Development of solid water phantom using wax

In this work, we develop wax-based solid water phantoms for CT systems that have radiation characteristics close to those of water for clinically appropriate CT tube voltages. Most commercial solid water phantoms are made with non-water-based materials for durability. However, manufacture-grade solid water is difficult to replicate in a common lab setting and ingredients can be toxic. We have developed a wax-based solid water phantom for a coronary calcified plaque phantom for our ongoing research project where calcium-based material and fatty material are mixed into the water-equivalent material. We chose soy wax as a main ingredient because it is non-toxic and can be easily used to develop more realistic coronary plaques with a variety of compositions (e.g., more wax for fattier plaque). We determined additional ingredients and concentrations needed to make solid water phantoms via least squares method where the mass fraction of each material was estimated by minimizing the difference between the linear attenuation coefficients of water and the mixture. Based on the analytical calculation, physical solid water phantoms were developed and were scanned using micro-CT and clinical CT systems to experimentally verify the optimal concentration of the mixed material and phantom homogeneity. The CT values of our solid water phantom at the optimal concentration was found comparable to that of water and had similar variance. In addition to supporting our plaque phantom development, this solid water phantom could be used as a basis to develop a variety of other complex tissue-mimicking phantoms for use in clinical CT scanner.