Hyperpolarized 83Kr MR Relaxation Measurements in Excised Rat Lungs

Introduction: Because of its spin I = 9/2, the noble gas isotope Kr possesses a nuclear electric quadrupole moment that is a source for rapid relaxation. However, its surprisingly long gas-phase T1 times of up to several hundred seconds at ambient pressure allow for Kr hyperpolarization that is 3-4 orders of magnitude above the equilibrium polarization at 9.4 T field strength [1,2]. The quadrupolar dominated longitudinal Kr relaxation can be utilized for MR studies of surrounding surfaces since it is susceptible to the surface-to-volume ratio, surface hydration, and surface temperature [3]. Hyperpolarized (hp) Kr has been shown to provide T1 relaxation weighted MRI contrast that is highly sensitive to the surface chemistry in low surface-to-volume model surface systems [1]. In a recent study, a special ventilation chamber was devised that allowed for in situ hp Kr MRI of excised rat lungs [4]. In the present work an improved hp Kr delivery system is used to obtain hp Kr T1 relaxation (spatially not resolved) in excised rat lungs as a function of lung inflation.