Heart disease is the leading cause of death in the United States, but evaluating it carries risks of its own. Though often beneficial, X-ray angiography and CT angiography require dangerous iodine tracer and ionizing radiation to probe in the blood vessels and brain. Iodine tracers can be life-threatening to patients with chronic kidney disease, which include over half of Americans over the age of 70. Further, the number of patients with kidney disease is rapidly increasing due to comorbidity with Type 2 diabetes and high blood pressure, as well as aging demographics.

Fig. 1 – A closeup of the bore showing two printed parts that are the transmit and receive coil, as well as a flat sample holder.

That’s why researchers at The University of California at Berkeley are developing a new medical imaging technology called X-space Magnetic Particle Imaging (MPI). The technology has the potential to deliver safe, non-invasive angiography without the dangers of iodine or radiation, according to Patrick Goodwill, UC Berkeley research associate. The MPI scanner will let doctors look inside the heart and brain by detecting, from outside the body, the location of iron oxide nanoparticle tracers injected into the bloodstream. The tracers are nontoxic and safe for use in patients, including those with kidney disease.

Images are especially sharp: “MPI is the first whole-body imaging technology to see a radiation-free tracer with perfect contrast,” said Goodwill, developer of both the theory and first X-space MPI scanner. “This will give doctors a powerful new diagnostic tool. MPI will be the safest way to get an angiogram in the future.”

Goodwill and a team of graduate engineering students in UC Berkeley Professor Steve Conolly’s laboratory are building MPI scanners that can image small animals today. These devices are precursors to human-scale scanners, which will be available toward the end of the decade.

As a healing, engineering, and business proposition, time is of the essence. To speed development, the team has begun fabricating its own prototype parts. “Since we’re building the world’s first MPI scanners, we can’t just buy parts off the shelf,” Goodwill explained.

Load-bearing parts are fabricated out of G10 glass epoxy laminate in a traditional machine shop, with a typical turnaround time of two to three weeks, or more. For non-load bearing parts, including many of the device’s most complex, the team is using a 3D printer from 3D Systems (Rock Hill, SC).

Using the “ZPrinter,” Goodwill’s team is manufacturing MPI scanner prototype parts such as transmit coils, receive coils, heated beds for animals being scanned, and even custom components for delivering anesthesia to the animals before scanning. “Every scanner we’ve built has incorporated at least two or three ZPrinted parts,” said Goodwill. There are 30 parts in each device, not including fasteners, ranging from 192 cm3 to 675 cm3.

Fig. 2 – A projection magnetic particle imaging (MPI) scanner developed at UC Berkeley. The MPI scanners can image small animals; humanscale scanners will be available toward the end of the decade.

A 3D printer creates physical models from 3D data much as a document printer creates business letters from a wordprocessing file. The Berkeley team’s ZPrinter 150 3D printer uses binder from an inkjet to harden composite material layer by layer into the desired shape. ZPrinters are the fastest, most affordable 3D printers and the only ones capable of simultaneously printing in multiple colors.

Berkeley purchased the ZPrinter after trying another 3D printer that was expensive (costing up to $1,500 per part in materials) and time-consuming (taking as much as 20 hours for a single part). The ZPrinter creates parts in half the time, at a fraction of the price, and even produces multiple parts in each build cycle. “We can build 30 parts for the price of one,” Goodwill said.

The performance of the MPI system is intimately related to the shape of the transmit and receive coils. These are the parts that send out electromagnetic signals to nanoparticles, whose “replies” are detected by the receiver coils.

“The biggest benefit of 3D printing our own parts is rapid iteration of the design. These are intricate parts that would require an expensive 5-axis CNC machine for a machine shop to mill plus days or weeks of setup time,” said Goodwill. “With the 3D printer, we can design, print, wind, and integrate an entire transmit and receive subsystem in under a week, which simply wouldn’t have been possible before. Now, whenever we have an inspiration, we try it out with a real part. We hit 3D Print on the way out the door and put the part to use the next morning.”

Fig. 3 – A heated animal bed used by Goodwill's team in UC Berkeley Professor Steve Conolly’s laboratory.

Goodwill trains all his students on 3D CAD software. Once students have modeled the design, they save it in a standard 3D printing format such as .STL or .ZPR. With the file now printable, they launch 3D Systems’ ZPrint software on their PCs. Using ZPrint, they can scale up or scale down the file they wish to print, orient the part in the build chamber, and direct the 3D printer to print multiple versions of the part in the same build (with or without variations). Then the ZPrint software slices the 3D model file into hundreds of digital cross-sections, or layers. Each 0.004 inch (0.1 mm) slice corresponds to a layer of the model to be fabricated in the ZPrinter. Clicking on 3D Print sends the digital layer files to the ZPrinter, and the model begins printing immediately.

The ZPrinter prints each layer, one on top of the other, to construct the physical part in the build chamber of the machine. After the ZPrinter completes the final layer, a short drying cycle runs and the physical model can be removed.

“ZPrinting is the fastest way we can create the parts we need to rapidly iterate our design,” said Goodwill. “As a result, we can bring MPI to the general public sooner because we believe patients need this technology.”

This article was written by Patrick Goodwill, Research Associate at the University of California at Berkeley and developer of the first X-space MPI scanner. For more information about the Zprinter, visit http://www.info.hotims.com/40431-160 .