Hyperpolarized Xenon Brain MRI

Abstract

IntroductionSince hyperpolarized 129 Xe MRI was first demonstrated in the lung, air space imaging using hyperpolarized noble gases ( 129 Xe and 3 He) 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 129 Xe 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: Properties of xenonXenon, with the chemical element symbol Xe and atomic number 54, is a member of the zero-valence elements that are called noble gases or inert gases. Xenon was discovered in the residue left over from evaporating components of liquid air by William Ramsay and Morris Travers in England in 1898, then was named by Ramsay from Greek word έ , with the meaning 'foreign' and 'strange'. Natural abundant xenon is made of nine stable isotopes, and more than 35 unstable isotopes have been characterized. Nuclei of two isotopes, 129 Xe and 131 Xe, have non-zero spin quantum number: 26.4% of 129 Xe with a nuclear spin I=1/2 ; and 21.2% of 131 Xe with a nuclear spin I=3/2 ( 133 Xe is used as a radioisotope in nuclear medicine). These two isotopes are both detectable by NMR with sensitivities of 0.021 ( 129 Xe, per nucleus relative to proton assuming thermal polarization) and 2.710 -3 ( 131 Xe). The highly enhanced signal of hyperpolarized xenon and extremely long relaxation time greatly simplified and enhanced NMR experiments, and it is the fundamental for possible biological application in MRI.Xenon, chemically inert with the external electronic orbits fully occupied, is well known as a noble gas at room temperature and an atmospheric pressure. However, the liquid and solid

Preclinical MRI Using Hyperpolarized 129Xe

“…T 1[tissue] is an important parameter for pulse sequence optimization but its measurement has been confounded by low SNR and physiological effects (e.g., wash-out). Many studies have attempted to measure T 1[tissue] in the rat and mouse brains but the values range from a few seconds to tens of seconds and consensus has not been reached in the field [ 110 , 113 , 116 , 117 , 118 , 119 , 120 ]. Likewise, a range of transverse relaxation rates have been measured for HXe in the rat brain.…”