Construction and verification of a physical chest phantom from suitable tissue equivalent materials for computed tomography examinations

Abstract

Physical phantoms are used to optimize various imaging modalities (e.g. computed tomography) in terms of X-ray image quality and absorbed dose. In this regard, this study tried to design and construct a suitable physical phantom with high accuracy and low price in diagnostic energy range. The phantom geometry was selected to be similar to a 5 cm thick cross-sectional slice of an adult human chest. To choose the appropriate tissue-equivalent materials, the physical properties (mass density, electron density and effective atomic number) of a wide range of available polymers were discussed and their accordance with those of human tissues were investigated. Phantom body was made of polymethylmethacrylate and 17 holes were considered in the phantom for placement of different tissue-equivalent materials. According to the physical properties, polypropylene, polyethylene, acrylonitrile butadiene styrene, polyurethane, polyamide and polyoxymethylene were selected and prepared for replacement of adipose, breasts, muscle, liver, cartilage and ribs, respectively. In addition, two different polyurethane foams were made of their raw materials for replacement of the lungs in inhalation and exhalation modes. Then, the prepared phantom was scanned by Siemens somatom sensation 64-slice scanner at tube voltage of 120 kVp and Hounsfield units of tissue-equivalent materials were measured. In addition, using theoretical relationships and goodness of fit test, their Hounsfield units were calculated. It was observed that, the calculated values were able to predict the measured values with the accuracy of 99%. Finally, the Hounsfield units of real human tissues were determined by the mathematical relationship obtained in the previous step; and in order to verify the outcomes, they were compared with other published reports. It was found that the Hounsfield units of real human tissues obtained using this physical phantom and Gammex RMI 465 phantom (scanned by Siemens somatom sensation 64) had the least differences. This demonstrated the high precision of the phantom and selected tissue substitutes, so it could be used in diagnostic energy range.