Visualizing multiple sclerosis with a new MRI procedure

Multiple sclerosis (MS) is a neurological disease that usually results in permanent disability. It affects around 2.9 million people worldwide, including around 15,000 in Switzerland alone. One of the main characteristics of the disease is that it causes the patient’s immune system to attack and destroy the myelin sheaths of the central nervous system.

These protective sheaths insulate the nerve fibers, much like the plastic covering around a copper wire. Myelin sheaths ensure that electrical impulses travel quickly and efficiently from one nerve cell to another. If they become damaged or thin, it can lead to irreversible problems with vision, speech and coordination.

However, until now it has not been possible to visualize myelin sheaths well enough to reliably diagnose and treat MS. Researchers at ETH Zurich, led by Markus Weiger and Emily Baadsvik from the Institute of Biomedical Engineering, have developed a new magnetic resonance imaging (MRI) procedure that maps the state of myelin sheaths more precisely than before. The researchers successfully tested the procedure on healthy people for the first time.

Their research resulted in two articles, including one published in Scientists progress and one published in Magnetic resonance in medicine.

In the future, the MRI system, equipped with a special head scanner, could help doctors recognize MS at an early stage and better monitor the progress of the disease. The technology could also facilitate the development of new MS drugs. But it doesn’t stop there: the new MRI method could also be used by researchers to better visualize other types of solid tissue such as connective tissue, tendons and ligaments.

Quantitative myelin maps

Conventional MRI machines only capture indirect and inaccurate images of the myelin sheaths. This is because most of these devices work by reacting to water molecules in the body that have been stimulated by radio waves in a strong magnetic field. But the myelin sheaths, which surround nerve fibers in several layers, are mainly made of fatty tissue and proteins.

That said, there is water, known as myelin water, trapped between these layers. Standard MRIs construct their images primarily using signals from hydrogen atoms present in this myelin water, rather than directly imaging the myelin sheaths.

The new MRI method from ETH researchers solves this problem and directly measures the myelin content. It puts numerical values ​​on MRI images of the brain to show how much myelin is present in a particular area compared to other areas in the image. A number 8, for example, means that the myelin content at this stage is only 8% of a maximum value of 100, indicating significant thinning of the myelin sheaths.

Essentially, the darker the area and the smaller the number in the image, the more reduced the myelin sheaths have been. This information should allow doctors to better assess the severity and progression of MS.

Measure signals in a few millionths of a second

However, it is difficult to directly image myelin sheaths. This is because the signals that MRI triggers in tissues are very short-lived; signals emanating from myelin water last much longer.

“In simple terms, the hydrogen atoms in myelin tissue move less freely than those in myelin water. This means that they generate much briefer signals, which disappear again after a few microseconds,” explains Weiger. “And keeping in mind that a microsecond is equal to a millionth of a second, that is a very short time indeed.” A conventional MRI scanner cannot capture these fleeting signals because it does not take measurements quickly enough.

To solve this problem, the researchers used a specially customized MRI head scanner that they developed over the past 10 years in collaboration with the companies Philips and Futura. This scanner is characterized by a particularly strong magnetic field gradient. “The greater the change in the intensity of the magnetic field generated by the three coils of the scanner, the faster the information about the position of the hydrogen atoms can be recorded,” explains Baadsvik.

Generating such a strong gradient requires strong current and sophisticated design. Because researchers only scan the head, the magnetic field is more contained and concentrated than with conventional devices. Additionally, the system can quickly switch from transmitting radio waves to receiving signals; the researchers and their industrial partners have developed a special circuit for this purpose.

The researchers have already successfully tested their MRI procedure on tissue samples from MS patients and two healthy individuals. They then want to test it themselves on MS patients. Whether the new MRI head scanner will make its way into hospitals in the future now depends on the medical industry. “We’ve shown that our process works,” Weiger says. “It is now up to industrial partners to implement and market it.”