4D Flow MR Imaging of the Left Atrium: What is Non-physiological Blood Flow in the Cardiac System?

Figures

• 

  Fig. 1. Left atrial blood flow pattern in healthy subjects. The emitter planes are located at each pulmonary vein (green-right superior, orange-right inferior, blue-left superior, and red-left inferior pulmonary veins) (a). Physiological collision was observed at the center of the left atrium (b). Following this, physiological vortical flow (yellow arrows) was observed in the left atrium (c). Physiological vortices have key functional contributions in maintaining kinetic energy and preventing blood flow stasis.

• 

  Fig. 2. Flowchart of the MR simulation methodology. Original TEE data (A) are separated into RR-intervals and converted to grayscale (B, left), and velocity measures are extracted from the color Doppler images (B, right). Each complex image (magnitude: grayscale, phase: velocity) undergoes a Fourier transform to simulate MRI k-space (C). K-space lines are randomly selected using one of three acquisition schemes (sample selection from three heartbeats shown in (C) in (D, left)) to create 2D PC MRI k-space data (D, right), which undergoes an inverse Fourier transform to calculate a simulated MR reconstruction of 2D PC MRI magnitude and velocity images (E). LA: left atrium, LV: left ventricle. This figure was reused from a published paper with permission.18

• 

  Fig. 3. Average TEE data over all acquired heartbeats for one representative atrial fibrillation patients at systole (top row) and diastole (bottom row). Four chamber view is shown. The reconstructed velocity images from the MR simulations are also shown. MRI 1–3 denote the three different k-space sampling schemes used for the simulation of prospectively gated 2D PC-MRI data. In the images of diastole, the high flow in right atrium and right ventricle was also observed. LA, left atrium; LV, left ventricle. This figure was reused from a published paper with permission.18

• 

  Fig. 4. 5D flow MRI framework. A, Pulse sequence: free-running acquisition with 3D velocity encoding following a 3D radial, spiral phyllotaxis sampling. Interspersed SI projections were used to extract the acquired cardiac and respiratory signals (B). C, histogram of RR intervals for an AF patient. Each heartbeat was assigned to a bin based on its length (blue, orange, yellow, purple, and RR1-RR4). Bins with < 300 lines of k-space per cardiac phase were rejected (black). D, data were binned into a respiratory or RR dimension, cardiac phase dimension, and velocity encode. SI, superior–inferior. This figure was reused from the ISMRM proceeding as Ma L, Yerly J, Di Sopra L, et al. Decoding the Effects of Rhythm on Hemodynamics in Patients with Atrial Fibrillation Using a 5D Flow Framework. Proc. Intl. Soc. Mag. Reson. Med. 28 (2020) 1085.

• 

  Fig. 5. Sensitivity analysis for the identification of LA stasis and LA peak velocity thresholds. A: LA stasis (top) as a function of the LA velocity threshold (% LA velocities < LA velocity threshold, vstasis_thresh) for all four groups (young volunteers, age appropriate controls, paroxysmal AF, and persistent AF). Corresponding P values for pair-wise comparisons of LA stasis between groups are shown below. B: Peak LA velocities (top) for different thresholds (% of top LA velocities, vstasis_thresh) and P values for between group comparisons (bottom). The individual data points represent averaged over all subjects in each group. Error bars indicate inter-individual standard deviations of LA flow metrics. LA, left atrium. This figure was reused from a published paper with permission.23

• 

  Fig. 6. Peak velocity (A) and stasis (B) in the LA compared with the LAA in n = 75 subjects (15 controls and 60 AF patients). AF, atrial fibrillation; LA, left atrial; LAA, left atrial appendage. This figure was reused from a published paper with permission.26

• 

  Fig. 7. Schematic drawing shows the theory of pulmonary vein thrombogenesis after lobectomy. A PV Stump of variable length is present after lobectomy. This stump has areas of slow flow, especially at the corners (blue circular arrows), and these areas are predisposed to thrombogenesis. Red arrows = blood flow. LA, left atrium; PV Stump, pulmonary vein stump. This figure was reused from a published paper with permission.59

• 

  Fig. 8. Left atrial blood flow pattern in the patient with left upper lobectomy. Color-coded pathlines show the flow pattern in the left atrium. The green area represents regions of the RIPV, RSPV, and LIPV. The red area represents the LSPV stump. Pathlines are drawn from the VOI of each of three pulmonary veins (RSPV, RIPV, and LIPV). The yellow arrows indicate the direction of the blood flow. All of the pathlines are directed to the mitral valve; there is no flow directed to the junction between the left atrium and the LSPV. LIPV, left inferior pulmonary vein; LSPV, left superior pulmonary vein; RIPV, right superior pulmonary vein; RSPV, right superior pulmonary vein. This figure was reused from a published paper with permission.57

• 

  Fig. 9. Collision pattern of blood flow in the patients without thrombosis after left upper lobectomy. The left atrium and ventricle were segmented as yellow translucent VOIs. Each colored pathline represents blood flow from each pulmonary vein (Light blue, RSPV flow; blue, RIPV flow; light green, LIPV flow). The time order is from a to d. In this figure, the LIPV flow and RSPV flow collide with each other in c and flow to the mitral valve in d. The 2D overlay view shows clear collision of the flow from the right superior and left inferior pulmonary veins at the diastolic phase (arrow in e). The merged blood flow becomes the driving force behind the formation of the vortex flow in the left atrium (arrowheads in e). The velocity-weighted map more clearly depicts high velocity on and around inflow from the pulmonary vein (arrows in f), which gradually distributes to the remaining areas of left atrium (arrowheads in f). LIPV, left inferior pulmonary vein; RIPV, right superior pulmonary vein; RSPV, right superior pulmonary vein. This figure was reused from a published paper with permission.58

• 

  Fig. 10. No collision pattern of blood flow in the patients with LSPV stump thrombus and cerebral infraction 4 days after left upper lobectomy. Cerebral infraction was followed by MRI scan, and LSPV stump thrombus was followed by contrast-enhanced CT scan. LSPV thrombus disappeared when 4D flow MRI was performed. The left atrium and ventricle were segmented as yellow translucent VOIs. Each colored pathline represents the blood flow from each pulmonary vein (Light blue; RSPV flow, blue; RIPV flow, light green; LIPV flow). The time order is from a to d. In this figure, the flow does not collide and dissipate to the left atrium wall. The 2D overlay view shows that the flows from the right superior and left inferior pulmonary veins pass each other at the diastolic phase (arrow in e). The velocity-weighted map acknowledges the slow flow areas where blood flow has been left out (arrowheads in f). Note that the velocity scale is the same as that in Figure 10-e and f. LIPV, left inferior pulmonary vein; LSPV, left superior pulmonary vein; RIPV, right superior pulmonary vein; RSPV, right superior pulmonary vein. This figure was reused from a published paper with permission.58