Automated Method for Evaluation of Z-axis Laser Alignment Accuracy using the Siemens Computed Tomography Phantom

Purpose: This study aims to develop an automated system for measuring z-axis laser alignment in computed tomography (CT) using a Siemens CT phantom. Methods: The automatic method for measuring z-axis laser alignment involves many steps . The image of the second module of the Siemens CT phantom was segmented. The radius of the phantom image was measured. The profile of pixel value along the two engraved notches was made at the 97% of phantom’s radius. The distance between two peaks of the pixel value profile, indicating the distance between two engraved notches, was measured. The distance was then converted from pixel units to millimeter units. This distance indicated the z-axis displacement ( d ). The automated method was evaluated for various set distances ( d ) ranging from 0 to 9 mm and for different slice thicknesses from 0.6 to 5 mm. The results of automated d measurements were compared to the manual d measurements. Results: The coefficient of correlation ( R ) between automated and set d are above 0.99. Measured d values with the automatic method are slightly lower compared to those from the manual method. The average differences between automatic and manual d results range from 0.14 mm to 0.26 mm across various nominal slice thicknesses. Conclusions: The developed software for automated z-axis laser alignment offers reliable, objective, and accurate results. This approach has the potential to help medical practitioners perform quality control of z-axis laser alignment.