"Solid X-Ray", Feature Article, July 2007

solid x-ray

Advances in rapid prototyping give the technology new roles in medical treatments.

by Jean Thilmany, Associate Editor

want an exact likeness of your spinal cord? Need it fast? Need a reliable way to create a prosthetic that's a perfect fit? Maybe you don't need such a thing right now. But you might one day, and that's where advances in rapid prototyping technology come into play.

The same advances in materials and lower costs that now drive rapid prototyping growth in manufacturing are hastening its adoption in the medical field, where models produced by the method are being used in new and unexpected ways.

According to Terry Wohlers, president of Wohlers Associates Inc., a consulting firm in Fort Collins, Colo., that follows rapid prototyping and reverse engineering technology, many physicians are turning to rapid prototyping because it can give them models of their patients' internal organs or bones. The plastic models are essentially printed in three dimensions from a patient's computer tomography or MRI scans.

Although rapid prototyping first made the scene little more than two decades ago, the technique has quickly grown from its original use—producing prototype parts cheaply and quickly—to find widespread application across a range of fields. Today, some manufacturers are using the technology not only for prototyping but also for turning out small runs of production parts that can be incorporated right into assemblies, Wohlers said.

The medical profession has its own important uses for the technology. Doctors use models as study aids to plan surgery. Before making the first surgical incision, these doctors know exactly what they'll find inside the patient's body. If a patient has a tumor within an organ, for example, the 3-D model depicts it so the doctor knows exactly where and how to find it.

At Walter Reed Army Medical Center in Washington, D.C., the 3-D Medical Applications Center has, since 2002, used an in-house rapid prototyping machine to build 3-D anatomical models.

"Having a patient-specific model in hand allows surgeons to go into the operating room with more confidence," said Stephen Rouse, a doctor at the center. "It also allows them to sit down with a patient and show them the model so they, too, can better understand."

Many physicians now use rapid prototyping techniques to build 3-D models. They can study the model—like this one depicting conjoined twins—before making the first incision. Lower model shows proposed course of surgery.

The 3-D models let doctors see and touch the diseased part of a patient's anatomy as they'll see it in the operating room. Doctors at Walter Reed use the models to plan and practice for quicker and better surgery, said Maj. Donald Gajewski, a musculoskeletal oncology surgeon at the medical center.

"This helps with pre-operative planning in ways that were not formerly possible," he said.

Doctors who don't practice at Walter Reed still want access to the same type of models. Most hospitals have no rapid prototyping equipment, so doctors call upon the services of a handful of independent service companies that make medical models. The doctor sends a patient's CT or MRI scan, and the service company quickly produces what amounts to a 3-D X-ray that doctors can feel with their hands.

According to Andy Christensen, president of Medical Modeling in Golden, Colo., "We're a medical rapid-prototyping service bureau, much like those with techniques for engine parts, car parts, and consumer product parts. We take medical images from an MRI or CT scan for a doctor with elaborate reconstructive surgery to perform. We can print a model of someone's bone structure.

"If someone's crushed their pelvis in a car accident, doctors use the model in their hand like a jigsaw puzzle to see how the pelvis will go back together," Christensen said. "They also may put in a metal plate on the hip to hold those segments together and they can figure out how that would work.

"They've already seen all the fragments ahead of time," Christensen said. "And they can do surgery quicker and provide a better outcome because they know what they'll see."

Mechanical Engineering profiled Christensen's company in a June 1999 article, "Saving Face." During the past eight years, medical uses for rapid-prototyping technology have grown and changed.

Today, Christensen is adding a new technique called electron-beam melting, which relies upon melted titanium powder to produce implantable metal devices from CT-scan information. The technology, from Arcam of Boras, Sweden, builds up the metal parts via rapid prototyping. So far, Christensen's company has used its newest building system to produce metal plates that can be fitted into the pelvis or other parts of the body.

Medical Modeling now also makes its models via 3-D printing as well the stereolithography technique that has been its mainstay. Stereolithography, which produces a 3-D object by building up and curing a liquid resin one layer at a time under a computer-guided laser, creates very accurate models, Christensen said. They are translucent and particularly useful for judging bone volume and thickness. Models that include air-filled structures like the sinuses are best depicted in translucent material because doctors can see through the sinuses to the bone beyond.

"Seeing where these structures are in relation to the bone can make a big difference," Christensen said. "If your face is crunched up in an accident, putting the pieces back together can be tricky if you don't know how thick the bone is in a certain area."

The models created on his company's new 3-D printers are white. The 3-D printer builds by layers, too. It is faster than stereolithography, but is not as accurate. They're less expensive and are mainly used as broad concept models by medical practitioners, Christensen said.

The medical-model market is still a considerable distance from being fully realized, Christensen said.

"A lot of what's been going on the last five years has been education," he said. "We're telling doctors how a 3-D model can influence their surgical plan. We've seen the market grow, but it's still a long way from where it will be a decade down the road."

There are relatively few companies in the medical model-building business, and they have not been at it long. Javelin 3D of Park City, Utah, two years ago quit doing mechanical design work—chiefly producing stereolithography files from manufacturers' CAD files—to focus on making medical models via rapid prototyping, said Alair Emory, senior partner.

RP4Baghdad uses RP to treat Iraqi civilians with head injuries. RP firms make models like these of a patient's face to aid in reconstructive surgery.

At present, according to Emory, because there are so few companies in the business, Javelin 3D doesn't really compete with Christensen's company and the handful of other medical modeling companies, although they offer much the same service. Rather, they work together to build awareness of the field.

RP4Baghdad is a humanitarian effort founded in mid-2005 by members of the U.S. rapid prototyping and manufacturing industry. It calls upon rapid prototyping techniques to help treat Iraqi civilians with severe injuries to the head and face. Iraqi doctors send CT information to program participants, and project members produce models of a patient's face to assist in complex reconstructive surgeries.

"The models, unlike two-dimensional X-rays, provide detailed, 3-D replicas of the treatment area, giving both patient and physician superior presurgical information," according to Omar Al Ani, an Iraqi surgeon.

Medical models begin with CT or MRI patient scans of the particular area of a patient's body to be treated. The scans capture a series of images taken one thin slice at a time. Traditionally, each cross-section image was examined to diagnose and treat a variety of conditions, including head trauma and cancer, Rouse said.

But with today's software—like the Velocity2 Plus package that Javelin 3D sells—that same information can be converted into a CAD file. The CAD information is then essentially rendered as an object, which exactly mirrors the CT or MRI information specific to a patient.

To make models like this of conjoined twins, practitioners begin with a patient's CT or MRI scans. Info is turned into a CAD file, then printed.

During the past five years, the way doctors use these models has evolved with the technology, Emory said. One company that uses Javelin 3D's services makes devices fitted to individual patients to stabilize the spine. For this company, Javelin 3D turns CT-scan information into a stereolithography file, Emory said. The file is then transferred to a CAD system. The company uses the CAD of the patient's actual spine to confirm that stabilizing devices will fit. The design doesn't rely on generic human-spine information, she said.

According to Emory, one of her friends, who ran his own rapid prototyping bureau, introduced the idea of a 3-D model to his own doctor.

When diagnosed with congestive heart failure, the friend called Emory and sent over a CT-scan file that he'd requested from his doctor.

"At his next meeting with his doctor, he went in with a model of his heart and asked the doctor to show him exactly what was going on," she said. "The doctor was so excited he asked if they could have it and put it on display in the lobby of the hospital. Little things like that will get it to become commonplace in the United States."

The technology is also migrating from medical to forensic. Javelin 3D is seeing some work come in from lawyers trying medical malpractice cases and from individuals feuding with their insurance plans. "If a person's injured and disputing, their lawyer can send files from CT to build the physical model to show what's wrong," she said.

Her company, for example, created a model for a Canadian woman who broke three bones in her arm in a fall. After reading about Javelin 3D's work, the woman contacted Emory directly. She was in a dispute with her doctor, claiming that the doctor hadn't set her bones correctly, causing her continued pain. The doctor said the woman wasn't carrying out her physical therapy correctly, Emory said.

The woman had a doctor take CT scans of both her left and right arms. Her left arm hadn't been damaged in the fall, so it was used for comparison.

"We did the reconstruction and just in the first picture of the stereolithography file you could see compared to her left arm the right arm was just flat," Emory said. "She got a lawyer; we built a model; they did a trial, and she won her case. She also had to have two more reconstructive surgeries and the new doctor said it was helpful to have our models to plan a surgery."

While the medical modeling field is still in its infancy in the United States, it's growing quite quickly in Europe, both Emory and Christensen said.

"They have a socialized medical approach and so they can do things that we can't," Emory said. "They don't have to go through insurance reimbursement to show individual by individual that rapid prototyping is the best way to handle things because it minimizes cost."

According to Christensen, his company operates similarly to a standard rapid prototyping bureau, but, of course, there are differences. They stem mainly from insurance issues.

"We're in the rapid prototyping community, but kind of detached," he said. "We're faced with issues of cost containment by insurance companies wanting it cheaper all the time."

Still, accepted by insurance plans or not, the use of rapid prototyping for medical modeling will find its way into the mainstream—and find more medical significance—in the not-too-distant future, Emory said.

"I think the whole field is fascinating, but when I go to dinner parties and explain it, people roll their eyes," she said. "I just tell them, when you get really sick, remember this conversation."