How does image quality affect radiologists' perceived ability for image interpretation and lesion detection in digital mammography?

Abstract

Objectives: To study how radiologists' perceived ability to interpret digital mammography (DM) images is affected by decreases in image quality.

Methods: One view from 45 DM cases (including 30 cancers) was degraded to six levels each of two acquisition-related issues (lower spatial resolution and increased quantum noise) and three post-processing-related issues (lower and higher contrast and increased correlated noise) seen during clinical evaluation of DM systems. The images were shown to fifteen breast screening radiologists from five countries. Aware of lesion location, the radiologists selected the most-degraded mammogram (indexed from 1 (reference) to 7 (most degraded)) they still felt was acceptable for interpretation. The median selected index, per degradation type, was calculated separately for calcification and soft tissue (including normal) cases. Using the two-sided, non-parametric Mann-Whitney test, the median indices for each case and degradation type were compared.

Results: Radiologists were not tolerant to increases (medians: 1.5 (calcifications) and 2 (soft tissue)) or decreases (median: 2, for both types) in contrast, but were more tolerant to correlated noise (median: 3, for both types). Increases in quantum noise were tolerated more for calcifications than for soft tissue cases (medians: 3 vs. 4, p = 0.02). Spatial resolution losses were considered less acceptable for calcification detection than for soft tissue cases (medians: 3.5 vs. 5, p = 0.001).

Conclusions: Perceived ability of radiologists for image interpretation in DM was affected not only by image acquisition-related issues but also by image post-processing issues, and some of those issues affected calcification cases more than soft tissue cases.

Key points: • Lower spatial resolution and increased quantum noise affected the radiologists' perceived ability to interpret calcification cases more than soft tissue lesion or normal cases. • Post-acquisition image processing-related effects, not only image acquisition-related effects, also impact the perceived ability of radiologists to interpret images and detect lesions. • In addition to current practices, post-acquisition image processing-related effects need to also be considered during the testing and evaluation of digital mammography systems.

Keywords: Breast cancer; Digital mammography; Perception; Quality control.

Fig. 1

Pipeline of the image quality modification. In the case of contrast modifications, the “for presentation” image was degraded. In the case of reducing the resolution or modifying the noise, the “for processing” image was modified first and then processed. In all cases, the final output was “for presentation” images

Fig. 2

Distribution of the median of the radiologist index (1–7) for the lowest acceptable level of image quality by degradation type, corresponding index 1 to reference image, for (upper) calcifications and (lower) soft tissue cases. Boxplot explanation (right)

Fig. 3

Histogram corresponding to the levels of degradation (1–7, corresponding index 1 to reference image) that radiologists selected as still acceptable in images with lower resolution and quantum noise for (top row) calcification cases; and (bottom row) soft tissue cases

Fig. 4

Effects of increasing quantum noise in the image corresponding to a case with calcifications