The Return of Z
Editor's Corner | One of our fellows a few months back came to my office to show me a plastic model of the coronary arteries. Having made my own coronary models in the past by injecting a liquid plastic into the coronaries of an ex vivo pig heart, I thought it was nice but not original.
On closer inspection, I realized that the coronary arteries were irregular. There was a stenosis in the proximal LAD, and a mesh-like impression in the mid-right coronary artery that looked like a stent. It wasn’t a plastic model, but rather a coronary image from a CT scan printed with a 3D printer. The stenosis was readily visible in three dimensions, and the relations of the coronaries in 3D space were immediately evident.
Next, we looked down into a reconstruction of an aortic root that contained, at its base, a reproduction of an aortic valve with nodules on the valve that represented calcification. The valve was stenosed and the plastic rendering showed the sinuses of Valsalva and the valve, readily providing a better understanding of how to position a Transcatheter Aortic Valve Replacement (TAVR) valve in the aortic root.
A colleague recently published a report of a 3D printed model of the right atrium and inferior vena cava (IVC) in order to position a valve at the caval-atrial junction in a patient with severe tricuspid regurgitation1. The team successfully positioned the valve to allow pressure in the IVC to be reduced to normal. One can find literature on 3D printed models of spinal vertebrae, facial bones, complex congenital hearts, urologic structures, and other body locations where a visible model of the region provides important insight into surgical planning. It can also provide patients with a view of complex anatomy for a better understanding of their disorder.
These physical models of cardiac anatomy are possible because of the development of printers that can take information from a 3D image(CT or MRI scan, or 3D echo) and, using special software, convert the 3D information into instructions for a printer to print a series of 2D images that represent slices of the image that can be stacked to produce a 3D rendering of the object of interest.
Applications Stack Up
Once prohibitively expensive, there are now 3D printers priced to be affordable for a small business or home use. The units are used to produce prototype models of small tools or machine parts, toys and even small machines themselves. The potential is unlimited and has changed the way we think of images in cardiology.
In math class, we became used to the X-Y plane where everything appeared in two dimensions. More advanced math incorporated the third dimension (the Z coordinate) to analyze phenomena in three-dimensional space. In physics, three-dimensional space is the norm for analysis of anything that moves. We grew up in the cath lab looking at video screens that displayed cardiac anatomy in two dimensions. We looked at echo machine screens to see cardiac anatomy, valve functionand flow in two dimensions. CT displays are two-dimensional screens that try to provide a 3D concept by rotating the image. However, having a physical reproduction of the aortic root, mitral, or tricuspid annulus provides a better understanding of the region of interest and improves the ability to visualize, for example, how a new valve will fit the exact anatomy of the patient being considered for therapy.
The ability to produce actual physical models of the circulation is another step in improving therapy for valvular heart disease. Other applications being considered include the production of tailored mitral valves and other cardiac structures. The printed physical models can be made from porous bioabsorbable materials that can act as scaffold for growing a new heart structure. Tailored tissue valves for mitral or tricuspid replacement can be constructed in this way, and there is interest in creating myocardial patches that can be overlaid on a segment of scarred myocardium to produce functioning myocardium. Over time, the scaffold material would be absorbed, leaving a functional tissue structure.
Bony structures are particularly amenable to 3D modeling. A stenotic spinal canal or arthritic intervertebral joints can be examined in detail to plan surgical nerve root decompression procedures and reconstruction of tumors allows for a more precise plan for resection.
The return of Z, the third dimension in spatial reconstruction, promises to provide a major advancement in our ability to repair or reconstruct areas of the body that heretofore were often off limits to such precise therapy. This new method of visualization is a big step forward, and I expect it will become as ubiquitous as the video screen we currently use in the cath lab and operating room.
- O’Neill B, Wang DD, Pantelic M, et al. J Am Coll Cardiol Img 2015;8:221-5.
Article written by Alfred A. Bove, MD, PhD, who is professor emeritus of medicine at Temple University School of Medicine in Philadelphia, and former president of the ACC.
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