Real-time phase-contrast flow MRI of the ascending aorta and superior vena cava as a function of intrathoracic pressure (Valsalva manoeuvre)

Abstract

Objective: Real-time phase-contrast flow MRI at high spatiotemporal resolution was applied to simultaneously evaluate haemodynamic functions in the ascending aorta (AA) and superior vena cava (SVC) during elevated intrathoracic pressure (Valsalva manoeuvre). Methods: Real-time phase-contrast flow MRI at 3 T was based on highly undersampled radial gradient-echo acquisitions and phase-sensitive image reconstructions by regularized non-linear inversion. Dynamic alterations of flow parameters were obtained for 19 subjects at 40-ms temporal resolution, 1.33-mm in-plane resolution and 6-mm section thickness. Real-time measurements were performed during normal breathing (10 s), increased intrathoracic pressure (10 s) and recovery (20 s).Results: Real-time measurements were technically successful in all volunteers. During the Valsalva manoeuvre (late strain) and relative to values during normal breathing, the mean peak flow velocity and flow volume decreased significantly in both vessels (p , 0.001) followed by a return to normal parameters within the first 10 s of recovery in the AA. By contrast, flow in the SVC presented with a brief (1-2 heartbeats) but strong overshoot of both the peak velocity and blood volume immediately after pressure release followed by rapid normalization. Conclusion: Real-time phase-contrast flow MRI may assess cardiac haemodynamics non-invasively, in multiple vessels, across the entire luminal area and at high temporal and spatial resolution. Advances in knowledge: Future clinical applications of this technique promise new insights into haemodynamic alterations associated with pre-clinical congestive heart failure or diastolic dysfunction, especially in cases where echocardiography is technically compromised.The Valsalva manoeuvre attempts to increase the intrathoracic pressure by a forceful expiration against a closed glottis, typically for a few seconds. The resulting haemodynamic response is characterized by a sinusoidal waveform of arterial pressure and stroke volume. The pattern is caused by an acute increase in intrathoracic pressure (Phase 1), a decreased stroke volume secondary to decreased venous return (Phase 2), an acute decrease of intrathoracic pressure during early recovery (Phase 3) and a subsequent increase in stroke volume accompanied by a reflex bradycardia (Phase 4). 3 In general, however, the clinical relevance of the Valsalva manoeuvre suffers from difficulties in the non-invasive quantification of blood flow dynamics and the inability to assess haemodynamic functions simultaneously in the superior vena cava (SVC) and with respect to left-ventricular outflow. 4 Moreover, because the manoeuvre is inevitably associated with a forced and increased breathing frequency during strain release, echocardiographic studies may be compromised by the lack of an appropriate acoustic window.On the other hand, MRI techniques have emerged as a new diagnostic standard for simultaneous evaluation of leftventricular and right-ventricular function. 5 In particular,

Pseudo‐spiral sampling and compressed sensing reconstruction provides flexibility of temporal resolution in accelerated aortic 4D flow MRI: A comparison with k‐t principal component analysis

“…By contrast, motion artifacts are reduced in the 4D flow scans due to the respiratory gating but cannot be eliminated. Moreover, increased intrathoracic pressure during breath hold is associated with flow and stroke volume decrease, which can be another reason for differences between 2D flow and 4D flow MRI . Finally, the difference in peak systolic segmentation for the 4D flow scans in contrast to the time‐resolved segmentation of the 2D flow scans are another possible source of errors …”

“…Moreover, increased intrathoracic pressure during breath hold is associated with flow and stroke volume decrease, which can be another reason for differences between 2D flow and 4D flow MRI. 35,36 Finally, the difference in peak systolic segmentation for the 4D flow scans in contrast to the time-resolved segmentation of the 2D flow scans are another possible source of errors. 37 Additional studies can make use of PROUD CS acceleration as a valuable tool in clinical research to speed up 4D flow acquisitions.…”

Advanced flow MRI: emerging techniques and applications

“…A systematic analysis of the impact of beat-to-beat variations on LA flow characteristics is thus not possible, particularly in the presence of arrhythmia. Recent advances in MRI data acquisition strategies allow for real-time assessment of beat-to-beat variation in the presence of AF and breathing exercises (such as the Valsalva and Mueller manoeuvres) 8,161,162 . To achieve sufficiently high frame rates needed for real-time flow acquisitions, optimised and accelerated 2D flow imaging pulse sequences have been developed, which combine effective data readout modules (e.g., echo planar imaging, EPI) with data undersampling and parallel imaging data reconstruction (e.g., compressed sensing, k-t-acceleration in spatial and temporal dimension).…”

W(h)ither human cardiac and body magnetic resonance at ultrahigh fields? technical advances, practical considerations, applications, and clinical opportunities

“…cardiac arrhythmias) constraints, which might cause inappropriate diagnostic information. Free breathing real time cardiac MRI achieves diagnostic quality in a single heartbeat and bears the potential to change the landscape of cardiac diagnostics . These developments will afford an improved clinical accuracy and efficacy of CMR.…”