Revealing Sub-Voxel Motions of Brain Tissue Using Phase-Based Amplified MRI (aMRI)

Magn Reson Med. 2018 Dec;80(6):2549-2559. doi: 10.1002/mrm.27236. Epub 2018 May 30.

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Algorithms
  • Arnold-Chiari Malformation / diagnostic imaging*
  • Brain / diagnostic imaging*
  • Cerebellar Ataxia / diagnostic imaging
  • Child, Preschool
  • Computer Simulation
  • Female
  • Foramen Magnum / diagnostic imaging
  • Healthy Volunteers
  • Humans
  • Image Interpretation, Computer-Assisted / methods
  • Image Processing, Computer-Assisted / methods
  • Magnetic Resonance Imaging*
  • Male
  • Movement
  • Phantoms, Imaging
  • Video Recording