4D flow cardiovascular magnetic resonance consensus statement

Abstract

Pulsatile blood flow through the cavities of the heart and great vessels is time-varying and multidirectional. Access to all regions, phases and directions of cardiovascular flows has formerly been limited. Four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has enabled more comprehensive access to such flows, with typical spatial resolution of 1.5×1.5×1.5 – 3×3×3 mm3, typical temporal resolution of 30–40 ms, and acquisition times in the order of 5 to 25 min. This consensus paper is the work of physicists, physicians and biomedical engineers, active in the development and implementation of 4D Flow CMR, who have repeatedly met to share experience and ideas. The paper aims to assist understanding of acquisition and analysis methods, and their potential clinical applications with a focus on the heart and greater vessels. We describe that 4D Flow CMR can be clinically advantageous because placement of a single acquisition volume is straightforward and enables flow through any plane across it to be calculated retrospectively and with good accuracy. We also specify research and development goals that have yet to be satisfactorily achieved. Derived flow parameters, generally needing further development or validation for clinical use, include measurements of wall shear stress, pressure difference, turbulent kinetic energy, and intracardiac flow components. The dependence of measurement accuracy on acquisition parameters is considered, as are the uses of different visualization strategies for appropriate representation of time-varying multidirectional flow fields. Finally, we offer suggestions for more consistent, user-friendly implementation of 4D Flow CMR acquisition and data handling with a view to multicenter studies and more widespread adoption of the approach in routine clinical investigations.

Aortic Valve Stenosis Alters Expression of Regional Aortic Wall Shear Stress: New Insights From a 4‐Dimensional Flow Magnetic Resonance Imaging Study of 571 Subjects

“…All subjects underwent a standard‐of‐care thoracic cardiovascular MRI exam including 2‐dimensional (2D) time‐resolved ECG gated (CINE) balanced steady state free precession imaging of the heart and aortic valve as well as 3D contrast‐enhanced magnetic resonance angiography following the administration of contrast media (either 0.2 mmol/kg of gadopentate dimeglumine, 0.1 mmol/kg of gadobenate dimeglumine, or 0.1 mmol/kg of gadofosveset trisodium) to provide a comprehensive evaluation of aortic morphology and valve function as previously reported 15, 16. In addition, 4D flow MRI (time‐resolved 3‐directional phase contrast MRI with 3D velocity encoding) was acquired in a sagittal oblique 3D volume covering the thoracic aorta using prospective ECG gating and a respiratory navigator gating 17. 4D flow pulse sequence parameters were as follows: spatial resolution=2.2 to 4.2 mm×1.7 to 2.9 mm×2.2 to 4.0 mm; field of view=320 to 470 mm×234 to 382 mm×66 to 120 mm; temporal resolution=32.8 to 43.2 ms (11–31 cardiac time frames); echo time=2.1 to 2.8 ms; repetition time=4.1 to 5.4 ms; flip angle=7 to 15°.…”

Transcatheter aortic valve replacement alters ascending aortic blood flow and wall shear stress patterns: A 4D flow MRI comparison with age-matched, elderly controls

“…Four-dimensional (4D) flow magnetic resonance imaging (MRI) is a novel imaging technique capable of assessing aortic blood flow in three directions as a function of time, allowing for quantification of aortic haemodynamics [4]. Various advanced parameters can be derived from 4D flow MRI-acquired velocity data that may provide novel insight into aortic haemodynamics after TAVR, such as wall shear stress (WSS), flow eccentricity and flow displacement [5][6][7].…”

4D-Flow MRI: Technique and Applications

“…In the case of the real-time slice tracking method, the diaphragm position is measured immediately prior to every data acquisition and then the gradients are modified in real time so that the measured layer corresponds to the current heart position. This makes it possible to define a larger navigator window, typically 5 -8 mm, thereby shortening the acquisition time [1]. Gating in relation to the cardiac cycle is performed in an analogous manner.…”

“…Therefore, a compromise must be made on an individual basis for each patient. A voxel size with an isotropic edge length of 2.5 -3.0 mm for the heart and thoracic/abdominal vessels and 0.7 -1.5 mm for intracranial vessels has become established [1]. The highest possible temporal resolution of approximately 40 ms per 3 D dataset is needed to be able to record even brief flow phenomena [2].…”

“…Of course, the contrast agent improves the contrast between blood and surrounding tissue. However, care must be taken since the washout of the contrast agent changes the T1 time of the blood and it is not yet fully understood how this affects measurement results [1].…”