Integrated Bloch-Siegert B1 mapping and multislice imaging of hyperpolarized 13C pyruvate and bicarbonate in the heart

Hyperpolarization of 13C labeled substrates via dynamic nuclear polarization has been used as a method to noninvasively study real-time metabolic processes occurring in vivo. In these studies, proper calibration of radiofrequency transmit power is required to efficiently observe rapidly decaying magnetization. Conventional transmit radiofrequency field mapping methods rely on placing magnetization in a fixed, known state prior to imaging, making them unsuitable for imaging of hyperpolarized magnetization. Recently, a phase-based B1 mapping method based on the Bloch-Siegert shift has been reported. This method uses a B1-dependent shift in the resonance frequency of nuclei in the presence of an off-resonance radiofrequency pulse. In this article, we investigate the feasibility of Bloch-Siegert B1 mapping and observation of metabolism of hyperpolarized pyruvate in vivo, in a single injection. The technique is demonstrated with phantom experiments, and in normal rat and pigs in vivo. This method is anticipated to improve quantitative measurements of hyperpolarized 13C metabolism in vivo by enabling accurate flip-angle corrections. This work demonstrates the use of Bloch-Siegert B1 mapping under challenging out-of-equilibrium imaging conditions. Magn Reson Med, 2011. © 2011 Wiley-Liss, Inc.