The Role of Velocity Map Quality in Estimation of Intravascular Pressure Distribution

Phase-Contrast MR imaging methods are widely used for measurement of blood flow velocity components. Also there are some other tools such as CT and Ultrasound for velocity map detection in intravascular studies. These data are used in deriving flow characteristics. Some clinical applications are investigated which use pressure distribution in diagnosis of intravascular disorders such as vascular stenosis. In this paper an approach to the problem of measurement of intravascular pressure field by using velocity field obtained from flow images is proposed. The method presented in this paper uses an algorithm to calculate nonlinear equations of Navier- Stokes, assuming blood as an incompressible and Newtonian fluid. Flow images usually suffer the lack of spatial resolution. Our attempt is to consider the effect of spatial resolution on the pressure distribution estimated from this method. In order to achieve this aim, velocity map of a numerical phantom is derived at six different spatial resolutions. To determine the effects of vascular stenoses on pressure distribution, a stenotic phantom geometry is considered. A comparison between the pressure distribution obtained from the phantom and the pressure resulted from the algorithm is presented. In this regard we also compared the effects of collocated and staggered computational grids on the pressure distribution resulted from this algorithm.

Authors:

• Ali Pashaee
• Parisa Shooshtari
• Gholamreza Atae
• Nasser Fatouraee

Keywords:

• Flow imaging
• pressure distribution estimation
• phantom
• resolution.

References:

[1] N. Pelc, R. Herfkens, A. Shimakawa, and D. Enzmann, "Phase contrast
cine magnetic resonance imaging," Magn. Reson. Quart., vol. 7, no. 4,
pp. 229-254, 1991.
[2] M. T. Vlaardingerbroek, and J. A. Den Boar, Magnetic Resonance
Imaging: Theory and Practice. 3rd ed., New York: Springer Verlag,
2003.
[3] M. Markl, F. P. Chan, M. T. Alley, K. L. Wedding, M.T. Draney, C. J.
Elkins, D. W. Parker, R. Wicker, C. A. Taylor, R. J. Herfkens, and N. J.
Fig. 8 The Mean-squared error for pressure gradient on centerline
at various resolutions.
Pelc, "Time-resolved three-dimensional phase-contrast MRI," J. Mag.
Reson. Imaging, vol. 17, pp. 499-506, 2003.
[4] N. L. Greenberg, P. M. Vandervoort, M. S. Firstenberg,M. J. Garcia, and
J. D. Thomas, "Estimation of diastolic intraventricular pressure gradients
by Doppler M-mode echocardiography," Am. J. Physiol. Heart Circ.
Physiol., vol. 280, pp. H2507-H2515, 2001.
[5] J. M. Tyszka, D. H. Laidlaw, J. W. Asa, and J. M. Silverman, "Three-
Dimensional, Time-Resolved (4D) Relative Pressure Mapping Using
Magnetic Resonance Imaging," Journal of Magnetic Resonance
Imaging, vol. 12, pp. 321-329, 2000.
[6] T. Ebbers, L. Wigstrom, A. Bolger, J. Engvall, and M. Karlsson,
"estimation of relative cardiovascular pressures using time-resolved
three-dimensional phase-contrast MRI," Magnetic Resonance Imaging,
vol. 45, pp. 872-879, 2001.
[7] G. Z. Yang, P. J. Kilner, N. B. Wood, S. R. Underwood, and D. N.
Firmin, "Computation of flow pressure fields from magnetic resonance
velocity mapping," Magnetic Resonance Imaging, vol. 36, pp. 520-526,
1996.
[8] S. M. Song, R. M. Leahy, D. P. Boyd, B. H. Brundage, and S. Napel,
"Determining cardiac velocity fields and intraventricular pressure
distribution from a sequence of Ultrafast CT cardiac images," IEEE
Trans. Med. Imaging, vol. 13, no. 2, pp. 386-397, 1994.
[9] J. H. Ferziger, and M. Peric, Computational methods for fluid dynamics.
3rd ed., New York: Springer-Verlag, 2002.
[10] A. Nasiraei-Moghaddam, G. Behrens, N. Fatouraee, R. Agarwal, E. T.
Choi, and A. A. Amini, "Factors affecting the accuracy of pressure
measurements in vascular stenoses from phase-contrast MRI," Magnetic
Resonance in Medicine, vol. 52, pp. 300-309, 2004.