Hyperpolarization: "An MRI device the size of two to three shoeboxes could soon sit on your desk"

Interview with Dr. Jan-Bernd Hövener, University Medical Center Freiburg

Magnetic resonance imaging (MRI) is a well-established procedure in clinical diagnostics. It creates a signal with millions of nuclear spins, which in turn is converted into images. Very large magnets are being used to align the nuclear spins. Researchers at the University Medical Center Freiburg study a new method that can do without expensive magnets. Dr. Jan-Bernd Hövener, head of the research team reveals more about hyperpolarization and the opportunities this method provides for medical technology.


Photo: Dr. Jan-Bernd Hövener

Dr. Jan-Bernd Hövener; ©private

MEDICA.de spoke with him about compass needles, parahydrogen and MRI devices the size of shoeboxes.

Dr. Hövener, what is hyperpolarization?

Jan-Bernd Hövener: Hyperpolarization serves to tap into previously unutilized MRI potential. The signal that creates the MR image is generated with the help of nuclear spins. The nuclear spins can be envisioned as small compass needles in the nucleus. However, unlike a compass needle, which we know from a hiking compass for example, the nuclear spins are very light.

If you gave every person on Earth a hiking compass, seven billion compass needles would point north. If we made an MR image of this, we would also receive the signal strength of seven billion compass needles. The compass needles from an MRI however, are much weaker. If we gave every person on Earth such a nuclear spin to hold, almost all of the spins would point in different directions. On average, only about a handful of the seven billion nuclear spins point north. The MRI signal’s strength is only about one-billionth of the Earth’s magnetic field, even though its potential is much greater. This is why strong magnets are needed for diagnostics to align a larger, but still very small number of these nuclear spins.

A magnet in the MRI machine has a magnetic field strength of 1.5-3 Tesla. By comparison, magnets that lift cars at a junkyard have approximately 0.1-0.2 Tesla magnetic field strength– thus up to 20 times less. You are able to align significantly more of these nuclear compass needles with that amount of magnet field strength; however, it’s still only a small portion. A 3-Tesla tomograph aligns less than ten pieces out of a million. The goal of hyperpolarization is to significantly increase the number of nuclear spins that "point north".
Grafic: Hyperpolarization

The goal of hyperpolarization is to significantly increase the number of nuclear spins that are used in a MRI machine; © Hövener

There are various hyperpolarization methods that have in part been known for decades and that are being studied. What distinguishes your method from others?

Hövener: The previous hyperpolarization methods have achieved amazing results, but they all have a few weak points. On the one hand, the hyperpolarized signal is transient – it only exists for a certain amount of time. On the other hand, the molecules can only be polarized one time with the previous methods. Generally, they cannot be reused and aligned again. Moreover, the aligned nuclear spins are being destroyed by the MRI sequence itself.

How do you avoid these challenges with the new method?

Hövener: We conduct the hyperpolarization by parahydrogen and a catalyst. Hydrogen gas has special properties with which we are able to continuously align specific molecules – as long as there is parahydrogen. Even though polarization is still destroyed by an MRI measurement, it restores again within a few short seconds. We are also able to absorb every molecule as frequently as we like with the gas.

What advantages does parahydrogen offer compared to a magnet?

Hövener: Magnets that are used in MRI devices are very large and heavy. A machine that operates with parahydrogen no longer needs this expensive magnet to produce magnetization of polarized molecules. In this case, a two-kilogram magnet with a strength of five-thousandth of one Tesla is enough. In terms of space, you can envision the MRI device to be the size of about two to three shoeboxes that you can place on your desk. We can align nuclear spins in some molecules as if we had a large 100 Tesla or larger magnet. Such magnets are currently not feasible.

However, we need to expressly point out that our method is currently still in the fundamental research phase. Right now, we are able to create beautiful images of a test tube, but not of living organisms yet.
Photo: Dr. Hövener in his laboratory

Dr. Hövener and his colleagues conduct the hyperpolarization by parahydrogen and a catalyst. This gas has special properties that allow to tap into previously unutilized MRI potential; © private

What risks does hyperpolarization involve?

Hövener: A traditional MRI uses a native signal, meaning the signal produced by the object itself and the magnetic field. This is why we also see the entire hand when we image a hand. This is not possible with hyperpolarization: we polarize a contrast agent, which you are then able to see. Giving a contrast agent always involves risk.

However, this method has big advantages for specific applications. If you had a contrast agent for a specific tissue such as a tumor for instance, the MRI is also only going to show the tumor tissue.

How else could you utilize the MRI’s potential?

Hövener: We know from chemistry and biomedicine that magnetic resonance can measure metabolism. Therefore, it is not just able to generate the well-known black and white images, but can also provide physiological and metabolic information. Imagine you wouldn’t need to remove tissue to measure values, but would be able to calculate them from the outside. This was also the hope of researchers when MRI was invented, and this method, called spectroscopy works. However, it turned out that the signal is generally too weak to measure many important diagnostic parameters. Hyperpolarization may be a method with which this early promise can be fulfilled. There is intensive research all over the world in this area.

For which other areas of research could hyperpolarization by parahydrogen be relevant?

Hövener: In medicine, this procedure is not just conceivable for patient use, but also in preclinical research, for instance for research into the behavior of certain cells compared with other cells or substances. During the course of continued research it might turn out that hyperpolarization is not suited for an application with patients, but is a valuable tool for fundamental research in medicine as well as physics. That alone would be a tremendous success. Interestingly, a few days ago I was contacted by someone who wants to use hyperpolarization for soil research to measure soil properties with magnetic resonance. So many different areas would be conceivable for this application.

Read more about this topic in the original article by Dr. Hövener and his colleagues: Hövener J.-B., Schwaderlapp N., Lickert T., Duckett S.B., Mewis R.E., Highton L.A.R., Kenny S.M., Green G.G.R., Leibfritz D., Korvink J.G., Hennig J., von Elverfeldt D. A hyperpolarized equilibrium for magnetic resonance. Nature Communications, 2013.doi: 10.1038/ncomms3946
Photo: Michalina Chrzanowska; Copyright: B. Frommann

© B. Frommann

The interview was conducted by Michalina Chrzanowska and translated by Elena O'Meara.