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

Abstract

Purpose To demonstrate the presence of MT asymmetry in human cervical spinal cord due to the interaction between bulk water and semisolid macromolecules (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 radiofrequency irradiation at different frequency offsets, were used. Results Our results show that the z-spectrum in gray/white matter 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 SE-EPI sequence than in 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.

Minimizing the effects of magnetization transfer asymmetry on inhomogeneous magnetization transfer (ihMT) at ultra-high magnetic field (11.75 T)

“…This frequency shift center was shown to be located in the chemical shift range of aliphatic protons in the 1 H NMR spectrum, i.e., 0-3.5 ppm upfield to water resonance. In particular, in WM, a value of ~2.3-2.5 ppm upfield to water frequency has been found in experiments performed on humans at 3 T [12,31,32] and on rats at 4.7 T [13,32]. In our study, MTRasym in WM was nulled for fc ~ 1.3 ppm upfield to water resonance.…”

Longitudinal assessment of spinal cord injuries in nonhuman primates with quantitative magnetization transfer

“…To date, simpler metrics such as MTR (32) have been the major approach to assess changes in macromolecular composition in neurological disorders (33,34), neuromuscular diseases (35), liver fibrosis (36), and cancer (37). MTR has also been shown to be sensitive to changes in protein content and has been used previously in studies of SC (12,38,39). The sensitivity and reproducibility of MTR measure can be influenced by various experimental parameters.…”

Uniform magnetization transfer in chemical exchange saturation transfer magnetic resonance imaging

“…Such effects, commonly referred to as the magnetization transfer (MT) mechanism, may affect the water signal intensity over a broad frequency range and may lead to an inevitable interference with the desirable CEST contrast. This interference can be reduced by the difference analysis as mentioned above, but its complete removal is not trivial because the MT effect may itself be asymmetric around the water111617. Here, we introduce a saturation technique that can isolate genuine CEST effects by making MT effects uniform.…”