Image-Based Computational Simulation of Flow Dynamics in a Giant Intracranial Aneurysm
David A. Steinmana,b,c,
Jaques S. Milnera,
Chris J. Norleya,
Stephen P. Lowniea,c,d and
David W. Holdswortha,b,c
a Imaging Research Laboratories, Robarts Research Institute, University of Western Ontario, London, Canada
b Departments of Medical Biophysics, University of Western Ontario, London, Canada
c Diagnostic Radiology, University of Western Ontario, London, Canada
d Clinical Neurological Sciences, University of Western Ontario, London, Canada
View larger version (70K):
[in a new window]
|
FIG 1. Geometry of aneurysm and parent vessel, shown in anteroposterior (left column) and lateral (right column) views.
A and B, Maximum intensity projections obtained through the CT reconstructed data illustrate the geometrical complexity of the aneurysm and parent vessel. Angled arrows identify blebs on the right and posterior sides of the aneurysm sac. Horizontal arrows point to an apparent stenosis of the petrous segment, which may be attributed to compression of the vessel against adjacent bone.
C and D, Corresponding views of the finite element mesh show the geometric faithfulness and spatial resolution of the CFD model; for clarity, only the corner nodes of the quadratic finite elements are shown. Note the model coordinate system: ± x = left/right, ± y = anterior/posterior, ± z = superior/inferior.
| |
View larger version (46K):
[in a new window]
|
FIG 2. Virtual slipstreams, shown at selected times in lateral (top row) and anteroposterior (bottom row) oblique views, provide an overview of the aneurysm hemodynamics.
A, Early systole (t = 50 ms). Slipstreams showed little mixing or spreading as they approached the neck.
B, Peak systole (t = 150 ms). Slipstreams spread and began to mix as they entered both the proximal and distal ends of the neck.
C, Early diastole (t = 300 ms). Slipstreams mixed as they impacted the posterior wall of the aneurysm and swirled in the right and inferior directions.
D, Late diastole (t = 800 ms). Within 0.5 second, the aneurysm was almost entirely opacified by vigorously mixed slipstreams.
| |
View larger version (94K):
[in a new window]
|
FIG 3. More detailed views of the complex aneurysm hemodynamics are provided at selected times and for selected planes via conventional field plots of sagittal (top row), coronal (middle row), and axial (bottom row) planes, each from the nominal center of the aneurysm. Contours of velocity magnitude (V, in cm/s) are shown with vectors superimposed to indicate the magnitude and direction of in-plane flow components. White circles identify the approximate center of each vortex. S, superior; I, inferior; A, anterior; P, posterior; R, right; L, left.
A, Peak systole (t = 150 ms).
B, Early diastole (t = 300 ms).
C, Mid-diastole (t = 450 ms).
D, Late diastole (t = 600 ms).
| |
View larger version (76K):
[in a new window]
|
FIG 4. Computed wall shear stress patterns are shown in oblique posterior (left panels) and anterior (right panels) views.
A and B, Contours of cycle-averaged wall shear stress magnitude (WSS, dynes/cm2).
C and D, Contours of oscillatory shear index (OSI, dimensionless), a measure of the relative variability of the wall shear stress over the cardiac cycle.
| |
View larger version (71K):
[in a new window]
|
FIG 5. Two sequential frames from 2-Hz cine digital subtraction angiograms. These zoomed views correspond to the orientation and extent of the CFD model in the lower panels of Figure 2C and D.
A, Aneurysm filling dynamics, shown approximately 0.5 second after selective injection into the internal carotid artery, show good general agreement with the corresponding virtual slipstreams shown in Figure 2C.
B, One frame (ie, 0.5 second) later, the aneurysm is already largely opacified, which also is consistent with the corresponding virtual slipstreams shown in Figure 2D.
| |
View larger version (114K):
[in a new window]
|
FIG 6. Illustration of a possible relationship between coil compaction and computed flow dynamics.
A, Lateral digital subtraction angiogram obtained at 6-month follow-up examination shows compaction of the coil mass away from the neck and toward the posterior wall of the aneurysm.
B, High speed flow entering the aneurysm (shown by using a 15 cm/s isovelocity surface from the cycle-averaged velocity field superimposed on a projection of the aneurysm model approximately corresponding to that in shown in A) is also directed toward the posterior wall of the aneurysm.
| |
