Examination of carotid pre-bifurcation expansion to predict boundary layer separation
Examination of carotid pre-
bifurcation expansion to predict
boundary layer separation
Ashley, John, Minh, Jeff, Aaron
• The purpose of this study is to develop a new
procedure or index for predicting coronary
artery disease in patients by using fluid
mechanics and bimolecular principals along with
ultrasound imaging techniques.
• Carotid has been subjected to extensive studies to
try to find factors that can predict atherosclerosis
• Atherosclerotic risk is currently determined using
Carotid Intima Media Thickness (CIMT)
• Measurement of arterial wall thickness,
• This and most other correlations fail to
include measurements which can predict
boundary layer separation
• Most predictors don’t take into
account fluid mechanical effects which
can lead to low wall shear stress (WSS)
and wall thickening causing plaque
• Geometry from beginning of expansion
to the bifurcation point is most likely to
initiate boundary layer separation
Figure 1. The black rectangle
encompasses the region of interest
for this diffuser model.
• Relating this pre-bifurcation expansion to a diffuser, we
• The change in pressure and
• Bifurcation angle can lead to boundary layer separation
• Boundary layer separation corresponds to low wall shear
• Areas of low wall shear stress have been shown to correlate
to the buildup of atherosclerotic plaque.
• Increased atherosclerotic risk corresponds
to pressure changes and large bifurcation
angles in the pre-bifurcation expansion.
Procedure: Developing an
Index• Using MRI images from literature
with pre-assigned risk levels created
an index that assessed risk based
• Pressure Change
• Bifurcation angle
Procedure: Applying the Index
• Test the system on 6 subjects
• Four measurements taken using ultrasound
• D1 – Diameter at beginning of expansion
• D2 – Diameter at widest point in bifurcation
• L – Length between diameters
• Velocity of the blood in the carotid at D1
• Calculate pressure change and bifurcation angle
• Creating the Index
• For the geometries from literature, no velocity measurements
were known, so pressure change for all risk levels were
calculated with the same velocity
• So little trend is visible with respect to the pressure change
• In reality, these velocities would be different
• The accuracy of the index requires a longer term study
• Our patients were young and healthy, and since our index is truly
predictive, we would need to retest the same patients later in life
to see if the predictions were correct.
Technician D1 D2 L V1 Theta ΔP
1 0.556 1.223 0.98 71.2 0.597595 2426.45
2 0.575 0.965 1.06 72.4 0.352553 2290.50
3 0.533 1.180 1.27 71.1 0.471178 2422.39
4 0.540 1.120 1.18 72.0 0.456845 2451.93
Data taken from same patient by multiple technicians
• Boundary layer separation can be mathematically related to
pressure difference and bifurcation angle.
• Our proposed index cannot be confirmed without long-term
• The relation between pressure difference and risk requires
more data to accurately determine
• Trends evident in sample data warrant further investigation
• 2D geometry capability
• Probe depth
• Grainy image of ultrasound
• Young age group
• Bernoulli’s assumptions
• Multiple “technician” error
• 3D CFD fluid flow
• 3D scanned
• Development of
References•  P. B. Bijari, B. A. Wasserman, and D. A. Steinman, “Carotid Bifurcation Geometry Is an Independent Predictor of Early
Wall Thickening at the Carotid Bulb,” Stroke, vol. 45, no. 2, pp. 473-478, Feb, 2014.
•  P. Bokov, P. Flaud, A. Bensalah et al., “Implementing Boundary Conditions in Simulations of Arterial Flows,” Journal of
Biomechanical Engineering-Transactions of the Asme, vol. 135, no. 11, pp. 9, Nov, 2013.
•  I. B. Casella, "A Practical protocol to measure common carotid artery intima-media thickness," 515-520, C. Presti, ed.,
•  J.-J. Chen, "Skin-scanning technique for superficial blood flow imaging using a high-frequency ultrasound system," C.-H.
Cheng, ed., Ultrasonics, 2014, pp. 241-246.
•  J. Chen, "Numerical investigation of the non-Newtonian pulsatile blood flow in a bifurcation model with a non-planar
branch," X.-Y. Lu, ed., Journal of Biomechanics, 2005, pp. 818-832.
•  T. Ding, "Ultrasound line-by-line scanning method of spatial-temporal active cavitation mapping for high-intensity
focused ultrasound," S. Zhang, ed., Ultrasonics, 2014.
•  Y. Fan, "Numerical Simulation of Pulsatile non-Newtonian flow in the carotid artery bifurcation," W. Jiang, ed., The
Chinese Society of Theoretical and Applied Mechanics, 2009, pp. 249-255.
•  A. Harloff, S. Berg, A. J. Barker et al., “Wall shear stress distribution at the carotid bifurcation: influence of eversion
carotid endarterectomy,” European Radiology, vol. 23, no. 12, pp. 3361-3369, Dec, 2013.
•  H. Karimpour, and E. Javdan, “SIMULATION OF STENOSIS GROWTH IN THE CAROTID ARTERY BY LATTICE BOLTZMANN
METHOD,” Journal of Mechanics in Medicine and Biology, vol. 14, no. 2, pp. 20, Apr, 2014.
•  N. Katakami, H. Kaneto, and I. Shimomura, “Carotid ultrasonography: A potent tool for better clinical practice in
diagnosis of atherosclerosis in diabetic patients,” Journal of Diabetes Investigation,vol. 5, no. 1, pp. 3-13, Jan, 2014.
•  K. H. Nam, T. H. Bok, C. Jin et al., “Asymmetric radial expansion and contraction of rat carotid artery observed using a
high-resolution ultrasound imaging system,” Ultrasonics, vol. 54, no. 1, pp. 233-240, Jan, 2014.
•  R. M. Nerem, “VASCULAR FLUID-MECHANICS, THE ARTERIAL-WALL, AND ATHEROSCLEROSIS,” Journal of
Biomechanical Engineering-Transactions of the Asme, vol. 114, no. 3, pp. 274-282, Aug, 1992.
•  A. Olsson, "Numerical and experimental studies of flat-walled diffuser elements for valve-less micropumps," G.
Stemme, ed., Elsevier Science, 2000, pp. 165-175.
•  J. F. Polak, "Carotid-Wall Intima-Media Thickness and cardiovascular events," M. J. Pencina, ed., The New England
Journal of Medicine, 2011, pp. 213-221.
•  U. G. R. Schulz, "Major Variation in Carotid Bifurcation Anatomy," A Possible Risk Factor for Plaque Development?, P.
M. Rothwell, ed., Stroke, 2001, pp. 2522-2529.
•  R. K. Singh, "Measurement of Instantaneous Flow Reversals and Velocity Field in a Conical Diffuser," R. S. Azad, ed.,
Elsevier Science, 1995, pp. 397-419.
•  F. M. White, "Fluid Mechanics," Mcgraw Hill, 2011.
•  D. M. Wootton, and D. N. Ku, “Fluid mechanics of vascular systems, diseases, and thrombosis,” Annual Review of
Biomedical Engineering, vol. 1, pp. 299-329, 1999.
•  M. M. Zarandi, "Effects of bifurcation angle on the wall shear stress in stenosed coronary artery bifurcation," R.