Keywords:
CNS, Neuroradiology brain, MR, Experimental, MR-Functional imaging, Experimental investigations, Imaging sequences, Technical aspects, Cerebrospinal fluid, Haemodynamics / Flow dynamics, Obstruction / Occlusion
Authors:
A. Najafi1, T. D. J. Sartoretti2, C. A. Binkert1, S. Sartoretti-Schefer1, M. Wyss2; 1Winterthur/CH, 2Zürich/CH
DOI:
10.1594/ecr2018/C-1577
Results
The accuracy of a phase contrast MR measurement is adequate for the studied flow rates (0.1 – 0.5 ml/s),
with a maximal undervaluation of 5-10 % in higher flows (Fig.
5).
Slice thickness does not have a substantial influence on the measured flow parameters (Fig.
6).
In-plane resolution on the other hand has a substantial impact on the mean and peak flow velocity,
presumably due to partial volumes effects of larger flow with low velocity.
The selected VENC should be the same as or slightly higher than the expected flow velocity in order to obtain higher signal in the phase image and to prevent phase aliasing.
If the VENC is chosen too high the peak velocity is overestimated (Fig.
6) while the flow rate is less affected.
Best results are obtained when the phase contrast sequence is optimized in slice thickness (max.
3 mm),
in-plane resolution (≤ 0.5 x 0.5mm2) and velocity encoding parameters (VENC; 24 cm/sec).
Slice placement (Fig.7) and ROI diameter (Fig.
8) have major influences on the measured flow values (Table 1).
The slice should always be placed in the narrowest point of the stenosis und strictly rectangular to the aqueduct.
Hence it is essential to include a planning high resolution 3D T2w TSE sequence for precise anatomical depiction.
ROI diameter should enclose the aqueduct with as little surrounding tissue as possible.
Our software required a minimum of 10 pixels to calculate reliable values.
Since the sequence used in the phantom experiment was not ECG-triggered,
the influence of the number of acquired phases on flow parameters could not been studied.
An optimal measurement would have highest possible spatial resolution (high in-plane resolution and thin slice) to minimize partial volume effects and highest temporal resolution (high number of heart phases).