**1. Introduction**

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Since hyperpolarized 129Xe MRI was first demonstrated in the lung, air space imaging using hyperpolarized noble gases (129Xe and 3He) has progressed at a rapid rate (Goodson, 2002; Zhou, 2011c). Owing to high lipid solubility, absence of background signal in biological tissue, non-invasiveness, lack of radioactivity, different relaxation to oxygenated and deoxygenated blood, and larger chemical shift to the neighbor environment, hyperpolarized 129Xe magnetic resonance imaging (MRI) has a great potential as a tool for studying the brain, especially for the assessment of cerebral blood flow (CBF) related to the brain function and activities.

In this chapter, we will review the progress of recent research on hyperpolarized xenon brain MRI, and compare this novel technique with the conventional proton MRI in order to comment the possible innovation and development in the future. This chapter contains six main parts as follows:
