2012 Proceedings - International Tissue Elasticity Conference

041 COMPARING THE PERFORMANCE OF SPARSE ARRAY AND PLANE WAVE IMAGING
SYSTEMS IN NON–INVASIVE VASCULAR ELASTOGRAPHY.
Sanghamithra Korukonda 1 , Rohit Nayak 1 , Marvin. M. Doyley 1
1 Electrical and Computer Engineering Department, University of Rochester, Rochester, NY, 14627 USA.
Background and Aims: Non–Invasive Vascular Elastography (NIVE) of the carotid artery is an emerging
diagnostic technique that can improve the detection and characterization of cardiovascular disease. To
fully describe arterial motion and produce reliable strain elastograms, it is necessary to acquire high
quality axial and lateral displacements. Parallel–receive imaging techniques allow for real time imaging of
the artery along with customized beamforming for improved displacement estimation and strain recovery.
The aim of this work is to compare the efficacy of two such techniques viz. sparse array [1] and
compounded plane wave [2] imaging in the context of NIVE.
Methods: Simulation and experimental studies were performed to compare the two techniques in terms of
standard image quality (IQ) metrics such as root mean square error and elastographic contrast to noise
ratio. Finite element modeling software, Abaqus, was used to generate mechanical models of carotid
cross–sections subjected to an intra–luminal pressure of 600Pa. Field II was used to simulate a 128 element
simulated linear array (center frequency 5MHz and sampling frequency of 40MHz) modeled on the
specification of the L14–5/38 probe. Sparse array (SA) scans with 15 transmit elements and 15 plane wave
(PW) scans steered over ±14º, in increments of 2º, were acquired of the pre– and post–compressed carotid
cross–sections. SA and PW images were beamformed by numerically summing coherent wavefronts at each
location within the image. Compounded PW images (CPW) were obtained by spatially adding steered PW
images. 2D cross–correlation analysis was performed to obtain axial and lateral displacement estimates
that were combined to generate radial and circumferential strain. Experimental studies were performed
with a SONIX RP system (Ultrasonix, Inc., Vancouver, Canada), equipped with an L14–5/38 linear array
probe to corroborate the simulation study. Tissue–mimicking vessel phantoms subjected to intra–luminal
pressures differences ranging from 5–20mmHg were imaged using the SA and PW systems.
Results: Strain elastograms obtained with the SA, PW and CPW systems were inspected visually and
evaluated using predefined IQ metrics. While CPW imaging improves the error produced by PW strain
elastograms, the SA strain elastograms exhibit 20% less error than the PW systems. Figure 1 shows strain
elastograms obtained from a simulated phantom containing a soft plaque (3 o’clock). The plaque, seen as a
region of localized high strain, is clearly demarcated in the radial (b) and circumferential (d) strain
elastograms obtained with the SA. The plaque is also seen the plane wave elastograms (b, d), though it is
not as clearly defined. Compounding improves the strain images (d, h), but the images are not as clear as
those obtained with the sparse array. Similar observations were made in the experimental studies.
Conclusions: Both PW and SA systems produce reasonable vascular strain elastograms. While
compounding improves the lateral sensitivity of PW imaging, SA imaging produces superior strain
elastograms both in simulation and experiment. These results warrant pre–clinical investigations into the
utility of sparse array based vascular elastography.
Acknowledgements: This work was supported by startup funds from the University of Rochester.
References:
[1] S. Korukonda and M.M. Doyley: Axial and Lateral Strain Estimation using a Synthetic Aperture Elastographic
Imaging System. Ultrasound in Medicine and Biology, Vol. 37, No. 11, pp. 1893–1908, 2011.
[2] G. Montaldo, M. Tanter, J. Berco, N. Benech, and M. Fink: Coherent Plane-Wave Compounding for Very High
Frame Rate Ultrasonography and Transient Elastography. IEEE Trans. on UFFC, 56(3), pp. 489–506, 2009.
Figure 1: Comparison of radial (a–d) and circumferential
(e–h) strain elastograms obtained from sparse
array (SA), plane wave (PW) and compounded
plane wave (CPW) imaging systems with the
theoretical values obtained from the
simulation.
indicates Presenter 95