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Additive Manufacturing Aids Surgery at Mayo Clinic

Bruce Morey
By Bruce Morey Senior Technical Editor, SME Media
By Larry Adams Contributing Writer, SME Media

Additive technology lets physicians hold a tumor in the palm of their hands

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Dr. Jonathan Morris, MD, Radiologist and head of the Mayo Clinic’s 3D Anatomic Modeling Laboratory with just some of the 3D printed models of various organs used for surgery planning or training.

Lungs, hearts, tumor-filled skulls, brains, livers, kidneys, and rib cages, are packed into shelves at the 3D Anatomic Modeling Laboratory at Mayo Clinic. These body parts are not flesh and bone, however. They are 3D printed patient specific models, and they are helping shape how Mayo Clinic conducts surgeries and delivers health care.

At the lab five floors above the operating rooms in Rochester, Minn., radiologists, engineers and imaging technologists work in collaboration with some of the world’s best surgeons and medical specialists to make these life-sized and often life-saving models. In a bucolic community of soybean and corn fields, gently rolling hills and a meandering river, this workshop-cum-manufacturing facility is one of the driving forces in the growth of additive manufacturing in the medical arena.

Despite the high-technology and the buzzing activity in the facility, the sophisticated work is done with one idea in mind—the needs of the patient comes first. These seven words are an institutional norm that has driven health care here for more than 150 years. The not-for-profit medical center believes that finding the answers to complex, complicated and often dire health prognosis’ requires teamwork by a multidisciplinary group of specialists and minds that are willing and open to new ideas.

Nothing shows this more than the institution’s embrace of additive manufacturing (AM), and the case that took 3D printing from the testing stage to a tool used across multiple disciplines nearly every day.

Visualizing Problems

Additive manufacturing at Mayo Clinic had its start in 2006 when it aided in the effort to separate conjoined twins. The surgical staff approached radiologists Dr. Jane Matsumoto, and Dr. Jonathan Morris, which led to the development of the first clinical 3D printed anatomic model at Mayo Clinic.

The infants were born joined at their abdomen and chest; their fused livers especially, were problematic as the organs were skewed and growing into each other’s chest walls.

The pediatric surgeons led by Dr. Christopher Moir wanted to understand the complex vascular and biliary anatomy better to plan the difficult operation. The radiology team, in conjunction with Mayo Clinic’s Division of Engineering delivered a life-size, 3D-printed model of the fused livers. According to a research paper presented by Mayo Clinic personnel, “nearly 6,000 radiographic images were acquired, two detailed volume rendered visualization studies were compiled, three different 3D stereolithographic models were developed and five individualized anatomic illustrations created from a vast array of medical images. All developed in an effort to educate a care team of over 70 people.”

After months of planning the children were separated during a 12-hour surgery and now live independent lives.

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A 3D model of a chondrosarcoma cancer embedded in a pelvis. The green shape is the cancer that needs to be removed and the model helped an interdisciplinary team of surgeons plan the operation.

From that single model sprung the Anatomic Modeling Lab that has produced thousands of models, said Dr. Jonathan Morris, who now heads the clinical AM endeavors. The institution operates a slew of 3D printers that use different AM technologies to custom-build models of patient-specific anatomy to help physicians make diagnoses, prepare for surgeries, and help patients understand procedures.

Morris notes that when using the models, discussion by surgeons increases compared to when exclusively using two-dimensional images generated by X-rays, CT scans, and MRIs. “The surgeons hold the model up, turn it around, look at it upside down,” he said. The physical 3D object gives them a haptic, tactile experience and helps them understand what they may see in the OR, which is difficult when looking at a static two-dimensional image.

From Humble Beginnings

Rochester is a somewhat unlikely place for one of the world’s best medical institutions. The small city developed from a wagon train stop, but soon settlers came to live in the area including the British born William Mayo who, in 1863, established a surgical practice. After a deadly tornado, Mayo, his two sons, William and Charles, along with the Sisters of St. Francis, erected a new hospital in 1889. Its mission is to “inspire hope and contribute to health and well-being by providing the best care to every patient through integrated clinical practice, education and research.”

Today, more than 3.5 million patients from 50 countries annually make the Mayo Clinic a health care destination. The Mayo Clinic actually consists of two hospitals in Minnesota, with large hospitals in Florida and Arizona, and affiliated hospitals throughout Minnesota, Wisconsin, and Iowa.

Since its beginnings, the Mayo Clinic has employed staff engineers to develop surgical instruments, tools, and advanced procedures that are used in hospitals and medical facilities around the world. In fact, in 2014, in celebration of its sesquicentennial, the hospital released a list of 150 advances that Mayo staff has developed.

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The process of creating the CAD model used to print the anatomical model is a labor intensive process of segmenting medical images, such as X-rays, CT scans or MRIs.

“Because we are in an isolated area of the country, the Mayo brothers brought on people to help develop tools to improve care,” said Morris. Essentially, if a challenge presented itself, engineers, doctors, and other medical professionals would tackle it.

The same might be said of today’s Mayo staff, especially when it comes to additive manufacturing.

AM’s Growing Importance

The AM team makes models made from a variety of raw materials in powder, liquid, and filament forms. The materials can be rigid or flexible, biocompatible and sterilizable or have other properties relevant to the patient’s needs. They come in a variety of colors, and these colors typically represent different anatomies. Bones are white. Aortas are red. Tumors are green. In addition, the team develops 3D printed patient specific osteotomy cutting guides to aid in surgery. These tools can save time in the operating room, reduce the time under anesthesia, improve outcomes and in some cases reduce costs, all in an effort to aid in the patient’s overall health care.

For instance, 3D models of a heart and vascular system shows the complex spatial relationship between these structures, relationships that vary greatly from patient to patient, and may not be intuitive from two-dimensional images.

“To make (decisions based) on CT scans, that are scanned into 0.75 mm slices, and then recreate this (relationship) in your mind, would require a lot of mental gymnastics,” said Morris.

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Part of the mission of the lab is to evaluate new technologies, like exploring how to use virtual reality in surgical planning.

He adds that nearly every medical and surgical specialty at Mayo Clinic has accessed and benefited from AM. These specialties include otorhinolaryngology (ear, nose and throat), orthopedic surgery, oncologic surgery, neurosurgery, thoracic surgery, and cardiovascular surgery. Surgeries for which 3D printed anatomic models have proved to be helpful include head and neck surgery, complex facial or airway reconstruction, heart surgery, lung surgery, joint reconstruction, and tumor removal. One of the newest areas of exploration is intrauterine surgery, i.e., surgery in the womb.

These 3D models play an important role not just for a surgery, but in educating medical students, residents, fellows and experienced surgeons learning new or uncommon procedures that might be difficult, considering a dearth of cadavers affecting learning institutions.

One example is a tiny infant’s brain. “Very rarely could you hold an infant skull or an infant brain in your hand,” said Morris. “But, with all of the imaging data, we can print it out. If we have 30 people in a classroom, each could have a model of the brain.”

In-House Manufacturing

AM is made easier at Mayo Clinic because it is performed in-house as opposed to outsourcing the job. Surgeons can come to the lab when available to discuss their specific needs and models are generated quickly and precisely. It might take hours to plan and a day to produce the models, but that is still faster than the weeks it might take to outsource. Timing can be critical because a patient may fly in on a Monday, meet their doctors, undergo testing, and “have surgery scheduled for that Thursday,” Morris said.

Mayo Clinic’s multidisciplinary approach and organizational structure allows for this level of collaboration. The 3D printing capability at Mayo grew up in an environment in which it was seen as another tool that surgeons can use. “Here, surgeons that have a clinical need on a complex case, come and request a 3D printed model and if it fits the needs of the patient we do it,” he said.

To accommodate the growing AM demand, the institution expanded its space, hired additional staff, and added equipment. Subspecialty radiologists oversee all models created by the lab. The department hired two full-time biomedical engineers to work primarily in the hospital, which doesn’t include the 70 engineers employed at the Mayo Clinic (see page 37), and plan to add a third biomedical engineer this year. Also, image segmenters were hired to make the models from CT or MRI scans. Supporting these efforts are healthcare technology management personnel hired to keep the 3D printers running.

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Biomedical engineers Amy Alexander and Hunter Dickens with Mayo Clinic 3D Anatomic Modeling Laboratory’s newest 3D printer.

After a radiologic study has been protocoled and acquired with 3D printing in mind, the segmenters trace out the various organs and body parts from an image for printing. The tumor or damaged area that needs to be removed surgically is identified by a radiologist who determines tumor margins.

For instance, a large pelvic tumor scheduled to be removed has a model made. To create this model, the bones, the arteries, the ureters (the duct through which urine passes) are segmented by a technologist. “That’s five different CT scans that have to be co-registered to each other. The segmenter does a lot of it, but it is the radiologist’s job to segment the tumor and assure the rest is accurate,” said Morris.

To ensure quality, every 3D printer gets tested on a regular basis. While Mayo Clinic has the technology to do CT (computer tomography) to ensure repeatability and accuracy, the lab primarily relies on coupons, phantoms and fiduciary markers to evaluate, analyze, and tune the devices.

Myriad AM Technologies

The Mayo Clinic uses several AM technologies and keeps redundant types of equipment to ensure that if one or more printer goes down, they can keep production running. Technologies include material extrusion technology, vat polymerization, material and binder jetting, and powder sintering. The printers vary by cost, as well as by available material choices, color options, rigidness of the model and supporting structure and more.

The modeling lab uses three material extrusion machines, two of which are the Ultimaker S5, which is a fused filament fabrication (FFF) device, also known as a fused deposition model (FDM) machine, and the PRUSA i3 MK3S extruding machine.

This printing process uses a filament of solid thermoplastic material that is pushed through a heated nozzle, melting it in the process. Material is deposited on a build platform along a predetermined path, and the filament solidifies to form a solid object.

Vat polymerization is a 3D printing process where a light source selectively cures a photopolymer resin in a vat. The two most common forms of vat polymerization are SLA (stereolithography) and DLP (digital light processing). The fundamental difference between these types of 3D printing technology is the light source they use to cure the resin. SLA printers use a laser beam to cure individual points of resin on a build platform, while the DLP uses UV light from a projector to cure resin one layer at a time by projecting an entire layer at once into the vat.

The vat polymerization technology in use includes four SLA models from Formlabs called the Form2 printer. A third Formlabs SLA machine, the Form3L, the bigger brother to the Form2 printer, is schedule for installation in 2020. On the DLP side, the lab operates the NewPro3D NP1 machine that reportedly performs ultra-fast 3D printing of photopolymers.

Another technology in use is powder bed fusion, Mayo uses selective laser sintering (SLS), in which small powder particles are exposed to heat by high-power laser fusing them together. The lab uses the EOS P110 Formiga. EOS machines are often used to sinter metal, but the company has put the technology to use sintering plastic with a 30W CO2 laser.

The lab also uses Stratasys Objet 500 Connex3 material jetting technology, the 3D Systems’ ProJet 660 Pro binder jetting, and in 2020 will add the HP 580 printer for material jetting to the mix. These devices act akin to an inkjet printer. Material jetting uses droplets of material that are selectively deposited and cured on a build plate. The droplets are cured when exposed to light, and objects are built up one layer at a time. Different materials and colors can often be printed simultaneously.

The binder jetting process uses a liquid bonding agent that selectively binds regions of a powder bed. Binder jetting moves a print head over the powder surface depositing binder droplets that are typically 80 µm in diameter. These droplets bind the powder particles together to produce each layer of the object.

Spreading the Word

The number of machines needed, and the various machine types in use at the lab, can be daunting to some labs not familiar with the additive manufacturing environment. To share its institutional knowledge, a pledge made more than a century ago by the Mayo Brothers, Morris travels around the country “teaching people what we do, helping other labs establish themselves.”

Mayo is also working with the Radiological Society of North America to develop standards. A working group was established to work on additive manufacturing issues including software, infrastructure and IT, according to Morris. The RSNA 3D Printing Special Interest Group (SIG) was launched to help move the industry forward. Its mission statement reads: To promote the highest quality 3D printing applied to medicine via education and research, collaboration, and research.

As the Mayo Clinic continues its AM pursuit, it would not be surprising if important advancements are made by the staff and added to another list of advancements created for the Clinic’s 200th anniversary.

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