Data_Sheet_1_Measuring Arterial Pulsatility With Dynamic Inflow Magnitude Contrast.pdf

The pulsatility of blood flow through cerebral arteries is clinically important, as it is intrinsically associated with cerebrovascular health. In this study we outline a new MRI approach to measuring the real-time pulsatile flow in cerebral arteries, which is based on the inflow phenomenon associated with fast gradient-recalled-echo acquisitions. Unlike traditional phase-contrast techniques, this new method, which we dub dynamic inflow magnitude contrast (DIMAC), does not require velocity-encoding gradients as sensitivity to flow velocity is derived purely from the inflow effect. We achieved this using a highly accelerated single slice EPI acquisition with a very short TR (15 ms) and a 90° flip angle, thus maximizing inflow contrast. We simulate the spoiled GRE signal in the presence of large arteries and perform a sensitivity analysis. The sensitivity analysis demonstrates that in the regime of high inflow contrast, DIMAC shows much greater sensitivity to flow velocity over blood volume changes. We support this theoretical prediction with in-vivo data collected in two separate experiments designed to demonstrate the utility of the DIMAC signal contrast. We perform a hypercapnia challenge experiment in order to experimentally modulate arterial tone within subjects, and thus modulate the arterial pulsatile flow waveform. We also perform a thigh-cuff release challenge, designed to induce a transient drop in blood pressure, and demonstrate that the continuous DIMAC signal captures the complex transient change in the pulsatile and non-pulsatile components of flow. In summary, this study proposes a new role for a well-established source of MR image contrast and demonstrates its potential for measuring both steady-state and dynamic changes in arterial tone.

脑动脉血流的搏动性具有重要的临床意义，因其与脑血管健康存在内在关联。本研究提出了一种新型磁共振成像（MRI）方法，用于测量脑动脉的实时搏动性血流，该方法基于与快速梯度回波采集相关的流入效应。与传统的相位对比技术不同，这种我们命名为动态流入幅度对比（dynamic inflow magnitude contrast，DIMAC）的新方法无需使用速度编码梯度，因为其对血流速度的敏感性完全源自流入效应。我们通过采用极短重复时间（TR，15 ms）、90°翻转角的高速单切片回波平面成像（EPI）采集方案实现了这一点，从而最大化了流入对比效果。我们针对大动脉环境下的扰相梯度回波（GRE）信号进行了模拟，并开展了敏感性分析。敏感性分析结果表明，在高流入对比条件下，相较于血容量变化，DIMAC对血流速度具有更高的敏感性。我们通过两项独立实验采集的体内数据验证了这一理论预测，这两项实验旨在验证DIMAC信号对比的实用性。我们开展了高碳酸血症激发实验，通过实验手段调控受试者的动脉张力，进而调节动脉搏动性血流波形。此外，我们还开展了大腿袖带放气激发实验，旨在诱发一过性血压下降，并证明连续DIMAC信号能够捕捉血流搏动性与非搏动性成分的复杂瞬态变化。综上，本研究为一种成熟的磁共振成像对比源赋予了新的应用场景，并证明了其在测量动脉张力稳态与动态变化方面的应用潜力。