Sonoelasticity imaging: Theory and experimental verification

Abstract

Sonoelasticity is a rapidly evolving medical imaging technique for visualizing hard tumors in tissues. In this novel diagnostic technique, a low-frequency vibration is externally applied to excite internal vibrations within the tissue under inspection. A small stiff inhomogeneity in a surrounding tissue appears as a disturbance in the normal vibration eigenmode pattern. By employing a properly designed Doppler detection algorithm, a real-time vibration image can be made. A theory for vibrations, or shear wave propagation in inhomogeneous tissue has been developed. A tumor is modeled as an elastic inhomogeneity inside a lossy homogeneous elastic medium. A vibration source is applied at a boundary. The solutions for the shear wave equation have been found both for the cases with tumor (inhomogeneous case) and without tumor (homogeneous case). The solutions take into account varying parameters such as tumor size, tumor stiffness, shape of vibration source, lossy factor of the material, and vibration frequency. The problem of the lowest detectable change in stiffness is addressed using the theory, answering one of the most critical questions in this diagnostic technique. Some experiments were conducted to check the validity of the theory, and the results showed a good correspondence to the theoretical predictions. These studies provide basic understanding of the phenomena observed in the growing field of clinical Sonoelasticity imaging for tumor detection.

Comparison of Vibrational Displacements Generated by Different Types of Surface Source in a Soft Tissue

“…[14] obtained displacement images formed by horizontal shear wave. Sandrin et al [9] proposed using dual cylindrical rod vibrators arranged side by side which were placed on both ends of a transducer array in order to generate a large amplitude shear wave in an imaging region of interest.…”

“…Gao et al [14] theoretically analyzed the displacement pattern of a shear wave generated in tissue due to a low frequency vibration applied. They considered an attenuating medium that includes hard lesions.…”

“…(1) can be obtained using Fourier transform in an analogous manner to solving a two-dimensional Lamb problem in a half space [24]. Expressing the displacement as the sum of the gradient of scalar potential and the curl of vector potential, we obtain two separate wave equations for longitudinal and shear waves [14,25]. Taking …”

Normalization of Multifocal Acoustic Radiation Force Impulse Images

“…Other external means have been also proposed for tissue stimulation, such as mechanical shakers (Gao et al, 1995) or vibrators for transient elastography (Catheline et al, 1999).…”

Ultrasound Stimulated Acoustic Emission: Preliminary in Vivo Results

“…The method resulted in high-resolution images of the shear modulus of normal and pathologic tissues and obtained a sensitivity of about 0.1 mm. Others have used ultrasound to measure tissue displacement associated with externally applied compressive and cyclic forces [21].…”