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

Abstract

Introduction: Wall 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.

Methods: A 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.

Results: The 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).

Conclusion: We 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.

Fig 1

a) The surface reconstruction of the healthy right carotid artery based on which the phantom was built b) The sketch of the pulsatile water flow set-up c) The velocity profile measured at CCA (left) and at ICA (right) measurement planes.

Fig 2

a) Flow waveforms at different spatial(sr) and temporal(tr) resolutions. Dashed lines show the PC-MRI measurements and the red line shows the ultrasound probe measurement. Spatial resolution varied between 0.2mm and 1 mm and the temporal resolution varied between 9.1 ms and 142.9 ms. b) Ultrasound probe vs. PC-MRI flow measurements.

Fig 3

a) Mean flow [mL/s] vs. spatial resolution [mm] b) Mean flow [mL/s] vs. temporal resolution [ms] c) Peak flow [mL/s] vs. spatial resolution and d) Peak flow [mL/s] vs. temporal resolution at the CCA and ICA. Red lines show the mean and peak flow measured by ultrasound probe.

Fig 4

a) WSS [Pa] vs. spatial resolution [mm] b) WSS [Pa] vs. temporal resolution [ms] c) OSI vs. spatial resolution and d) OSI vs. temporal resolution.

Fig 5. The mean WSS [Pa] of each quarter by CFD and by PC-MRI measurements at different spatial and temporal resolutions in the CCA and ICA.

* shows the highest WSS quarter and + shows the lowest WSS quarter.

Fig 6. The mean OSI of each quarter by CFD and by PC-MRI measurements at 4 different spatial and temporal resolutions in the CCA and ICA.

* shows the highest OSI quarter and + shows the lowest OSI quarter.