The aim of this study was to acquire the transient MRI signal of hyperpolarized tracers and their metabolites efficiently, for which specialized imaging sequences are required. In this work, a multi-echo balanced steady-state free precession (me-bSSFP) sequence with Iterative Decomposition with Echo Asymmetry and Least squares estimation (IDEAL) reconstruction was implemented on a clinical 3 T positron-emission tomography/MRI system for fast 2D and 3D metabolic imaging. Simulations were conducted to obtain signal-efficient sequence protocols for the metabolic imaging of hyperpolarized biomolecules. The sequence was applied in vitro and in vivo for probing the enzymatic exchange of hyperpolarized [1-13 C]pyruvate and [1-13 C]lactate. Chemical shift resolution was achieved using a least-square, iterative chemical species separation algorithm in the reconstruction. In vitro, metabolic conversion rate measurements from me-bSSFP were compared with NMR spectroscopy and free induction decay-chemical shift imaging (FID-CSI). In vivo, a rat MAT-B-III tumor model was imaged with me-bSSFP and FID-CSI. 2D metabolite maps of [1-13 C]pyruvate and [1-13 C]lactate acquired with me-bSSFP showed the same spatial distributions as FID-CSI. The pyruvate-lactate conversion kinetics measured with me-bSSFP and NMR corresponded well. Dynamic 2D metabolite mapping with me-bSSFP enabled the acquisition of up to 420 time frames (scan time: 180-350 ms/frame) before the hyperpolarized [1-13 C]pyruvate was relaxed below noise level. 3D metabolite mapping with a large field of view (180 × 180 × 48 mm3 ) and high spatial resolution (5.6 × 5.6 × 2 mm3 ) was conducted with me-bSSFP in a scan time of 8.2 seconds. It was concluded that Me-bSSFP improves the spatial and temporal resolution for metabolic imaging of hyperpolarized [1-13 C]pyruvate and [1-13 C]lactate compared with either of the FID-CSI or EPSI methods reported at 3 T, providing new possibilities for clinical and preclinical applications.

中文翻译：

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体内超极化丙酮酸到乳酸转化的动态2D和3D映射，在3 T下具有有效的多回波平衡稳态自由进动。

这项研究的目的是有效地获取超极化示踪剂及其代谢产物的瞬态MRI信号，为此需要专门的成像序列。在这项工作中，在临床3 T正电子发射断层扫描/ MRI系统上实现了具有回波不对称和最小二乘估计（IDEAL）迭代迭代迭代分解的多回波平衡稳态自由进动（me-bSSFP）序列。 2D和3D代谢成像。进行仿真以获得用于超极化生物分子的代谢成像的信号有效序列方案。该序列在体外和体内均用于探测超极化的[1-13 C]丙酮酸盐和[1-13 C]乳酸盐的酶促交换。化学位移分辨率是使用最小二乘法实现的，迭代化学物种分离算法的重建。在体外，将来自me-bSSFP的代谢转化率测量值与NMR光谱和自由感应衰变化学位移成像（FID-CSI）进行了比较。在体内，用me-bSSFP和FID-CSI为大鼠MAT-B-III肿瘤模型成像。用me-bSSFP采集的[1-13 C]丙酮酸盐和[1-13 C]乳酸盐的2D代谢产物图谱显示与FID-CSI相同的空间分布。用me-bSSFP和NMR测定的丙酮酸-乳酸转化动力学非常吻合。使用me-bSSFP进行的动态2D代谢物映射可在超极化[1-13 C]丙酮酸放松至低于噪声水平之前，获取多达420个时间帧（扫描时间：180-350 ms /帧）。具有大视野（180×180×48 mm3）和高空间分辨率（5.6×5）的3D代谢物图谱。使用me-bSSFP在8.2秒的扫描时间内进行了6×2 mm3的脱模。结论是，与3T报道的FID-CSI或EPSI方法相比，Me-bSSFP改善了超极化[1-13 C]丙酮酸盐和[1-13 C]乳酸盐代谢成像的空间和时间分辨率，提供了临床和临床前应用的新可能性。