Corrections to "The Role of Viscosity in the Impulse Diffraction Field of Elastic Waves Induced by the Acoustic Radiation Force" and "Supersonic Shear Imaging: A New Technique for Soft Tissue Elasticity Mapping"

Comparative analysis of conventional ultrasound and shear wave elastography features in primary breast diffuse large B-cell lymphoma

BACKGROUND

Primary breast diffuse large B-cell lymphoma (PB-DLBCL) is a rare subtype of non-Hodgkin lymphoma that accounts for < 3% of extranodal lymphomas and 1% of breast tumors. Its diagnosis and management are challenging because of its rarity, heterogeneity, and aggressive behavior. Conventional ultrasound (US) is the first-line imaging modality for breast lesions; however, it has limited specificity and accuracy for PB-DLBCL. Shear wave elastography (SWE) is a novel US technique that measures tissue stiffness and may reflect the histological characteristics and biological behavior of breast lesions.

AIM

To compare the conventional US and SWE features of PB-DLBCL and evaluate their diagnostic performance and prognostic value.

METHODS

We retrospectively reviewed the clinical data and US images of 32 patients with pathologically confirmed PB-DLBCL who underwent conventional US and SWE before treatment. We analyzed conventional US features (shape, margin, orientation, echo, posterior acoustic features, calcification, and vascularity) and SWE features (mean elasticity value, standard deviation, minimum elasticity value, maximum elasticity value, and lesion-to-fat ratio) of the PB-DLBCL lesions. Using receiver operating characteristic curve analysis, we determined the optimal cutoff values and diagnostic performance of conventional US and SWE features. We also performed a survival analysis to assess the prognostic value of conventional US and SWE features.

RESULTS

The results showed that the PB-DLBCL lesions were mostly irregular in shape (84.4%), microlobulated or spiculated in margins (75%), parallel in orientation (65.6%), hypoechoic in echo (87.5%), and had posterior acoustic enhancement (65.6%). Calcification was rare (6.3%) and vascularity was variable (31.3% avascular, 37.5% hypovascular, and 31.3% hypervascular). The mean elasticity value of PB-DLBCL lesions was significantly higher than that of benign breast lesions (113.4 ± 46.9 kPa vs 27.8 ± 16.4 kPa, P < 0.001). The optimal cutoff value of the mean elasticity for distinguishing PB-DLBCL from benign breast lesions was 54.5 kPa, with a sensitivity of 93.8%, specificity of 92.9%, positive predictive value of 93.8%, negative predictive value of 92.9%, and accuracy of 93.3%. The mean elasticity value was also significantly correlated with Ki-67 expression level (r = 0.612, P < 0.001), which is a marker of tumor proliferation and aggressiveness. Survival analysis showed that patients with higher mean elasticity values (> 54.5 kPa) had worse overall survival (OS) and progression-free survival (PFS) than those with lower mean elasticity values (< 54.5 kPa) (P = 0.038 for OS and P = 0.027 for PFS).

CONCLUSION

Conventional US and SWE provide useful information for diagnosing and forecasting PB-DLBCL. SWE excels in distinguishing PB-DLBCL from benign breast lesions, reflects tumor proliferation and aggressiveness, and improves disease management.

Magnetic resonance shear wave elastography using transient acoustic radiation force excitations and sinusoidal displacement encoding

A magnetic resonance (MR) shear wave elastography technique that uses transient acoustic radiation force impulses from a focused ultrasound (FUS) transducer and a sinusoidal-shaped MR displacement encoding strategy is presented. Using this encoding strategy, an analytic expression for calculating the shear wave speed in a heterogeneous medium was derived. Green's function-based simulations were used to evaluate the feasibility of calculating shear wave speed maps using the analytic expression. Accuracy of simulation technique was confirmed experimentally in a homogeneous gelatin phantom. The elastography measurement was compared to harmonic MR elastography in a homogeneous phantom experiment and the measured shear wave speed values differed by less than 14%. This new transient elastography approach was able to map the position and shape of inclusions sized from 8.5 to 14 mm in an inclusion phantom experiment. These preliminary results demonstrate the feasibility of using a straightforward analytic expression to generate shear wave speed maps from MR images where sinusoidal-shaped motion encoding gradients are used to encode the displacement-time history of a transiently propagating wave-packet. This new measurement technique may be particularly well suited for performing elastography before, during, and after MR-guided FUS therapies since the same device used for therapy is also used as an excitation source for elastography.

A parametric evaluation of shear wave speeds estimated with time-of-flight calculations in viscoelastic media

Shear wave elasticity imaging (SWEI) uses an acoustic radiation force to generate shear waves, and then soft tissue mechanical properties are obtained by analyzing the shear wave data. In SWEI, the shear wave speed is often estimated with time-of-flight (TOF) calculations. To characterize the errors produced by TOF calculations, three-dimensional (3D) simulated shear waves are described by time-domain Green's functions for a Kelvin-Voigt model evaluated for multiple combinations of the shear elasticity and the shear viscosity. Estimated shear wave speeds are obtained from cross correlations and time-to-peak (TTP) calculations applied to shear wave particle velocities and shear wave particle displacements. The results obtained from these 3D shear wave simulations indicate that TTP calculations applied to shear wave particle displacements yield effective estimates of the shear wave speed if noise is absent, but cross correlations applied to shear wave particle displacements are more robust when the effects of noise and shear viscosity are included. The results also show that shear wave speeds estimated with TTP methods and cross correlations using shear wave particle velocities are more sensitive to increases in shear viscosity and noise, which suggests that superior estimates of the shear wave speed are obtained from noiseless or noisy shear wave particle displacements.

A parametric evaluation of shear wave speeds estimated with time-of-flight calculations in viscoelastic media

Shear wave elasticity imaging (SWEI) uses an acoustic radiation force to generate shear waves, and then soft tissue mechanical properties are obtained by analyzing the shear wave data. In SWEI, the shear wave speed is often estimated with time-of-flight (TOF) calculations. To characterize the errors produced by TOF calculations, three-dimensional (3D) simulated shear waves are described by time-domain Green's functions for a Kelvin-Voigt model evaluated for multiple combinations of the shear elasticity and the shear viscosity. Estimated shear wave speeds are obtained from cross correlations and time-to-peak (TTP) calculations applied to shear wave particle velocities and shear wave particle displacements. The results obtained from these 3D shear wave simulations indicate that TTP calculations applied to shear wave particle displacements yield effective estimates of the shear wave speed if noise is absent, but cross correlations applied to shear wave particle displacements are more robust when the effects of noise and shear viscosity are included. The results also show that shear wave speeds estimated with TTP methods and cross correlations using shear wave particle velocities are more sensitive to increases in shear viscosity and noise, which suggests that superior estimates of the shear wave speed are obtained from noiseless or noisy shear wave particle displacements.

Current advances and research in ultrasound imaging to the assessment and management of musculoskeletal disorders

Currently evidence-based practice has given scientific weight to the physical therapist profession; it is essential that all medical professional and physical therapists know the usefulness of new tools that optimize the effectiveness of their interventions and allow the growing of the scientific knowledge base. The use of ultrasound imaging (USI) by physiotherapists has evolved in recent years, consolidating as an increasingly standardized technique, low cost compared to other imaging techniques, quickly of execution, feasible and reliable tool. USI offers a wide range of opportunities in clinical practice as well as in different research areas. Therefore, ultrasound has been currently used as a diagnostic tool by physicians and in recent years there has been an expansion of the use of ultrasound equipment by non-physicians professionals such as physical therapist or physical trainers, who incorporates USI as a means of assessing musculoskeletal system architecture and composition, musculoskeletal changes in dysfunction, pain or injury conditions, as an interventional technique assisting echo-guided procedures or using the visual real-time information as a biofeedback in control motor approaches, as guiding tool in clinical decisions as well as to improve the understanding of tissue adaptations to exercise or movement. The purpose of this article is to review and provide an overview about the currently research of the USI applications and their benefits for the diagnosis and management in individuals with musculoskeletal conditions.