Brain Pulsation Imaging Using Non-Balanced Steady-State Free Precession With 3D-EPI Readout

To present a new, fast MR imaging method for visualization and quantification of pulsatile displacement in brain tissue and fluid.

The natural phase-contrast of non-balanced steady-state free precession combined with careful tuning of the intrinsic spoiler gradients is harnessed to measure displacement along specific physical directions. Efficient segmented 3D-EPI allows for whole brain coverage within TR = 0.15 s. Motion sensitive terms are added to the extended phase graph theory and simulations are used to optimize the sequence parameters and to calibrate the phase sensitivity. Pilot data on 4 healthy volunteers are acquired at 7T and analyzed after cardiac retrogating. A set of three 1-min scans with spoiler gradients along orthogonal axes is required to estimate full 3D displacement vectors.

Simulations show that pulsatile displacements up to around 1 mm can be resolved with the proposed method. In vivo example data are in general agreement with predictions from simulations. The precision of the displacement measurements is estimated to be 0.01 mm using repeated scans of the same subject, and while estimated displacement values agree well with literature values for example tissue ROIs, the measurement accuracy needs to be further explored. The method provides a detailed view of the pulsatile motion along all three physical axes and with full 3D coverage of the brain.

Brain Pulsation Imaging allows for quantitative measurements of displacement vectors through the cardiac cycle with whole brain coverage within 3-5 min. The method is robust and should have significant potential for clinical application.