A simple phantom study of the effects of dose reduction (by kVp increment) below current dose levels on CR chest image quality

Purpose: To assess the applicability of a simple commercial chest phantom incorporating a quasi anthropomorphic insert, in image quality and dose optimisation studies in computed radiography (CR). Methods: Lung and mediastinal lesions simulated with gelatine were positioned on the chest phantom and exposures made at the current chest radiography dose, set as Dref in the study. Further exposures were made at doses below Dref to study the effect of reducing patient dose below current dose levels, on the clarity and detectability of lung lesions in computed radiography. Lesion detectability and clarity was assessed by four observers using a commercial image viewing software without image manipulation, and a local image viewing software that allowed image contrast enhancement. The possibility of extending dose reduction below current dose levels (Dref) was assessed for both unmanipulated and manipulated images, from comparison of doses that produced statistically significant differences in image quality from Dref. Results: Results show that as the dose was decreased below Dref, both the clarity and detectability of lesions in the lung images worsened when there was no facility to manipulate the image. The onset of a significant difference in image clarity in the lung area occurred at 0.06 mGy while significant detectability changes were observed at 0.04 mGy. Similar changes in image quality were observed with the use of image manipulation. However, dose reduction produced statistically significant differences (p < 0.05) in both image clarity and detectability at 0.10 mGy. Image clarity and detectability in the mediastinal area showed no statistical difference at all doses (p > 0.05) with and without image manipulation. Conclusion: The clarity and detectability of lesion images as a function of patient doses in computed radiography may be dependent on whether or not contrast enhancement techniques are employed. There is also evidence to suggest that low dose images of the high density mediastinum can be enhanced with post processing, making exposure at high doses unnecessary. Further work and clinical trials would be needed to confirm the generalizablity of these findings.