Linear regression correlation. Net flow values (ml) in the ascending aorta of both techniques by the two observers are plotted on both X-axis and Y-axis. The X-axis represents the four-dimensional (4D) method of flow analysis while the Y-axis represents the two-dimensional (2D) method of flow analysis in all four graphs. Graph A, and C represent Health volunteers, B and D represent patients with bicuspid aortic valve (BAV). A line of identity (dashed) y=x is added. The regression line (solid) indicates the offset between the two methods.