Quality control test of cone beam computed tomography – constancy tests

Abstract

Purpose: The paper describes tests of CBCT cone beam scanners carried out to ensure projection quality. Design/methodology/approach: During the studies, phantoms were scanned with a leading brand volumetric CT scanner according to the device manufacturer's recommendations. The water phantom and phantom made of PMMA with materials of different radiological densities were used in the performed tests. The image area during the tests was determined as a cylinder with diameter of 80 mm and height of 90 mm. In turn, exposure parameters were selected on the basis of clinically applied protocols of cranial imaging. Within carried out research, tests of noise level were performed, image homogeneity was analysed and Hounsfield units constancy was determined. To this end, 18 quality control tests were analysed, which were performed at intervals of about 30 days. Images obtained during phantom scans were analysed by determining the Hounsfield value of selected areas and their changes over time. Findings: The analysis of all carried out projection quality control tests showed that they met the criteria set by the manufacturer, falling within the predefined value ranges. One of the performed tests presented results approaching the limit of acceptable values. After notifying this case, it was shown that the CT scanner was serviced during that period. The obtained results of the quality control tests of water phantom as well as of the material phantom imaging were maintained at similar levels after the service activities. No changes were observed in the obtained mean values of Hounsfield units, which would indicate a decrease in diagnostic quality of CBCT projections. Research limitations/implications: The results presented in this publication require further analysis. These should be complemented by incl. analyses of spatial resolution and image geometry. Practical implications: Carried out research has shown that cyclical quality control testing by a qualified operator is an essential activity to ensure high diagnostic quality of the device. In addition, this analysis showed that procedures of in-service tests should not be omitted and delayed. Originality/value: Originality in these tests is the possibility to improve the procedures for performing basic quality control tests.