Echo planar imaging–induced errors in intracardiac 4D flow MRI quantification

Abstract

To assess errors associated with EPI-accelerated intracardiac 4D flow MRI (4DEPI) with EPI factor 5, compared with non-EPI gradient echo (4DGRE).Methods: Three 3T MRI experiments were performed comparing 4DEPI to 4DGRE: steady flow through straight tubes, pulsatile flow in a left-ventricle phantom, and intracardiac flow in 10 healthy volunteers. For each experiment, 4DEPI was repeated with readout and blip phase-encoding gradient in different orientations, parallel or perpendicular to the flow direction. In vitro flow rates were compared with timed volumetric collection. In the left-ventricle phantom and in vivo, voxel-based speed and spatio-temporal median speed were compared between sequences, as well as mitral and aortic transvalvular net forward volume. Results:In steady-flow phantoms, the flow rate error was largest (12%) for high velocity (>2 m/s) with 4DEPI readout gradient parallel to the flow. Voxel-based speed and median speed in the left-ventricle phantom were ≤5.5% different between sequences. In vivo, mean net forward volume inconsistency was largest (6.4 ± 8.5%) for 4DEPI with nonblip phase-encoding gradient parallel to the main flow. The difference in median speed for 4DEPI versus 4DGRE was largest (9%) when the 4DEPI readout gradient was parallel to the flow.Conclusions: Velocity and flow rate are inaccurate for 4DEPI with EPI factor 5 when flow is parallel to the readout or blip phase-encoding gradient. However, mean differences in flow rate, voxel-based speed, and spatio-temporal median

Age- and sex-specific reference values of biventricular flow components and kinetic energy by 4D flow cardiovascular magnetic resonance in healthy subjects

“…4D flow CMR using echo-planar imaging (EPI) had good in-scan consistency and strong scan-rescan reproducibility for the LV inflow and outflow assessment [ 23 ]. As discussed by Westenberg et al [ 34 ], only the flow velocity in the non-blip EPI direction is correctly encoded, and in particular (high) velocities in the direction of the readout gradient are fraught with systematic inaccuracies. These inaccuracies seem to be within reasonable error limits for valvular flow evaluations [ 34 ].…”

“…As discussed by Westenberg et al [ 34 ], only the flow velocity in the non-blip EPI direction is correctly encoded, and in particular (high) velocities in the direction of the readout gradient are fraught with systematic inaccuracies. These inaccuracies seem to be within reasonable error limits for valvular flow evaluations [ 34 ]. Flow component analysis has been demonstrated feasible and applicable for different sequences and different scanners [ 8 – 10 , 16 , 17 ].…”

4D Flow cardiovascular magnetic resonance consensus statement: 2023 update

“…These approaches are ultimately limited by the irrecoverable T2* decay and phase disruptions of the signal during extended readouts. Echo planar imaging with a modest EPI factor of up to 5 appears useful to speed up 4D Flow CMR data acquisition in regions of normal cardiac blood flow and especially when the acquisition volume can be planned in such a way, that anticipated main flow in readout direction can be avoided [ 99 , 141 – 143 ]. We therefore advise against the use of echo planar imaging for high flow velocity in anatomies where the main flow direction can change with respect to the gradient directions, such as in the ascending aorta and aortic arch.…”

Why 4D Flow MRI? Real Advantages

“…With the advent of 4D Flow MRI, the imaging time was significantly shortened to around 10 min; however, the current clinical environment requires an even shorter imaging time. The imaging time can be further shortened to a few minutes by using recent cutting-edge technologies such as echoplanar imaging 22,23 and sparse imaging. 24,25 Optimization of velocity encoding Currently, there is only one velocity encoding (VENC) that can be applied in a single session of the scan; hence, the actual flow velocity may often exceed this value.…”