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Abstract:
Seven-dimensional flow quantification techniques (3D spatial encoding, 3-direction velocity encoding, and time resolution) are widely used for the study of flow patterns in blood vessels. The existing methods [1] are based on radiofrequency spoiled gradient echo sequences that give very low signal from fluids because of spin saturation effects when TR << T1. In this work, we show the feasibility
of a flow sensitive phase-contrast balanced SSFP (PC-bSSFP) sequence, which holds a T2/T1 contrast, and results in a significantly higher signal to noise ratio in fluids. As a drawback, the implementation of a bSSFP sequence requires attention to issues concerning steady-state and artifacts. In order to avoid steady-state disruption, leading to signal loss and artifacts, flow compensation over
repetition time was implemented in our sequence. Additionally, it was critical to optimize the gradient
parameters in order to obtain the desired flow sensitivity while maintaining the shortest possible TR, not only for temporal resolution but also for reducing bSSFP-specific banding artifacts. Our implementation allowed us to extend the field of application of 7D flow measurement sequences to the study of cerebro-spinal fluid (CSF) flow patterns, which are still unclear in the present state of research.
