Magnetic resonance elastography
|Magnetic resonance elastography|
Magnetic resonance elastography of the brain. A T1 weighted anatomical image is shown in the top-left, and the corresponding T2 weighted image from the MRE data is shown in the bottom-left. The wave image used to make the elastogram is shown in the top-right, and the resulting elastogram is in the bottom-right.
|Purpose||measures the mechanical properties of soft tissues|
Magnetic resonance elastography (MRE) is a non-invasive medical imaging technique that measures the stiffness of soft tissues by generating shear waves in tissue, imaging their propagation using MRI, and processing the images to generate a stiffness map (elastogram). It is one of the most commonly used elastography techniques.
MRE was first described by Muthupillai et al. in 1995. Because diseased tissues are often stiffer than the surrounding normal tissue, MRE has been applied to visualize a variety of disease processes which affect tissue stiffness in the liver, breast, brain, heart, and skeletal muscle. For example, breast tumors are much harder than healthy fibroglandular tissue. MRE is similar to palpation; however, whereas palpation is a qualitative technique performed by physicians, MRE is a quantitative technique performed with a radiologist.
Liver fibrosis is a common result of many chronic liver diseases; progressive fibrosis can lead to cirrhosis. MRE of the liver provides quantitative maps of tissue stiffness over large regions of the liver. This non-invasive technique is able to detect increased stiffness of the liver parenchyma, which is a direct consequence of liver fibrosis. It helps to stage liver fibrosis or diagnose mild fibrosis with reasonable accuracy.
MRE of the brain was first presented in the early 2000s. Elastogram measures have been correlated with memory tasks, fitness measures, and progression of various neurodegenerative conditions. For example, regional and global decreases in brain viscoelasticity have been observed in Alzheimer’s disease and multiple sclerosis. It has been found that as the brain ages, it loses its viscoelastic integrity due to degeneration of neurons and oligodendrocytes.
MRE has also been applied to functional neuroimaging. Whereas functional magnetic resonance imaging (fMRI) infers brain activity by detecting relatively slow changes in blood flow, functional MRE is capable of detecting neuromechanical changes in the brain related to neuronal activity occurring on the 100-millisecond scale.
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