Dual Component Analysis for In Vivo T₂ ^* Decay of Hyperpolarized ¹³C Metabolites

Abstract

Original ArticlePurpose: To investigate the exchange and redistribution of hyperpolarized 13 C metabolites between different pools by temporally analyzing the relative fraction of dual T 2 * components of hyperpolarized 13 C metabolites. Materials and Methods: A dual exponential decay analysis of T 2 * is performed for [1-13 C] pyruvate and [1-13 C] lactate using nonspatially resolved dynamic 13 C MR spectroscopy from mice brains with tumors (n = 3) and without (n = 4) tumors. The values of shorter and longer T 2 * components are explored when fitted from averaged spectrum and temporal variations of their fractions. Results: The T 2 * values were not significantly different between the tumor and control groups, but the fraction of longer T 2 * [1-13 C] lactate components was more than 10% in the tumor group over that of the controls (P < 0.1). The fraction of shorter T 2 * components of [1-13 C] pyruvate showed an increasing tendency while that of the [1-13 C] lactate was decreasing over time. The slopes of the changing fraction were steeper for the tumor group than the controls, especially for lactate (P < 0.01). In both pyruvate and lactate, the fraction of the shorter T 2 * component was always greater than the longer T 2 * component over time. Conclusion:The exchange and redistribution of pyruvate and lactate between different pools was investigated by dual component analysis of the free induction decay signal from hyperpolarized 13 C experiments. Tumor and control groups showed differences in their fractions rather than the values of longer and shorter T 2 * components. Fraction changing dynamics may provide an aspect for extravasation and membrane transport of pyruvate and lactate, and will be useful to determine the appropriate time window for acquisition of hyperpolarized 13 C images.

Acquisition strategies for spatially resolved magnetic resonance detection of hyperpolarized nuclei

“…The transverse relaxation including static field (B 0 ) inhomogeneity effects (R 2 * or T 2 *) can be derived from FID measurements [123,147,314]. In cases with minimal variation across the excited slice or volume, a simple nonimaging FID can be fit.…”