The Effect of Spatial and Temporal Resolution of Cine Phase Contrast MRI on Wall Shear Stress and Oscillatory Shear Index Assessment

IntroductionWall shear stress (WSS) and oscillatory shear index (OSI) are associated with atherosclerotic disease. Both parameters are derived from blood velocities, which can be measured with phase-contrast MRI (PC-MRI). Limitations in spatiotemporal resolution of PC-MRI are known to affect these measurements. Our aim was to investigate the effect of spatiotemporal resolution using a carotid artery phantom.MethodsA carotid artery phantom was connected to a flow set-up supplying pulsatile flow. MRI measurement planes were placed at the common carotid artery (CCA) and internal carotid artery (ICA). Two-dimensional PC-MRI measurements were performed with thirty different spatiotemporal resolution settings. The MRI flow measurement was validated with ultrasound probe measurements. Mean flow, peak flow, flow waveform, WSS and OSI were compared for these spatiotemporal resolutions using regression analysis. The slopes of the regression lines were reported in %/mm and %/100ms. The distribution of low and high WSS and OSI was compared between different spatiotemporal resolutions.ResultsThe mean PC-MRI CCA flow (2.5±0.2mL/s) agreed with the ultrasound probe measurements (2.7±0.02mL/s). Mean flow (mL/s) depended only on spatial resolution (CCA:-13%/mm, ICA:-49%/mm). Peak flow (mL/s) depended on both spatial (CCA:-13%/mm, ICA:-17%/mm) and temporal resolution (CCA:-19%/100ms, ICA:-24%/100ms). Mean WSS (Pa) was in inverse relationship only with spatial resolution (CCA:-19%/mm, ICA:-33%/mm). OSI was dependent on spatial resolution for CCA (-26%/mm) and temporal resolution for ICA (-16%/100ms). The regions of low and high WSS and OSI matched for most of the spatiotemporal resolutions (CCA:30/30, ICA:28/30 cases for WSS; CCA:23/30, ICA:29/30 cases for OSI).ConclusionWe show that both mean flow and mean WSS are independent of temporal resolution. Peak flow and OSI are dependent on both spatial and temporal resolution. However, the magnitude of mean and peak flow, WSS and OSI, and the spatial distribution of OSI and WSS did not exhibit a strong dependency on spatiotemporal resolution.引言：壁切应力（Wall shear stress, WSS）和振荡剪切指数（Oscillatory shear index, OSI）与动脉粥样硬化性疾病密切相关。上述两项参数均由血流速度数据推导而来，而血流速度可通过相位对比磁共振成像（phase-contrast MRI, PC-MRI）进行测量。已有研究证实，PC-MRI的时空分辨率局限性会对上述测量结果造成影响。本研究旨在利用颈动脉体模，探究时空分辨率对相关测量参数的影响。 方法：将颈动脉体模连接至可提供脉动血流的血流装置，MRI测量平面分别设置于颈总动脉（common carotid artery, CCA）与颈内动脉（internal carotid artery, ICA）。采用30种不同的时空分辨率设置开展二维PC-MRI测量。通过超声探头测量结果对MRI血流测量数据进行验证。采用回归分析对比不同时空分辨率下的平均流量、峰值流量、血流波形、WSS及OSI，并以%/mm和%/100ms为单位报告回归直线的斜率。同时对比不同时空分辨率下低、高WSS及OSI区域的分布差异。 结果：PC-MRI测得的颈总动脉平均流量（2.5±0.2mL/s）与超声探头测量结果（2.7±0.02mL/s）具有良好一致性。平均流量（mL/s）仅与空间分辨率相关（颈总动脉：-13%/mm，颈内动脉：-49%/mm）。峰值流量（mL/s）同时受空间分辨率（颈总动脉：-13%/mm，颈内动脉：-17%/mm）与时间分辨率（颈总动脉：-19%/100ms，颈内动脉：-24%/100ms）的影响。平均WSS（Pa）仅与空间分辨率呈负相关关系（颈总动脉：-19%/mm，颈内动脉：-33%/mm）。OSI分别受颈总动脉的空间分辨率（-26%/mm）及颈内动脉的时间分辨率（-16%/100ms）影响。多数时空分辨率设置下，低、高WSS及OSI区域的分布匹配度良好：颈总动脉的WSS匹配30/30例，颈内动脉为28/30例；颈总动脉的OSI匹配23/30例，颈内动脉为29/30例。 结论：本研究证实，平均流量与平均WSS均不受时间分辨率的影响；峰值流量与OSI同时受空间分辨率与时间分辨率的影响。然而，平均流量与峰值流量、WSS与OSI的数值大小，以及OSI和WSS的空间分布均未表现出对时空分辨率的强依赖性。