Window settings for the study of calcified carotid plaques with multidetector CT angiography

Abstract

CT angiography (CTA) shows high sensitivity in detecting calcified plaques, but sometimes a bias in the exact quantification of stenosis degree occurs, mainly caused by the high linear attenuation coefficient of the calcified plaques. The purpose of this technical study was to evaluate the most appropriate CT window parameters for the assessment of calcified plaques stating which of them can provide the best inter-observer agreement. Scatter-plots and regression results showed the correlation between both width and level respectively depending on intraluminal Hounsfield units (HU) value (width = intraluminal HU x 2.07; level = intraluminal HU x 0.72). Obtained data indicated that the presence of different stenosis degrees did not modify visualization parameters.

Fig 1.

A, Scatterplot between width and level (NASCET II-V) with linear regression through the origin, with a 99% mean predictive interval and 99% individual predictive interval. Width = 2.81 × Level. B, Scatterplot between intraluminal Hounsfield unit values (IntraluminHU) and level (NASCET II-V) with linear regression through the origin with a 99% mean predictive interval and a 99% individual predictive interval. Level = 0.72 × Intraluminal HU. C, Scatterplot between intraluminal Hounsfield unit value and width (NASCET II-V) with linear regression through the origin with a 99% mean predictive interval and 99% individual predictive interval. Width = 2.07 × Intraluminal HU Value.

Fig 2.

Bland-Altman plots of intraobserver variability in the window width (A), window level (B), and intraluminal Hounsfield unit measurements (C). Obs indicates observer. Intralumin-HU indicates intraluminal Hounsfield unit.

Fig 3.

A 68-year-old man. CT axial images applying different window parameters. A and B, Intraluminal Hounsfield unit value is 547 (right bulbus). With a 275 width and 30 level (A) and 600/200 (B), it is not possible to differentiate lumen from calcification. C, With 800/300, it is possible to differentiate opacified lumen and calcification. D, By using equations described in this article, we obtained window parameters of 1132/394; a clear differentiation between lumen and parietal calcifications is visible.