Subj:	Imaging and Biomechanics seminars

Date:  2/13
Time:  12-1 pm
Place:  Bldg 10, Room 1C520 (large radiology conference room)
Titles/Speakers:

1."New Methods for Computational Fluid Dynamics Modeling of
  Carotid Artery from Magnetic Resonance Angiography"
      Presented by Juan R. Cebral, School of Computational Sciences,
      George Mason University
      (see below for abstract)

2."Tracheal and Central Bronchial Aerodynamics Using
  Virtual Bronchoscopy"
      Presented by Ronald M. Summers, Diagnostic Radiology Dept., NIH
      (see below for abstract)


3."Interpretation of arterial velocity waveforms"
    Presented by Peter J. Yim, Imaging Sciences Program, NIH
    (see below for abstract)

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1.New Methods for Computational Fluid Dynamics Modeling of Carotid Artery
from Magnetic Resonance Angiography
   Presented by Juan R. Cebral, School of Computational Sciences, George
Mason University

ABSTRACT: Computatinal fluid dynamics (CFD) models of the carotid artery
are constructed from contrast-enhanced magnetic resonance angiography
(MRA) using a deformable model and a surface-merging algorithm. Physiologic
flow conditions are obtained from cine phase-contrast MRA at two slice
locations below and above the carotid bifurcation. The methodology was
tested on image data from a rigid flow-through phantom of a carotid artery
with 65% degree stenosis. Predicted flow patterns are in good agreement
with MR flow measurements at intermediate slice locations. Our results show
that flow in a rigid flow-through phantom of the carotid bifurcation with
stenosis can be simulated accurately with CFD.The methodology was then
tested on flow and anatomical data from a normal human subject. The sum of
the instantaneous flows measured at the internal and external carotids
differs from that at the common carotid, indicating that wall compliance
must be modeled. Coupled fluid-structure!
  calculations were able to reproduce the significant dampening of the
velocity waveform observed between different slices. Our results confirm
that image-based CFD techniques can be applied to the modeling of
hemodynamics in compliant carotid arteries. These capabilities may
eventually allow physicians to predict and evaluate the outcome of
interventional procedures noninvasively.



2.  Tracheal and Central Bronchial Aerodynamics Using Virtual Bronchoscopy
   Presented by Ronald M. Summers, Diagnostic Radiology Dept., NIH

ABSTRACT:Virtual bronchoscopy reconstructions of the airway noninvasively
provide usefulmorphologic information of structural abnormalities such as
stenoses and masses.  In this paper, we show how  virtual bronchoscopy can
be used to perform aerodynamic calculations in anatomically realistic
models. Pressure and flow patterns in a human airway were computed
noninvasively. These showed decreased pressure and increased shear stress
in the region of a stenosis.


3. Interpretation of arterial velocity waveforms
    Presented by Peter J. Yim, Imaging Sciences Program, NIH

ABSTRACT: Blood flow temporal waveforms change with position along an
artery.  The change in the flow waveforms can be accounted for by a
transmission line model of flow.  According to this model, pulse waves
propagate at a finite velocity in both directions along the artery.  In
principle, given flow waveforms measured at three locations along an
artery, the pulse-wave velocity, (c) can be determined from the wave
equation (d2Q/dt2=c2d2Q/dz2, Q is flow, t is time, z is position).  Given
the vessel diameter, the vessel-wall compliance can be derived from
pulse-wave velocity.  However, direct solution of the wave equation for
pulse-wave velocity is highly susceptible to flow-measurement error. Also,
the solution requires the division operation which is numerically unstable.
Thus, we propose a new method for estimating pulse-wave velocity from
arterial flow waveforms. In our method, ideal flow waveforms are
reconstructed from three measured flow waveforms.  The ideal waveform!
 s are reconstructed by minimization of the total error between the ideal
and measured waveforms subject to constraints of the wave equation.  Ideal
flow waveforms are reconstructed for a range of assumed pulse-wave
velocities.  The true pulse-wave velocity is considered to be that which
produces the minimum total error.  The method applies to blood flow
measurements made with phase-contrast magnetic resonance imaging.