Real time phase encoded MR for assessment of acute variability of central pulse wave velocity

Background

The variability of pulse wave velocity (PWV) with changing arterial wall stress may reflect the degree of aortic stiffness independent of arterial pressure. We implemented a real-time MR flow technique so as to be able to assess acute changes in PWV due to affected arterial blood and/or intra thoracic pressure. The aim of this study was to assess the accuracy of rapid PWV assessment using the real time MR technique.

Methods

We developed a novel real-time MR dual-slice protocol (RT-DS), with interleaved through-plane acquisitions of projected left to right velocity to rapidly measure central pulse wave velocity (PWV). An automated in-house post-processing tool measures mean velocity pulse wave transit time and aortic length, permitting PWV assessment from projected image data. In a pulsatile flow phantom, RT-DS-derived PWV was validated against pressure-wire-PWV (gold-standard) and in-plane 2D phase-contrast MRI (PC-MRI). In 17 healthy adult volunteer scans (mean age, 32 ± 7; mean arterial blood pressure 89 ± 7 mmHg), agreement of PWV by RT-DS was compared with in-plane PC-MRI.

Results

Excellent correlation of assessed PWV between pressure wire (6.35 ± 0.18 m/s) and both RT-DS and PC-MRI scans were observed, (6.20 ± 0.61 m/s, P = 0.70, and 6.33 ± 0.70 m/s, P=0.96, respectively), in vitro. Volunteer velocity profiles with located wave ‘foot’ locations using both MR scanning protocols are shown in the figure below for comparison. In the volunteer cohort, the RT-DS and PC-MRI scans showed a correlation of 0.9, (r2=0.25, P > 0.04). RT-DS derived PWV was lower than standard PC-MRI (mean difference, -0.46 ± 0.78 m/s). Inter-scan variability of PWV by RT-DS was 0.41±0.32 m/s. Regional PWV between ascending/descending and descending/abdominal aorta lacked reproducibility.

Figure 1

PC-MRI (left) and RT-DS (right) velocity profiles with located wave ‘feet’ from a volunteer scan

Conclusions

Real-time dual-slice projection phase-contrast MRIS is accurate and reproducible to assess the aortic PWV. The method has potential to detect acute the variability of PWV in response to variation in arterial blood and/or intra thoracic pressure as a measure of arterial stiffness.

Funding

Medical Research Council, UK.