ausblenden:
Schlagwörter:
asymmetric echo; nonlinear inverse reconstruc-
tion; cardiovascular blood flow; phase-contrast flow MRI;
radial MRI; real-time MRI
Zusammenfassung:
Purpose: To provide multidimensional velocity compensation
for real-time phase-contrast flow MRI.
Methods: The proposed method introduces asymmetric gradi-
ent echoes for highly undersampled radial FLASH MRI with
phase-sensitive image reconstruction by regularized nonlinear
inversion (NLINV). Using an adapted gradient delay correction
the resulting image quality was analyzed by simulations and
experimentally validated at 3 Tesla. For real-time flow MRI the
reduced gradient-echo timing allowed for the incorporation of
velocity-compensating waveforms for all imaging gradients at
even shorter repetition times.
Results: The results reveal a usable degree of 20% asymme-
try. Real-time flow MRI with full velocity compensation elimi-
nated signal void in a flow phantom, confirmed flow
parameters in healthy subjects and demonstrated signal
recovery and phase conservation in a patient with aortic valve
insufficiency and stenosis. Exemplary protocols at 1.4–1.5 mm
resolution and 6 mm slice thickness achieved total acquisition
times of 33.3–35.7 ms for two images (7 spokes each) with
and without flow-encoding gradient.
Conclusion: Asymmetric gradient echoes were successfully
implemented for highly undersampled radial trajectories. The
resulting temporal gain offers full velocity compensation for
real-time phase-contrast flow MRI which minimizes false-
positive contributions from complex flow and further enhances
the temporal resolution compared with acquisitions with
symmetric echoes.
