Diagnostic Performance of Strain- and Shear-Wave- Elastography in an Elasticity Phantom: A Comparative Study

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1 Diagnostic Performance of Strain- and Shear-Wave- Elastography in an Elasticity Phantom: A Comparative Study Poster No.: C-2135 Congress: ECR 2014 Type: Scientific Exhibit Authors: J. F. Carlsen 1, M. R. V. Pedersen 2, C. Ewertsen 3, S. Rafaelsen 2, Keywords: DOI: A. Saftoiu 4, L. B. Lonn 5, M. Bachmann Nielsen 6 ; 1 Frederiksberg C/ DK, 2 Vejle/DK, 3 Copenhagen OE/DK, 4 Craiova/RO, 5 Copenhagen Ø/DK, 6 Copenhagen/DK Ultrasound physics, Oncology, Elastography, Ultrasound, Experimental investigations, Observer performance, Comparative studies, Tissue characterisation, Cancer /ecr2014/C-2135 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 11

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3 Aims and objectives Strain-elastography and shear-wave-elastography are both sonographic methods used to assess the stiffness of tissue [1,2]. Both methods have been used in assessing malignancy in focal lesions [3,4], and recently a comparative study of diagnostic performance in breast cancer diagnosis of the two methods was published [5]. Strain-elastography displays tissue strain in either color- or a grey scale elastograms. The elastograms can be semi-quantified using either strain-ratios (SR) [6] or strain-histograms (SH) [7], where the strain of the lesion is related to the strain of the surrounding healthy tissue. Shear-wave velocity (SWV) measurements are direct measurements of shearwaves arising when tissue is stimulated using acoustic radiation force impulses [1]. The velocity of the shear waves measured is directly proportional to tissue stiffness. The primary aim of this study was to investigate and compare the ability of strain- and shear wave elastography to determine lesion stiffness in an elasticity phantom. The second aim was to determine the effect of lesion size on the elasticity measurements. Methods and materials Examinations were performed on an Acuson S3000 system (Siemens, Mountain View, CA, USA). All examinations were done by two investigators on an elasticity phantom (Elasticity QA, model 049A, CIRS (CIRS, Virginia, USA)) (Figure 1). Twenty targets of varying diameter (16.7, 10.4, 6.5, 4.1 and 2.5 mm) and stiffness (80, 45, 14, and 8 kpa), placed at a depth of 3.5 cm were scanned. Both strain- and shear-wave-elastography was performed ten times for each of the targets scanned, yielding 200 measurements for each method used. For the shear-wave examinations the region of interest (ROI) was placed in the middle of the target, using a color-depiction of the elasticity of the target and its surroundings (Figure 2). For the strainelastography both strain-ratios and strain-histogram analysis was performed. Strainratios were calculated from grey scale strain-elastogram still-frames (Figure 3), strainhistogram analysis was performed on color elastography videos (Figure 4 and 5) at a length of minimum five seconds. Strain-histogram analysis was performed using the free software ImageJ (downloaded at nih.gov) [8]. The units for shear-wave measurements were m/s, while both strain-ratios and strain-histogram analysis were unit less, ranging from 0 to indefinite and 0 to 255 respectively. Page 3 of 11

4 Statistics: Statistical analysis was done using the software SAS version 9.3 (Copyright 2012, SAS Institute Inc., SAS Campus Drive, Cary, North Carolina 27513, USA). To evaluate the impact of size on elastographic assessments of target stiffness, mixed models analysis was performed including target stiffness, target size and the interaction thereof as model parameters. The significance level was set at To evaluate the performance of each elastographic method at different levels of target stiffness, data was divided on a binary scale three times with one data division between each of the target elasticities. The three resulting sets of binary data were used for ROCcurve analysis, allowing for direct comparison of the three methods at different levels of target elasticity. Images for this section: Fig. 1: Schematic illustration of the elasticity phantom used (Elasticity QA, model 049A, CIRS (CIRS, Virginia, USA)). Page 4 of 11

5 Fig. 2: Example of shear wave velocity measurement of a 80 kpa, 16.1 mm target. Shear wave velocities are displayed on a color scale from blue(soft) to red (hard). The measurement was performed in the middle of the target. The unit of the measurement is m/s. Page 5 of 11

6 Fig. 3: Example of strain ratio calculation of an 8 kpa, 16.1 mm target. Strain ratio calculations were performed on grey-scale-elastograms, with black signifying soft tissue and white signifying hard tissue. ROI A is placed within the target. ROI B is placed in the surrounding medium, at the same depth as the target. Strain ratios are calculated as: Mean strain in ROI B / Mean strain ROI A. Strain ratios are unit less. Page 6 of 11

7 Fig. 4: Example of strain histogram analysis of a 45 kpa, 16.1 mm target. The ROI was placed as to cover as much of the target as possible. Page 7 of 11

8 Fig. 5: The resulting strain histogram from figure 4. The strain histogram displays the number of pixels on the y-axis (unit less) and the colors of the elastogram on a linear scale from red (soft) to blue (hard) on the x-axis (unit less). By calculating the mean color number of the histogram, a quantification of the mean strain of the target ranging from 0 to 255 is achieved. The strain histogram quantification is unit less. Page 8 of 11

9 Results Results: The mean shear-wave-velocities, strain-ratios and strain-histogram values with corresponding standard deviations are presented in table 1. Table 1 80 kpa 45 kpa 14 kpa 8 kpa SWV 2.93 (0.54) 2.76 (0.34) 1.98 (0.21) 1.70 (0.37) SH (18.5) (27.3) 71.3 (27.1) 44.5 (17.0) SR 2.12 (0.67) 1.16 (0.20) 0.68 (0.15) 0.48 (0.10) Means and standard deviations from each of the different target stiffness measured for each of the methods evaluated. 50 scans of each target stiffness was performed. The p-values of the comparison of accuracy of shear-wave-velocity with strain-ratios and strain-histograms respectively, using ROC-curve analysis are presented in table 2. Table 2 8 kpa SH vs. SWV SR vs. SWV vs. 14, 45, and 80 kpa 8 and 14 kpa vs. 45 and 80 kpa 8, 14, and 45 kpa vs. 80 kpa P-values of differences between AUROC-data of strain- and shearwave-elastography diagnostic perfomance at different levels of elasticity. Page 9 of 11

10 The impact of size using mixed models analysis was significant (p=0.001), for all three elastographic methods assessed. Conclusion Our study shows that different elastographic methods perform differently in targets of varying stiffness. As the mean elasticity of malignant tumors differ from tissue to tissue [9], one should consider which elastographic method to use in different tissues. In stiffer lesions (high kpa), strain elastography seems to be better at discerning different target elasticities from each other. Furthermore we have shown that one should consider the size of the lesion evaluated when doing both strain- and shear-wave elastography, as size has significant impact on both methods. Personal information References 1. Bamber J, Cosgrove D, Dietrich CF, Fromageau J, Bojunga J, et al. (2013) EFSUMB Guidelines and Recommendations on the Clinical Use of Ultrasound Elastography. Part 1: Basic Principles and Technology. Ultraschall Med 34: doi: / s Cosgrove D, Piscaglia F, Bamber J, Bojunga J, Correas J-M, et al. (2013) EFSUMB Guidelines and Recommendations on the Clinical Use of Ultrasound Elastography.Part 2: Clinical Applications. Ultraschall in der Medizin - European Journal of Ultrasound 34: doi: /s Sadigh G, Carlos R, Neal C, Dwamena B (n.d.) Accuracy of quantitative ultrasound elastography for differentiation of malignant and benign breast abnormalities: a metaanalysis. Breast Cancer Research and Treatment: 1-9. doi: /s x. 4. Jin Z-Q, Li X-R, Zhou H-L, Chen J-X, Huang X, et al. (2012) Acoustic radiation force impulse elastography of breast imaging reporting and data system category 4 breast lesions. Clin Breast Cancer 12: doi: /j.clbc Chang JM, Won J-K, Lee K-B, Park IA, Yi A, et al. (2013) Comparison of Shear- Wave and Strain Ultrasound Elastography in the Differentiation of Benign and Malignant Page 10 of 11

11 Breast Lesions. American Journal of Roentgenology 201: W347-W356. doi: / AJR Wang ZL, Li JL, Li M, Huang Y, Wan WB, et al. (2013) Study of quantitative elastography with supersonic shear imaging in the diagnosis of breast tumours. Radiol Med 118: doi: /s x. 7. Sãftoiu A, S#ftoui A, Gheonea DI, Ciurea T (2007) Hue histogram analysis of real-time elastography images for noninvasive assessment of liver fibrosis. AJR Am J Roentgenol 189: W doi: /ajr Rasband WS (2012) ImageJ: Image processing and analysis in Java. Astrophysics Source Code Library -1: Krouskop TA, Wheeler TM, Kallel F, Garra BS, Hall T (1998) Elastic Moduli of Breast and Prostate Tissues under Compression. Ultrason Imaging 20: doi: / Page 11 of 11