MRE-IA in Liver Disease and Neurovascular Imaging

Overview

The objective of this research project is to develop Magnetic Resonance Elastography by Intrinsic Activation (MRE-IA) imaging methods at two imaging centers (CRCHUS and CRCHUM) for use in ongoing studies in liver disease and neurovascular imaging. MRE is a developing MR imaging modality that provides detailed maps of tissue's mechanical properties, based on displacement measurements made during the propagation of low amplitude vibrations through the region of interest. MRE-IA uses the pressure pulses of the cardiac cycle to induce the vibrations needed for MRE image reconstruction. MRE-IA has already been demonstrated based on the use of existing, clinically approved MR imaging sequences, and once this capability has been established at the two centers, initial trials will be done to demonstrate the method's potential in liver and neurovascular imaging. In the case of the liver, this pilot project funding will be used to perform MRE-IA imaging in patients with chronic liver disease and focal liver lesions. Results will be analyzed to establish the relationship between the mechanical properties mentioned above and disease stage. In the neurovascular case, imaging will be conducted under basic visual and motor stimulus conditions in healthy subjects, and results compared non-stimulus control images to determine changes in the above properties based on brain function. In addition, MRE-IA images will be compared with BOLD imaging to investigate the role of fluid conductivity in fMRI results.

Unlike current MRE methods which require the application of cyclical mechanical excitations with an external driver, MRE-IA is a recently developed MRE modality that uses the naturally occurring cardiac pressure cycle to generate the displacements used for elastic property reconstruction. With no external activation, MRE-IA provides a simple pathway towards in-vivo elastography results that avoids the discomfort, poor coupling, and high attenuation often observed in MRE extrinsic vibration drivers. Goals: The principal goal of this project is to establish Magnetic Resonance Elastography by Intrinsic Activation (MRE-IA) imaging methods at the imaging centers of the Centre de recherche du centre hospitalier universitaire de Sherbrooke (CRCHUS) and the Centre de recherche du centre hospitalier universitaire de Montréal (CRCHUM). Each imaging center will then focus on separate sub-goals: improving liver disease assessment with MRE-IA (CRCHUM) and evaluating the role of fluid conductivity and changes in elastic properties with mental tasks (CRCHUS). Hypothesis: There are two main hypotheses underlying this project: (1) that internal activation provides an effective, robust displacement source for MRE image reconstruction that eliminates the problems of discomfort, high attenuation, artefact sensitivity, and low signal to noise associated with traditional extrinsic MRE methods; and (2) that the advanced material property maps provided by MRE-IA, such as viscoelastic damping, poroelastic effects and anisotropy, will lead to better classification and understanding of both diseased and healthy tissue states. Methods: The image acquisition methodology for this project will be identical at both imaging centers. Intrinsic activation MRE displacement data will be obtained through the use the Q-Flow angiographic sequence available on the Philips 3T systems at both the CRCHUS and CRCHUM. MRE-IA for diffuse and focal liver disease (CRCHUM): The objective of this study is to demonstrate the feasibility of MRE-IA imaging in the assessment of liver disease. MRE-IA will be performed in three populations (10 healthy volunteers, 25 patients with diffuse liver disease and 10 patients with focal liver lesions) Intrinsic MRE: MRE-IA images are reconstructed from phase-contrast sequences that are currently available on MRI scanners at CHUM and CHUS. Post-processing of the images with finite element analysis (FEA) mechanical simulations allows calculation of poroviscoelasticity parameters (i.e. porosity, bulk modulus, storage modulus \[G'\], and loss modulus \[G''\]). These poroviscoelasticity parameters will be correlated with histopathological markers of disease severity (fibrosis, inflammation, fat) in patients with chronic liver disease and with the final diagnosis (type of liver lesion). Cerebral function imaging via MRE-IA (CRCHUS): The objective of this study is to investigate the changes in mechanical properties during the performance of mental tasks and the role of inherent fluid conductivity in the BOLD imaging used in fMRI methods. Multiple imaging sessions will be performed to investigate changes to MRE-IA property maps to visual (V1) stimulation. Imaging sessions will be include either V1 (n=6) or non-stimulus (n=3) cases. Each case will include both MRE-IA and fMRI acquisitions.