Nuclear Medicine News: Taking PET for a Walk
By Dave Yeager
Vol. 17 No. 11 P. 8
An experimental device may allow better imaging for a range of conditions.
PET imaging has many uses, but two of its limitations are that it requires patients to remain still and the scans can take as long as 80 to 130 minutes, depending on tracer uptake and clinical indication. A group of researchers at various institutions are working on a PET scanner prototype that would allow a patient who has difficulty remaining still—a person with Parkinson's disease, for example—to be imaged in a less restrictive setting in a shorter amount of time. The project is called the AM-PET Helmet (www.pethelmet.org).
Because it sits on the patient's head, the AM-PET Helmet can correct for motion better than a traditional PET scanner. The researchers are working to make the scanner more sensitive than traditional scanners as well, the goal being to increase the sensitivity by a factor of 10. This would allow patients to be scanned more often—most clinical guidelines recommend only one PET scan per patient per year—potentially speeding up the testing of pharmaceuticals for various medical conditions.
"We have a formula for building an imager that will be 10 times more sensitive [than current PET machines] to image the brain," says Stan Majewski, PhD, a physicist and a professor in the department of radiology and medical imaging at the University of Virginia.
Julie Brefczynski-Lewis, PhD, a research assistant professor in the department of physiology and pharmacology at the West Virginia University (WVU) School of Medicine, lead investigator, and the only neuroscientist on the team, says there are many potential uses for a mobile PET scanner.
"It applies to so many things. It applies to stroke rehabilitation and studying how walking and balance work in a real behavioral environment. Instead of somebody in an fMRI [functional MRI] scanner imagining that they're walking, you can actually have them walking. And that's what we're doing right now at WVU: We're adapting a system that's used in physical therapy," Brefczynski-Lewis says. "You can see what the brain is doing while they're walking or balancing and maybe, eventually, how it's different in someone with Parkinson's or someone learning to walk again after a stroke or someone with some sort of disorder affecting balance, which affects many elderly people as well as others."
The project was inspired by a concept at the US Department of Energy's Brookhaven National Laboratory involving the development of extremely small sensors. The researchers on that project made a very small detector that could fit on the head of a rat that they called the RatCAP. At the time, Majewski was working at the Thomas Jefferson National Accelerator Facility in Newport News, Virginia, and he filed a patent on a human imager, the PET Helmet.
In 2009, Majewski moved to WVU and began working with Brefczynski-Lewis. In 2014, he moved to the University of Virginia, but he continues to work on the project. He says researchers from all over the world are interested in the technology, and he has spent a lot of time finding collaborators and fundraising in the United States and abroad for the project.
Form Follows Function
The AM-PET Helmet consists of a ring of 12 2-in sensors, each one being a small imager with wires running from the sensor to a workstation. The workstation harmonizes the sensor channels to reconstruct an image of a section of the subject's brain. The weight of the helmet is supported by a harness system.
"The patient sits comfortably in a chair," Majewski says. "It has flexible supports similar to bungee cords, but they are very high-performance flexible cords. There is a bar mounted close to the ceiling, but it is still very flexible; the patient can move plus or minus 45 degrees and can lift it up. Most of the weight is supported by [the] mechanics [of the setup]."
The researchers are in the process of incorporating a Biodex Unweighing System with the helmet. Brefczynski-Lewis expects that process to be completed soon. She hopes to collect enough data from the helmet to take to the Society for Neuroscience conference in November.
There are researchers from several fields, such as neurological disorder studies, behavioral studies, and ambulatory studies, working on the project. Brefczynski-Lewis says they are exploring different uses because it may be advantageous to build different devices for different applications. Majewski adds that different designs come with trade-offs. For example, a more mobile design may have lower resolution and sensitivity, or an Alzheimer's scanner may require a longer scan but not require the patient to walk.
"Some of the changes that our team would like to make are optimizing the detectors and the electronics to have the best balance between being lightweight and having high sensitivity," Brefczynski-Lewis says. "It will be a couple of years before we have the whole ring in the right size and shape that we want. Then we can start thinking of becoming more widely available for commercialization."
Majewski says a mobile, high-performance PET imaging system could be useful for many conditions, such as glioblastoma, traumatic brain injury, dementia, or tremors. Brefczynski-Lewis says it could be highly useful for functional imaging as well. Along with tracking which parts of the brain light up when a subject performs a specific task, she is hoping to be able to see which neurotransmitters are being released in the brain and why.
"You can immerse someone in an environment that induces cravings, for example, and have them behave naturally in that environment, which is something you can't do with fMRI," Brefczynski-Lewis says.
The researchers are currently working with F-18 FDG to improve the scanner's temporal resolution and correlate their subjects' brain activity with their readings. Farther down the road, they are hoping to build a system small enough to be carried in a backpack or possibly a helmet with a Wi-Fi connection to the workstation. Majewski says he's talked to researchers at Stanford about working on the Wi-Fi aspect. In the meantime, the main factor that will determine the form and use of the AM-PET Helmet is money.
"We all believe that it's a good idea. We all believe that we need to go to the next stage," Majewski says. "We know how to build the next stage. We just need funding."
— Dave Yeager is the editor of Radiology Today.