Anthropomorphic head phantom for quantitative image quality assessment in cone beam computed tomography

Abstract

Introduction: In this study, a novel anthropomorphic head phantom for quantitative image quality assessment in cone beam computed tomography (CBCT) is proposed. The phantom is composed of tissue equivalent materials (TEMs) which are suitable for ‘ home made’ fabrication methods such as silicone casting and 3D printing and equipped with inserts for quantitative measurement of the contrast resolution. A monocalcium phosphate/gypsum mixture (MCPHG), nylon and a silyl modified polymer gel (SMP) are proposed as bone, muscle and brain equivalent materials respectively. Methods: The TEMs within a prototype were evaluated for their radiodensity in terms of Hounsfield Units (HU). Separate TEM samples were evaluated for their scatter magnitude and spatial distribution. The measurements were compared with theoretical HU values and Monte Carlo based scatter simulations of bone, muscle and brain tissue. Results: The median radiodensity and inter quartile range (IQR) of the MCPHG and SMP were found to be within the range of the theoretical radiodensity for bone and brain tissue: 922 (IQR = 156) and 47 (IQR = 7) HU respectively. The median radiodensity of nylon was slightly outside of the HU range of muscle tissue, but within the HU range of a combination of muscle and adipose tissue: -18 (IQR = 40) HU. The median ratios between the measured scatter characteristics and simulated tissues were between 0.84 and 1.13 after removal of one outlier (IQR between 0.05 and 0.14). Conclusions: The preliminary results of this study show that the proposed design and TEMs are potentially suitable for the fabrication of a ‘ home made’ anthropomorphic head phantom for quantitative image quality assessment in CT or CBCT.