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H${}_{3}$LiIr${}_{2}$O${}_{6}$ shows no magnetic order down to lowest temperatures, raising hopes for a true Kitaev spin liquid. Its structure reveals H bonds between honeycomb layers and theory has proposed hydrogen disorder to affect the magnetic exchange. Using dielectric spectroscopy, the authors report here dipolar relaxations in H${}_{3}$LiIr${}_{2}$O${}_{6}$ and D${}_{3}$LiIr${}_{2}$O${}_{6}$, mirroring the dynamics of protons or deuterons within the double-well potentials of the H bonds. Under cooling, thermal activation crosses over into quantum tunneling, establishing a quantum paraelectric state with quasistatic disorder. This supports the realization of the long-pursued Kitaev spin liquid.

PURPOSE 31P MR spectroscopic imaging (31P SI) was evaluated in a clinical study as a method for monitoring presurgical devascularization of meningiomas. The aim was to assess noninvasively metabolic alterations in tumor and in healthy brain tissue before and after embolization. METHODS Localized 31P MR spectra of the brain were obtained by means of 2D-SI (voxel size: 36 cm3) using a 1,5-T whole-body MR tomograph. RESULTS Eleven of 19 patients with intracranial meningiomas examined in this study underwent preoperative embolization therapy; eight patients were examined before and after treatment. After embolization, alterations of pH and of the concentrations of high-energy phosphates (nucleoside-5' triphosphate = NTP, phosphocreatine = PCr), inorganic phosphate (Pi), and membrane constituents were observed in the tumors. A tendency of [Pi] increase and decrease of [NTP], [PCr], and pH predominated, which is explained by ischemic processes after tumor devascularization. CONCLUSION 31P SI is applicable in clinical studies and detects alterations of phosphate metabolism in a meningioma after embolization.