Colour Maps and Reproducibility of Sonographic Endometrial Thickness Measurements

Abstract

The colour map function is widely available on modern ultrasound equipment and may enhance ultrasound visualisation. However, there is little evidence of its use. This research investigates if colour maps affect reproducibility of sonographic endometrial thickness measurements. A longitudinal greyscale image of the uterus and endometrium are acquired from 25 women by transvaginal ultrasound scans. The colour map function is applied to this image in red, purple, pink, green and blue. 4 reviewers independently and blindly obtain 2 endometrial thickness measurements from each image. Bland and Altman’s 95% limits of agreement are applied to the data. The average intra-reviewer and inter-reviewer agreement is 0.929 and 0.935 respectively. The agreement of the measurements within each colour map is 0.949 jointly for grey, green, pink and purple, 0.939 for red and 0.918 for blue. The agreement of measurements from images with colour map vs. greyscale is 0.980 jointly for green and purple, 0.975 for red, 0.970 for blue and 0.965 for pink. The average kappa statistic based on categorising measurements into normal, borderline and abnormal, is 0.80. Colour maps do not affect the reproducibility of endometrial thickness significantly and may be used interchangeably with greyscale images during the ultrasound examination.