Magnetization Transfer Imaging (MTI) MRI scan is a specialized MRI technique that enhances visualization of tissue microstructure, especially myelin in the brain, by detecting subtle changes missed by a standard MRI scan.
It has been highly useful in assessing Multiple Sclerosis (MS) lesions, quantifying disease burden, and monitoring treatment effects on white matter damage and brain atrophy, revealing microscopic damage even in seemingly normal areas.
MTI uses radiofrequency pulses to excite water protons in macromolecules like myelin, revealing the integrity and content of myelin sheaths, crucial for nerve signal transmission.
The MTI method is a selective tissue signal suppression technique in MRI. It is based on the magnetization transfer effect and provides quantitative measures like the Magnetization Transfer Ratio (MTR). The MTR reflects the protons bound to macromolecules in different tissues, which reveals the degree of proton exchange between free water and macromolecules. It primarily measures the degree of myelination, axon integrity, and macromolecules on the cell membrane of the central nervous system and provides pathological information such as overall disease burden, lesion severity, and brain tissue loss (atrophy).
The magnetization transfer (MT) effect of the brain arises from biological macromolecules in the neuronal cell membrane and organelle membranes, such as cholesterol, galactose cerebroside, and phospholipid in a myelin sheath. With MTR, the ability of these macromolecules to exchange magnetization with surrounding water molecules in the brain is measured.
MTR can be measured in different segments of the entire optic nerve, which provides useful information on the progressive nature of demyelination and remyelination over time. The decrease of MTR occurs due to axonal injury caused by demyelination and Waller degeneration, and the increase of MTR may indicate remyelination.
Kitsos et al. evaluated the brain and optic nerve pathways of 26 patients with POAG and found that the MTR of the optic chiasm, geniculocalcarine, and the visual cortex decreased significantly compared with the control group. Zhang et al. studied the geniculocalcarine and striatal region of patients with primary glaucoma by using the region of interest (ROI) analysis of MTR. They found that the MTR of bilateral geniculocalcarine and striatal region in patients with glaucoma decreased, suggesting that there is geniculocalcarine demyelination and degeneration of striatal region in primary glaucoma.
Ho et al., found that the MTR of the sclera, cornea, optic nerve, and the lens cortex in the glaucoma group was higher than that of the anterior chamber and the vitreous body.
However, MTI has a few limitations. It cannot identify the different types and stages of glaucoma, which may affect the results of the examination. A larger sample size of homogeneous samples should be carried out, and the clinical indicators of glaucoma, such as IOP and VF defect, should be associated with the changes of MTR to draw more convincing conclusions from studies using MTI.
No comments:
Post a Comment