Manual or auto-mode: Does this affect radiation dose in digital mammography without compromising image quality?

INTRODUCTION: In current practice, auto-filter exposure mode is used for most screening mammography examinations. However, with better understanding of the side effects of radiation, it is important to examine exposure parameters and practises to minimise radiation dose to patients. The purpose of this phantom study is to investigate the impact that different exposure modes (manual, auto-time and auto-filter) have on radiation dose, while maintaining images of diagnostic quality. METHODS: This study was conducted in three stages. In the first stage, 125 images were taken using a Gammex 156 phantom with polymethyl methacrylate blocks to reflect varying thicknesses (4.5, 5.0, 5.5, 6.0 and 6.5 cm). In the second stage, three mammographers independently assessed image quality and assigned scores based on the number of distinct fibers, masses and speck groups visible. Images with acceptable quality were further investigated in the third stage by comparing their average glandular dose (AGD) using the Kruskal-Wallis H test and Dunn's post-hoc pairwise analysis. RESULTS: Significant differences in AGD were shown between the auto-filter mode and manual mode techniques for 6.0 cm, and between auto-time mode and manual mode techniques for 6.5 cm (p < 0.05). CONCLUSION: For 4.5, 5.0 and 5.5 cm phantoms, as AGD was not significantly different among the different modes, the auto-filter may remain the most practical option. However, significant reductions in AGD were obtained for the 6.0 and 6.5 cm phantoms when manual mode techniques were used. IMPLICATIONS FOR PRACTICE: Manual mode techniques can potentially provide dose-saving opportunity in 6.0 and 6.5 cm breast thickness though future work on human breast should be done to confirm this. Results from this study will support future research based on patient data.

Mammography test sets: reading location and prior images do not affect group performance.

AIM: To examine how the location where reading takes place and the availability of prior images can affect performance in breast test-set reading. MATERIALS AND METHODS: Under optimized viewing conditions, 10 expert screen readers each interpreted a reader-specific set of images containing 200 mammographic cases. Readers, randomly divided into two groups read images under one of two pairs of conditions: clinical read with prior images and laboratory read with prior images; laboratory read with prior images and laboratory read without prior images. Region-of-interest (ROI) figure-of-merit (FOM) was analysed using JAFROC software. Breast side-specific sensitivity and specificity were tested using Wilcoxon matched-pairs signed rank tests. Agreement between pairs of readings was measured using Kendall's coefficient of concordance. RESULTS: Group performances between test-set readings demonstrated similar ROI FOMs, sensitivity and specificity median values, and acceptable levels of agreement between pairs of readings were shown (W = 0.75-0.79, p < 0.001) for both pairs of reading conditions. On an individual reader level, two readers demonstrated significant decreases (p < 0.05) in ROI FOMs when prior images were unavailable. Reading location had an inconsistent impact on individual performance. CONCLUSION: Reading location and availability of prior images did not significantly alter group performance.

Assessing reader performance in radiology, an imperfect science: lessons from breast screening.

The purpose of this article is to review the limitations associated with current methods of assessing reader accuracy in mammography screening programmes. Clinical audit is commonly used as a quality-assurance tool to monitor the performance of screen readers; however, a number of the metrics employed, such as recall rate as a surrogate for specificity, do not always accurately measure the intended clinical feature. Alternatively, standardized screening test sets, which benefit from ease of application, immediacy of results, and quicker assessment of quality improvement plans, suffer from experimental confounders, thus questioning the relevance of these laboratory-type screening test sets to clinical performance. Four key factors that impact on the external validity of screening test sets were identified: the nature and extent of scrutiny of one's action, the artificiality of the environment, the over-simplification of responses, and prevalence of abnormality. The impact of these factors on radiological and other contexts is discussed, and although it is important to acknowledge the benefit of standardized screening test sets, issues relating to the relevance of test sets to clinical activities remain. The degree of correlation between performance based on real-life clinical audit and performances at screen read test sets must be better understood and specific causal agents for any lack of correlation identified.