Abstract
Cerebral viscoelastic constants can be measured in a noninvasive, image-based way by magnetic resonance elastography (MRE) for the detection of neurological disorders. However, MRE brain maps of viscoelastic constants are still limited by low spatial resolution. Here we introduce three-dimensional multifrequency MRE of the brain combined with a novel reconstruction algorithm based on a model-free multifrequency inversion for calculating spatially resolved viscoelastic parameter maps of the human brain corresponding to the dynamic range of shear oscillations between 30 and 60 Hz. Maps of two viscoelastic parameters, the magnitude and the phase angle of the complex shear modulus, |G*| and φ, were obtained and normalized to group templates of 23 healthy volunteers in the age range of 22 to 72 years. This atlas of the anatomy of brain mechanics reveals a significant contrast in the stiffness parameter |G*| between different anatomical regions such as white matter (WM; 1.252±0.260 kPa), the corpus callosum genu (CCG; 1.104±0.280 kPa), the thalamus (TH; 1.058±0.208 kPa) and the head of the caudate nucleus (HCN; 0.649±0.101 kPa). φ, which is sensitive to the lossy behavior of the tissue, was in the order of CCG (1.011±0.172), TH (1.037±0.173), CN (0.906±0.257) and WM (0.854±0.169). The proposed method provides the first normalized maps of brain viscoelasticity with anatomical details in subcortical regions and provides useful background data for clinical applications of cerebral MRE.
Highlights
Magnetic resonance imaging (MRI) is inarguably one of the most powerful neuroradiological modalities
Column (a) presents DGÃD and w without any filter, i.e. the wave data were used without further preprocessing for calculating the curl components cÃm, which were used without modification in inversion eqs.(6) and (8)
In this study we introduce several innovations as steps toward high-resolution cerebral magnetic resonance elastography (MRE) in a clinical experimental setting: i) we used a nonmagnetic driver system that has never before been tested for brain MRE
Summary
Magnetic resonance imaging (MRI) is inarguably one of the most powerful neuroradiological modalities. MRI methods sensitive to network structures, such as diffusion tensor imaging (DTI), have significantly contributed to our current knowledge of the brain’s structures and anatomy [1]. Like the majority of MRI-based methods, neuroradiological MRI depicts brain morphology based on the amount of water protons present and their relaxivity or mobility. Anatomy can be defined by the constitutive properties of tissues based on the firmness and the mechanical interconnectedness of the underlying tissue matrix. With this approach, physical parameters such as shear elasticity or shear viscosity provide a key to the understanding of multiscalar mechanical structures such as viscoelastic networks consisting of cells and elements of the extracellular matrix
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