Quantitative shear wave ultrasound elastography: initial experience in solid breast masses

Abstract

IntroductionShear wave elastography is a new method of obtaining quantitative tissue elasticity data during breast ultrasound examinations. The aims of this study were (1) to determine the reproducibility of shear wave elastography (2) to correlate the elasticity values of a series of solid breast masses with histological findings and (3) to compare shear wave elastography with greyscale ultrasound for benign/malignant classification.MethodsUsing the Aixplorer® ultrasound system (SuperSonic Imagine, Aix en Provence, France), 53 solid breast lesions were identified in 52 consecutive patients. Two orthogonal elastography images were obtained of each lesion. Observers noted the mean elasticity values in regions of interest (ROI) placed over the stiffest areas on the two elastography images and a mean value was calculated for each lesion. A sub-set of 15 patients had two elastography images obtained by an additional operator. Reproducibility of observations was assessed between (1) two observers analysing the same pair of images and (2) findings from two pairs of images of the same lesion taken by two different operators. All lesions were subjected to percutaneous biopsy. Elastography measurements were correlated with histology results. After preliminary experience with 10 patients a mean elasticity cut off value of 50 kilopascals (kPa) was selected for benign/malignant differentiation. Greyscale images were classified according to the American College of Radiology (ACR) Breast Imaging Reporting and Data System (BI-RADS). BI-RADS categories 1-3 were taken as benign while BI-RADS categories 4 and 5 were classified as malignant.ResultsTwenty-three benign lesions and 30 cancers were diagnosed on histology. Measurement of mean elasticity yielded an intraclass correlation coefficient of 0.99 for two observers assessing the same pairs of elastography images. Analysis of images taken by two independent operators gave an intraclass correlation coefficient of 0.80. Shear wave elastography versus greyscale BI-RADS performance figures were sensitivity: 97% vs 87%, specificity: 83% vs 78%, positive predictive value (PPV): 88% vs 84%, negative predictive value (NPV): 95% vs 82% and accuracy: 91% vs 83% respectively. These differences were not statistically significant.ConclusionsShear wave elastography gives quantitative and reproducible information on solid breast lesions with diagnostic accuracy at least as good as greyscale ultrasound with BI-RADS classification.

Anisotropy of Solid Breast Lesions in 2D Shear Wave Elastography is an Indicator of Malignancy

“…Therefore the lesions of group A and B dichotomised according to a threshold for each parameter, identified from the literature [2,5,16] as follows: that is an ultrasound diameter of 15 mm, E max of 80 kPa, E mean of 50 kPa and a SD of 7 kPa. Furthermore the sub-groups were divided into all (total), benign and malignant lesions.…”

“…Evans et al obtain four SWE images per lesion; each two in two orthogonal planes [5]. Observation of anisotropy during routine SWE evaluation of breast lesions prompted this study.…”

Breast elastography: A literature review

“…Once local propagation velocity of the pressure waves is measured RSV creates a two-dimensional map representing the distribution. The exact values of tissue stiffness expressed in kiloPascals (kPa) can be measured in areas of lesser deformability [28]. ARFI "shear wave" and RSV are quantitative imaging techniques that provide quantitative measures of tissue stiffness with a reduced interobserver variability.…”

“…The technical equipment currently displays 3e4 elastographic images per second concurrently with the US image. When abnormal stiffness is identified in a specific area of interest, values of maximum and average stiffness and standard deviation can be measured [28]. RSV allows both qualitative and quantitative assessments.…”

“…The values that have emerged in clinical trials (42e45.3 AE 41.1 kPa in benign lesions and 146.6 AE 40.05 kPa in malignant lesions) differ significantly between benign and malignant lesions [3,49]. Some authors have proposed the use of a mean elasticity cut-off of 50 kPa to differentiate benign from malignant lesions [28].…”