‘Wearable’ PET brain scanner enables studies of moving patients

Julie Brefczynski-Lewis, a neuroscientist at West Virginia University, places a helmet-like PET scanner on a research subject. The mobile scanner enables studies of human interaction, movement disorders, and more. (credit: West Virginia University)

Two scientists have developed a miniaturized positron emission tomography (PET) brain scanner that can be “worn” like a helmet.

The new Ambulatory Microdose Positron Emission Tomography (AMPET) scanner allows research subjects to stand and move around as the device scans, instead of having to lie completely still and be administered anesthesia — making it impossible to find associations between movement and brain activity.

Conventional positron emission tomography (PET) scanners immobilize patients (credit: Jens Maus/CC)

The AMPET scanner was developed by Julie Brefczynski-Lewis, a neuroscientist at West Virginia University (WVU), and Stan Majewski, a physicist at WVU and now at the University of Virginia. It could make possible new psychological and clinical studies on how the brain functions when affected by diseases from epilepsy to addiction, and during ordinary and dysfunctional social interactions.

The AMPET idea was sparked by the Rat Conscious Animal PET (RatCAP) scanner for studying rats at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory.** The scanner is a 250-gram ring that fits around the head of a rat, suspended by springs to support its weight and let the rat scurry about as the device scans. (credit: Brookhaven Lab)

Because AMPET sits so close to the brain, it can also “catch” more of the photons stemming from the radiotracers used in PET than larger scanners can. That means researchers can administer a lower dose of radioactive material and still get a good biological snapshot. Catching more signals also allows AMPET to create higher resolution images than regular PET.

The researchers plan to build a laboratory-ready version next.

Seeing more deeply into the brain

A patient or animal about to undergo a PET scan is injected with a low dose of a radiotracer — a radioactive form of a molecule that is regularly used in the body. These molecules emit anti-matter particles called positrons, which then manage to only travel a tiny distance through the body. As soon as one of these positrons meets an electron in biological tissue, the pair annihilates and converts their mass to energy. This energy takes the form of two high-energy light rays, called gamma photons, that shoot off in opposite directions. PET machines detect these photons and track their paths backward to their point of origin — the tracer molecule. By measuring levels of the tracer, for instance, doctors can map areas of high metabolic activity. Mapping of different tracers provides insight into different aspects of a patient’s health. (credit: Brookhaven Lab)

PET scans allow researchers to see farther into the body than other imaging tools. This lets AMPET reach deep neural structures while the research subjects are upright and moving. “A lot of the important things that are going on with emotion, memory, and behavior are way deep in the center of the brain: the basal ganglia, hippocampus, amygdala,” Brefczynski-Lewis notes.

“Currently we are doing tests to validate the use of virtual reality environments in future experiments,” she said. In this virtual reality, volunteers would read from a script designed to make the subject angry, for example, as his or her brain is scanned.

In the medical sphere, the scanning helmet could help explain what happens during drug treatments. Or it could shed light on movement disorders such as epilepsy, and watch what happens in the brain during a seizure; or study the sub-population of Parkinson’s patients who have great difficulty walking, but can ride a bicycle .

The RatCAP project at Brookhaven was funded by the DOE Office of Science. RHIC is a DOE Office of Science User Facility for nuclear physics research. Brookhaven Lab physicists use technology similar to PET scanners at the Relativistic Heavy Ion Collider (RHIC), where they must track the particles that fly out of near-light speed collisions of charged nuclei. PET research at the Lab dates back to the early 1960s and includes the creation of the first single-plane scanner as well as various tracer molecules.

3D-printed ‘bionic skin’ could give robots and prosthetics the sense of touch

Schematic of a new kind of 3D printer that can print touch sensors directly on a model hand. (credit: Shuang-Zhuang Guo and Michael McAlpine/Advanced Materials )

Engineering researchers at the University of Minnesota have developed a process for 3D-printing stretchable, flexible, and sensitive electronic sensory devices that could give robots or prosthetic hands — or even real skin — the ability to mechanically sense their environment.

One major use would be to give surgeons the ability to feel during minimally invasive surgeries instead of using cameras, or to increase the sensitivity of surgical robots. The process could also make it easier for robots to walk and interact with their environment.

Printing electronics directly on human skin could be used for pulse monitoring, energy harvesting (of movements), detection of finger motions (on a keyboard or other devices), or chemical sensing (for example, by soldiers in the field to detect dangerous chemicals or explosives). Or imagine a future computer mouse built into your fingertip, with haptic touch on any surface.

“While we haven’t printed on human skin yet, we were able to print on the curved surface of a model hand using our technique,” said Michael McAlpine, a University of Minnesota mechanical engineering associate professor and lead researcher on the study.* “We also interfaced a printed device with the skin and were surprised that the device was so sensitive that it could detect your pulse in real time.”

The researchers also visualize use in “bionic organs.”

A unique skin-compatible 3D-printing process

(left) Schematic of the tactile sensor. (center) Top view. (right) Optical image showing the conformally printed 3D tactile sensor on a fingertip. Scale bar = 4 mm. (credit: Shuang-Zhuang Guo et al./Advanced Materials)

McAlpine and his team made the sensing fabric with a one-of-a kind 3D printer they built in the lab. The multifunctional printer has four nozzles to print the various specialized “inks” that make up the layers of the device — a base layer of silicone**, top and bottom electrodes made of a silver-based piezoresistive conducting ink, a coil-shaped pressure sensor, and a supporting layer that holds the top layer in place while it sets (later washed away in the final manufacturing process).

Surprisingly, all of the layers of “inks” used in the flexible sensors can set at room temperature. Conventional 3D printing using liquid plastic is too hot and too rigid to use on the skin. The sensors can stretch up to three times their original size.

The researchers say the next step is to move toward semiconductor inks and printing on a real surface. “The manufacturing is built right into the process, so it is ready to go now,” McAlpine said.

The research was published online in the journal Advanced Materials. It was funded by the National Institute of Biomedical Imaging and Bioengineering of the National Institutes of Health.

* McAlpine integrated electronics and novel 3D-printed nanomaterials to create a “bionic ear” in 2013.

** The silicone rubber has a low modulus of elasticity of 150 kPa, similar to that of skin, and lower hardness (Shore A 10) than that of human skin, according to the Advanced Materials paper.


College of Science and Engineering, UMN | 3D Printed Stretchable Tactile Sensors


Abstract of 3D Printed Stretchable Tactile Sensors

The development of methods for the 3D printing of multifunctional devices could impact areas ranging from wearable electronics and energy harvesting devices to smart prosthetics and human–machine interfaces. Recently, the development of stretchable electronic devices has accelerated, concomitant with advances in functional materials and fabrication processes. In particular, novel strategies have been developed to enable the intimate biointegration of wearable electronic devices with human skin in ways that bypass the mechanical and thermal restrictions of traditional microfabrication technologies. Here, a multimaterial, multiscale, and multifunctional 3D printing approach is employed to fabricate 3D tactile sensors under ambient conditions conformally onto freeform surfaces. The customized sensor is demonstrated with the capabilities of detecting and differentiating human movements, including pulse monitoring and finger motions. The custom 3D printing of functional materials and devices opens new routes for the biointegration of various sensors in wearable electronics systems, and toward advanced bionic skin applications.