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MU engineering team's invention could lead to compact, portable X-ray source

Friday, February 8, 2013 | 6:00 a.m. CST
Brady Gall, a graduate research assistant and doctoral student in MU's Computer and Electrical Engineering Department, holds the the X-ray source in a laboratory Feb. 1 in Lafferre Hall. His team invented the source, which will be used to create compact, portable, battery-powered X-ray machines.

COLUMBIA — After months of staring at a blank computer monitor, Brady Gall saw a blue and white blip appear on the screen.

At first, Gall didn’t believe it. He and his team members’ morale had reached a low point, and they were beginning to think the device they were working on would never begin to produce X-rays like they wanted it to.

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But there they were — pixels bursting to life on his screen in the form of a graph that could mean only one thing: Four years of work, seven researchers’ mental energy and countless hours of tinkering, rethinking and retinkering had ended in invention.

Gall raced from his cluttered laboratory in MU's Lafferre Hall to the next room, where Scott Kovaleski, the leader of the project, was working.

"Dr. Kovaleski," Gall said. "I think we’re making X-rays."

The computer was registering X-rays generated by a device invented by Gall, an MU doctoral student in electrical engineering and a graduate research assistant, and Kovaleski, the interim chairman of MU's Electrical and Computer Engineering Department and an associate professor there. Also involved were current and former MU students including Mark Kemp, Andrew Benwell, Emily Baxter and James VanGordon.

The device, which produces X-rays in an unprecedented way, is likely to lead to the creation of compact, portable X-ray machines that would alter the way the technology is used in an array of fields and industries.

How it works

Normally, an X-ray source has three major components: a tube, a cathode and an anode. Both the cathode, a metal filament, and the anode, a positively charged disc of tungsten, are located inside of the tube.

A high-voltage electrical current is applied to the cathode, which heats it and causes it to emit electrons. The anode then pulls the electrons through the tube with great force. When the electrons hit the anode, X-rays are created.

The MU team’s device operates quite differently. It has one major component: a lithium niobate crystal, which Kovaleski referred to as "the magic material" that makes the X-ray source work.

The crystal is shaped like a long, thin stick of gum —  four inches long, half an inch wide and an eighth of an inch thick — and is partially covered in highly conductive silver paint.

To power the technology, an alternating electrical current of 10 volts is applied to one of the crystal’s ends. The current has to correspond to the particular frequency at which the crystal would "ring" if you were to, say, tap it with a small hammer.

This causes the crystal to swell and contract; in other words, it "squeezes" the crystal, Kovaleski said. The squeezing causes the 10-volt current to amplify into a 120,000-volt current, which draws electrons from the crystal and propels them forward. As soon as these electrons hit a metallic target, they turn into X-rays.


DIAGRAM: Portable X-ray source

An MU engineering team has developed a new type of radiation source that could lead to the creation of portable X-ray machines. The device uses a crystal the size of a piece of gum to amplify electrical currents and create X-rays. (Graphic: Libby Burns/Missourian)


"I compare it to pushing a kid on a swing," Gall said. "You don’t have to push really, really hard to get (the kid) going high. As long as you time the pushes right, it’ll start swinging more and more, and soon, without even breaking a sweat, the kid is going really, really high."

In Gall’s analogy, pushing the child higher is like applying the current and letting the crystal amplify it. He went on to say that if you were to give the swinging child a baseball, he would be able to throw the ball far, due to the height he had reached.

In the same way, electrons can be drawn and "thrown" from the crystal once the voltage reaches a certain "height."

New use for old knowledge

The MU device's ability to amplify currents using the "magic" crystal is one of the things that makes it innovative. It does this by reversing what's called the piezoelectric effect, in which stress is applied to certain kinds of crystal to create electricity.

The team's device flips the effect by using electricity to apply stress to the crystal.

Piezoelectric transformers, which harness the traditional effect, are used in common applications including gas grill lighters, some types of speakers, LCD monitors in laptops and halogen lights.

However, other piezoelectric transformers haven’t come close to creating the voltage the MU team’s new device does.

Those used in everyday capacities create about 30 volts. The transformer that generated the highest voltage the team has found in scientific literature created about 5,000 volts. The team’s device, on the other hand, can generate a whopping 120,000 volts.

Gall thinks the reason others haven’t pursued the technology, which the team stumbled upon while creating plasma for space propulsion applications, is because of its finicky nature.

"They’re very touchy," Gall said of working with the devices. "I know that’s not a technical term, but it’s the best way I can describe it. It’s almost like, if you get up on the wrong side of the bed in the morning, it’s not going to work."

Whereas other researchers have abandoned the technology after a few failed tests, the MU team persisted, Gall said.

"We had to think outside of the box. We had to think, 'How else can we probe this device?' or 'How else can we maybe take advantage of some aspect that other people were neglecting?' It’s really that sort of creative thinking that allowed us to demonstrate (that the technology works.)"

New device's advantages

At the moment, the device can be tweaked to produce two types of radiation: X-rays and, more recently, neutron radiation, which can be used in scanning applications similar to those of X-rays.

The technology’s nature allows it to effectively run on a battery and have an "on and off" function that could allow it to replace other radiation sources in a wide variety of industries.

Though there are some fairly portable X-ray sources out there, Kovaleski said these last two functions make the team’s device superior.

"They don’t have the operating capability, operating range or the versatility that our source has," Kovaleski said. "There are some really small sources that can make high voltages and X-rays, but they can only do it in very short bursts, and you can only do so many bursts.

"Ours, which is a similar power level, should be able to generate X-rays over much larger amounts of time with smaller amounts of power in a much smaller package."

Uses for a portable X-ray source

Kovaleski and Gall said a variety of fields and industries might gain from having portable X-ray sources.

Once the device is made into an X-ray machine — which could happen in as few as three years — it could have a major impact on medicine in rural and impoverished areas, for example.

Sometimes these areas don’t have a reliable enough power source to operate a traditional medical X-ray, Kovaleski said. Because the new X-ray machine will be battery-powered, it could be used to treat people in these areas. Doctors could use it after a disaster that eliminates power sources.

Its portability could reduce the amount of radiation patients are exposed to at the dentist. X-rays used in dentistry are placed around the outside of patients’ heads, which exposes much of the area to radiation. On the other hand, the MU team’s X-ray machine could be small enough to place inside of patients’ mouths, sending radiation through their cheeks as opposed to their entire heads.

"We like to eliminate radiation wherever we can," Kovaleski said. "It’s not that it’s not safe at current doses, but it’s just that it’s safer when there’s less."

Though it will not be powerful enough to replace airports’ full-body and luggage scanners, the X-ray machine could be used for a few other homeland security functions as well. Kovaleski said a bomb technician could use it to look inside of a bomb and determine how to disable it without touching it. This would reduce the risk of the bomb exploding while it’s being examined. 

Kovaleski said that if the team were to eventually develop a scanning machine that used their device's ability to produce neutrons, it could be used to check for nuclear material inside of things like cargo containers. 

Because of its ability to operate off a battery, the X-ray machine could be used in interplanetary rovers. These rovers, which often convert solar energy into battery power, could use the X-ray to analyze samples in a way they haven't been able to before. 

Additionally, the X-ray machine could help archaeologists to see inside of artifacts such as sarcophagi, geologists to better analyze samples and industrial radiographers to more easily inspect things like welds and die-casts. 

'On and off' capability

The device's other prominent characteristic, its "on and off" function, could allow the device to serve as a safer alternative to radioisotope radiation sources.

For example, it could change the way radiation sources are used in oil drilling, Kovaleski said. Usually, radioisotope sources are dropped into oil boreholes after they have been drilled so that information about the geology surrounding the hole can be gathered.

The problem is that radioisotope sources are inherently radioactive — there's no way to turn them on or off. So, if a radioisotope source gets stuck in a borehole and can't be retrieved, safety standards dictate the hole has to be filled in and drilled elsewhere, at a huge cost to the oil company.  

However, if a device that scanned using neutron radiation was created based on the team's invention, it could serve the same purpose as the radioisotope sources with only a fraction of the risk. Because the team's source can be turned on and off, if it got stuck in a borehole, the oil company need only to replace the device, rather than having to spend a massive amount redrilling the hole.

Next steps

For now, the team plans to work on creating images based on the device's X-ray output. Research on its ability to produce neutron radiation, which is in its early stages, will also continue.

"We've done two different experiments where we've demonstrated with statistical significance that, yes, we have neutrons, but it's not so much that we want to publish again," Gall said. "We have really promising initial results."

Kovaleski said he looks forward to seeing what the team's work leads to and is excited to see how scientists and innovators end up building on the team's invention in the future.

"By making things cheaper and smaller, you suddenly remove the limit for people to use their creativity and come up with stuff you never thought of," he said. "What I'm interested in is the stuff that I have not even considered that someone might be able to use a really low-power X-ray source to develop.

"If someone had something that was really low-power and cheap and small, what would they be able to do with it that hasn't occurred to me? That's what I want to find out."

Supervising editor is Elizabeth Brixey.


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