Stiffness-weighted magnetic resonance imaging.
An imaging method is introduced in which the signal in MR images is affected by the stiffness distribution in the object being imaged. Intravoxel phase dispersion (IVPD) that occurs during MR elastography (MRE) acquisitions decreases the signal in soft regions more than in stiff regions due to changes in shear wave amplitude and wavelength. The IVPD effect is enhanced by lowpass filtering the MR k-space data with a circular Gaussian lowpass filter. A processing method is introduced to take the time series of MRE magnitude images with IVPD and produce a final stiffness-weighted image (SWI) by calculating the minimum signal at each pixel from a small number of temporal samples. The SWI technique is demonstrated in phantom studies as well as in the case of a preserved postmortem breast tissue specimen with a stiff lesion created by focused ultrasound ablation to mimic a breast cancer. When free of significant sources of depth-dependent wave attenuation, interference, and boundary effects, SWI is a simple, fast, qualitative technique that does not require the use of phase unwrapping or inversion algorithms for localizing stiff regions in an object.