Magnetization transfer (MT) asymmetry around the water resonance in human cervical spinal cord

Abstract

Purpose: To demonstrate the presence of magnetization transfer (MT) asymmetry in human cervical spinal cord due to the interaction between bulk water and semisolid mac- romolecules (conventional MT), and the chemical exchange dependent saturation transfer (CEST) effect. Materials and Methods: MT asymmetry in the cervical spinal cord (C3/C4-C5) was investigated in 14 healthy male subjects with a 3T magnetic resonance (MR) system. Both spin-echo (SE) and gradient-echo (GE) echo-planar imaging (EPI) sequences, with low-power off-resonance radiofre-quency irradiation at different frequency offsets, were used. Results: Our results show that the z-spectrum in gray/white matter (GM/WM) is asymmetrical about the water resonance frequency in both SE-EPI and GE-EPI, with a more significant saturation effect at the lower frequencies (negative frequency offset) far away from water and at the higher frequencies (positive offset) close to water. These are attributed mainly to the conventional MT and CEST effects respectively. Furthermore, the amplitude of MT asymmetry is larger in the SE-EPI sequence than in the GE-EPI sequence in the frequency range of amide protons. Conclusion: Our results demonstrate the presence of MT asymmetry in human cervical spinal cord, which is consistent with the ones reported in the brain. © 2009 Wiley-Liss, Inc.