3D printed ventricular septal defect patch: a primer for the 2015 Radiological Society of North America (RSNA) hands-on course in 3D printing

Abstract

Hand-held three dimensional models of the human anatomy and pathology, tailored-made protheses, and custom-designed implants can be derived from imaging modalities, most commonly Computed Tomography (CT). However, standard DICOM format images cannot be 3D printed; instead, additional image post-processing is required to transform the anatomy of interest into Standard Tessellation Language (STL) format is needed. This conversion, and the subsequent 3D printing of the STL file, requires a series of steps. Initial post-processing involves the segmentation-demarcation of the desired for 3D printing parts and creating of an initial STL file. Then, Computer Aided Design (CAD) software is used, particularly for wrapping, smoothing and trimming. Devices and implants that can also be 3D printed, can be designed using this software environment. The purpose of this article is to provide a tutorial on 3D Printing with the test case of complex congenital heart disease (CHD). While the infant was born with double outlet right ventricle (DORV), this hands-on guide to be featured at the 2015 annual meeting of the Radiological Society of North America Hands-on Course in 3D Printing focused on the additional finding of a ventricular septal defect (VSD). The process of segmenting the heart chambers and the great vessels will be followed by optimization of the model using CAD software. A virtual patch that accurately matches the patient's VSD will be designed and both models will be prepared for 3D printing.

Keywords: 3D Printing; Computed-aided design; Congenital heart disease; Hands-on Course; Medical education; Patch; Precision medicine; Radiological Society of North America; Segmentation; Ventricular septal defect.

Fig. 1

Schematic representation of the anatomy and blood circulation in a normal heart (left) and in the case of double outlet right ventricle (right)

Fig. 2

Mimics software environment project screen

Fig. 3

Thresholding segmentation process. Thresholding can be selected from the Menu Toolbar (1) or from the Segment tab (2). In the Thresholding window (bottom right) a HU range from 440 to 3071 is set (3). After clicking Apply (4) the contrast material in the heart and vessels appears green in the images

Fig. 4

Region Growing segmentation process. Region Growing can be selected from the Menu Toolbar (1) or from the Segment tab (2). A seed point is selected by left clicking a seed point in the heart atrium (3). Once selected a yellow mask is generated and the Region Growing window can be closed (4)

Fig. 5

Calculate 3D window. The Yellow mask is selected and Quality is set to optimal

Fig. 6

3D View of the created 3D Object –Yellow (1). Review of the anatomical structures

Fig. 7

Renaming the 3D Object–Yellow (1) to Heart Contrast

Fig. 8

Exporting from Mimics to 3-matic

Fig. 9

3-matic software environment project screen

Fig. 10

Wrap operation. Scene Tree and Operations tab selections

Fig. 11

Toggling between the visibility of the original and the wrapped Heart Contrast model

Fig. 12

Smooth operation. Operations tab selections

Fig. 13

Hollow operation. Operations tab selections

Fig. 14

Hollow operation end result. Note the differences between the model pre (left) and post adding a wall thickness (right)

Fig. 15

Trim operation. Operations tab selections

Fig. 16

Exposing the ventricular septal defect. Trimming the hollowed heart model by designing a triangle by connecting 3 distinct landmark points

Fig. 17

Reviewing the anatomy after revealing the ventricular septal defect. The initial (Heart Contrast) model in yellow and the hollowed model (Heart Contrast_wrapped) representing the wall of the heart chambers and the vasculature model in blue are superimposed in order to appreciate the anatomical relationships

Fig. 18

Intracardiac view of the ventricular septal defect (highlighted with a yellow circle below) and the outflows of the aorta and the pulmonary artery. Left panel shows view from right and right panel shows view from left

Fig. 19

Removal of floating shells. Clicking on a point anywhere on the model in the marked area turns orange (left). Applying the Invert Marking transfers the marked area from the heart to all floating shells

Fig. 20

Create Curve operation. Operations tab selections

Fig. 21

Creating the ventricular septal defect Curve. Note that the curve is not closed

Fig. 22

Close Curve operation. Operations tab selections

Fig. 23

Creating a new ventricular septal defect 3D object that will represent the Patch

Fig. 24

Fill Hole Freeform operation. Scene Tree and Operations tab selections

Fig. 25

Fill Hole Freeform end-result. A ventricular septal defect filling surface (representing the Patch) with no wall thickness

Fig. 26

Adding a wall thickness to the Patch using the Hollow operation. Operations tab selections

Fig. 27

Hollow operation end-result. The Patch now has obtained the needed wall thickness

Fig. 28

Visualizing the accurate matching of the Patch and the ventricular septal defect

Fig. 29

Objet Studio Server connection window

Fig. 30

Objet Studio software environment project screen

Fig. 31

Inserting the STL files of the patch and the trimmed heart models to Objet Studio

Fig. 32

Objet Studio software representation of the build tray of the printer with the two models imported and automatically oriented

Fig. 33

Single zoomed Isometric view of the models on the build tray. The Trimmed Heart and the Patch models are indicated

Fig. 34

Single zoomed Top view of the models on the build tray

Fig. 35

4 window zoomed Northeastern view of the models on the build tray

Fig. 36

Single zoomed Northeastern view of the models on the build tray

Fig. 37

Production estimate window

Fig. 38

Job manager module