Assessing Tumor Mechanics by MR Elastography at Different Strain Levels.

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.