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Magn Reson Med. 2018 May 30. doi: 10.1002/mrm.27236. [Epub ahead of print]

Revealing sub-voxel motions of brain tissue using phase-based amplified MRI (aMRI).

Author information

1
Department of Radiology, Stanford University, Stanford, California.
2
Stevens Institute of Technology, Hoboken, New Jersey.
3
Department of Anatomy and Medical Imaging, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand.

Abstract

PURPOSE:

Amplified magnetic resonance imaging (aMRI) was recently introduced as a new brain motion detection and visualization method. The original aMRI approach used a video-processing algorithm, Eulerian video magnification (EVM), to amplify cardio-ballistic motion in retrospectively cardiac-gated MRI data. Here, we strive to improve aMRI by incorporating a phase-based motion amplification algorithm.

METHODS:

Phase-based aMRI was developed and tested for correct implementation and ability to amplify sub-voxel motions using digital phantom simulations. The image quality of phase-based aMRI was compared with EVM-based aMRI in healthy volunteers at 3T, and its amplified motion characteristics were compared with phase-contrast MRI. Data were also acquired on a patient with Chiari I malformation, and qualitative displacement maps were produced using free form deformation (FFD) of the aMRI output.

RESULTS:

Phantom simulations showed that phase-based aMRI has a linear dependence of amplified displacement on true displacement. Amplification was independent of temporal frequency, varying phantom intensity, Rician noise, and partial volume effect. Phase-based aMRI supported larger amplification factors than EVM-based aMRI and was less sensitive to noise and artifacts. Abnormal biomechanics were seen on FFD maps of the Chiari I malformation patient.

CONCLUSION:

Phase-based aMRI might be used in the future for quantitative analysis of minute changes in brain motion and may reveal subtle physiological variations of the brain as a result of pathology using processing of the fundamental harmonic or by selectively varying temporal harmonics. Preliminary data shows the potential of phase-based aMRI to qualitatively assess abnormal biomechanics in Chiari I malformation.

KEYWORDS:

Chiari I malformation; amplified MRI; balanced steady-state free precession (bSSFP); cardiac-gated; free-form deformation; phase contrast MRI; phase-based video motion processing

PMID:
29845645
DOI:
10.1002/mrm.27236

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