1D versus 3D blood flow velocity and pulsatility measurements of lenticulostriate arteries at 7T MRI

Abstract

Purpose7T MRI enables measurements of blood flow velocity waveforms in small, perforating cerebral arteries. As these vessels can be tortuous, acquisition methods sensitive to flow in only one direction may not be sufficient to accurately determine the dynamic blood flow velocity. In this study, we compared 1D with 3D velocity encoding to measure the blood flow velocity and pulsatility in the lenticulostriate arteries (LSAs). MethodsBlood flow velocity waveforms were measured in the LSAs of 18 subjects (age range: 20–74 years) using prospectively gated single-slice phase contrast (PC) MRI at 7T. For each subject, blood flow velocity waveforms were acquired in a single slice with one velocity encoding as well as three orthogonal velocity encodings. The peak velocity and pulsatility index (PI) were determined in the largest, perpendicularly planned LSA, one obliquely planned LSA and three smaller LSAs. The peak velocity and PI were compared between 1D and 3D measurements using Bland-Altman analysis, with the 95% limits of agreement (LOA) taken into account. ResultsFor the largest, perpendicularly planned LSA, the peak velocity was slightly lower (0.2 cm/s, 1.7%) for 1D compared to 3D measurements, with an LOA range from the mean difference of (−0.27;0.27). The PI was slightly higher (0.01, 1.6%) for the 1D measurement, and an LOA range from the mean difference in PI of (−0.045;0.045). The obliquely planned LSA and three smaller LSAs demonstrated larger deviations (range mean percentage difference: 3.9–8.2%). Conclusion1D velocity encoding using 2D PC MRI provides sufficiently accurate dynamic velocity and pulsatility measurements in slices perpendicularly planned to single, large LSAs compared to 3D velocity encoding, while increasing errors are obtained with obliquely planned slices. A greater error is indicated when measuring multiple (possibly tortuous or obliquely planned) smaller LSAs in one scan using one-directional single-slice PC MRI.