Development of length standard phantom for length measurement correction in x-ray image.

Specific tissue lengths or volumes in x-ray images are measured for diagnostic and therapeutic purposes. Measurements are used to make clinical decisions; however, the accuracy of these measurements has not been studied. In this study, based on the sources of uncertainty, an SI-traceable length standard phantom and an x-ray imaging system calibration method are proposed. The uncertainty in the length of the fabricated standard phantom is determined using a toolmaker's microscope. The sources of uncertainty in an x-ray imaging system, such as magnification, pixel-to-millimeter unit conversion, and penumbra effect, are considered, and the lengths of the phantom before and after imaging system calibration were compared. The maximum deviation of length measurements with and without calibration is (-0.11 ± 0.10) and (-3.37 ± 0.15) mm (k = 2, 95% level of confidence), respectively. The proposed phantom and calibration method can be used for calibrating x-ray images and obtaining their length correction values. Furthermore, length correction values are expected to be useful for diagnosis and treatment planning, where precise length measurements are essential.