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
Methods and materials
A sagittal 3D T2 weighted T2w TSE sequence of the cranium was obtained for planning (Fig.
1).
The phase contrast sequence,
using cardiac triggering either via electrocardiogram or peripheral-pulse device,
is then set strictly perpendicular (transversal) over the aqueduct.
This sequence generates magnitude and phase images,
in our case an anatomical magnitude image (FFE/M),
a magnitude phase contrast image (PCA/M),
and the phase of the phase contrast image (PCA/P) (Fig.
2).
A processing software then calculates the flow parameters from the PCA/P image.
Cardiac triggering allows the acquisition of several images per heartbeat relating to heart cycle,
which determines the time resolution of a phase contrast sequence (Fig.
3).
Flow velocity and the flow direction are encoded and presented in the PCA/P grayscale image.
The setting of the direction of the velocity encoding parameter (VENC) defines the appearance of the signal on the PCA/P image.
In a transversal acquisition plane the encoding of the flow direction is feet - head.
Post-processing is done semi-automatically,
only a region of interest (ROI) has to be manually defined.
Different flow parameters are obtained: forward flow volume (ml),
backward flow volume (ml),
regurgitation fraction,
absolute stroke volume (ml),
mean flux (ml/sec),
stroke distance (cm),
mean velocity (cm/sec),
peak velocity (cm/sec) and peak pressure gradient.
Various technical factors were then evaluated for their impact on the obtained flow parameters: anatomical positioning of the phase contrast sequence in the aqueduct,
MR-sequence related factors (slice thickness,
in-plane resolution,
VENC) and post-processing related factors (size of manually placed ROI).
The accuracy for low flow rates and the impact of varying sequence parameters was studied in phantom studies.
Physiological saline solution was pumped several times through a flexible tube of 1.5 mm diameter with an MR Injector.
The flexible tube was placed between two phantom bottles (Fig.
4).
Phase contrast measurements were obtained on a 3T scanner with an 8-channel head coil.
For the phantom a non-ECG triggered phase contrast MR sequence with the following parameter was used: FOV 120 x 120 mm2,
acquisition voxel size 0.4 x 0.4 x 2.0 mm3,
TR 17 ms,
TE 10 ms,
flip angle 15°,
number of signal averages (NSA) 2,
VENC 20 cm/sec,
acquisition time 20 s.
Each time one parameter was varied while the others were kept constant.