ABSTRACT
Song Hu, Konstantin Maslov, and Lihong V. Wang Optical Imaging Laboratory, Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, 63130-4899, USA
13.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361 13.2 Dark-Field PAM and Its Limitation in Spatial Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362 13.3 Resolution Improvement in PAM by Using Diffraction-Limited Optical Focusing . . . . . . . . . 363 13.4 Bright-Field OR-PAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364 13.5 In Vivo Microvascular Imaging Using OR-PAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368 13.6 Conclusion and Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373
Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
Microcirculation, the distal functional unit of the cardiovascular system, provides an exchange site for gases, nutrients, metabolic wastes, and thermal energy between the blood and tissues. Pathologic microcirculation reflects the breakdown of homeostasis in organisms, which ultimately leads to tissue inviability. Thus, in vivo microvascular imaging is of significant physiological and pathophysiological importance. In this chapter, we report on optical-resolution photoacoustic microscopy (OR-PAM), a reflection-mode micrometer-resolution absorption microscopy recently developed in our laboratory. It permits in vivo, noninvasive, label-free, three-dimensional (3D) microvascular imaging down to single capillaries. Using spectroscopic measurements, OR-PAM can differentiate oxy-and deoxy-hemoglobin, allowing the quantification of total hemoglobin concentration (HbT) and hemoglobin oxygenation saturation (sO2)—the valuable functional parameters involved in neural, hemodynamic, and metabolic activities.
