Hyperpolarized krypton-83 as a contrast agent for magnetic resonance imaging

Abstract

For the first time, magnetic resonance imaging (MRI) with hyperpolarized (hp) krypton-83 ( 83 Kr) has become available. The relaxation of the nuclear spin of 83 Kr atoms (I ‫؍‬ 9͞2) is driven by quadrupolar interactions during brief adsorption periods on surrounding material interfaces. Experiments in model systems reveal that the longitudinal relaxation of hp 83 Kr gas strongly depends on the chemical composition of the materials. The relaxationweighted contrast in hp 83 Kr MRI allows for the distinction between hydrophobic and hydrophilic surfaces. The feasibility of hp 83 Kr MRI of airways is tested in canine lung tissue by using krypton gas with natural abundance isotopic distribution. Additionally, the influence of magnetic field strength and the presence of a breathable concentration of molecular oxygen on longitudinal relaxation are investigated.NMR ͉ optical pumping ͉ pulmonary ͉ MRI ͉ xenon H igh nuclear spin polarization in noble gasses can be generated through rubidium vapor spin exchange optical pumping (RbSEOP) (1) and allows for NMR signal enhancements of many orders of magnitude (2). Hyperpolarized (hp) 3 He and hp 129 Xe (both I ϭ 1͞2) have both been used in a wide range of NMR and magnetic resonance imaging (MRI) experiments that are otherwise impossible (3-15). In particular hp 3 He has been applied for medical MRI diagnosis of pulmonary diseases (16)(17)(18)(19). One of the fundamental parameters with high diagnostic value for hp 3 He MRI is the spin-density that is a result of the helium concentration in a particular volume. Spin-density mapping of hp 3 He can be applied to visualize ventilation in lungs. Other useful parameters are 3 He diffusion that provides information about alveolar size distributions in lung tissue and hp 3 He relaxation that depends on oxygen partial pressure in lungs. In vivo MRI of airways with hp 129 Xe as a contrast agent (19-21) suffers from a lower sensitivity compared with hp 3 He. However, 129 Xe adds a further parameter not available by 3 He, namely, the chemical shift that allows for insights into the local environment of the xenon atoms (22-27). The 129 Xe chemical shift has been used extensively for research in materials science, engineering, and xenon dissolved in liquids including human blood (3,5,6,8,9,12,28). The chemical shift obtained from hp 129 Xe can be used to generate an in vivo MRI contrast that is a probe for gas perfusion in lungs (i.e., exchange of the gaseous xenon with the lung parenchyma) (29).3 He and 129 Xe are the only spin I ϭ 1͞2 stable isotopes of the noble gas group, but there are three more NMR active isotopes in this group with higher spin that possess a nuclear electric quadrupole moment. The three quadrupolar isotopes are 21 Ne (I ϭ 3͞2, natural abundance 0.27%), 83 Kr (I ϭ 9͞2, natural abundance 11.5%), and 131 Xe (I ϭ 3͞2, natural abundance 21%). Quadrupolar interactions in these noble gas atoms cause spin relaxation and coherent spin evolution that are probes for the shape, size, and symmetry of void spaces as well as the ...

250GHz CW gyrotron oscillator for dynamic nuclear polarization in biological solid state NMR

“…Extension of electron-nuclear and other high polarization transfer experiments involving noble gases, para-hydrogen, semiconductors, or photosynthetic reaction centers [11][12][13][14][15][16][17][18][19][20][21][22][23] to contemporary solid state and solution experiments is very appealing, since it could significantly enhance the sensitivity in a variety of NMR experiments. In particular, the theoretical enhancement for electron-nuclear polarization transfers is approximately ~(γ e /γ I ), where now the ratio is ~660, because of the large magnetic moment of the electron relative to the 1 H, making the gains in sensitivity large.…”

MRI of Heterogeneous Hydrogenation Reactions Using Parahydrogen Polarization

“…Previously demonstrated applications include hyperpolarized lung imaging [109,124,131], or measuring profiles of fluid flow in porous media [73] or micro-channels [76,78]. Heterogenized catalysts can also contribute to the rapidly advancing area of studying catalyzed reactions with NMR micro-fluidic technology [122,154].…”

“…These limitations have led to the use of hyperpolarized gases [40,71,88,109,124,131] such as 129 Xe, 3 He and, more recently, 83 Kr. Other approaches have used fast-relaxing inert fluorinated gases [95,130] to improve SNR per unit time via fast signal averaging or higher gas pressures to directly increase SNR [102].…”

NMR Hyperpolarization Techniques of Gases

“…Although the vast majority of SEOP experiments have employed the spin I=1/2 noble gas isotopes 129 Xe and 3 He, the quadrupolar species 21 Ne (I=3/2), [36] 83 Kr (I=9/2), [37] and 131 Xe [38] (I=3/2) can also be polarized via this method. For the alkali metal vapor, Rb is most-commonly employed for practical reasons-including its low melting point [39] (facilitating vaporization) and the availability of high-powered lasers resonant with its D1 transition [40] ; however, K and Cs are also utilized (particularly for 3 He [41] and 129 Xe, [42] respectively).…”

“…[8] . A wide range of nuclei can be directly hyperpolarized, including 1 H, [9] 3 He, [10] 7 Li [11] , 13 C, [1c, 12] 15 N, [13] 19 F, [14] 31 P, [15] 83 Kr, [16] and 129 Xe, [4,17] among others. [18] Hyperpolarized (HP) substances are revolutionizing the fields of NMR spectroscopy and magnetic resonance imaging (MRI), because many applications that were previously impractical because of weak NMR signals (e.g.…”