ABSTRACT

Pathological conditions change the cellular structure of tissue resulting in an alteration of cellular elasticity. Elastic change is an effective measure of pathology and is therefore of great interest for clinical diagnosis. Magnetic resonance elastography (MRE) is an emerging imaging technique that measures in vivo stiffness. MRE consists of inducing mechanical stress using actuators to encode stress in tissue and using magnetic gradients to measuring resulting displacement in MRI phase images. Numerous actuator designs for static/quasi-static and harmonic stress generation exist, including designs based on piezoelectric, acoustomechanical, pneumatic and electromagnetic principles. The inverse problem reconstructs elasticity values for tissue from displacement measurements and can be solved both numerically and analytically.
A survey of MRE publications in various anatomical regions reveals it may be of both diagnostic and prognostic value. While the technique is tentatively explored in some body regions, such as bone, cartilage and the eye, it has been widely used in the area of liver imaging. Liver MRE has shown high sensitivity and specificity and shows promise in hepatic fibrosis staging. A concentration of work in breast MRE has yielded promising results, with MRE showing sensitivity to breast cancer. In addition, MRE is useful in detecting skin lesions, in assessing muscle status and in "palpating" the brain noninvasively. MRE of the prostate and heart is challenging due to location, promising initial results have been obtained and may lead to further future applications. MRE of the lung is major area of research but the low density and low signal-to-noise in MRI are challenges. This paper provides a summary of research in all these areas.