Department of Medical Biophysics, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, Canada.
Magn Reson Med. 2012 Jan;67(1):62-71. doi: 10.1002/mrm.22977. Epub 2011 Jun 7.
Hyperpolarization of (13) C 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 (B₁⁺) 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 B(1) mapping method based on the Bloch-Siegert shift has been reported. This method uses a B(1) -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 B(1) mapping and observation of metabolism of hyperpolarized [1-¹³C] 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 (13) C metabolism in vivo by enabling accurate flip-angle corrections. This work demonstrates the use of Bloch-Siegert B(1) mapping under challenging out-of-equilibrium imaging conditions.
通过动态核极化使（13）C 标记的底物超极化已被用作一种非侵入性方法来实时研究体内发生的代谢过程。在这些研究中，需要适当校准射频发射功率以有效地观察迅速衰减的磁化强度。传统的发射射频场（B₁⁺）映射方法依赖于在成像之前将磁化强度置于固定的已知状态，因此不适合用于对超极化磁化强度进行成像。最近，已经报道了一种基于 Bloch-Siegert 位移的基于相位的 B₁ 映射方法。该方法利用在存在离共振射频脉冲时核的共振频率的 B₁ 依赖性位移。在本文中，我们研究了在单次注射中体内使用 Bloch-Siegert B₁ 映射和观察超极化[1-¹³C]丙酮酸代谢的可行性。该技术通过能够进行准确的翻转角校正，有望提高体内超极化（13）C 代谢的定量测量。这项工作证明了在具有挑战性的非平衡成像条件下使用 Bloch-Siegert B₁ 映射。
