Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas.
Department of Radiology and Biomedical Imaging, University of California at San Francisco, San Francisco, California.
Magn Reson Med. 2019 Jun;81(6):3754-3762. doi: 10.1002/mrm.27687. Epub 2019 Feb 22.
Various excitation strategies have been proposed for dynamic imaging of hyperpolarized agents such as [1- C]-pyruvate, but the impact of these strategies on quantitative evaluation of signal evolution remains unclear. To better understand their relative performance, we compared the accuracy and repeatability of measurements made using variable excitation angle strategies and conventional constant excitation angle strategies.
Signal evolution for constant and variable excitation angle schedules was simulated using a pharmacokinetic model of hyperpolarized pyruvate with 2 chemical pools and 2 physical compartments. Noisy synthetic data were then fit using the same pharmacokinetic model with the apparent chemical exchange term as an unknown, and fit results were compared with simulation parameters to determine accuracy and reproducibility.
Constant excitations and a variable excitation strategy that maximizes the HP lactate signal yielded data that supported quantitative analyses with similar accuracy and repeatability. Variable excitation angle strategies that were designed to produce a constant signal level resulted in lower signal and worse quantitative accuracy and repeatability, particularly for longer acquisition times.
These results suggest that either constant excitation angle or variable excitation angles that attempt to maximize total signal, as opposed to maintaining a constant signal level, are preferred for metabolic quantification using hyperpolarized pyruvate.
已经提出了各种激发策略来对 [1- C]-丙酮酸等超极化试剂进行动态成像，但这些策略对信号演变的定量评估的影响尚不清楚。为了更好地了解它们的相对性能，我们比较了使用可变激发角策略和常规恒定激发角策略进行测量的准确性和可重复性。
使用具有 2 个化学池和 2 个物理隔室的超极化丙酮酸药代动力学模型模拟恒定和可变激发角方案的信号演变。然后，使用相同的药代动力学模型拟合带有表观化学交换项作为未知项的噪声合成数据，并将拟合结果与模拟参数进行比较，以确定准确性和可重复性。
恒激发和最大 HP 乳酸信号的可变激发策略产生的数据支持具有相似准确性和可重复性的定量分析。旨在产生恒定信号水平的可变激发角策略导致信号降低，定量准确性和可重复性更差，尤其是在更长的采集时间。
这些结果表明，对于使用超极化丙酮酸进行代谢定量，优选使用恒激发角或尝试最大化总信号的可变激发角策略，而不是保持恒定的信号水平。
