Optimisation of the lateral lumbar spine projection using an air-gap technique

Abstract

Purpose: To investigate the feasibility of replacing an antiscatter grid with an air gap technique to achieve dose reduction for lateral lumbar spine radiography while maintaining image quality on a direct digital radiography (DDR) system. Methodology: The study comprised of 2 phases. Phase 1 - an experimental study using an anthropomorphic phantom to identify the optimal airgap technique. Phase 2 - lateral projections of the lumbar spine were performed on patients (n=50). Patients were randomly assigned into a control group (n=25 imaged using the antiscatter grid) and an experimental group (n=25 imaged using the airgap technique). The dose area product (DAP) of all examinations was recorded, keeping all other variables constant. Image quality evaluation was performed by 5 radiologists performing Absolute Visual Grading Analysis (VGA) using an image quality score tool, with resultant scores analysed using Visual Grading Characteristics (VGC). Results: A 10cm airgap in conjunction with a source to image distance (SID) of 121cm was found as the optimal airgap technique. The clinical application of this technique resulted in a statistically significant (p<0.05) reduction in radiation dose of 72% in terms of DAP. Image quality scores were higher for the antiscatter grid but variation between image quality of the two techniques was not significant (p>0.05). Conclusion: The results imply that replacing the antiscatter grid with an optimal airgap technique in lateral lumbar spine digital radiography, provides a significant dose reduction whilst still maintaining diagnostic image quality.