Assessment of Reynolds stress components and turbulent pressure loss using 4D flow MRI with extended motion encoding

Abstract

4D flow MRI with extended motion-encoding enables quantification of both the velocity and the Reynolds stress tensor. The additional information provided by this method improves the assessment of pressure gradients across a stenosis in the presence of turbulence. Unlike conventional methods, which are only valid if the flow is laminar, the proposed method is valid for both laminar and disturbed flow, a common presentation in diseased vessels. Magn Reson Med 79:1962-1971, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Validation of pressure drop assessment using 4D flow MRI‐based turbulence production in various shapes of aortic stenoses

“…4D flow MRI measurements were performed using a clinical 1.5T MRI scanner (Philips Achieva; Philips Medical Systems, Best, the Netherlands). A conventional gradient‐echo sequence with asymmetric 4‐point flow encoding was modified to have a six‐directional icosahedral flow encoding (ICOSA6) and one flow‐compensated reference encoding . To maintain the same experimental conditions for all flow rate and valves conditions, the following four different velocity encoding parameter (VENC) were repetitively used: 1, 2, 3, and 5 m/s.…”

“…Therefore, three velocity components (u, v, and w) and the Reynolds stress component tensor R ij can be obtained by measuring six nonorthogonal velocity encodings and finding the least square solutions of the six directional phase and magnitude data. 17 R ij is the six-element symmetric tensor as follows:…”

“…A conventional gradient-echo sequence with asymmetric 4-point flow encoding was modified to have a six-directional icosahedral flow encoding (ICOSA6) and one flow-compensated reference encoding. 11,17,24 To maintain the same experimental conditions for all flow rate and valves conditions, the following four different velocity encoding parameter (VENC) were repetitively used: 1, 2, 3, and 5 m/s. TE and TR were 1.5-2.2 ms and 3.2-3.9 ms, respectively.…”

4D Flow MRI quantification of blood flow patterns, turbulence and pressure drop in normal and stenotic prosthetic heart valves

“…Opening areas of the valves were calculate from the face-views ( Supplementary Figure 1) 4D Flow MRI measurement 4D Flow MRI measurements were performed using a clinical 1.5T MRI scanner (1.5T Philips Achieva; Philips Medical Systems, Best, The Netherlands). A conventional gradient-echo sequence with asymmetric four-point flow encoding was modified to generate a six-directional icosahedral flow encoding (ICOSA6) and one flow-compensated reference encoding [13,14,21]. Four different velocity encoding ranges (VENCs) were used for each experimental condition: 1, 2, 3 and 5 m/s.…”

“…When the velocity encoding direction is distributed to bisect the 2D plane in threedimensional Cartesian space (i.e., the XY, YZ or XZ plane), the obtained velocity and IVVV can be decomposed into two orthogonal components and its covariance term. Therefore, three velocity components (u, v, and w) and six elements of the Reynolds stress tensor Rij can be obtained by measuring six non-orthogonal velocity encodings and finding least square solutions for the six sets of directional phase and magnitude data [21].…”