Author + information
- Moses Mathur, MD, MSc∗ (, )
- Pravin Patil, MD and
- Alfred Bove, MD, PhD
- ↵∗Department of Medicine, Section of Cardiology, Temple University Hospital, 3401 North Broad Street, Suite 945, Zone C, Philadelphia, Pennsylvania 19140
We read with interest the article by O’Neill et al. (1) describing the utility of 3-dimensional printing (3DP) in caval valve implantation. Theirs is an interesting extension of earlier work by Kim et al. (2). Both groups provide glimpses into the true incremental value of printing-graspable 3D models in structural heart disease (SHD), namely, the ability to optimize device selection through direct physical interaction.
Many hurdles must be crossed, however, before 3DP can become mainstream technology in SHD. Sengupta et al. (3) raised the issue of cost-effectiveness. Beyond that, several technical factors must first be standardized and validated.
First, the fundamentals of 3DP must be well understood by the clinician. This includes an understanding of details such as the following: 1) primary data acquisition; 2) model extraction (image processing); 3) printer specifications; and 4) material properties. Attention to such detail will reveal technical discrepancies that could influence clinical results. One author provided a proof-of-concept report testing the cost-effectiveness and anatomic accuracy of 3DP (4); however, larger scale studies are needed.
Second, the role of image processing is critical and yet underappreciated. As in all clinical imaging, the balance between signal and noise must be maintained. Similar precaution applies to imaging-derived 3DP. Kim et al. (2) describe multistep model extraction that includes “shrink-wrapping” deformation, noise averaging, and outer/inner surface creation using viewing windows. Although these steps are essential to model extraction, each step steers us further away from source data. At what point does the anatomic model become an aesthetic sculpture?
This is illustrated by our own 3DP experience. We derived a 3D model of an aortic root with anomalous coronaries from a cardiac computed tomography angiography image using a Siemens Sensation 64-slice scanner (Siemens Medical Solutions Inc., Malvern, Pennsylvania) and printed it on a Stratasys Dimension Elite station (Stratasys Ltd., Minneapolis, Minnesota) using acrylonitrile butadiene styrene plastic (Figure 1). Our model was not manually edited. Figure 1A shows a fracture due to fragility at a previous stent site (arrow). Since the contrast-endovascular interface is nonuniform, variability in extraction results in “holes” in the model (Figure 1B). Image processing can “fix” these holes and offset fragility; however, this diverts us away from true anatomy.
Lastly, the elasticity of print materials must be validated against that of cardiac tissues. Without this, physical interaction with models is unreliable. The material properties of the IVC model of O’Neill et al. (1) are unclear. In this case, printing with stiff plastic, rubber, or metal could potentially alter device selection. Recently, a mitral valve was printed with pliable materials (5). As elucidated in this work, using materials mimicking tissue properties could lead to applications in ex vivo device testing and training. In our own aortic root model (Figure 1B), for example, printing with a pliable material could enable preliminary test interactions with transcatheter valves.
In conclusion, we share the enthusiasm for the potential of 3DP in SHD. However, multiple technical aspects must be first standardized and validated before meaningful clinical strides can be made with 3DP in the clinical domain.
Please note: Dr. Bove is a consultant for and owns stock in Insight Telehealth Systems LLC; and has received a research grant from Merck Schering Plough and honoraria from Merck Co. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
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