QUALITY CONTROL OF CONVENTIONAL X-RAY TUBE IN THREE TERTIARY HOSPITALS IN SOUTH-EAST, NIGERIA

Background: Quality control of conventional x-ray tube ensures that the patient integral radiation dose is minimized and image quality is improved, by controlling the x-ray beam to reduce scatter radiation. Objective: To assess x-ray tubes for half value layer (HVL), x-ray field and light field congruence using known standard. Methodology: The HVLs were measured using calibrated, non-invasive, digital multifunctional detector meter that incorporate computer output. The detector was positioned at the center of the collimated beam axis with focus-to-image distance (FID) of 100 cm. Tube potentials of 80 and 100 kVp were selected, and used to make exposures. The corresponding HVLs were then recorded. Also, x-ray field and light field congruence were measured by placing 18 cm x 24 cm cassette loaded with film at FID of 100 cm. The collimator light was in ON position and metal markers were used to delineate the periphery of the light field. Misalignment was calculated from the developed radiographs using standard formula. Results: The HVL ranged from 3.40 to 4.4mmAl. Also, the sum of the misalignment in both orthogonal directions ranged from 7.21 to 9.70 % of FID in all three centers. Conclusion: The HVL were within standard limit at 80 and 100 kVp in all the centers studied. However, x-ray field and light field were grossly misaligned.