Development of L1 Vertebral Anthropomorphic Model for Densitometric Phantom Improvement

The aim of the study was to develop L1 vertebral anthropomorphic model to improve the previously developed PHK FK2 phantom.

The vertebra was made using 3D printing by a digital model obtained from DICOM files of the abdominal CT examination. The phantom construction consists of three layers of different X-ray density. In the base made of photopolymer resin there is a cylindrical recess filled with a plastic mixture to imitate the normal state of the spongy substance (high density), osteopenia (moderate density decrease) and osteoporosis (significant decrease in density). Mineral density is regulated by changing β-tricalcium phosphate concentration. The cortical layer is modelled by applying metal foil on the base surface.

In X-ray tube voltage of 120 kV, the mean square deviations of the measured X-ray density values of the vertebral body, spongy substance and the cortical layer were 12.40, 3.96, and 57.23 HU, respectively. The mineral density assessment of the spongy substance for three X-ray tube voltages (100, 120, 140 kV) showed the mean absolute error to be 7.4 mg/ml, and the mean relative error - 7.3% (variation coefficient). The correction coefficient equal 7 mg/ml was used to correct the values, and after using the coefficient the mean absolute error decreased up to 0.4 mg/ml, and the mean relative error - up to 0.4% (variation coefficient). The relative measurement errors of the ventral, medial and dorsal vertebral body dimensions were 3.6, 2.7, and 2.9%, respectively.

The methods used in developing a vertebral model can be applied in modeling the entire range of the mineral density of bone spongy substance: from osteoporosis to norm. The developed model demonstrates high stability of X-ray characteristics and anatomical accuracy; therefore, it can be used for equipment calibration, quality control of diagnostic systems, and in the training process to demonstrate the bone structure changes.