Personalised 3D printed models created from cardiac imaging data, mainly from cardiac CT images have been increasingly used in cardiovascular disease, primarily in the preoperative planning and simulation of complex surgical procedures, as well as medical education. 3D printed models are proved to be highly accurate in replicating normal anatomy and cardiac pathology with reported differences less than 0.5 mm between 3D printed models and original sources images. Further to these applications, a new research direction of utilising 3D printed models is to study the optimal CT scanning protocols in cardiovascular disease with the aim of reducing radiation dose while preserving diagnostic image quality. To achieve this goal, an appropriate printing material is essential to ensure that the printed models possess elasticity and flexibility similar to normal tissue properties.
Zhonghua Sun, a John Curtin Distinguished Professor and medical imaging researcher from Curtin University, Australia has been in search of suitable 3D printing materials to print realistic models, and more importantly, to print cardiovascular models with similar tissue properties to replicate heart and aortic arteries. Prof. Sun's research interests lie in 3D image visualization and diagnosis; 3D printing, virtual reality and artificial intelligence in medical applications, specifically in the cardiovascular disease. In his recent work, published in Current Medical Imaging, Prof. Sun and his team presents research findings for printing the aorta models with printing materials having similar CT attenuation to that of normal aortic wall on both pre- and post-contrast CT scans. This study further advances the current applications of 3D printing in cardiovascular disease to another level by presenting evidence that 3D printed personalised aorta models can be used to study optimal CT protocols, in addition to the value that 3D printed aorta models serve as a useful tool for pre-surgical planning and simulation of endovascular repair of aortic disease.
In his latest article, Prof Sun and his team reported findings on how the identified materials can be used to print realistic aorta models. They first created a 25-mm long type B aortic dissection model from CT images, then printed 4 models with use of two materials, namely Agilus from Stratasys and Visijet CE-NT from 3D Systems. These materials are soft and can be mixed with another material such as photopolymer resin to create a range of products with different elastic properties. These 4 aortic models consisted of two Agilus models printed with A40 and A50, representing two different degrees of hardness, another two Visijet models printed with Visijet CE-NT with different hardness, A30 and A70. The Visijet CE-NT A30 has a tensile strength between 0.2 and 0.4 which is close to the aging arteries, while Agilus A40 and A50 have a tensile strength of 0.5 to 1.5. The 4 aorta models were scanned on a 192-slice CT scanner with the standard aorta CTA protocol, and the scans were performed with and without use of contrast medium to measure CT attenuation at true lumen, false lumen, intimal flap and two junction areas between the true and false lumens. Results showed that Agilus models had higher CT attenuation than Visijet CE-NT models on non-contrast CT images, with Agilus A50 having an average CT attenuation similar to that of original CT images. On contrast images, only Visijet CE-NT A30 produced CT attenuation similar to that of original images, while the remaining models printed with other materials resulted in significantly higher CT attenuation than that of original images. This study shows that Visijet CE-NT A30 is considered an appropriate material to print aortic dissection model due to its similar elasticity to the normal aorta.
Aorta CT angiography (CTA) is currently the reference method in preoperative assessment of aortic aneurysm and dissection. Further, CTA is commonly used to follow-up patients treated with endovascular stent grafts. Therefore, regular CTA follow-ups of these patients at 3, 6 and 12 months, yearly thereafter contribute to cumulative radiation dose, which raises serious concerns due to radiation-induced malignancy. Dose optimization is clinically important to these patients receiving multiple CT scans. "3D printed aortic models with Visijet CE-NT material give the appearance of translucent light yellow allowing its use for education purpose, in addition to its reported value in guiding complex aortic surgery or endovascular aortic repair," says Prof. Sun. He also added "printing aortic dissection models is very challenging compared to other cardiovascular models due to very thin membranous structure of the intimal flap." The CTA images used in this study represented nice anatomical structures including intimal flap which were segmented and printed without any difficulty. This confirms the importance of quality of source images to guarantee printing high-quality models.
Prof. Sun's team is continuing to work on printing more anatomical structures including ribs, thoracic vertebrae, soft tissues, lungs and heart which allows for simulation of more realistic environment. "The phantom should be improved to mimic the in vivo circumstance and this allows for investigation of optimal aorta CT scanning protocols for detection of aortic dissection," says Prof. Sun.
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