2012 Proceedings - International Tissue Elasticity Conference

027 ELASTIC MODULUS RECONSTRUCTION FOR TRANSVERSE VASCULAR CROSS–SECTIONS
WITH AND WITHOUT COMPOUND STRAIN IMAGING.
HHG Hansen 1 , Michael S Richards 2 , Marvin M. Doyley 2 , Chris L. de Korte 1 .
1 Radboud University Nijmegen Medical Center, Geert Grooteplein 10, Nijmegen, THE NETHERLANDS;
2 University of Rochester, Hopeman Engineering Building, Rochester, NY, 14627, USA.
Background: Atherosclerotic plaques with a large soft lipid pool and a thin fibrous cap are more prone to
rupture than fibrotic plaques [1]. The elastic Young’s modulus for both types of plaques differs. Young’s
modulus images can be derived from displacement maps of the arterial wall obtained after deformation [2].
Aims: This study investigated if the reconstruction of relative Young modulus images for transverse
vessel cross–section could be improved by using beam steered acquisitions and subsequent compounding
of the angular axial displacement estimates [3,4].
Methods: Three vessel phantoms were created from gelatin–agar solutions: homogeneous phantoms with a
concentric and an eccentric lumen and a two–layered phantom with a soft layer inside and an eccentric
lumen. Radiofrequency (RF) data were obtained of the phantoms before and after 4mmHg intraluminal
pressure increase at beam steering angles of -30º, 0º and 30º using a linear array transducer (L11–3, Philips,
fc = 7.5MHz). In analogy to these experiments, RF data were simulated for a similar transducer using Field II©
[5]. 2D displacements for each angle were estimated using a coarse–to–fine 2D cross–correlation based
algorithm. Relative Young’s modulus images of the phantoms were constructed using the 0º axial
displacement field combined with either the 0º lateral displacement field or the lateral displacement field
obtained by compounding the axial displacement fields of +30º and -30º beam steering. To compare the
accuracy of the modulus reconstruction the median absolute differences between the axial and lateral
displacements input to and output by the reconstruction method were calculated. Furthermore, for both
approaches the median and inter–quartile range (IQR) of the relative modulus estimates for each separate
phantom layer were calculated and compared to the real values.
Results: The median difference between lateral displacements used as input for the reconstruction and
those corresponding to the reconstructed modulus image was reduced by a factor two to three when
using the lateral displacements derived from compounding instead of 0º lateral estimates. The relative
Young’s modulus images also became more accurate when using compounding: the IQR reduced
approximately a factor 2 compared to the images derived from 0º estimates only.
Conclusions: Compounding enables a more accurate reconstruction of the relative Young’s modulus for
vascular structures in a transverse imaging plane than 0º imaging can. However, future studies will have
to be performed to show the suitability of this technology for vulnerable plaque detection.
Acknowledgements: This research is supported by the Dutch Technology Foundation STW (NKG 07589), Applied
Science Division of NWO and the Technology Program of the Ministry of Economic Affairs. The authors also
acknowledge Philips Medical Systems for their support.
References:
[1] Finn et al.: Arteriosclerosis Thrombosis and Vascular Biology, 30, pp. 1282–92, 2010.
[2] Richards et al.: Physics in Medicine and Biology, 56(22), pp. 7223–46, 2011.
[3] Hansen et al.: Physics in Medicine and Biology, 55(11), pp. 3201–18, 2010.
[4] Techavipoo et al.: IEEE Transactions on Medical Imaging, 23(12), pp. 1479–89, 2004.
[5] Jensen et al.: Medical and Biological Engineering and Computing, 34(Suppl. 1, Pt 1), pp. 351–53, 1996.
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