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Pulmonary artery stiffness assessed by velocity-encoding MRI: comparison of techniques
Journal of Cardiovascular Magnetic Resonance volume 13, Article number: P362 (2011)
The pulmonary artery (PA) plays an essential role in smoothing the transition from right-ventricular pulsatile flow to the nearly steady-flow at capillary level. The loss of PA compliance has considerable influence on elevated right-ventricle workload. MRI velocity-encoding is an effective technique for assessing pulse-wave-velocity (PWV) by measuring the disturbances in flow or vessel diameter the pressure wave causes . Two methods have been proposed for measuring PWV: transit-time (TT) and flow-area (QA)[2, 3]. Nevertheless, no data is available that compares the two methods, especially over wide range of PWV values, or at 3.0-Tesla, which is the purpose of this study.
Twenty-five volunteers(Table 1) were scanned on 3.0-Tesla Siemens scanner. Two velocity-encoding sequences were applied to each subject. The first sequence was optimized for high temporal-resolution (heart-phases=128, pixel-size =1.25mm, venc=150cm/s), and implemented twice: at main PA and either right or left PA locations (Figure 1). The second sequence was optimized for high spatial-resolution (heart-phases=80, pixel-size=0.6mm, venc=150cm/s), and implemented once at the main PA location (Figure 1). The images were analyzed with MATLAB, as previously described for TT and QA methods( Figures 2 and 3) [2, 3]. Inter-method, inter-observer and intra-observer variabilities were calculated using Bland-Altman analysis.
The MRI exam lasted for 15-20 minutes. Image analysis lasted for 1 minute and 4 minutes for the TT and QA methods, respectively. The TT and QA methods showed good agreement (P>0.1). The Bland-Altman analysis resulted in mean±SD of 0.13±0.35m/s for the measurement differences. All the differences lied within the ±2SD limit. The correlation coefficient between the two methods was r=0.93. The repeated measurements showed low inter-observer and intra-observer variabilities (Figure 4). The mean±SD of the TT/QA measurement were -0.05±0.2/-0.01±0.38 m/s and 0.02±0.27/0.02±0.4 m/s for inter-observer and intra-observer, respectively. The corresponding correlation coefficients were r=0.96/0.92 and r=0.94/0.90.
Discussion and conclusions
The TT and QA techniques showed good agreement in estimating PWV, although the QA method resulted in larger variabilities than in TT. Long processing time was required in the QA method, mostly for identifying vessel cross-sections. However, the TT method required double the imaging time as in QA due to the acquisition of two slices. The use of 3.0-Tesla allowed for improving the temporal and spatial resolutions in the TT and QA sequences, respectively. In conclusion, each technique has its own advantages and disadvantages. The choice depends on patient condition, heart rate, and required image quality.
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Ibrahim, E.H., Shaffer, J.M. & White, R.D. Pulmonary artery stiffness assessed by velocity-encoding MRI: comparison of techniques. J Cardiovasc Magn Reson 13, P362 (2011). https://doi.org/10.1186/1532-429X-13-S1-P362
- Pulmonary Artery
- Pulsatile Flow
- Main Pulmonary Artery
- Left Pulmonary Artery
- Artery Stiffness