Design of a 3D printed coronary artery model for CT optimization

Introduction: To design a custom phantom of the coronary arteries to optimize CT coronary angiography (CCTA) protocols. Methods: Characteristics of the left and right coronary arteries (mean Hounsfield Unit (HU) values and diameters) were collected from consecutive CCTA examinations (n 1/4 43). Four different materials (two mixtures of glycerine, gelatine and water, pig hearts, EcoflexTM silicone) were scanned inside a Lungman phantom using the CCTA protocol to find the closest model to in vivo data. A 3D printed model of the coronary artery tree was created using CCTA data by exporting a CT volume rendering into Autodesk MeshmixerTM software. The model was placed in an acid bath for 5 h, then covered in EcoflexTM, which was removed after drying. Both the EcoflexTM and pig heart were later filled with a mixture of contrast (Visipaque 320 mg I/ml), NaCl and gelatin and scanned with different levels of tube current and iterative reconstruction (ASiR-V). Objective (HU, noise and size (vessel diameter) and subjective analysis were performed on all scans. Results: The gelatine mixtures had HU values of 130 and 129, EcoflexTM 65 and the pig heart 56. At the different mA/ASiR-V levels the contrast filled EcoflexTM had a mean HU 318 +/- 4, noise 47 +/- 7HU and diameter of 4.4 mm. The pig heart had a mean HU of 209 +/- 5, noise 38 +/- 4HU and a diameter of 4.4 mm. With increasing iterative reconstruction level the visualisation of the pig heart arteries decreased so no measurements could be performed. Conclusion: The use of a 3D printed model of the arteries and casting with the EcoflexTM silicone is the most suitable solution for a custom-designed phantom. Implications for practice: Custom designed phantoms using 3D printing technology enable cost effective optimisation of CT protocols. (c) 2021 The College of Radiographers. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).