Atomic sensors reveal hidden dynamics of molecular polarization

Magnetic resonance imaging (MRI) has long been a cornerstone of modern medicine, providing highly detailed images of internal organs and tissues. MRI machines, large tube-shaped magnets commonly found in hospitals, use powerful magnets to map the densities of water and fat molecules in the body.

In addition to these molecules, other substances like metabolites can also be mapped, but their concentrations are often too low to produce clear images. To overcome this limitation, a technique known as hyperpolarization is used to enhance the magnetic resonance signal of these substances, making them more visible during MRI scans.

Hyperpolarization involves preparing a substance outside the body to a state where its magnetization, essential for creating MRI images, is near its maximum. This process can increase the signal thousands of times compared to its natural state. Once hyperpolarized, the substance is injected into the patient and transported to the target organ or tissue. However, before this happens, it is crucial to confirm that the substance is correctly hyperpolarized through rigorous quality control processes.

Current quality control techniques face two significant challenges. First, these methods often reduce the magnetization of the sample during the reading process, thereby decreasing its ability to improve MRI analysis. Second, the time required for the measurement can be long, during which the magnetization of the substance naturally decreases, thus limiting the possibility of consecutive measurements. This results in a lack of critical data that could otherwise help maximize the effectiveness of hyperpolarization.

Additionally, once the sample is hyperpolarized, there is a risk that it will lose its magnetization during transport to the MRI machine. Traditional quality control techniques, due to their slowness, may not detect this loss of time.

Today, a collaboration between IBEC researchers Dr. James Eills (now at Forschungszentrum Jülich, Germany) and Dr. Irene Marco Rius, as well as ICFO researchers Professor Morgan W. Mitchell and Dr. Michael CD Tayler, demonstrated how atomic sensor techniques overcome limitations. conventional sampling when measuring the magnetization of hyperpolarized materials. This advance was recently reported in the journal Proceedings of the National Academy of Sciences.

The team notably used optically pumped atomic magnetometers (OPM), whose operating principles fundamentally differ from traditional sensors, making it possible to detect in real time the fields produced by hyperpolarized molecules. The nature of OPMs allowed these researchers to perform continuous, high-resolution, non-destructive observations throughout the entire experiment, including the hyperpolarization process itself.

According to the authors, if the domain of hyperpolarization detection were cinema, previous methods would be akin to a sequence of still photos, leaving the plot between the freeze frames open to the viewer’s suggestion.

“Instead, our technique is more like a video, where you see the whole story frame by frame. Essentially, you can observe continuously and without resolution limits, and this way you don’t miss any details,” explains Dr. Michael Tayler, ICFO. researcher and co-author of the article.

Revealed behaviors of chemical compounds during magnetization

The team tested their OPMs by monitoring the hyperpolarization of clinically relevant molecules. The unprecedented resolution and real-time tracking of atomic sensors allowed them to observe how polarization in a metabolite compound ((1-¹³C)-fumarate) evolved in the presence of a magnetic field.

The atomic sensors revealed “hidden spin dynamics” that had gone unnoticed until now, providing a new route to optimizing hyperpolarization early in the process.

“Previous methods masked subtle oscillations in the magnetization profile, which were previously undetected,” notes Tayler. “Without OPM, we would have reached suboptimal final polarization without even realizing it.”

Beyond simple observation, the method could be used to control the polarization process in real time and stop it at the most opportune moment, for example when maximum polarization is reached.

The study revealed another unexpected behavior when the team applied a magnetic field to repeatedly magnetize and demagnetize the hyperpolarized fumarate molecule. They expected to see the magnetization increase to a maximum and then return to zero again and again, each time moving smoothly from one state to the next. Contrary to these simple expectations, the molecule exhibited complex dynamics due to hidden resonances at certain magnetization-demagnetization durations and magnetic fields.

“This understanding will help us detect unwanted behaviors and adjust parameters (like cycle duration or magnetic field strength) to avoid them,” says Tayler.

The work represents an advancement in hyperpolarized MRI technology, thanks in large part to the collaborative efforts of IBEC’s Molecular Imaging for Precision Medicine Group and ICFO’s Atomic Quantum Optics Group. IBEC’s expertise in hyperpolarization methods and ICFO’s expertise in OPM detection technologies were essential in achieving the results.

“This is a great example of the new science that can be achieved when researchers from different disciplines work together, and the proximity of IBEC and ICFO has allowed us to collaborate closely and achieve something truly new “, recognizes Dr. James Eills, IBEC. researcher and first author of the article.

Dr. Tayler reflects on the team’s success, saying: “The OPM measures worked wonderfully from the start. The exquisite sensitivity of the sensors revealed hidden dynamics that we had not anticipated, as if they were intended for this purpose. The ease of use and wealth of new information make it a powerful tool for hyperpolarization monitoring.

Benefits for MRI and other future applications

The immediate application of this study would be to integrate portable atomic sensors in the quality control of clinical samples for MRI, which is currently implemented by the ICFO team of the Spanish Ministry project “SEE-13 -MRI”. In this way, one could guide the molecules to the highest possible polarization level during hyperpolarization and reliably certify the polarization level before the substances are injected into patients.

This development could significantly reduce the costs and logistical challenges of metabolic MRI. If so, this would expand its reach from the handful of specialized research centers where it is currently used to many hospitals around the world.

However, the potential of atomic sensors extends well beyond medical imaging. The same real-time non-destructive tracking system using optically pumped magnetometers (OPMs) could be applied to monitor macromolecules in chemical processes, study high-energy physics targets, or even optimize spin-based algorithms in the quantum computing.

According to Dr. Tayler, “The method we developed opens new avenues not only for improving MRI, but also for various fields that rely on precise magnetic detection, and we are excited about its further development. »