Design Optimization for Accurate Flow Simulations in 3D Printed Vascular Phantoms Derived from Computed Tomography Angiography

Abstract

3D printing has been used to create complex arterial phantoms to advance device testing and physiological condition evaluation. Stereolithographic (STL) files of patient-specific cardiovascular anatomy are acquired to build cardiac vasculature through advanced mesh-manipulation techniques. Management of distal branches in the arterial tree is important to make such phantoms practicable. We investigated methods to manage the distal arterial flow resistance and pressure thus creating physiologically and geometrically accurate phantoms that can be used for simulations of image-guided interventional procedures with new devices. Patient specific CT data were imported into a Vital Imaging workstation, segmented, and exported as STL files. Using a mesh-manipulation program (Meshmixer) we created flow models of the coronary tree. Distal arteries were connected to a compliance chamber. The phantom was then printed using a Stratasys Connex3 multimaterial printer: the vessel in TangoPlus and the fluid flow simulation chamber in Vero. The model was connected to a programmable pump and pressure sensors measured flow characteristics through the phantoms. Physiological flow simulations for patient-specific vasculature were done for six cardiac models (three different vasculatures comparing two new designs). For the coronary phantom we obtained physiologically relevant waves which oscillated between 80 and 120 mmHg and a flow rate of ~125 ml/min, within the literature reported values. The pressure wave was similar with those acquired in human patients. Thus we demonstrated that 3D printed phantoms can be used not only to reproduce the correct patient anatomy for device testing in image-guided interventions, but also for physiological simulations. This has great potential to advance treatment assessment and diagnosis.

Figures

Figure 1

3D data volumes uploaded to Vital Images and the coronary vasculature is segmented out. Vessel centerline manually segmented to avoid vessel stenosis.

Figure 2

Merged Approach 3D printed as a single material

Figure 3

Flow diagram showing the steps used in the Common Outflow Compliance Approach from the time the STL is imported into Meshmixer to the completion of the segmentation process.

Figure 4

Flow diagram showing steps performed to customize flow simulation chamber for patient-specific vessels. (a)Customizable flow chamber is inserted and (b) a vessel support mesh is appended to the base. (c) The Boolean Difference Operation ensures no region of overlap and (d) the vessel and base are fit together.

Figure 5

Flow diagram showing steps performed from the time the STL is imported into Meshmixer to 3D model ready to be printed using the Targeted Outflow Compliance Approach.

Figure 6

Diagram showing the addition of the aorta with extending coronary arteries and the base reservoir after performance of the Boolean Difference Operation ready to be 3D printed.

Figure 7

The reinforcements and the base are combined to create a sturdy base for the coronary arteries that allows for easy cleaning without subjecting the model to mesh tearing ease.

Figure 8

Compliance Experimental Design

Figure 9

Three examples of coronary arteries captured in Vital Images as well as Multi-Planar Reconstructions (MPR’s) to edit centerlines of vessels.

Figure 10

Meshmixer comparison of three different model design approaches for patient A, B, and C.

Figure 11

Simplified and Complex Coronary Models 3D printed and compared both frontal view and bottom view

Figure 12

Compliance curve of FLX9760poly-blend material. An increase in pressure caused the diameter of both the minor and the major axes of the vessel to expand.

Figure 13

Pressure waves measured at the aorta (P1) and outlet (P2) for the merged model and Common outflow compliance where P1 is the proximal pressure and P2 is the distal pressure.

Figure 14

Multi-material compliance comparison