial resolution beyond the acoustic diffraction limit, which enables to assess microvasculature with the sub-diffraction resolution, maintaining high temporal resolution.;We envision that the developed novel imaging technologies will provide a strong motivation and a key technical foundation to build an ultrasound and photoacoustic multimodal imaging system, which will be useful in pre-clinical and clinical research in the future, and eventually translated into clinics. |
