Magnetisation Transfer Ratio
Also known as: MTR, magnetization transfer, MT imaging
Magnetisation Transfer Ratio (MTR) is an MRI method that measures the exchange of magnetization between free water protons and protons bound to macromolecules (primarily myelin lipids and proteins). Introduced by Wolff and Balaban in 1989, MTR reflects tissue macromolecular content and is particularly sensitive to myelination, providing a non-invasive estimate of myelin density.
Key highlights
- Directly sensitive to macromolecular content (myelin lipids and proteins)
- Complements DTI and diffusion metrics; provides different microstructural contrast
- Well-validated biomarker for myelin; correlates with histological myelin staining
- Clinically feasible; MT-weighted acquisitions easily added to standard MRI protocols
Intuition
This section is available to Pro members. Upgrade to Pro
How it works
This section is available to Pro members. Upgrade to Pro
When to use it
MTR is appropriate for detecting myelination changes, demyelination in multiple sclerosis, and characterizing tissue microstructure. Use MTR to assess myelin integrity independently of other metrics (FA, diffusion). Avoid MTR when sensitivity to non-myelin microstructure is desired or when scanning protocols prohibit MT-weighted acquisitions.
Strengths & limitations
- Directly sensitive to macromolecular content (myelin lipids and proteins)
- Complements DTI and diffusion metrics; provides different microstructural contrast
- Well-validated biomarker for myelin; correlates with histological myelin staining
- Clinically feasible; MT-weighted acquisitions easily added to standard MRI protocols
- Non-specific to myelin; MTR sensitive to proteins, lipids, and other macromolecules
- Not quantitative at tissue level; MTR is affected by water content and tissue architecture
- Limited tissue contrast; MTR differences between gray matter and white matter moderate
- Sensitive to acquisition parameters (saturation pulse shape, offset frequency); standardization incomplete
Common pitfalls
This section is available to Pro members. Upgrade to Pro
Applications
This section is available to Pro members. Upgrade to Pro
Frequently asked
What is the physical basis of magnetization transfer?
Magnetization transfer reflects chemical exchange of magnetization between water protons and macromolecules (primarily myelin lipids and proteins). Bound protons have short T2 and are not directly visible. By saturating their magnetization (radiofrequency pulse at their resonance), water magnetization is transferred to them, reducing detectable water signal. Transfer efficiency correlates with macromolecular content.
How do I interpret MTR values?
MTR ranges from 0–100% (percent reduction in water signal with MT saturation). Typical white matter MTR ~30–50%; gray matter MTR ~10–20%; cerebrospinal fluid near 0%. Higher MTR indicates more macromolecules (myelin). Clinical demyelinating lesions typically show MTR reduction of 20–30% compared to normal white matter.
Can MTR distinguish demyelination from remyelination?
Yes, partially. Demyelination reduces MTR rapidly (days–weeks). Remyelination gradually increases MTR over months. MTR can track remyelination therapy response. However, MTR alone cannot distinguish complete from partial remyelination; combine with other metrics (qMRI, T1 mapping) for comprehensive assessment.
How does MTR relate to other myelin-sensitive metrics?
MTR, radial diffusivity (RD from DTI), and quantitative T1 all reflect myelin. They measure different properties: MTR reflects macromolecular content; RD reflects perpendicular water diffusion (myelin-restricted); T1 reflects tissue relaxation. Combining metrics improves specificity. For myelination assessment, use MTR + DTI + T1 mapping together.
Sources
- 1.Wolff, S. D., & Balaban, R. S. (1989). Magnetization transfer contrast (MTC) and tissue water proton relaxation in vivo. Journal of Magnetic Resonance Imaging, 10(2), 135–148.
- 2.Henkelman, R. M., Huang, X., Lago, A., & Stanisz, G. J. (1993). Quantitative interpretation of magnetization transfer. Magnetic Resonance in Medicine, 29(6), 759–766.
You have read it. What now?
Cite this page
ScholarGate. (2026, June 3). Magnetisation Transfer Ratio. ScholarGate. https://scholargate.app/neuroimaging/magnetisation-transfer-ratio