Investigation of hyperpolarized substrate metabolism has been showing utility in real-time determination of in-cell and in vivo enzymatic activities. Intracellular reaction rates may vary during the course of a measurement, even on the very short time scales of visibility on hyperpolarized MR, due to many factors such as the availability of the substrate and co-factors in the intracellular space. Despite this potential variation, the kinetic analysis of hyperpolarized signals typically assumes that the same rate constant (and in many cases, the same rate) applies throughout the course of the reaction as observed via the build-up and decay of the hyperpolarized signals. We demonstrate here an acquisition approach that can null the need for such an assumption and enable the detection of instantaneous changes in the rate of the reaction during an ex vivo hyperpolarized investigation, (i.e. in the course of the decay of one hyperpolarized substrate dose administered to a viable tissue sample ex vivo). This approach utilizes hyperpolarized product selective saturating-excitation pulses. Similar pulses have been previously utilized in vivo for spectroscopic imaging. However, we show here favorable consequences to kinetic rate determinations in the preparations used. We implement this acquisition strategy for studies on perfused tissue slices and develop a theory that explains why this particular approach enables the determination of changes in enzymatic rates that are monitored via the chemical conversions of hyperpolarized substrates. Real-time changes in intracellular reaction rates are demonstrated in perfused brain, liver, and xenograft breast cancer tissue slices and provide another potential differentiation parameter for tissue characterization.

中文翻译：

---

超极化产物选择性饱和激发，可实时测定代谢反应速率的变化。

对超极化底物代谢的研究已显示出实时测定细胞内和体内酶活性的效用。由于许多因素，例如底物的可用性和细胞内空间中的辅助因子，细胞内反应速率在测量过程中可能会发生变化，即使在超极化MR的可见度非常短的时间尺度上也是如此。尽管存在这种潜在的变化，但对超极化信号的动力学分析通常假设在反应的整个过程中都应用相同的速率常数（并且在许多情况下，采用相同的速率），就像通过超极化信号的建立和衰减所观察到的那样。我们在这里展示了一种获取方法，该方法可以消除对这种假设的需要，并能够在离体超极化研究期间（即，在给予一种超极化底物剂量衰减的过程中）检测反应速率的瞬时变化。离体活组织样本）。这种方法利用了超极化的产品选择性饱和激励脉冲。先前已经在体内将类似的脉冲用于光谱成像。但是，我们在这里显示了对所用制剂中动力学速率测定的有利结果。我们将这种获取策略用于灌注组织切片的研究，并开发出一种理论来解释为什么这种特定方法能够确定酶速率的变化，该变化可通过超极化底物的化学转化来监测。在灌注的脑，肝和异种移植乳腺癌组织切片中证实了细胞内反应速率的实时变化，并为组织表征提供了另一个潜在的分化参数。