New images through high magnetic field strengths
Thoralf Niendorf
Professor Niendorf, you lead the Experimental Ultrahigh Field MR lab at the Max Delbrück Center, which focuses on the potential of magnetic resonance imaging with extremely high magnetic field strengths. Was this also the theme of your conference?
Ultrahigh field magnetic resonance imaging (UHF-MR) was of course the focus of our symposium. But we also wanted to reach as many people with an interest as possible. To that end, there was also a presentation on MRI at low field strengths, which, unlike the procedures most used in clinics today, doesn’t operate at 1.5 or 3 Tesla but only at 0.55 Tesla. This method is significantly more cost-effective, which helps improve access to diagnostic imaging in less wealthy regions. We had 120 researchers attending the conference in person and about 170 participants joined online. Thanks to virtual participation, experts from around the world came together, including from the US, Australia and China.
What sort of progress did they report?
The focus of the clinical applications was the heart and kidneys. Diseases of these two organs are among the leading causes of death worldwide. In the case of the heart, the blood flow to the heart muscle and early functional disorders can be imaged with increasing ease and precision. I was particularly pleased with the results related to the kidneys.
Can you give an example?
Most kidney diseases are caused by a lack of oxygen. Until now, this hypoxia could not be diagnosed. There are markers that detect existing kidney damage, but they generally react too late. With UHF-MR, we can now image the oxygen content of the kidneys, which gives us something like an early warning system for the onset of kidney diseases.
How advanced is this form of early detection?
In animals, we can reliably image the oxygen content of the kidneys. Now, the challenge is to determine how these methods can be transferred to human medicine, where the scanners are much larger. The speakers presented that they can create images of the human kidney of good quality and with sufficient spatial resolution. This opens the door for feasibility studies on MR oximetry in humans.
What magnetic field strengths are needed for this?
The experimental studies were conducted at 9.4 Tesla, supporting the use of UHF-MR. However, there are currently only about 100 devices worldwide for use in human medicine that work at 7 Tesla. Despite this, we would like to see broader clinical use. That’s why we’ve taken on the challenge transferring this method to 3 Tesla, and we’ve been pretty successful at it.
How has heart imaging improved?
At 7 Tesla, we now not only get higher resolution and higher contrast images, but the images are also more uniform. The quality of the image now really reflects the properties of the tissue and not the interference. With a new method of parallel excitation, UHF-MR of the heart is now truly clinically applicable. Now we can see things that were previously hidden from us.
Where is UHF-MR already being successfully used in human medicine today?
It is well-established for brain imaging. It allows us to more easily diagnose and monitor the progression of neurodegenerative and neuroinflammatory diseases like Alzheimer’s, multiple sclerosis or epilepsy. The superior spatial resolution of UHF-MR-generated images also allows us to visualize tiny brain lesions that remain hidden at 3 Tesla. The fact that we are a bit behind when it comes to the heart is mainly because of its constantly being in motion.
What field strengths do you envision being used in the future?
Currently, there is exactly one device worldwide for human studies that operates at 10.5 Tesla. It’s located at the University of Minnesota in Minneapolis. The first 14 Tesla device for human use has also been approved and is under construction. In our own research group, we have also shown through simulations that cardiac MRI is feasible even at 21 Tesla, and that we are able to overcome any physical limitation.
What do you hope to achieve with devices of this kind?
We can achieve resolutions of just a few micrometers — and unlike conventional microscopy, we can do this in living, functioning organs. The second great advantage of UHF-MR is that it not only makes hydrogen nuclei visible, like conventional MRI scanners do, but also the nuclei of other elements such as sodium, potassium or phosphorus. All of these elements play a huge role in metabolism. In the future, we also want to make metabolic processes visible to us. Images of that kind will provide us with much better and earlier information about the causes and processes of diseases than morphological structures.
At the 15th Annual Scientific Symposium Ultrahigh Field Magnetic Resonance, scientists shared their latest findings in magnetic resonance imaging.
Why do we need higher magnetic field strengths to make these elements visible?
The reason is quite simple: They are present at much lower concentrations in the tissues. Hydrogen nuclei are much more abundant there.
What obstacles still need to be overcome on the way to widespread use?
The technical problems have largely been solved. At the moment, the biggest hurdles are economic. We need investors who believe in the enormous potential of UHF-MR and who are willing to fund these projects.
Don't such high field strengths also pose risks for the people being examined?
We consider the risks to be very manageable. It’s known that exposure to strong magnetic fields can lead to dizziness and cognitive impairments. However, all previous studies show that both symptoms disappear once you leave the magnetic field. Of course, we need to continue to investigate these effects in experimental studies. And we are able to do this: We can generate these magnetic fields, even if the corresponding MRI devices that work with them don’t yet exist.
Interview by Anke Brodmerkel.
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