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Technique Enhances MRI Images for Cartilage, Brain Tissue

MRI machine (NIH)

MRI machine (NIH)

Radiologists and chemists at New York University devised a method to improve magnetic resonance images (MRIs) usually obscured by large molecular masses, when using a common method for chemically saturating certain molecules. The team led by NYU radiologist Ravinder Regatte and chemist Alexej Jerschow reported their findings last week in the online journal Scientific Reports.

The NYU researchers studied MRIs using an image enhancement technique known as chemical exchange saturation transfer that sorts out the varying signals emitted by protons in different molecules. The technique selectively saturates proton signals associated with targeted molecules exchanged with surrounding water molecules to enhance their visibility.

Problems occur with chemical exchange saturation transfer, however, in the presence of large, complex molecules like proteins and carbohydrates, known as macromolecules. Because of their size and frequent presence in the body, macromolecules obscure the smaller molecules of interest when using this transfer technique. Regatte, Jerschow, and colleagues sought a way to neutralize the interference of macromolecules, which occurs with scans of skeletal and brain tissue.

In earlier work, the researchers developed and tested a non-invasive imaging technique for enhancing images of glycosaminogycan molecules, found as building blocks in cartilage tissue, using chemical exchange saturation transfer (CEST). The technique separated glycosaminogycan protons from the surrounding water molecules, which provided an available contrast agent for monitoring with MRI scans.

This enhancement technique may have enabled better MRIs of glycosaminogycan, but the images were still obscured by macromolecules. In the new paper, the NYU team used multiple irradiation frequencies to first highlight and detect the wider range of frequencies emitted by the macromolecules, and then neutralize their signals in the MRI scans. The researchers tested the technique with MRI scans of knee joints of five healthy male volunteers.

“We have found a way to eliminate signals of certain molecules,” says Jerschow, “and thereby clean up the image of parts of the body that could be used by medical professionals in order to make diagnoses.” Those parts of the body include brain tissue, as well as skeletal tissue like cartilage.

“This method,” adds Regatte, “gives us the opportunity to correct existing CEST methods by focusing on molecular signals of interest with much better precision than currently exists.”

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