Photoacoustic bone characterization: A progress review

Bone diseases are chronic diseases that cause changes in the physical structure and chemical composition of the bones. The incidence of bone diseases ranks first among the five major diseases of middle-aged and elderly people, causing significant strain on public health resources. The early prevention and treatment of bone diseases can avoid the occurrence of bone tumors, fractures and other serious bone diseases as well as a series of complications. Therefore, for the early screening and early diagnosis of bone diseases, it is urgent to develop diagnostic methods that can be easily promoted and can evaluate bone health. Based on the clinical requirements for the detection of physical structure characteristics and molecular metabolism characteristics of bone tissues, the development of a non-invasive and non-radiative in vivo detection method that can simultaneously evaluate the microstructure and metabolic information of bone is of great scientific significance and clinical value for the early diagnosis, treatment and monitoring of bone diseases. Photoacoustic imaging (PAI) combines the advantages of selective optical absorption of different chromophores in biological tissues and high penetration depth of ultrasound, providing imaging information on the macroscopic physiological structure and microscopic molecular level of biological tissues. Thus, it has great potential in the application of biomedical imaging. Among them, PAI and PA detection technology of bone is an important branch of clinical application fields. However, bone tissue is a complex biological medium. From the perspective of physical structures, the whole bone tissue can be regarded as a non-uniform layered curved structure composed of soft tissue, cortical bone and cancellous bone, in which cancellous bone is a solid-liquid two-phase porous structure (the bone trabecular frame can be regarded as the solid phase, and bone marrow clusters filled in the pores can be regarded as the liquid phase). In terms of chemical composition, bone tissue is composed of a variety of chemical components, including bone minerals, collagen, lipids, hemoglobin, water and so on. Complex physical structures and chemical components lead to distributed optical and acoustic sources, complex optical and acoustic transmission modes in bone tissue, and there are serious scattering and attenuation, which seriously affects the accuracy of bone microstructure and metabolism detection, and makes the transformation of relevant PA theories and detection methods for clinical applications face great challenges. This review systematically discusses the mechanism of PAI and PA detection for complex bone tissue and the progress of existing academic research on the application of various bone diseases, including the theory of PA wave generation and propagation in bone tissue, PA bone analysis methods, PA bone imaging methods, and their experimental and clinical applications. Finally, this review analyzes the current challenges in this field and anticipates future development trends based on the current research status of the PA technology.