Accelerated phase contrast MRI using hybrid one- and two-sided flow encodings only (HOTFEO)

The aim of this work was to develop and evaluate a fast phase contrast magnetic resonance imaging (PC-MRI) technique with hybrid one- and two-sided flow encodings only (HOTFEO) for accurate blood flow and velocity measurements of three-directional velocity encoding PC-MRI. Four-dimensional (4D) PC-MRI acquires flow-compensated (FC) and three-directional flow-encoded (FE) echoes in an interleaved fashion. We hypothesize that the blood flow velocity direction (not magnitude) has minimal change between two consecutive cardiac phases. This assumption provides a velocity direction constraint that can achieve 4/3-fold acceleration using three-directional FE data to calculate FC data instead of acquiring them. The HOTFEO acquisition pattern can address the ill-conditioned constraint and improve the calculation accuracy. HOTFEO was evaluated in healthy volunteers and compared with conventional two-dimensional (2D) and 4D flow imaging techniques with FC and three-directional FE acquisitions (FC/3FE). Compared with FC/3FE, Bland-Altman tests showed that the 4/3-fold accelerated HOTFEO technique resulted in relatively small bias error for total volumetric flow (0.89% for prospective 2D data, -1.19% for retrospective 4D data and -3.40% for prospective 4D data) and maximum peak velocity (0.50% for prospective 2D data, -0.17% for retrospective 4D data and -2.00% for prospective 4D data) measurements in common carotid arteries. HOTFEO can accelerate three-directional velocity encoding PC-MRI whilst maintaining the measurement accuracy of the total volumetric flow and maximum peak velocity.