MR-acoustic radiation force imaging (MR-ARFI) and susceptibility weighted imaging (SWI) to visualize calcifications in ex vivo swine brain

作者：Bitton Rachel R^*; Butts Kim R

来源：Journal of Magnetic Resonance Imaging, 2014, 39(5): 1294-1300.

DOI：10.1002/jmri.24255

• MR-ARFI
• acoustic radiation force
• MR-HIFU
• MR guided focused ultrasound
• calcification
• susceptibility weighted

Purpose
To present the use of MR-acoustic radiation force imaging (MR-ARFI) and susceptibility weighted imaging (SWI) to visualize calcifications in ex vivo brain tissue as a planning indicator for MR-guided focused ultrasound (MRgFUS).
Materials and Methods
Calcifications were implanted in ex vivo swine brain and imaged using SWI, MR-ARFI, and computed tomography (CT). SWI-filtered phase images used 3D gradient recalled echo (GRE) images with a Fourier-based unwrapping algorithm. The MR-ARFI pulse sequence used a 2DFT spin-echo with repeated bipolar encoding gradients in the direction of the longitudinal ultrasound beam. MR-ARFI interrogations scanned a subregion (14 x 10 x 12 mm) of the brain surrounding the calcification. They were combined into a single displacement weighted map, using the sum of squares method. Calcification size estimates were based on image profiles plotted along the +/- x and +/- z direction, at the full-width half-maximum.
Results
Both MR-ARFI and SWI were able to visualize the calcifications. The contrast ratio was 150 for CT, 12 for SWI, and 12 for MR-ARFI. Profile measures were 1.35 x 1.28 mm on CT, 1.24 x 1.73 mm on SWI, and 2.45 x 3.02 mm on MR-ARFI. MR-ARFI displacement showed a linear increase with acoustic power (20-80W), and also increased with calcification size.
Conclusion
The use of SWI-filtered phase and MR-ARFI have the potential to provide a clinical indicator of calcification relevance in the planning of a transcranial MRgFUS treatment. J. Magn. Reson. Imaging 2014;39:1294-1300.

• 出版日期2014-5