Abstract
Brain diseases need advanced detection methods to diagnosis abnormalities. Advanced imaging techniques have been developed and applied in different stages for several requirements related to anatomical, functional, and metabolic imaging for the human brain. Among them, photoacoustic imaging has the advantages of high resolution and deep penetration with rich optical contrast, which plays an important role in brain imaging. The characteristic of photoacoustic imaging brings the opportunity for different objects with multi-scale observation in the human brain. In this chapter, the authors introduce the principle and theory of photoacoustic imaging, review the modality of the present photoacoustic imaging systems and applications for brain diseases, and summarize the trends of this imaging technique.
TopBackground
The human brain is an essential and complex organ for human activity (Insel et al., 2013). Different regions of the brain have distinct functions to control and manage human life, such as vision, auditory, olfaction, emotion, motor, language, judgment, creativity, etc. In the neural system, the neuron transports information about sensing and the corresponding responses(Yuste, 2015). The vascular system provides nutrition such as oxygen and then brings away the metabolites such as carbon dioxide (Zhu et al., 2020). Other surrounding tissues mechanically support the brain and complete the full process of information processing. However, abnormal physiological and pathological phenomena influence the human brain's activities and can furthermore threaten its survival. Therefore, efficient imaging of human brain diseases is expected.
The PAI technology, which combines the advantages of both optics and ultrasound, is a relatively novel method for medical imaging without ionizing radiation (Yao & Wang, 2014a). Compared with traditional optical imaging methods, the PA method overcomes the obstacle of light scattering through biological tissue. Owing to the variations of the PA effect in different biological tissues, the optical absorption by those tissues results in high contrast among them. In addition, the PA wave generated by deep tissue can be detected by an ultrasound transducer without mutual interference of transmission and degradation of the signal quality (Yao & Wang, 2018). With the advantages of combined optical specificity and acoustic penetration, PAI has been introduced to bridge the gaps between the resolution and penetration depth in brain imaging.
Key Terms in this Chapter
Spatial Resolution: The term referes to distance between independent measurements or the measurement of the smallest object. In other hands, the spatial resolution represents the physical dimension for a pixel of the image.
Photoacoustic Computed Tomography: The imaging modality is one type of photoacoustic imaging, which uses a diffused optical source with a scanning-single ultraosound transducer or ultrasound array for detection.
Spatial Sampling: The brief represents a process of extracting subsets of data from the spatial population according to certain rules, and the subsets can be used as inferences for drawing the spatial population.
Field of View: The term that defines the extent of observable area at any given condition. In the cases of the imaging system or detect sensors, it is describe by solid angle of the detector.
Photoacoustic Microscopy: The imaging modality is one type of photoacoustic imaging, which uses a focused optical source or a focused acoustic detector.
Alzheimer’s Disease: Is one brain disorder that slowly destroys memory, thinking, and behavior.
Photoacoustic Imaging: The imaging modality is based on the photoacoustic effect to get the signal and recontructe into images.
Photoacoustic Effect: The effect is the formation of acoustic waves leading by light absorption in material sample, also named as optoacoustic effect. To produce this effect, the light must change the intensity following the time usually as pulsed light.
Nyquist Therom: The therom is known as a sampling theorem, which is principle that the sampling interval must be at least twice its frequency or at most half of its wavelength.