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Ghost Of A Chance

Spectral CT offers new possibilities.

A research team in New Zealand led by Anthony Butler, MB, ChB, PhD, a radiologist at the University of Otago, Christchurch in New Zealand, has designed a new scanner that can capture 3D color X-rays of the human body. Its developers believe that this tool, which utilizes a Medipix3 chip, will someday assist in diagnosing cancers and blood diseases without invasive surgery.

"It functions much like a camera and allows us to see the details of various tissues, such as bones, fats, water, and cartilage," Butler says. "It's a whole new X-ray experience and a big upgrade from black-and-white film."

He explains that the scanner counts subatomic particles as they meet pixels when its electronic shutter is open, allowing it to generate high-resolution images of soft tissues, including minute disease markers.

"The scanner matches individual X-ray photon wavelengths to specific materials and then assigns a corresponding color to the scanned objects," Butler says. "The tool then translates the data into a three-dimensional image."

Gary E. Friedlaender, MD, an orthopedic surgeon at Yale University, says by linking the slices together in this way, one can literally visualize the three dimensions and manipulate them, and, while not new, MARS Bioimaging has done it in a way that is highly effective.

"What they've added is the ability to differentiate tissues, and they've used arbitrary colors to identify those tissues," he says. "It's been done on a grayscale, with black and white, but they've added these dynamic colors, which will make a difference."

From Particles to Animals Butler's father, Phil, is a medical and particle physicist who was on the New Zealand team at CERN, the European Organization for Nuclear Research, evaluating detectors for a large hadron collider. Butler explains that CERN in the '70s and '80s was looking at new ways to measure particles for its experiments, and the researchers knew that the older system was not going to offer enough functionality in the modern computer world, so they developed direct conversion detectors. These direct conversion detectors, also called photon counting detectors, take a particle such as an X-ray photon and turn it into an electrical current. The detectors then analyze the current and provide a signal, allowing researchers to analyze a particle beam in any way they want.

"I had just finished my radiology residency, and I actually also just finished my PhD," Butler says. "My father said, 'Why don't you look at the stuff at CERN and see if it's really going to be useful?'"

So, starting in 2005, Butler and his team began working with that technology to build CT scanners and, in 2007, released their first one—a four-energy photon counting spectral CT scanner.

"We always had in the back of our mind that it was one thing to build a CT scanner. It was really important to understand how it could be used," Butler says, "We brought in a team of about 50 people in New Zealand; a third of them worked for MARS Bioimaging Ltd, and the other two-thirds worked at the university's physics department."

At the time, the team was looking at ex vivo specimens—surgical specimens and animal models of disease in mice, rabbits, rats, etc, and spent the next four years translating its findings to human imaging.

"The first human photon counting CT was actually done in Israel in 2008. That proved that you could scale the technology up in terms of speed, but it wasn't really practical and they gave up shortly after," Butler says. "What we've done is, by focusing on the small animal models, we've really had a good understanding of how this sort of technology can help in things like heart disease or cardiovascular disease and how it can be used to personalize medicine in cancer and seeing the targeted nanoparticles and nanoprobes that are coming out of the pharmaceutical industry."

Additionally, the team looked at bone health, imaging the microstructure of the bone and then simultaneously providing information about the mineralization of the bone in a way that can nearly eliminate metal artifacts.