Developing an ultrasound phantom using 3D printing for practicing minimally invasive intracardiac procedures.
Transseptal punctures are widely used by electrophysiologists to gain access to the left atrium of the heart. The procedure involves piercing the interatrial septum, at the fossa ovalis, using a needle catheter. Clinical experience, in particular the tactile feedback during the puncture, plays a key role. Currently, there are limited opportunities to practice the transseptal puncture out of a clinical setting. Therefore, I have created an ultrasound training phantom, using the novel gel wax material, to address this issue.
3D printed moulds, with accurate anatomic dimensions, were used to replicate cardiac vessels and chambers. The moulds were placed in a container and liquid gel wax, which melts at 130C, was poured into the container to take the shape of the mould. The gel wax was infused with 0.5% glass microspheres (0-63 microns) as a scattering agent to give the phantom tissue-like ultrasonic properties.
The resulting Phantoms allowed the position of the catheter needle to be visualised both directly and by using ultrasound imaging techniques. Moreover, the dimensions of my phantoms accurately matched that of a normal human heart. This was shown by the the small percentage error of 5.2%, 8.4% and 7.4% between the ultrasound phantom dimensions and the mould reference dimensions for Phantoms 3, 4 and 6 respectively. Phantom 6 was created using 3D cardiac data obtained from MRI scans and it showed that complex anatomic structures could be effectively captured in a gel wax training phantom.
This project has resulted in the first gel-wax based ultrasound training phantom for practicing and helping to minimise patient risk during the transseptal puncture procedure. Gel wax is clearly an effective material for replicating cardiac anatomy as it maintains it’s structure and remains hydrated for several weeks. Moreover, it is highly cost-effective. This experimental method limits the interatrial septum thickness to 5mm (as opposed to <1mm in vivo) as gel wax can tear during mould removal if it’s thinner. Manipulating anatomic data from MRI or CT scans requires significant technical ability. In the future, patient specific Phantoms with more relevant anatomy (e.g. aorta and pulmonary veins) would be useful training and planning tools for complex cases.