Sep 28, 2018 | By Thomas

Phantoms are numerical and physical models that represent the characteristics of some specified human anatomy. A physical phantom can be used to test various medical diagnostic imaging tools and wireless communication applications. Sossena Wood, a bioengineering PhD candidate at the University of Pittsburgh, has developed a 3D printed realistic phantom head for magnetic resonance research in the Swanson School of Engineering.

While electromagnetic numerical modeling has been the common resource to understand and analyze the interaction of electromagnetic fields and biological tissues, in the last few years, experimental phantoms are increasingly becoming a useful resource.

"In the RF Research Facility, we use a whole-body 7 Tesla magnetic resonance imager (7T MRI), which is one of the strongest clinical human MRI devices in the world," said Tamer Ibrahim, Associate Professor and Director of the University of Pittsburgh's Radiofrequency (RF) Research Facility. 7T ultrahigh field technology is a powerful tool, but unfortunately, there are a few setbacks that come with this type of imaging.

"As you move from lower to higher fields, the images produced become less uniform and localized heating becomes more prevalent," explained Ibrahim. He envisioned designing a 3D printed phantom head to use with the uniquely designed ultrahigh field technology in his lab.

"We wanted to develop an anthropomorphic phantom head to help us better understand these issues by providing a safer way to test the imaging. We use the device to analyze, evaluate, and calibrate the MRI systems and instrumentation before testing new protocols on human subjects."

Researchers are currently using numerical simulations to study the effect of electromagnetic (EM) fields on biological tissues at varying frequencies. Wood said, "EM numerical modeling has been a standard when analyzing these interactions, and we wanted to create a phantom that resembled the human form for use in validating the EM modeling, thereby providing a more realistic environment for testing."

A physical and realistic head phantom starts as a digital 3D design file of a human head. Wood started with a 3T MRI dataset of a healthy male, which she characterized by segmentation and broke into eight tissue compartments, a feature that differentiates her model from other basic phantom heads. The head phantom compartments consist of eight grouped classified tissues: brain, brainstem, eyes, air cavities, cerebellum, cerebrospinal fluid (CSF), muscle, and the remainder volume being a combination of the fat, bone, and skin. According to Wood, these compartments help improve image accuracy by acting as a sort of "speed bump" for the field.

A General workflow to design and fabricate an anthropomorphic heterogeneous head phantom using 3D printing.

Using 3D CAD software Geomagic Studios, each compartment was designed to reserve the mixture of the desired tissue over time. The next step was to print the prototype. The phantom model was printed in five separate parts in order to manually remove the inner structural supports that come out with 3D printing. "We used a plastic developed by DSM Somos® for our printing material because it allowed us to create durable and detailed parts with a similar conductivity to the human body," said Wood. "To help the model further mimic a real environment, we created filling ports on the prototype where we can deposit fluids that resemble various tissue types."

All images credit: University of Pittsburgh / RF Research Facility

Now that Wood has a fully 3D printed anthropomorphic phantom head, she is able to assemble it and begin testing. The phantom has many applications including testing to see if certain implants are able to go inside of an MRI or detecting the temperature rise in different tissues based on various RF instrumentation.

"With MR imaging, the power from the RF exposure is transformed into heat in the patient's tissue, which can have detrimental effects on the patient's health, especially with implants if not monitored by the scanner" explained Wood. "With our phantom head, we can test the safety of our imaging by putting probes inside of certain regions of the head and measuring the effects," said Ibrahim.

Ibrahim and Wood hope that this model will eventually be developed commercially and provide others with the ability to pursue research without relying on human testing.



Posted in 3D Printing Application



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