2012 Proceedings - International Tissue Elasticity Conference

071 ASSESSING ARTERY WALL DYNAMICS WITH HIGH FRAME RATE ULTRASOUND IMAGING
AND THREE DIMENSIONAL PHASE ANALYSIS.
Pieter Kruizinga 1 , Frits Mastik 1 , Nico de Jong 1,2,3 , Antonius FW van der Steen 1,2 and Gijs van Soest 1 .
1 Erasmus MC–Thorax Center, Rotterdam, THE NETHERLANDS; 2 Interuniversity Cardiology
Institute, Utrecht, The NETHERLANDS; 3 Delft University of Technology, Delft, The
NETHERLANDS.
Background: Viscoelastic properties of the human carotid artery (CA) wall and of possible lesions within
are key parameters in the clinical evaluation of the CA [1]. These viscoelastic properties can be assessed
by monitoring the motion of the arterial wall caused by arterial pulse waves [2]. Plane–wave ultrasound
(US) imaging is a high frame rate (>1kHz) technique that allows for monitoring arterial wall motion at all
relevant physiological speeds [3]. However, fast and robust extraction of accurate motion profiles from
multiple ultrasound frames remains challenging.
Aims: This study demonstrates that arterial wall motion can be assessed through three–dimensional (3D)
phase analysis of high frame rate ultrasound data.
Methods: To test our phase analysis method, we performed high frame rate plane wave US imaging of the
CA of a healthy volunteer. The ultrasonic plane waves were transmitted using a broadband (4–10MHz,
-6dB bandwidth) 128 elements linear array (Vermon). All 128 elements were excited simultaneously or
subsequently with a 1.5 cycle, 7MHz Gaussian modulated sine pulse. The array was interfaced with a
programmable US system using 12 bits digitization, 80 or 40MHz sampling (Lecoeur Electronic).
Acquisition depth was set to 2cm. The total acquisition time ranged from 0.8 to 2 seconds. Imaging frame
rates from 1 to 35kHz were realized through a tradeoff between the number of imaging frames,
acquisition time and sampling frequency. Through Fourier domain beamforming, we obtained the
reconstructed analytical signal. The magnitude was used for conventional B–mode imaging and the phase
for 3D motion analysis. We imaged displacement, velocity and acceleration based on the phase and its
first and second order time derivatives. Only the relevant phase samples were considered through a hard
threshold mask obtained from the magnitude data. The algorithm was implemented on graphic
processing unit (GPU) allowing for fast processing of the 3D motion analysis.
Results: Figure 1 shows the result of our 3D motion analysis of the lower arterial wall by displaying one
sample of all channels and all samples of one channel over time. Two frames were selected to emphasize
frame–to–frame dynamics captured with the 3D motion analysis. The velocity maps show a specular
pattern that reflects local variability in arterial wall dynamics. For all samples, we measured a total
displacement of 0.46mm, a velocity of 4.2mm/sec measured at the 95% percentile and -1.2mm/sec at
the 5% percentile. These values and the position, velocity and acceleration profiles we measured
correspond well to those found in literature.
Conclusions: Local arterial wall dynamics can be well assessed through 3D motion analysis of high
frame rate plane wave ultrasound data.
(a)
(b)
(c)
(d)
Figure 1: (a) B–mode envelope image of the lower arterial wall; (b, c) Two selected frames from the time–series in (d); (d) Time–series
of lower arterial wall (tissue velocity) of all samples of a single channel and all channels of a single sample over time
obtained with 2.5kHz frame rate US imaging. The data set shown is 2 seconds long.
References:
[1] Reneman RS, Meinders JM, Hoeks APG: Non-Invasive Ultrasound in Arterial Wall Dynamics in Humans: What
Have We Learned and What Remains to be Solved. European Heart Journal, 26, pp. 960–966, 2005.
[2] Meairs S, Hennerici M: Four-Dimensional Ultrasonographic Characterization of Plaque Surface Motion in
Patients with Symptomatic and Asymptomatic Carotid Artery Stenosis. Stroke, 30, pp. 1807–1813, 1999.
[3] Tanter M, Bercoff J, Sandrin L, and Fink M: Ultrafast Compound Imaging for 2-D Motion Vector Estimation:
Application to Transient Elastography. IEEE Trans. Ultrason. Ferroelect. Freq. Contr., 49, pp. 1363–1374, 2002.
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