Some of medicine's smallest patients can present its biggest imaging challenges. An infant's heart can be as small as a walnut, beating rapidly inside a body that will change dramatically as the child grows. Yet much of the equipment used in MRI comes in standard sizes better suited to adult bodies, and customized versions can cost thousands of dollars and take months or even years to manufacture.
USC researchers have developed a potential solution: flexible MRI sensors that can be customized to individual patients and 3D-printed in less than 10 minutes for about $30. In testing, the sensors produced roughly four times greater image contrast than standard commercial versions.
"By making customized MRI equipment faster and more affordable to produce, we have the potential to bring better imaging to patients who have traditionally had fewer options, especially infants and children," said Yasser Khan, assistant professor of electrical and computer engineering and biomedical engineering at the USC Viterbi School of Engineering, whose lab at the USC Michelson Center for Convergent Bioscience designs and 3D-prints the customized coils.
Paired with specialized MRI technology at the USC Michelson Center, the sensors can also help capture anatomy in motion, including something as small and fast-moving as a beating heart.
"We're bringing a level of precision and customization to MRI that isn't available today," he said.
A better fit for growing bodies
MRIs use powerful magnets and radio waves to generate signals from inside the body, which a computer then turns into detailed images. Devices called coils act like antennas to pick up those signals, and the closer they fit to the area being scanned, the clearer the image can be.
That makes fit especially important for small patients. A coil designed for an adult may leave gaps when placed around an infant or child, making it harder to capture a strong signal. And because children grow rapidly, equipment that fits at one stage may not fit as well a few years or even months later.
Khan compares the challenge to choosing the right camera lens.
"If you use a large lens to image something very small, you're not going to get the clearest picture," Khan said. "But if you can tailor the lens, in this case the MRI coil, to the individual patient, you can capture a much better image."
The researchers wanted to make a coil that could closely follow the contours of the body rather than leave space between the sensor and the skin. That required rethinking both the material and the way MRI coils are manufactured.
After about three years of experimentation, Khan's team developed a process for 3D printing conductive silver ink onto a thermoplastic elastomer, a soft, stretchable material with properties similar to human skin. The material can stretch roughly 5% to 10%, allowing the coil to bend and move with the body.
The team tested different flexible materials, plastics and formulations of printable metal before arriving at the combination of silver ink and thermoplastic elastomer. The researchers also had to develop the electronics needed to connect the unconventional coils to an MRI system.
Because the coils begin as digital designs, their dimensions can be changed quickly. A researcher can adjust the size or shape on a computer and print a new coil rather than wait for a specialized part to be manufactured.
"For a growing child, that could mean creating different coils as the body changes," Khan said. "The goal is to give children access to imaging equipment designed for their bodies, so doctors can get the clearest picture possible as they grow."
Built and tested under one roof
The technology grew out of the kind of interdisciplinary collaboration the USC Michelson Center was designed to foster, bringing engineers, imaging scientists and clinicians together to tackle complex challenges and accelerate scientific discovery.
In this case, two labs brought complementary expertise to the same problem.
The Khan Lab specializes in flexible and wearable electronics, including devices that can bend, stretch and conform to the body.
The Dynamic Imaging Science Center (DISC), led by Krishna Shrinivas Nayak, professor of electrical and computer engineering and biomedical engineering at USC Viterbi, develops advanced MRI technologies, including methods for capturing the body as it moves.
The DISC Lab is also home to what researchers describe as the only MRI system of its kind in the world, allowing USC scientists to test new technologies and push the boundaries of imaging the body in motion.
Clinical collaborators help connect those capabilities to the needs of patients. John Wood, director of cardiovascular MRI at Children's Hospital Los Angeles and professor of pediatrics and radiology at the Keck School of Medicine of USC, works with Nayak on some of the most difficult challenges in pediatric imaging, including real-time imaging of the fetal heart. His experience imaging children's hearts helps inform where new, more adaptable technologies could have the greatest impact.
"We need environments where different ideas can collide," Khan said. "This project wouldn't have happened without access to the MRI and conversations with cardiologists, radiologists and imaging scientists. When you bring that expertise together, you can solve problems none of us could solve alone."
