Evaluating the use of higher kVp and copper filtration as a dose optimisation tool in digital planar radiography

Abstract

Purpose: This phantom-simulated study aims to evaluate the use of higher kVp and additional copper filtration as a dose reducing strategy in optimising the AP abdomen, AP knee, AP lumbar spine, and lateral lumbar spine projections. Objectives: To establish the optimised combination of kVp and copper filtration thickness, for each of the projections, considering both radiation dose and image quality. Methodology: In phase 1, an anthropomorphic phantom was exposed at different kVp (-10kVp, standard kVp, +10kVp and +20kVp from standard kVp) and copper filtration thickness (at 0mm, 0.1mm, 0.2mm of copper). The DAP, mAs and exposure time were recorded for each projection. During phase 2, objective image quality was measured using Contrast-Noise Ratio (CNR) calculations, and subjective image quality was tested via a group of radiographers and radiologists who performed Visual Grading Analysis (VGA) by grading the image quality criteria of each projection. Results: The optimised protocol for the AP-abdomen, AP-knee, AP-lumbar spine and lateral lumbar spine was at 100kVp and 0.2mm of copper, 85kVp and 0.1mm of copper, 110kVp and 0.2mm of copper, 110kVp and 0.2mm of copper, respectively. The application of the selected protocols resulted in 71.98%, 62.50%, 64.51% and 71.85% reduction in DAP. Areas Under the Curve (AUC) of 0.883, 0.664, 0.708 and 0.516, respectively, of which the AP-abdomen showed that image quality is statistically improved compared with the standard (p<0.05). CNR values decreased linearly as both kVp and copper filtration thickness increases for all the projections. Conclusion: The results support using the higher kVp and additional copper filtration protocols mentioned above when imaging the AP abdomen, AP knee, AP lumbar spine, and lateral lumbar spine. A significant dose reduction was recorded whilst an acceptable level of image quality was maintained, which must be confirmed with clinical studies.