In Vivo Application of Sub-Second Spiral Chemical Shift Imaging (CSI) to Hyperpolarized 13C Metabolic Imaging: Comparison with Phase-Encoded CSI

Abstract

A fast spiral chemical shift imaging (CSI) has been developed to address the challenge of the limited acquisition window in hyperpolarized ¹³C metabolic imaging. The sequence exploits the sparsity of the spectra and prior knowledge of resonance frequencies to reduce the measurement time by undersampling the data in the spectral domain. As a consequence, multiple reconstructions are necessary for any given data set as only frequency components within a selected bandwidth are reconstructed “in-focus” while components outside that band are severely blurred (“spectral tomosynthesis”). A variable-flip-angle scheme was used for optimal use of the longitudinal magnetization. The sequence was applied to sub-second metabolic imaging of the rat in vivo after injection of hyperpolarized [1-¹³C]-pyruvate on a clinical 3T MR scanner. The comparison with conventional CSI based on phase encoding showed similar signal-to-noise ratio (SNR) and spatial resolution in metabolic maps for the substrate and its metabolic products lactate, alanine, and bicarbonate, despite a 50-fold reduction in scan time for the spiral CSI acquisition. The presented results demonstrate that dramatic reductions in scan time are feasible in hyperpolarized ¹³C metabolic imaging without a penalty in SNR or spatial resolution.

Keywords: Hyperpolarized metabolic imaging, ¹³C, Dynamic nuclear polarization, Pyruvate, Rat