Associations of edge-detected and manual-traced common carotid intima-media thickness measurements with Framingham risk factors: the multi-ethnic study of atherosclerosis

Abstract

Background and purpose: Carotid intima-media thickness (IMT) is a marker of cardiovascular disease derived from ultrasound images of the carotid artery. In most outcome studies, human readers identify and trace the key IMT interfaces. We evaluate an alternate approach using automated edge detection.

Methods: We studied a subset of 5640 participants with an average age 61.7 years (48% men) of the Multi-Ethnic Study of Atherosclerosis composed of whites, Chinese, Hispanic, and blacks that are part of the Multi-Ethnic Study of Atherosclerosis IMT progression study. Manual tracing IMT (mt-IMT) and edge-detected IMT (ed-IMT) measurements of the far wall of the common carotid artery served as outcome variables for multivariable linear regression models using Framingham cardiovascular risk factors and ethnicity as independent predictors.

Results: Measurements of mt-IMT were obtainable in 99.9% (5633/5640) and measurements of ed-IMT were obtainable in 98.9% (5579/5640) of individuals. Average ed-IMT was 0.19 mm larger than mt-IMT. Inter-reader systematic differences (bias) in IMT measurements were apparent for mt-IMT but not ed-IMT. Based on complete data for 5538 individuals, associations of IMT with risk factors were stronger (P<0.0001) for mt-IMT (model r2, 19.5%) than for ed-IMT (model r2, 18.5%).

Conclusions: We conclude that this edge-detection process generates IMT values equivalent to manually traced ones because it preserves key associations with cardiovascular risk factors. It also decreases inter-reader bias, potentially making it applicable for use in cardiovascular risk assessment.

Figure 1

Bland-Altman plot summarizing the differences between manual traced IMT and edge detected IMT values. Edge detected IMT values are subtracted from manual traced IMT.

Figure 2

a Paired differences between readers for manual traced IMT values. Readers 1 and 2 (inter-reader) are compared to reader 3. b Paired differences between readers for edge detected IMT values. Readers 1 and 2 (inter-reader) are compared to reader 3.

Figure 2

a Paired differences between readers for manual traced IMT values. Readers 1 and 2 (inter-reader) are compared to reader 3. b Paired differences between readers for edge detected IMT values. Readers 1 and 2 (inter-reader) are compared to reader 3.

Figure 3

Carotid artery far-wall interface differences. The lumen-intima interface (top arrow) is thinner than the media-adventitia interface(bottom arrow). This is in part due to the greater thickness of the adventitia.