High-resolution 31P echo-planar spectroscopic imaging in vivo at 7T

Abstract

Purpose: Conventional 31P chemical shift imaging is time-consuming and yields only limited spatial resolution. The purpose of this study was to demonstrate feasibility of 31P echo-planar spectroscopic imaging (EPSI) in vivo at 7T. Methods: A 3D 31P EPSI sequence with trapezoidal-shaped gradient pulses was implemented on a 7T MR scanner. To increase spectral width with reduced demand on gradient performance, a multishot approach was chosen. Acquisition weighting and 31P–{1H} double resonance for nuclear Overhauser signal enhancement were applied to increase sensitivity. Results: 3D 31P–{1H} EPSI data from model solution and from human calf muscle and brain were obtained from voxels with effective sizes of 4.1 to 16.2 cm3 in measurement times of approximately 10 min. Individual spectra showed well-resolved resonances of endogenous 31P-metabolites without artifacts. Volumetric high-resolution 31P-metabolite maps in vivo showed metabolic heterogeneity of different tissues. Conclusion: In vivo 31P EPSI at 7T yields high-quality metabolic images. The proposed multishot EPSI technique reduces the measurement times for acquisition of volumetric high-resolution maps of 31P-metabolites or intracellular pH in human studies. Magn Reson Med 79:1251–1259, 2018. © 2017 International Society for Magnetic Resonance in Medicine.