Effect of image settings on nuchal translucency thickness measurement by a semi-automated system.

ABSTRACT

OBJECTIVE: To investigate whether pre- and post-processing image settings affect NT measurements made by a semi-automatic method (SAM). METHODS: Different image settings (e.g. gain) were either adjusted one at a time on images that had been obtained during fetal NT scans (post-processing, n = 66), or adjusted one at a time during live scanning and image acquisition of the adult posterior tibial artery (pre-processing group, n = 91). The NT and luminal diameter of the posterior tibial artery, respectively, were measured by SAM on all original and adjusted images. RESULTS: Alteration of the image settings resulted in a statistically significant effect on the measurements taken by SAM, with an average pair difference ranging from 0.001 mm to 0.139 mm. Most of the differences were small and therefore the clinical impact would be negligible. The pair differences were greatest with a very high contrast setting, or without tissue harmonic imaging (THI); the paired difference in measurement in those with vs those without THI was more than 0.1 mm in over 40% of cases. CONCLUSIONS: Measurements made by SAM are affected by image settings.