Reply to the Letter to the Editor Regarding do Not Forget to Calculate the Mean Shear Wave Speed as Assessed by Acoustic Radiation Force Impulse Elastography as a Harmonic Mean, Not an Arithmetical Mean

2015 ◽  
Vol 41 (5) ◽  
pp. 1493-1494
Author(s):  
Simona Bota ◽  
Flaviu Bob
Pancreatology ◽  
2016 ◽  
Vol 16 (1) ◽  
pp. 106-109 ◽  
Author(s):  
Mirko D'Onofrio ◽  
Riccardo De Robertis ◽  
Stefano Crosara ◽  
Cristina Poli ◽  
Stefano Canestrini ◽  
...  

2017 ◽  
Vol 39 (5) ◽  
pp. 326-336 ◽  
Author(s):  
Niraj Nirmal Pandey ◽  
Gaurav Shanker Pradhan ◽  
Alpana Manchanda ◽  
Anju Garg

The objective of this study was to evaluate the role of ultrasound elastography using acoustic radiation force impulse (ARFI) quantification in characterizing and differentiating malignant versus benign thyroid nodules. A total of 40 thyroid nodules were evaluated with conventional sonography and ultrasound elastography using ARFI quantification. The final diagnosis was obtained from histologic findings. A total of 14 malignant and 26 benign nodules were diagnosed on the basis of histologic examination. Majority of the malignant thyroid nodules demonstrated presence of intranodular vascular flow, hypoechoic echotexture, absent halo, irregular margins and microcalcifications. However, a considerable overlap was noted in the sonographic features of malignant and benign thyroid nodules. On ARFI quantification, the mean shear wave speed (SWS) values ( M ± SD) of malignant and benign thyroid nodules were 3.131 ± 0.921 m/s and 1.691 ± 0.513 m/s, respectively. A significant difference was observed between the mean SWS values of malignant thyroid nodules and benign thyroid nodules ( p < 0.0001). Applying a cutoff value of 2.53 m/s, the sensitivity, specificity, and the area under the receiver operating characteristic curve for the differentiation were 85.71%, 96.15%, and 0.922, respectively. ARFI quantification is a promising elastography technique that provides quantitative information about tissue stiffness. It provides additional information and complements sonography as an effective diagnostic tool in characterizing and differentiating benign from malignant thyroid nodules.


Author(s):  
Carolina Amador ◽  
Matthew W. Urban ◽  
Shigao Chen ◽  
James F. Greenleaf

Elasticity imaging methods have been used to study tissue mechanical properties and have demonstrated that tissue elasticity changes with disease state. Quantitative mechanical properties can be measured in a model independent manner if both shear wave speed and attenuation are known. However, measuring shear wave speed attenuation is challenging in the field of elasticity imaging. Typically, only shear wave speed is measured and rheological models, such as Kelvin-Voigt, Maxwell and Standard Linear Solid, are used to solve for shear viscoelastic complex modulus. Acoustic radiation force has been used to study quasi-static viscoelastic properties of tissue during creep and relaxation conditions, however, as with shear wave propagation methods, a rheological model needs to be fit to the creep or relaxation experimental data to solve for viscoelastic parameters. This paper presents a method to quantify viscoelastic properties in a model-independent way by estimating complex shear elastic modulus over a wide frequency range using time-dependent creep response induced by acoustic radiation force. The acoustic radiation force induced creep (RFIC) method uses a conversion formula that is the analytic solution of the constitutive equation relating time dependent stress and time dependent strain. The RFIC method in combination with shear wave propagation is used to measure the complex shear modulus so that knowledge of the applied radiation force magnitude is not necessary. Numerical simulation of creep strain and compliance using the Kelvin-Voigt model shown that the conversion formula is sensitive to sampling frequency, the first reliable measure in time and the long term viscosity approximation. Experimental data are obtained in homogeneous tissue mimicking phantoms and excised swine kidneys.


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