| Physical phantoms are used to optimize various imaging modalities (e.g. computed tomography) in terms of Xray
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. |