2012 Proceedings - International Tissue Elasticity Conference

028 PLANE WAVE IMAGING FOR FAST VASCULAR STRAIN ESTIMATION.
HHG Hansen 1 , Bart Wijnhoven 1 , Chris L. de Korte 1 .
1 Radboud University Nijmegen Medical Center, Geert Grooteplein 10, Nijmegen, The NETHERLANDS.
Background: Ultrasound strain imaging can be used to assess local mechanical properties of tissue.
From conventional non–steered ultrasound acquisitions, the vertical displacement and strain can be
estimated accurately. For the estimation of strains in transverse vascular cross–sections an accurate
assessment of the horizontal displacement and strain component is also required. These can be derived
by compounding of axial displacements estimated at two additional beam steering angles [1]. However,
compounding might be difficult because the artery is in motion during the change of beam steering angle.
Therefore, high frame rates are required. Plane wave ultrasound transmission allows higher frame rates
[2,3]. However, the question is how plane wave transmission affects strain estimation accuracy.
Aim: To compare the strain estimation accuracy obtained with single or multi–angle plane wave
transmission and focused 0° and multi–angle focused imaging.
Methods: A finite element model (FEM) of a vessel with a vulnerable plaque was constructed. Based on the
FEM, the 2D displacement and strain fields were calculated for an intraluminal pressure increase of
4mmHg (strains ranged from 0 to ~5%). Radiofrequency (RF) data of the vessel before and after deformation
were simulated using Field II software. RF data were simulated for a linear array transducer (3–11MHz,
fc=8.5MHz, pitch=135μm) that either transmitted focused pulses or plane waves at beam steering angles of
-30°, 0° and 30°. In receive, dynamic focusing was applied by using delay–and–sum post–processing [4].
Band limited noise was added to obtain a signal–to–noise ratio of 20dB. Displacements were iteratively
estimated using 2D cross–correlation. Next, radial, circumferential and principal strains were derived using
1D least squares strain estimators, and the median and inter–quartile ranges (IQR) of the absolute
differences between the estimated strains and the FEM principal strains were determined. Strains were
compared to focused 0° transmission and reception, multi–angle focused transmission and reception,
0°plane wave transmission and multi–angle reception and multi–angle plane wave transmission and
reception.
Results: Table I shows the strain results for the various methods and the corresponding frame rates.
Compounding after focused transmission resulted in the most accurate strain results, followed by
compounding after multi–angle plane wave transmission, compounding after 0° plane wave transmission
and 0° focused imaging. The differences between the various methods were all significantly in favor of the
method with lower median value (Wilcoxon, P