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Page 2 of 11 Tredway et al. Mini-invasive Surg 2020;4:78 I http://dx.doi.org/10.20517/2574-1225.2020.77

(3D) printing has been in use since the 1980s, recent application of this technique to the field of CHD
has aided in both diagnosis of cardiac defects and pre-procedural planning, and has been shown to be
[1-4]
particularly beneficial in guiding treatment of patients with more complex intracardiac anatomy .
3D reconstruction of imaging data from computed tomography (CT), magnetic resonance imaging (MRI),
and 3D echocardiography allows for enhanced understanding of complex intracardiac anatomy prior to
[5]
surgical or catheter-based procedures . 3D models have been shown to be especially useful in devising
percutaneous interventions for treatment of CHD. In recent years, there has been a remarkable evolution
of catheterization techniques and technologies, including the development of numerous minimally invasive
[3,6]
techniques to treat patients with CHD . Catheter-based interventions have become the standard of care
[6]
for a variety of procedures involving valve pathology, septal defects, and vascular abnormalities . 3D
models have the potential to provide additional anatomic insight and can be used to mimic device or stent
implantations prior to the procedure. This is particularly useful for interventional cardiac procedures, as
3D models can be used to ascertain optimal shape and size of the device, understand how the device will fit
[1,2]
into a specified location, and simulate the procedure in order to determine the optimal approach . These
models also enable proceduralists to perform entire procedures beforehand, thereby providing a means
[5]
to anticipate complications, reduce radiation exposure, and potentially improve patient outcomes . Here,
we discuss the process by which patient-specific 3D cardiac models are produced, as well as numerous
applications of these models for use in percutaneous interventions in CHD.

IMAGE POSTPROCESSING
Prior to creating a 3D model, a volumetric imaging dataset is acquired. CT and MRI are the most
commonly used modalities for creating 3D reconstructions, although echocardiography and rotational
[5]
angiography have also been used . Preference of one modality over another depends largely on the
experience of the center, the structure of interest, and age of patient. CT has been shown to be the easiest
modality for model creation as it allows for particularly detailed segmentation of great vessels and
[5]
intracardiac anatomy due to high spatial resolution . Alternatively, MRI or contrast-enhanced magnetic
resonance angiography offers whole heart 3D datasets while avoiding radiation exposure, which is preferred
in younger patients . More recently, there have been several reports on the use of 3D echocardiography in
[1]
creating 3D reconstructions. Novel echocardiographic transducers as well as advancements in software and
hardware have enhanced echocardiographic images, making them more suited for 3D modeling . The use
[7]
of echocardiography is beneficial as it is more widely available and avoids both radiation exposure and the
[1]
necessity of radiocontrast administration . This modality, however, has an inferior tissue-to-blood pool
contrast, which makes image segmentation significantly more challenging. Echocardiography is also the
preferred means by which to visualize cardiac valves and the atrial septum, which are poorly delineated in
both CT and MRI. Hybrid imaging techniques have also been developed, which combine cross-sectional
datasets with ultrasound in order to create complete heart models with embedded valve leaflets for more
[2,7]
comprehensive visualization of intracardiac anatomy .
Following the acquisition of the imaging dataset, a 3D rendering is created through a process known
as segmentation . The files are first uploaded as a DICOM (Digital Imaging and Communications in
[8]
Medicine) dataset into 3D visualization software, such as Mimics (Materialise, Belgium), or open-source
software, such as 3D Slicer (Slicer Wiki). Pixel-intensity-based thresholding is then employed to highlight
the blood pool within the desired region. Subsequently, regions of interest are isolated through manual or
semi-automatic techniques. The process of segmentation is the most time-consuming step of creating a
3D reconstruction. Accuracy of the model is largely determined by blood pool-to-tissue contrast, spatial
resolution of the imaging technique, motion artifact of the image, and the technician’s understanding of
[1,8]
anatomic relationships . The 3D rendering is then imported as a stereolithography (stl) file into a 3D
visualization software, such as 3-Matic (Materialise, Belgium), or open source programs, such as Blender