Design of a cardiac phantom for development of electrophysiology sudies

Abstract

Atrial fibrillation (AF) is the most common form of arrythmia. Without treatment, the heart rhythm usually becomes permanently disrupted and can lead to various heart related complications as stroke or heart failure. Cardiac phantoms are needed for the development of electrophysiological instruments and for training and education of electrophysiologist. A tissue mimicking phantom is an accurate model of organs or tissues mimicking the real life like scenario for a desired goal. Currently, no cardiac phantoms are available containing all requirements needed. Therefore, as a first step towards an applicable cardiac phantom for development of electrophysiology studies, this Master Thesis focused on the design of an anatomically anthropomorphic left atrium (LA) phantom mimicking the dielectric properties of human heart tissue in the frequency range of 10 kHz – 20 kHz. To assess this research goal, the objective was divided into 3 subgoals: 1. Evaluate different tissue mimicking materials with additives to meet the main phantom requirements. Three promising types of phantoms were examined: agar-, gellan gum- and polyvinyl alcohol-cryogel-based (PVA-C) phantoms. The dielectric properties and stiffness of the phantoms were manipulated by varying the concentrations of materials and by using additives. Graphite powder, charcoal powder, salt and sodium acetate were examined for increasing the electrical conductivity and oil, sugar and PVC for decreasing its relative permittivity.2. Extensively evaluate the most promising cardiac phantom materials. The most promising hantom tissue materials, based on the main phantom requirements, was used for the final design of a LA phantom. The cardiac phantom was prepared four times for extensive examination based on all phantom requirements.3. Develop a phantom design with comparable anatomy.
As a last step, the phantom was fabricated with comparable anatomy. In this part, a suitable mould was prepared in order to get a hollow shaped phantom.

Results
A 13,0wt% PVA, 0,15wt% salt and 0,05wt% sodium acetate and tap water solution was used for the final LA phantom design. The flexible cardiac phantom is easily made, affordable and has a shelf life of at least 1 month. The average difference between the target values and the mean of all four prepared cardiac phantom samples is 21.9% and 15.0% for permittivity and conductivity, respectively. Storing the phantoms in an aqueous liquid results in diffusion of salt and sodium acetate and water absorption of the phantom material. Stability is reached after 1 week. Finally, a cylinder-shaped hollow cardiac phantom is produced, with the use of a 3D printed mould, as comparable shape of the LA.
Producing a cardiac phantom of PVA is proved to be a good model. This research shows the design of a low cost, easily produced hollow shaped cardiac phantom consisting of 13.0wt% PVA, 0.15wt% salt and tap water. Even though more future work needs to be done for the development of a cardiac phantom, this research functions as a proof of concept for the development of a flexible phantom with possibilities to manipulate the dielectric properties and to create a hollow shaped phantom. The use of PVA as tissue mimicking material (TMM) and the use of 3D printed PVA for creation of the hollow shapes shows promising results for future development.