Modern simulations could improve MRIs to find disease more efficiently


An illustration based on simulations of engineers at Rice University shows a gadolinium ion (blue) in water (red and white), with water from the internal sphere – the water most affected by gadolinium – highlighting. The researchers’ models of gadolinium in water show that there is room for improvement in compounds used as contrast agents in clinical magnetic resonance imaging. Credit: Illustration by Arjun Valiya Parambathu

Rice engineers are finding more efficient models for analyzing contrast agents that detect disease.

Gadolinium-based contrast agents, the gold standard in magnetic resonance imaging (MRI) for determining a patient’s health, may be improved, according to engineers at Rice University who are refining the models they were first used to improve oil and gas recovery.

The team led by Dilip Asthagiri and Philip Singer of the George R. Brown School of Engineering had studied how nuclear magnetic resonance tools, commonly used in the oil industry to characterize underground deposits, could be optimized through molecular dynamics simulations.

“We touched on a lot of fundamental scientific questions there, and we wondered if there were other ways to use these simulations,” Asthagiri said.

“There are about 100 million MRI scans taken worldwide each year, and about 40% of them use gadolinium-based contrast agents, but the way they model the MRI response to these agents didn’t not changed significantly since the 1980s, ”Singer said. “We thought it would be a good test bed for our ideas.”

The results of their research are published in the journal of the Royal Society of Chemistry Chemistry Physical Physical Chemical.

Their paper demonstrates how limiting the number of parameters in simulations has the potential to improve the analysis of gadolinium-based contrast agents and how effective they are in imaging for clinical diagnosis. Their goal is to make better and more customizable contrast agents.

Gadolinium ion surrounded by DOTA in water

An illustration based on simulations by engineers at Rice University shows a gadolinium ion (dark blue) surrounded by a chelate known as DOTA in water. The chelate is needed to minimize the retention of gadolinium in the body after magnetic resonance imaging. Green atoms are carbon and light blue is nitrogen. Credit: Illustration by Arjun Valiya Parambathu

Doctors use MRI scanners to “see” the state of soft tissues inside the body, including the brain, by inducing magnetic moments in the hydrogen nuclei of water molecules that are always present for s ‘align along the magnetic field. The device detects bright spots when aligned nuclei “relax” to thermal equilibrium after excitation, and the faster they relax, the brighter the contrast.

This is where gadolinium-based paramagnetic contrast agents come in. “Gadolinium ions increase sensitivity and make the signal brighter by decreasing the T1 relaxation time of hydrogen nuclei,” said Asthagiri. “Our ultimate goal is to help optimize and design these agents. “

Typically, gadolinium is “chelated” – surrounded by metal ions – to make it less toxic. “The body does not clear gadolinium on its own and must be chelated so that the kidneys can get rid of it after a scan,” Singer said. “But chelation also slows molecular rotation, which creates better contrast in the MRI image.”

The researchers noted that “chelate” comes from the Greek word for claw. “In this case, those claws grab hold of the gadolinium to make it stable,” he said. “We hope that our models will help us design a stronger grip, which will make them more secure while maximizing their ability to increase contrast. “

They recognized that gadolinium chelates, which revolutionized MRI testing when they were introduced in the late 1980s, have been controversial of late since it was discovered that patients with kidney failure were unable to remove all toxins. “They have since established that if you have good kidney function, the benefits outweigh the potential risks,” Singer said.

The team is also adapting its models beyond interactions with water. “In biological systems, cells have other constituents like osmolytes and denaturants like urea, so we model gadolinium with these different environments to build toward a variety of applications,” Asthagiri said.

Reference: “Prediction 1H NMR relaxation in Gd3+-aqua using molecular dynamics simulations ”by Philip M. Singer, Arjun Valiya Parambathu, Thiago J. Pinheiro dos Santos, Yunke Liu, Lawrence B. Alemany, George J. Hirasaki, Walter G. Chapman and Dilip Asthagiri, September 7, 2021 , Chemistry Physical Physical Chemical.
DOI: 10.1039 / D1CP03356E

The co-authors of the article are Rice graduate students Arjun Valiya Parambathu, Thiago Pinheiro dos Santos and Yunke Liu; principal researcher Lawrence Alemany; George Hirasaki, AJ Hartsook Professor Emeritus and Research Professor; and Walter Chapman, William W. Akers professor of chemical and biomolecular engineering.

Vinegar Technologies LLC, Chevron Energy Technology, the Rice University Consortium on Processes in Porous Media, the Department of Energy Office of Science, and the Texas Advanced Computing Center at the University of Texas at Austin supported the research.

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