Highly accelerated 4D flow cardiovascular magnetic resonance using a pseudo-spiral Cartesian acquisition and compressed sensing reconstruction for carotid flow and wall shear stress

摘要

The pseudo-spiral sampling strategy for Cartesian 3D k-space sampling, with two phase encoding directions (k ,k ) and one fully sampled frequency encoding direction (k ). In a regular Cartesian sampling strategy (k ,k )-profiles are acquired line-by-line. Additionally, in regular retrospectively triggered cardiac scans, each (k ,k )-profile is repeated within each cardiac cycle to ensure complete filling of k-t-space and a fully sampled time dimension for each (k ,k )-profile. The segments of 4xTR length indicate all 4 flow encoding segments of a 4D flow CMR scan, with the dark segments indicating the reference scan. This distribution shows all pseudo-spiral (k ,k )-coordinates sampled within one scan session. The pseudo-spiral trajectory creates a variable density distribution with an oversampled center. In a pseudo-spiral sampling strategy, (k ,k )-profiles are sampled from the center of k-space to the outside, however still on a Cartesian grid. To achieve undersampling in the temporal domain, (k ,k )-profiles are updated continuously within each cardiac cycle in addition to the pseudo-spiral sampling trajectory. After retrospective cardiac binning, this results in a sampling mask of white (sampled) and black (not sampled) (k ,k )-coordinates, with unique, incoherent sampling patterns per cardiac frames (see color coding in )