2012 Proceedings - International Tissue Elasticity Conference

Session FIP: Forward and Inverse Problems
Wednesday, October 3 1:30P – 2:45P
007 ELASTICITY IMAGE CALCULATION FROM X–RAY TOMOSYNTHESIS IMAGES UNDER
COMPRESSION.
JG Kim 1 , JH Shin 1 , SY Lee 1 .
1 Kyung Hee University, 1732 Deogyeong–daero, Yongin–si, Gyeonggi–do, KOREA.
Background: Ultrasound and MRI have been exclusively used for tissue elasticity imaging owing to their
high sensitivity to tissue displacements. But, ultrasound and MRI elastography have not been widely
adopted for routine clinical practice of breast cancer detection due to their low image quality.
Aims: We have tried to obtain elasticity images from x–ray tomography images with the motivation that
x–ray elastography would be a good complementary solution to the x–ray mammography that suffers from
low sensitivity and specificity in detecting early stage breast cancers.
Methods: We made a cylindrical–shaped elasticity phantom, shown in Figure 1a, which has a hard
cylindrical inclusion enclosed in a soft background. We took tomosynthesis images of the phantom using a
micro–CT by limiting the scan angle to less than 60° degrees. The tomosynthesis images have the in–plane
resolution of 74.3μm with the image matrix size of 560x560. Since x–ray imaging signal lacks phase
information, we applied amplitude–based image correlation to the two image sets, one obtained with less
compression and the other with more compression, to calculate displacements of the feature pattern
around a given pixel. The image correlation matrix size was 40x40x40, which limited the spatial resolution
of resulting displacement images. We calculated the displacements for all the pixels, and we derived the
strain map by applying differentiation to the displacement maps.
(a) (b)
Figure 1: (a) A photograph of the elasticity phantom and (b) a schematic of the compressing device.
Results: We have shown the displacement map on the lateral plane in the middle of the phantom in
Figure 2. The displacement maps have been obtained with varying the compressing force and compared
with the FEM analysis results. The displacement maps show high correlation with the maps calculated by
FEM simulation on the 3D phantom model. Figure 2c shows the corresponding strain maps derived from
the displacement image.
Figure 2:(a) Tomosynthesis Image; (b) Displacement Map; (c) Strain Map.
Conclusions: The strain images have high level of noise and artifacts as compared to static ultrasound
elastography images. However, we believe the experimental results suggest a possibility of x–ray
elastography.
Acknowledgements: This work was supported by the National Research Foundation of Korea (NRF) grant funded by
the Korea government (No: 2009–0078310).
References:
[1] J. Ophir et al.: Proceedings of the Institution of Mechanical Engineers, Part H: J Eng. Med, 213(3), pp. 203–233, 1999.
[2] J. Bishop et al.: Phys. Med. Biol, 45, pp. 2081–2091, 2000.
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