Analysis of MRI contrast agents: Engineers dig deep to detail magnetic mechanism of gadolinium-based agents

You can keep your best guesses. Engineers at Rice University’s George R. Brown School of Engineering are starting to understand exactly what goes on when doctors pump contrast agents into your body for an MRI scan.

In a new study that could lead to better scans, a Rice-led team digs deeper via molecular simulations that, unlike earlier models, make absolutely no assumptions about the basic mechanisms at play when gadolinium agents are used to highlight soft tissues.

The study led by Rice chemical and biomolecular engineer Philip Singer, former associate research professor Dilip Asthagiri, now of Oak Ridge National Laboratory, and graduate student Thiago Pinheiro dos Santos appears in Physical Chemistry Chemical Physics.

It employs the sophisticated models first developed at Rice for oil and gas studies to conclusively analyze how hydrogen nuclei at body temperatures “relax” under nuclear magnetic resonance (NMR), the technology used by magnetic resonance imaging, aka MRI.

Doctors use MRI to “see” the state of soft tissues, including the brain, in a patient by inducing magnetic moments in the hydrogen nuclei of water molecules to align with the magnetic field, a process that can be manipulated when gadolinium agents are in the vicinity. The device detects bright spots when the aligned nuclei relax back to thermal equilibrium following an excitation. The faster they relax, the brighter the contrast.

Gadolinium molecules are naturally paramagnetic and sensitive to magnetic excitation. Because they’re toxic, they are usually chelated when part of a contrast agent. “A chelate basically hugs the gadolinium and protects your body from directly interacting with the metal,” Pinheiro dos Santos said. “We’re asking, exactly how do these molecules behave?”

Though gadolinium-based contrast agents are injected by the ton into patients each year, how they work on a molecular level has never been fully understood.

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