Evaluation eines Echtzeit-Verfahrens zur quantitativen Flussmessung in der kardialen Magnetresonanztomographie

Abstract

The objective of the present work was to evaluate a novel real-time phase-contrast flow magnetic resonance imaging (MRI) technique for the assessment of cardiovascular flow. Real-time flow is based on a highly undersampled radial fast low angle shot (FLASH) sequence and image reconstruction by regularized nonlinear inversion. The technique allows flow quantification during free breathing and without the need for electrocardiogram (ECG)-synchronisation. Blood flow was studied in 10 healthy volunteers at 3 T by both real-time MRI and conventional ECG-synchronised cine MRI (with and without breath-holding) in the ascending aorta (AAo). Flow volumes and peak flow velocities were evaluated using standard post-processing software extended to real-time flow images. Phase offset values were obtained from phantom measurements using the in vivo contours of the AAo for all 10 subjects. Peak flow velocities were additionally compared to Doppler echocardiography. Furthermore, real-time flow MRI was applied in 20 healthy volunteers to evaluate haemodynamic alterations in the AAo and superior vena cava (SVC) during elevated intrathoracic pressure (Valsalva manoeuvre). Quantitative evaluations of flow volume were comparable for real-time and ECG-synchronised cine methods when real-time MRI data were averaged across heartbeats. For individual heartbeats, real-time MRI resulted in higher peak velocities for values above 120 cm/s as compared to cine MRI. Real-time MRI of peak flow velocities also revealed quantitative agreement with Doppler echocardiography, however, higher limits of agreement were observed. Phantom measurements confirmed low phase offset values for real-time MRI. Real-time measurements were technically successful during the Valsalva manoeuvre in all healthy volunteers allowing a detailed quantification of beat-to-beat haemodynamic alterations simultaneously in the AAo and SVC. The evaluated technique holds promise for accelerated flow quantification with high spatiotemporal resolution – particularly in patients that are not able to follow breath-holding instructions (e.g. paediatric patients) or in patients with irregular heartbeats due to cardiac arrhythmias – which will need to be addressed in future clinical investigations.