The Relevance of Cerebral MRI Elastography in the Mechanical Characterization of Glial Tumors

Initiated in 1996, magnetic resonance elastography detects the movement of tissues in the human body and monitors their response to mechanical stress in order to reveal their mechanical properties. These depend on the structure of the tissues, their biological conditions and the possible affections affecting them,. This technique, with recognized safety, allows us to replace the doctor's usual palpation of peripheral organs, such as the liver, or the breast, and to consider the exploration of deeper organs such as the heart or the brain ,. At the Bicêtre Inter-Establishment Center, under the direction of Ralph Sinkus of the Beaujon Hospital, the elastography of breast7 (for the exploration of tumors) and of the heart9 is already being studied . At the Hôpital de Beaujon, elastography was developed to study tumors, fibrosis and cirrhosis of the liver5. Through a vibrating bar, Mayo Clinic11, in the United States, then, in an oscillating cradle, Charity12, Germany, induced waves in the human brain and early measurements of the brain's elastography showed a Significant difference in the modulus of elasticity and viscosity of the white matter and the gray matter. The dependence of these modules on age and gender was discussed.

The elasticity measured by MRI of tumors of 38 to 75 mm in diameter could also be correlated with the tissue consistency of the samples obtained during a surgical reduction. Finally, in a patient with a temporal glioma, the mean modulus of elasticity in the tumor region was measured by elastography close to 30% greater than in the corresponding region of the healthy hemisphere.

But the difficulty of introducing a mechanical wave into the brain through the cranial chamber and the surrounding cerebro-spinal fluid limits the scope of the advanced results, which are essentially qualitative at the moment. The median amplitude of the displacements measured in the brain during these studies is only 7.33 μm at 40 Hz and drops to 2.70 μm at 120 Hz while it is more than 21 μm in the Liver and breast at 75 and 90 Hz respectively4. Recently, the IR4M has developed an original excitation device that allows to circumvent this limit. Displacements of cerebral tissues of several tens of micrometers have been reported by MRI and the inversion of the problem leading to the viscoelastic modules could be carried out on the whole of the human brain