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The right spin for quantum mechanics

New magnetic resonance techniques make it possible to observe biochemical processes in the body from the outside. The Inflammation Research Excellence Cluster wants to use this innovative approach to study the metabolism of intestinal bacteria.

Ilustration of quantums
© Hövener/pur.pur

Magnetic resonance imaging (MRI) is based on magnetic properties of hydrogen atomic nuclei. They align themselves in a magnetic field due to their spin. However, the signal is very weak. In a normal MRI (left), the signal of just a few atoms out of a million is used (violet arrows). Hyperpolarization (right) allows more molecules to align. This makes the MRT more sensitive.

Magnetic resonance imaging (MRT) is a great technique. It conjures up fantastic images from inside the body on the screen. "For example, we can watch the beating heart and observe in which region of the brain oxygen is consumed while I move my hand or think of chocolate ice cream," says Professor Jan-Bernd Hövener enthusiastically, only to discover, in a restrictive manner, that "the temporal, spatial and especially chemical resolution of MRI images is very limited. We are scratching the tip of the proverbial iceberg, but we know that there is much more under water that we could use for better diagnoses."

In order to get good MRI images at all, the clinic uses magnets with a strength of 1.5 to 3 Tesla. "Our research institute has a 7 Tesla machine. This is almost unimaginably strong - about 70 times stronger than a magnet that lifts cars at the scrap yard," says Hövener, who has held the professorship for translational magnetic resonance imaging since June 2017 and heads the Biomedical Imaging Section and the Molecular Imaging North Competence Center (MOIN CC) research center.

© pur.pur

Professor Jan-Bernd Hövener

Such strong magnetic fields are needed to induce the extremely weak atomic compass needles (nuclear spins) that are in every water molecule to align themselves even slightly to the north. "We know that there is a huge potential and that we could get much more and more important information from MRI." But that would require magnets of unimaginable strength. Hövener is pursuing an obvious alternative. He's trying to bind the MRI to himself. The tricks for this come from quantum mechanics.

Magnetic resonance is based on the so-called spin of atomic nuclei, which creates a magnetic moment not unlike that of a compass needle. Since hydrogen is present in each of our cells, these atomic compass needles are everywhere and can be used for imaging. However, they are so weak that at room temperature only a tiny fraction of them align along an external magnetic field.

The proportion of all spins that effectively "look" in one direction is called polarization and is a few millionths per tesla. The fact that the method still works is due to the large number of hydrogen nuclei in the body. Although the MRI only "sees" a few millionths of these, this is sufficient to assess the joint cartilage or measure the size of tumours, for example.

However, it is often not enough to depict metabolic processes that are of great medical interest. "The MR signal contains valuable chemical information," said Hövener. "However, the concentration of many metabolic products that are really interesting is far too low to be measured. The sensitivity of conventional technology is hardly sufficient for this", explains Hövener, who is very interested in chemical analysis using MRI and is establishing this technology in the Inflammation Research Excellence Cluster. "In principle we can do a virtual biopsy with MRI - we get the chemical information from the body without taking a sample or inserting a probe."

To get this information, the medical physicist uses so-called hyperpolarization methods. These are physical tricks that make the compass needles point in one direction so that they are more visible in the MRI. In order to study certain molecules, they are "polarized" in the laboratory, then injected or inhaled, and then followed their path in the body. What sounds so simple is quantum-mechanical and technically highly sophisticated. Initial experiments have shown that it basically works.

Hövener sees the benefit of this method, which is currently still experimental, particularly in the early detection of metabolic changes and therapy control. "The metabolism changes during therapy much earlier than macroscopic structures are remodeled. We hope to be able to see whether the therapy is effective a short time after it has started," said the physicist who is currently establishing a centre for hyperpolarisation research. "Thanks to the colleagues on site and the support of the university and faculty, the conditions in Kiel are ideal for this."

In the cluster, he plans to use hyperpolarisation MRI to investigate the metabolism of intestinal bacteria in detail. Hövener: "It is time to investigate inflammations with magnetic resonance and hyperpolarisation and to make a decisive contribution to their understanding and treatment. No one has ever examined the microbiome with this method. It seems to have a great influence on the inflammation of the intestine. We want to measure the metabolism non-invasively for the first time, first in cell culture and later in animals and humans. We hope to gain completely new insights into how the bacteria function and the daily interaction with them."

Author: Kerstin Nees