Assessing Tumor Mechanics by MR Elastography at Different Strain Levels

Abstract

Background Malignant tumors are associated with increased tissue rigidity, which can be an indicator of tumor progression. MR elastography (MRE) has the potential to study the variations of tumor mechanical properties. ex vivo studies have shown the ability of MRE to assess increase of mechanical properties; nevertheless, it has not yet been observed in vivo. Purpose To propose a method to assess the increase in mechanical properties of tumors in vivo under static external compression using MRE. Study Type Prospective, experimental study. Animal Model Forty‐six SCID mice with subcutaneous tumor implantation (patient‐derived hepatocellular carcinoma xenografts, Model 1, n = 13, and Model 2, n = 33). Field Strength/Sequence 7.0T; a spin echo sequence was used for anatomical images and a modified spin echo sequence for elastography acquisitions with a vibration frequency of 600 Hz. Assessment An inflatable balloon was placed on the abdomen to apply a load to the tumor. MRE acquisitions were performed at the basal state and at increasing compression levels. Anatomical images were used to calculate the octahedral shear strain between the tumor at the basal strain state and each strain level. For six mice (Model 2), each static preloading scan was acquired twice consecutively without moving the mouse to evaluate repeatability. Statistical Tests: The Bland–Altman method was used to assess repeatability. Correlations between tumor stiffness and deformation were evaluated with Pearson correlation coefficients. Results For stiffness (G*), a good repeatability was obtained between the acquisitions; the limits of agreement of the Bland–Altman test were [–10.17%; 11.49%] with an absolute bias of 0.66%. A significant correlation between tumor stiffness and deformation was observed for both models (Model 1: r = 0.57, P < 0.0001 and Model 2: r = 0.31, P < 0.0001). Data Conclusion We establish that tumor mechanical properties can increase under mechanical compression. This increase can effectively be monitored using a proposed MRE setup. Level of Evidence: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:1982–1989.

Inducing Biomechanical Heterogeneity in Brain Tumor Modeling by MR Elastography: Effects on Tumor Growth, Vascular Density and Delivery of Therapeutics

“…Due to changes in the cellular and extracellular matrix components, the compression of the tumor and the host tissue changes during tumor progression. These effects can result in changes in the stiffness of the tumor [ 26 , 32 , 91 , 92 ]. The incorporation of temporal variations in the elastic properties would be expected to change our results quantitatively.…”

High frequency ultrasound vibrational shear wave elastography for preclinical research

“…The same authors reported complex shear modulus for other orthotopic tumours including BT-474 (2.9 ± 0.2 m s −1 ), PANC1 (3.3 ± 0.2 m s −1 ), and other intracranial tumours from GTML/Trp53 (2.1 ± 0.2 m s −1 ) to U87 MG (2.5 ± 0.2 m s −1 ), and finally subcutaneous SW620 (2.3 ± 0.2 m s −1 ) (Li et al 2014b ). Page et al ( 2019 ), reported the shear elastic modulus of SA-LIV tumours using MR elastography at 600 Hz (1.3 m s −1 ). Ahmed et al ( 2020b ) used STL-SWE, an ARFI based ultrasound shear wave imaging modality to measure the shear wave speed of PDAC xenograft tumours (2.3 ± 0.5 m s −1 ) in mice.…”

MR Elastography in Cancer

“…Although the first represents a perfect soft solid, the second has strongly attenuating properties. 27 Magnetic resonance elastography holds great potential for the mechanical, noninvasive characterization of tumors in patients, 39 particularly for image-based quantification of solid stress 40,41 and tissue fluidity. 30,42 Current limits of MRE are related to its relatively low spatial resolution for the assessment of tumor heterogeneity as well as stability issues due to noise and possible negative interferences of propagating waves.…”