Comparison of Shear-Wave and Strain Ultrasound Elastography for Evaluating Fat Induration after Breast Reconstruction

I n autologous breast reconstruction after mastec-tomy, fat induration is a rather common complication that causes deep tissue infection, pain, and contracture deformity. Follow-up for fat induration provides important clues after breast reconstruction with an autologous flap because fat induration is the clinical stage before fat necrosis that may lead to the need for corrective surgery. Our understanding of fat necrosis until now has been limited because previous studies were based exclusively on physical examination and used diverse definitions. 1 Ultrasound elastography (UE) is a relatively novel technique that is being evaluated for use to measure tissue stiffness. We have previously reported that UE is useful for detection of fat induration and necrosis after breast reconstruction with an autologous flap. 2 There are presently 2 UE techniques available that are very different in terms of the forces being measured and in their display methods (Fig. 1). In strain elastogra-phy (STE), stress is applied by repeated manual compression of the transducer, and the amount of lesion deformation relative to the surrounding normal tissue is measured and displayed in color. In contrast to strain elastography, shear-wave elas-tography (SWE) uses an acoustic radiation force impulse, which allows measurement of the propagation speed of shear waves within the tissue to locally quantify its stiffness in either kilopascals or meters per second. 3,4 Previous studies have demonstrated that both STE and SWE can help characterize breast lesions as either benign or malignant on the basis of stiffness. However, to our knowledge, there have been no studies comparing the diagnostic performances of the 2 different techniques in the same region of fat induration. It is not known which one is better, STE or SWE, for follow-up for fat induration after breast reconstruction with an autologous flap. Fourteen patients, who had clinical fat indura-tion after breast reconstruction with a deep inferior epigastric perforator flap, were included in this study. Fat tissue stiffness in the palpable hard area was measured with each technique, and the data obtained by the same device operator were recorded on the same day on the same subjects. Intraclass correlation coefficients for repeatability assessment and correlation coefficients were used to evaluate the agreement between the 2 devices. As a result of our investigation, the intraclass correlation coefficients were 0.86 (95% confidence interval: 0.70–0.95) for strain elastography and 0.96 (90% confidence interval: 0.90–0.99) for shear-wave elastography. The correlation coefficients comparing fat tissue stiffness measured with …