Clinical Applications of Medical Modeling- Part One

There’s no question that computer modeling, simulation, and additive manufacturing have transformed clinical medicine around the world. What’s always fascinated me, though, is the variety of ways these technologies have been implemented in different hospitals and even different departments within the same hospital. As a prototyping fellow at Sinai BioDesign, a design and prototyping group within the Mount Sinai Hospital in New York, I’ve seen firsthand almost all of the ways 3D printing, and more broadly, 3D data can be leveraged within a health system. Like many other tools and data streams, there’s no single way 3D medical data is acquired or used within the health system. In each case, though, these printing, scanning, and rendering applications are crucial to clinical care and research. For part 1 of this Expert Corner blog, I’ll be focusing on use cases for 3D modeling and printing and in next week’s part 2 , I’ll be discussing clinical applications of 3D scanning technologies, the other side of the medical 3D coin.

At Sinai BioDesign, a large portion of our 3D modeling and printing work is focused on pre- and peri-operative applications; providing models of patients’ anatomy for crucial guidance before and during surgical procedures. It often comes as a surprise to people, though, to learn how often we never produce a printed model from the data we acquire. No matter the surgical plan, a 3D model (typically an STL file) is produced from medical imaging data (usually CT and MRI scans). Printing that 3D model, however, is not always the next step in the process.

Figure 1. An example of patient anatomy rendered in VR with the Surgical Theater system for pre-surgical planning

At Mount Sinai, the decision on whether or not to print a model often falls along surgical departmental lines, with rationales rooted in the nature of different surgeries. Our Department of Neurosurgery, for example, rarely leverages 3D printing in their pre- and peri-operative surgical guidance, opting instead to render the data with a variety of VR and AR tools. For pre-surgical planning, technologies like the Surgical Theater platform are used to produce 3D models of patients’ anatomy, which the surgeon can then manipulate on interactive displays and even “walk” through using VR headsets. While a 3D printed copy of a patient’s anatomy is easier to probe, manipulate, and analyze than the actual patient’s anatomy in the OR, it often doesn’t afford the kind of perspectives and spatial understanding that can be achieved through a VR rendering. Any view that would be blocked by actual anatomies, such as the skull, is also frequently blocked by the printed anatomy. In VR you can shift the transparency of different tissues in much the same way you can adjust the transparency of layers in Photoshop, but you can adjust colors and transparency in a 3D printed model.

Figure 2. Anatomical data from MRI scans overlaid on brain tissue, highlighting key features to avoid during tumor excision.

Furthermore, the tissues neurosurgeons operate on – mostly brain, blood vessels, and tumors located in and around brain and blood vessels – are very soft and materials with accurate mechanical properties cannot be produced through existing 3D printing technologies. As such, there is little to no tactile information gained through a printed anatomical model and the visual/spatial information is at best as good as what can be obtained through rendering the 3D models in VR. Lastly, Mount Sinai’s Neurosurgery Department frequently employs AR, heads-up display technologies as a means of peri-operatively visualizing anatomical data. This ability to overlay and highlight important anatomical information (say the location of a brain tumor, or important blood vessels that should be avoided) on the live visuals being captured in the OR is arguably even more useful than looking back and forth between a printed model and the patient (at least in the case of neurosurgery).

Figure 2.
Figure 3. The view of a tumor (green) located within the skull base, as viewed through an endoscopic camera inserted into the printed model

Although, as the neurosurgery examples show, the lifecycle of an STL in a hospital doesn’t always lead to a 3D printer, there are many cases in which it does, and many departments that almost always print anatomical models for surgical guidance. For purposes of surgical planning, the Ear, Nose, and Throat (ENT) department at Mount Sinai is one of the most avid users of printed anatomical models. Many ENT procedures require the use of endoscopic cameras and surgical tools, typically inserted via the nostrils. Unlike neurosurgery, the tissues involved in ENT procedures are bony and cartilaginous, much stiffer and more reasonably approximated by the thermoplastics and ceramic powders our anatomical models are printed out of. As such, performing a dry run of a planned ENT procedure on the printed copy of a patient’s anatomy comes much closer to approximating the conditions that will be experienced in the OR. Very often, this means using the same types of endoscopes as catheters on the printed model as would be used on the patient while evaluating maneuverability, fit, and overall strategy.

When not intended for patient-specific practice, Sinai BioDesign’s printed anatomical models are frequently used for more generalized practice, especially for neurological procedures such as stereoelectroencephalography (SEEG), which involved the placement of electrodes deep into the brain. As you might imagine, a procedure that involves drilling through the skull and inserting foreign objects into the brain is also a procedure that requires a lot of training and practice. Many of the commercially available practice models do a poor job of replicating actual human anatomy, so we’ve begun producing our own practice models using a combination of 3D printing and casting techniques. The skull and key vasculature to be avoided are printed from a hard, ceramic powder (which happens to feel fairly similar to bone, with respect to drilling) and a cast of a brain (my brain, in fact[1] ) made from a cryogel that replicates the mechanical properties of brain tissue is inserted inside the printed skull. The fully assembled models are then used with the SEEG drilling equipment for training courses for surgeons. These hybrid printed/cast anatomical models have been so successful at replicating human anatomy, at both the physical and mechanical levels, that the production of skulls for SEEG training is likely the single largest application of 3D printing at Mount Sinai.

Figure 4. A cast gel brain, mimicking the mechanics of actual brain tissue embedded in a printed skull mimicking the mechanics of bone for SEEG drilling practice

When considering the impact of 3D printing in medicine, we often primarily consider the impact of printed objects that are directly integrated into the surgical cycle, be they implants, prostheses, or pre-surgical planning models. It is important to remember, though – and I hope my examples from Sinai BioDesign illustrate this – that there are many ways 3D printing (and the 3D files that precede printing) impact clinical care even when not directly integrated into a surgery. Printed models, like our SEEG dummies, are helping democratize training for complex surgical procedures and creating more realistic practice environments. Furthermore, the digital models that produce all of these printed objects don’t even need to be physically manifested to have crucial clinical utility. In cases such as neurosurgery, where a printed model doesn’t necessarily add much to the pre-surgical planning process, VR pre-surgical “walkthroughs” and AR peri-operative guidance can decrease procedure durations and improve outcomes. 3D medical technologies will likely never be used in the same way everywhere, but I think it’s clear all of them will play a crucial role somewhere.

About the Author

Joseph Borrello

Joseph Borrello is currently a biomedical engineer and PhD Candidate at Mount Sinai, working in the labs of Drs. Kevin Costa and Junqian Xu, in addition to managing digital fabrication operations within the Sinai BioDesign innovation team. Previously, he worked at 3D Systems on technical development in the consumer marketing department and as a liaison with engineering project management teams.

He received his bachelors in Biomedical Engineering from Macaulay Honors College at The City College of New York, where he remains active in the Zahn Innovation Center, an on-campus tech startup incubator.

Joseph is also an active member of the New York City startup ecosystem. He is the founder of Proto-Sauce, which is developing new materials for resin-based 3D printing, as well as the CTO of Biosapien, leveraging 3D printing to produce personalized therapeutics. He also tries to summarize as many of the local happenings as he can in his newsletter Magnitude and Direction.

Finally, Joseph is also the editorial assistant for 3DHEALS Lattice newsletter, where he tirelessly curate the best content for healthcare 3D printing and bioprinting community with the 3DHEALS team.

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