**2. 3D models in cardiology research projects**

The use of imaging techniques in cardiology had its beginning with the advent of chest X-ray, in which a topographic image of the heart could be done in different projections (1). In this type of image, volumetric structures appeared overlapping each other in the X-ray film. Multiple projections helped the analysis of cardiac structures and the location of abnormalities. Another radioactivity utility was the use of radiotracers and detection chambers—developing the planar Gamma Cameras, in which two-dimensional images were generated by detecting gamma radiation emitted by the radiotracer distributed through the heart [4].

Eight selected experiments developed by a multidisciplinary team of physicians, designers, and physicists are described in order to highlight the potential of the combination of AM and NITs, demonstrating that 3D representation enhances the understanding for the diagnosis and

Four NITs were adopted so as to generate 3D imaging files: 3D ultrasound (3DUS), magnetic resonance imaging (MRI), computerized tomography (CT), and micro-computed tomography (micro-CT). The routine of imaging acquisition and the AM systems are similar regarding their logical method based on the virtual "slicing" of an object, generating an amount of layers

The consecutive construction of the projected 3D computer-aided design (CAD) model can be reached throughout the superimposition of those same layers. The additive materialization process begins with the 3D CAD model, which is then "sliced" into layers that contain spatial references to guide later the deposit of selected materials, layer by layer, resulting on a physical

The actual additive method is based upon the successive overlapping of thin layers of specific material substances, according to the appropriate technical method, and is carried out by transforming the 3D files into an STL (Standard Triangulation Language) extension, which consists basically of *X*, *Y*, and *Z* coordinates. Once the STL file is generated, the next step is the horizontal slicing of the whole 3D volumetric file using software appropriate to the specific hardware being used, and calculating the supporting structures when necessary. The building process starts with the sequential deposition of layers of material, the layer width ranging from

This process is then followed by a post-processing stage, an essential procedure in all current AM technologies, where the model has to be cleaned to remove the support material and/or residues used during the building process. In the case of some AM processes that work by using a laser beam to harden photosensitive materials, it is also necessary to position and expose the model inside an ultraviolet light camera in order to solidify the model completely. There are presently diverse systems of AM/3D printing technologies commercially available. Although they use different material processes, they are all based on the principle of physical materialization by layer deposition. One of the most important characteristics of the additive manufacturing technology is its capability of construction parts with any geometrical intricacy, a process in which subtractive technologies as CNC equipment are sometimes limited and time

The use of imaging techniques in cardiology had its beginning with the advent of chest X-ray, in which a topographic image of the heart could be done in different projections (1). In this type of image, volumetric structures appeared overlapping each other in the X-ray film. Multiple projections helped the analysis of cardiac structures and the location of abnormalities. Another radioactivity utility was the use of radiotracers and detection chambers—developing

microns to fractions of millimeters, depending on the technology chosen [1].

**2. 3D models in cardiology research projects**

treatment in medicine.

112 New Trends in 3D Printing

3D model.

consuming [1–3].

according to the thickness recommended [1].

The idea of generating images as sequences slices of the heart gave rise to tomographic techniques. In this field, computing tomography was developed with the use of radiation generated by an electrical current: spect scintigraphy imaging, using the radiotracers, and magnetic resonance imaging, by acquiring energy emitted by accommodation of the nuclear spins. The possibility of three-dimensional reconstruction using two-dimensional tomograph‐ ic images provided remarkable progress in the study of heart anatomy and diseases [5].

By the same principle of using two-dimensional images for three-dimensional reconstruction, the 3D echocardiography was developed. With this technique, it is possible to present the heart images in three dimensions. In addition, the heart movement is displayed, adding important information about the heart function, once it is a dynamic organ with constant movement [6– 8].

In assessing the evolution of image acquisition techniques, topographic, two-dimensional slices, three-dimensional reconstruction, 3D moving images, we can see that fewer mental process and imagination is required to design an imaginary volumetric structure through their 2D projections. This fact seems to be important, because each individual has different abilities to mental reconstruction of a 3D structure. Such variability can bring a discrepancy in the evaluation of the same case by different physicians. For example, during surgical planning, there is no guarantee that the tomographic images analysis, by the surgeon and the radiologist, generated similar mental conceptions in the mind of each of these professionals [1, 9, 10].

As a next step, the construction of patient-specific 3D heart models, using rapid prototyping techniques, probably, will bring benefits to the cardiovascular science. Recent publications have pointed to the possibilities generated by this technology in cardiology. In education and medical training, 3D printing of heart structures can assist in improving the learning curve. On the diagnostic process, probably, the congenital and valvular heart disease may be better studied with the printing of physical models. In the treatment, especially in surgical interven‐ tions, patient-specific three-dimensional models can help as a pre-step procedure for a more assertive surgical planning. Perhaps, it can be said that the three-dimensional physical models, in a certain way, standardize the imaginary mental process of 3D reconstruction. Furthermore, in these models, the structures are displayed in a three-dimensional space, unlike the conven‐ tional 3D images displayed on a two-dimensional screen. The 3D environment is also present in holographic projections and virtual reality simulations, where the structures are manipu‐ lated and analyzed in a 3D virtual space. Although promising, the calibration and quality control of the equipment that are involved in the rapid prototyping technique are key factors. In each process step, image acquisition, digital file segmentation, 3D printing, and systematic errors can be added, resulting in a physical model that do not represent the real organ [10, 11].

**Figure 1** shows a physical model, of a healthy heart of a medium height man, 50 years old. The digital archive of heart images was generated by performing an angio-CT scan, Somatom Sensation 64 × 0.6 mm (Siemens Inc., Germany).

**Figure 1.** A. 3D model of human heart from CT scanner with "arduino" electronic board controlling led inside the model to allow the visualization of different densities of the heart positioned on measuring scale table (scale reference: 1 cm2 )—(3D printed in photosensible resin—PROJET 3510 HD Plus—3D Systems)—Núcleo de Experimentação Tridi‐ mensional—NEXT PUC-Rio; B: Same 3D file printed in two parts to allow the visualization of the internal structures (3D printed in polyamide at EOS P110)—Instituto Nacional de Tecnologia—Laboratório de Modelos Tridimensionais —Ministério da Ciência, Tecnologia e Inovação.

Aortic valve can be affected by many diseases that culminate with the necessity of a heart surgery, for aortic valve replacement. In this surgical procedure, the native aortic valve, dysfunctional, is excised and a biological or metallic prosthesis is implanted in the aortic annulus. After this surgery, several complications may occur. When the suture fixing the prosthetic valve in the aortic annulus breaks, a hole is formed between the prosthetic ring and the aortic annulus, a process named as paraprosthetic leak. With this complication, during ventricular diastole, blood present in the aortic root returns to the left ventricle, causing volume overload that can result with a severe left ventricular dysfunction.

**Figure 2A** presents a physical model, in full scale, of a heart segment in which there is a paraprosthetic leak around a biological aortic valve prosthesis. This hole measures approxi‐ mately 1 cm. This model was carried out with the purpose of planning the percutaneous procedure that would be done to fix this abnormality. In **Figure 2B** and **C**, the implantation process of an occluder may be noted within the paraprosthetic leak. In this case, the physical model can help the physician to detect the spatial location of the defect to be corrected before the procedure is started. Besides that, the physical model can be used to test many types and sizes of percutaneous occluders. The digital archive of heart images was generated by performing an angio-CT scan, Somatom Sensation 64 × 0.6 mm (Siemens Inc., Germany).

**Figure 2.** A. 3D model of heart section from CT scanner files positioned on measuring scale table (scale reference: 1 cm2 ); B and C: detail highlighting paravalvular leak beside aortic bioprosthesis (3D printed in photosensible resin— PROJET 3510 HD Plus - 3D Systems)—Núcleo de Experimentação Tridimensional—NEXT PUC-Rio.
