Tomokazu Numano^{1,2}, Daiki Ito^{2,3,4}, Kazuyuki Mizuhara^{5}, Toshikatsu Washio^{2}, Tetsushi Habe^{3,4}, Toshiki Maeno^{3}, Masaki Misawa^{2}, and Naotaka Nitta^{2}

^{1}Radiological Sciences, Tokyo Metropolitan University, Tokyo, Japan, ^{2}National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan, ^{3}Tokyo Metropolitan University, Tokyo, Japan, ^{4}Keio University Hospital, Tokyo, Japan, ^{5}Tokyo Denki University, Tokyo, Japan

We developed a new technique for dynamic MR elastography (MRE) using a MR magnitude image. A general MRE uses a MR phase image as a wave image. Proposed technique was used a MR magnitude image instead of MR phase image as a wave image by using a special vibration. Proposed technique (special vibration MRE) performance was comparable to that of a continuous vibration MRE. Since special vibration MRE need an only few second vibration, it could dramatically eliminated the patients' vibration-related discomfort.

- Numano T, Mizuhara K, Hata J, et al. A simple method for MR elastography: a gradient-echo type multi-echo sequence. Magn Reson Imaging 2015;33(1):31-7
- Glaser KJ, Felmlee JP, Manduca A, et al. Shear stiffness estimation using intravoxel phase dispersion in magnetic resonance elastography. Magn Reson Med. 2003 Dec;50(6):1256-65.

**Variation of special vibration**

In general MRE, the vibration power is constant at during image acquisition; orange color line (100%). Special vibration (time-dependent vibration power in Gaussian distribution) is used for a MR magnitude image MRE. The special vibration is generated by Eq [1]. The peak of the special vibration is set to half time of the acquisition time. The width of the special vibration is controlled by the σ in Eq [1].

**MR magnitude image MRE (MI-MRE)**

a: The vibration effect of k-space in the continuous vibration is convolved in all spatial frequency domains as all area of k-space. The shear wave information was visualized on only MR phase image. b: The vibration effect of k-space in the special vibration is selectively convolved in only low-spatial frequency domain as only blue area of k-space. The shear wave information was visualized on both images. The shear wave information of phase image was low visibility compared with the one of continuous vibration.

**Spatial frequency analyses of special vibration**

a: Process of spatial frequency analyses. This process was performed at each vibration frequency and special vibration. b,c,d: The results of each spatial frequency analyses were organized into charts of each vibration frequency. In each vibration frequency, the spatial frequency was the same, but the intensity changed. e: The normalized intensity of each spatial frequency analyses were organized into chart. Amplitude Convex 05 lack the high spatial frequency domain, which reduces the normalized intensity at 100 Hz and 150 Hz.

**k-space data analyses of vibration frequency**

a: Process of k-space data analyses. Get the difference between the k-space data of continuous vibration and the one of special vibration. b: The difference domain of k-space (blue arrow) was observed on origin symmetry of k-space. The gap of the difference domain of k-space (white arrow) was broadening dependent on vibration frequency (or wavelength).

**Difference domain of k-space and special vibration**

For better view ability, these data was magnified at the center of k-space. The blue belt on k-space difference data were the width (duration and power) of special vibration. In Amplitude convex 05 and 50 Hz, the difference domain of k-space (blue arrow) and the blue belt was overlapped. In Amplitude convex 05 and 100 or 150 Hz, the blue arrow and the blue belt wasn’t overlapped.