Fig 4. (Case I) Secondary flow (flow perpendicular to the vessel axis) patterns visualized by using velocity vectors projected in a cross-sectional plane perpendicular to the vessel axis. Lateral view (A) and "en face" view (B) of the cross-sectional plane. Note that A was generated by rotating (1G) counter-clockwise 90°. This was done to better visualize the area of aneurysm development located mainly on the medial side of the vessel wall. C and D correspond to velocity vectors superimposed on the contours of secondary velocity magnitude during end diastole (C) and midsystolic deceleration (MSD) (D) for case I. Note that the strength of eddies increases during the deceleration phase of systole, which contributes to the formation of stagnation zone. E and F show the velocity vectors for case I at MSD (prior and post aneurysm development), emphasizing the change in the pattern as a result of formation of aneurysm. Range of velocity magnitude: C, 0–5.45 m/s; D, 0–1.3 m/s; E, 0–1.3 m/s; F, 0–1.3 m/s. Range of secondary flow vectors: C, 0–5.133 m/s; D, 0–0.675 m/s; E, 0–0.675 m/s; F, 0–0.72 m/s.