Dynamic volumetric hyperpolarized 13 C imaging with multi-echo EPI

Abstract

Purpose: To generate dynamic, volumetric maps of hyperpolarized [1-¹³ C]pyruvate and its metabolic products in vivo.

Methods: Maps of chemical species were generated with iterative least squares (IDEAL) reconstruction from multiecho echo-planar imaging (EPI) of phantoms of thermally polarized ¹³ C-labeled chemicals and mice injected with hyperpolarized [1-¹³ C]pyruvate on a preclinical 3T scanner. The quality of the IDEAL decomposition of single-shot and multishot phantom images was evaluated using quantitative results from a simple pulse-and-acquire sequence as the gold standard. Time course and area-under-the-curve plots were created to analyze the distribution of metabolites in vivo.

Results: Improved separation of chemical species by IDEAL, evaluated by the amount of residual signal measured for chemicals not present in the phantoms, was observed as the number of EPI shots was increased from one to four. Dynamic three-dimensional metabolite maps of [1-¹³ C]pyruvate,[1-¹³ C]pyruvatehydrate, [1-¹³ C]lactate, [1-¹³ C]bicarbonate, and [1-¹³ C]alanine generated by IDEAL from interleaved multishot multiecho EPI of live mice were used to construct time course and area-under-the-curve graphs for the heart, kidneys, and liver, which showed good agreement with previously published results.

Conclusions: IDEAL decomposition of multishot multiecho 13C EPI images is a simple, yet robust method for generating high-quality dynamic volumetric maps of hyperpolarized [1-¹³ C]pyruvate and its products in vivo and has potential applications for the assessment of multiorgan metabolic phenomena.

Keywords: IDEAL; hyperpolarized 13C; metabolic imaging; multiecho echo-planar imaging.