The (Totally True) Legend of Thomas Witzel and the Ultrahigh-field MRI Quench

Gary Boas

Sometimes we get the hero we need.

In the summer of 2017, the 7T MRI scanner at the MGH Martinos Center suffered a quench: a sudden loss of superconductivity resulting in a complete loss of the scanner’s magnetic field. In short, it broke. Without a magnetic field, the instrument was inoperable, unable to produce any kind of MR image.

A quench would be bad under the best of circumstances, but the outlook in this case was especially dire. The 7T, one of the most advanced MR scanners in the world when it was launched in the Center in 2001, had already outlived its design lifetime by six years. Worse still: Magnex Scientific, the UK-based company that built the magnet, had gone out of business some years before the quench, so the scanner was no longer supported by a vendor service contract. In more desperate moments, Center investigators would wonder whether it could ever be repaired.

Enter Thomas Witzel.

The director of the MR Imaging Core, Witzel is responsible for the maintenance and repair of all of the magnetic resonance instrumentation in the Center, including technical oversight of some of the most advanced scanners on the planet. Over the years, he has played an integral role in ensuring the smooth day-to-day operation of the Center’s many MR systems while spearheading major upgrade projects. A big bear of a man with an offbeat sense of humor, he is known far and wide as a technical maven, a veritable grandmaster in the world of MR hardware. If anyone could get the 7T up and running again, it would most certainly be him.

To help with the project—which was overseen by Center director Bruce Rosen and Larry Wald, director of the NMR Core at the Center—Witzel recruited Dick Marsh, a magnet service engineer with expertise in custom vacuum technology and cryogenics. Together, the two of them dove headlong into the many fixes needed to make the magnet operational again, tackling any problem they encountered with a combination of steely resolve and panache. “Thomas and Dick were a potent problem-solving team,” says Jason Stockmann, an instructor in the Center who develops MR hardware. Stockmann regularly contributed to the 7T recovery effort so he had a ringside seat to the seeming miracles the pair performed on a daily basis.

The seeming miracles were too numerous to list, he says, but a few examples give a good idea of the kinds of feats Witzel and Marsh regularly achieved. First, the magnet needed to be instrumented with new temperature, pressure, helium-level and boil-off sensors to allow data-logging of these parameters. But the original helium-level sensor was broken and inaccessible for repair, so they installed a new helium fill meter near the top of the cryostat to at least indicate when the magnet was full. Next, the magnet needed to be pre-cooled with liquid nitrogen to 77 Kelvin before switching to liquid helium for the final cool-down to below 4 Kelvin to achieve superconductivity in the niobium-titanium wires.  Before switching over to liquid helium, Witzel and Marsh had to be absolutely certain that no ice had formed in the cryostat during this process—nitrogen will freeze below 77 Kelvin. If it did, the consequences in the event of a second quench could be calamitous.

Finally, they had to figure out how to connect to and ramp current into the main field coil and the superconducting “shim” coils. This step called for them to open and close a superconducting switch in the coil while tremendous amounts of current were flowing in the loop: equivalent to some 20 kg of TNT.  So it required “not only great expertise,” Stockmann says, “but also a fair bit of courage.”

They achieved all of this and more using old, incomplete documentation that came with the magnet in 2001.

The recovery operation wrapped up in September of 2018 and the 7T is now humming along as it was before the quench. Thanks to the sterling efforts of Witzel and Marsh, Center investigators whose research depends on the magnet can now get back to the business of wielding it to address a broad range of important biomedical questions.

Stockmann marvels at what the pair accomplished.

“Thomas and Dick received some advice from magnet engineers in England,” he says, “but mostly they had to piece things together themselves using their wits, what little documentation they had access to, and some MacGyver-style improvisation. Only a few people in the world have the skills, expertise, audacity and tenacity to pull this off.”

The project was such an unequivocal success that Stockmann and other faculty who use the magnet decided they should do something both to applaud Thomas’ successful recovery operation and to express their gratitude to him.

So, on a chilly day in early October, they feted Witzel during one of the Center’s “Science on Tap” Friday afternoon socials, presenting him with tokens of their appreciation and bestowing upon him the first-ever “Golden Bore” award. (In keeping with the DIY spirit of the day, the trophy was based on a 3D model made by Stockmann’s brother; Stockmann himself 3D-printed the model and spray-painted it gold.) Witzel was initially perhaps a tiny bit annoyed to have been put on the spot; he is generally not a fan of being the center of attention. But in the end he realized how sincerely grateful the others were and graciously accepted the award.

“It was just a small gesture by us,” Stockmann says, “but we felt it was important to publicly thank Thomas for what can only be called a heroic effort.”