A Method for Characterization of Tissue Elastic Properties Combining Ultrasonic Computed Tomography With Elastography

Abstract

Objective. The correlation between various diseases and the change in the local mechanical properties of soft tissues has been long known. Over the past 20 years, there have been increasing research efforts to characterize mechanical properties of biological tissues using ultrasonic elastography. However, most of these works were based on characterization of only 1 type of waves (longitudinal or shear). The goal of this work was to devise a comprehensive ultrasound-based imaging method capable of measuring elastic parameters by combining both backscattered elastography and throughtransmitted ultrasonic computed tomography. Methods. Our suggested technique provides measurements of both longitudinal and shear wave velocities. This enables the noninvasive computation of several tissue elasticity parameters such as Young's and shear moduli, Poisson's ratio, and, more importantly, the bulk modulus, the determination of which requires both wave velocities. Four different phantom types were examined: agar-gelatin-based phantoms and porcine fat tissue, turkey breast tissue, and bovine liver tissue in vitro specimens. The values of Young's modulus, the shear modulus, and Poisson's ratio were estimated and were consistent with values published in the literature. Results. The average bulk modulus values of the phantoms ± SD were 2.83 ± 0.001, 2.25 ± 0.01, 2.48 ± 0.01, and 2.53 ± 0.02 GPa, respectively. A statistically significant difference (P < .001) in the values of the bulk modulus of the different phantoms was found. Conclusions. The bulk modulus is suitable for differentiation between different tissue types. The obtained results show the feasibility of using a comprehensive ultrasonic imaging technique for noninvasive quantitative tissue characterization. Key words: bulk modulus; computed tomography; elastic parameters; elastography; tissue characterization; wave velocity. 2 However, in many cases, the small size of a pathologic lesion or its location deep in the body makes its detection and evaluation by palpation difficult or impossible. Furthermore, palpation is nonquantitative and lacks accuracy in locating the lesion.

Planar strain analysis of liver undergoing microwave thermal ablation using x‐ray CT

“…Ablation and desiccation of the tissue leads to protein denaturation which is known to result in an increase in the elastic modulus of the tissue. Accordingly, some methods for elastic modulus imaging, [12][13][14][15] stiffness, [16][17][18] and strain imaging 19 have demonstrated their potential in evaluating thermal ablation zones and potentially provide some added value to the clinicians. However, in addition to the imaging modality itself, these methods commonly require supplementary equipment or devices to enable the measurements of the elasticity and stiffness changes.…”

Material properties of the heel fat pad across strain rates

“…The value assigned to the bulk modulus, $K$ (2 GPa), was defined from a preliminary sensitivity analysis in order to ensure incompressible behaviour of the material and it was within the range of values reported in the literature for the same (Gabler et al, 2014), or other incompressible biological tissues (Etoh et al, 1994, Glozman and Azhari, 2010). The optimisation algorithm was considered converged when the change in objective function and material constants in consecutive iterations was less than 0.001% and 0.0001 MPa, respectively.…”

Rapid method for assessing relative tissue stiffness using MR acoustic radiation force imaging

“…Imaging of tissue elasticity by ultrasound (Gao et al, 1996;Parker et al, 2005;Glozman and Azhari, 2010) has been rapidly developed since it was introduced in the mid-1980s. The implementation of acoustic radiation force imaging (ARFI) for that purpose (e.g., Nightingale et al, 2001;Cho et al 2010;Palmeri and Nightingale, 2011) has led to the development of commercial systems such as the ACUSON S2000 ultrasound scanner by Siemens Medical Solutions which utilizes transient acoustic radiation force, and the Aixplorer ultrasound scanner developed by SuperSonic Imagine for imaging of shear-wave propagation resulting from ARF excitation (Bercoff et al, 2004).…”