Princípios físicos da elastografia por ressonância magnética

Abstract

This work is the first effort to introduce in the Portuguese language a tool to study the mechanical properties of materials and living tissues with potential clinical applications. We seek to present proposals for the exploration of new methods of acquisition and processing of images generated by Magnetic Resonance Imaging (MRI) systems. Magnetic Resonance Elastography (MRE) is a new procedure that allows in-vivo measurement of the viscoelastic parameters of tissues, which is still in the research stage. Since it is based on Magnetic Resonance Tomography (MRT), it does not use any potentially harmful X-ray radiation. The MRE technique works by introducing periodical mechanical waves on the tissue surface, and using an actuator to drive the medium. The introduction of the sinusoidal mechanical wave into the tissue leads to a periodic forced vibration. Triggering the MRT measurements with this mechanical wave it is then leads to an enhancement of the image contrast, which is proportional to the wave property. Thus, magnetic resonance tomography works as a "stroboscopic camera" by creating a "snapshot" of the mechanical wave within the tissue. A continuous propagation of the wave can be used to produce a movie by taking a number of snapshots at different intervals. Phase-shift imaging resulting from the propagation of waves through the tissue is obtained using a MR method of phase-contrast technique. These phase-shift imaging sequences form the foundation of the subsequent reconstruction of the elastic parameters, which are represented by an image called elastogram. This new methodology allows quantitative and noninvasive measurements of elastic properties of tissues to help radiologists into making precise diagnosis in order to confirm preexisting ones. © Sociedade Brasileira de Física.