Reproducibility of Computer-Quantified Carotid Plaque Echogenicity

Abstract

Background and Purpose-We sought to assess the reproducibility, interobserver variability, and application to clinical studies of a new method for the quantitative assessment of carotid plaque echogenicity. Methods-Carotid plaques were scanned with the use of ultrasound, and their images were stored in a computer. They were normalized by assigning certain gray values to blood and adventitia, and the gray scale median (GSM) was used to quantify their echogenicity. The variability between storage media, between degrees of magnification, and between probes was assessed. The method was applied to 232 asymptomatic carotid plaques causing 60% to 99% stenosis in relation to the presence of ipsilateral CT-demonstrated brain infarcts. In all parts of the study the plaque GSM was measured before and after normalization to evaluate its effect. Interobserver agreement for the scanning process was assessed. Results-The GSM mean difference before and after normalization for variability studies of storage media, degrees of magnification, and probes was Ϫ14.5 and Ϫ0.12, 2.24 and 1.68, and Ϫ8.3 and Ϫ0.7, respectively. The median GSM of plaques associated with ipsilateral nonlacunar silent CT-demonstrated brain infarcts was 14, and that of plaques that were not so associated was 30 (Pϭ0.003). The interobserver GSM difference was Ϫ0.05 (95% CI, Ϫ1.7 to 1.6). Conclusions-Our method decreases the variability between storage media and between probes but not the variability between degrees of magnification. It separates echomorphologically the carotid plaques associated with silent nonlacunar CT-demonstrated brain infarcts from plaques that are not so associated.

Carotid Plaque Echolucency Increases the Risk of Stroke in Carotid Stenting

“…9,10,12,21 Only after the introduction of the image normalization did GSM become a highly reproducible index, allowing us to compare images from different scanners by different ultrasonographers and through different peripherals. 11 To establish an indication to treat patients with an echolucent plaque, we should compare the long-term results of the CAS (as emerging from the follow-up of the ICAROS patients) with those of medical therapy and CEA. The ongoing Asymptomatic Carotid Stenosis and Risk of Stroke (ACSRS) study 27 is analyzing the rate of neurological events in patients with echolucent carotid plaques, as measured by GSM, treated with the best medical therapy alone.…”

“…B-mode scan settings were adjusted as previously described. 11 A 15-second super-VHS video or magneto-optical disk recording was performed to show the vessel and plaque from a longitudinal view. Images were then sent to the coordinating center and transferred onto a personal computer.…”

“…9,10 Only after the introduction of the image normalization did GSM become a highly-reproducible index of the echolucency of carotid plaques with low interobserver and interscanner variability. 11 Several studies indicated that echogenicity is related to the histological components of carotid plaques 12,13 and that carotid plaque echolucency (low echogenicity) is associated with the development of neurological events 14 -17 and with an increased number of emboli after CEA and CAS. 18 -20 On the basis of these assumptions, our groups suggested that plaque echogenicity measured by GSM can be a useful indicator of embolic potential in the carotid arteries.…”

Stratifying risk: asymptomatic carotid disease

“…The morphologic classification and the corresponding ultrasound images is shown on Figure 1. In addition to the macroscopic ultrasonic evaluation of echogenicity, the GSM defined that a score is obtained using computer software as a surrogate marker of plaque vulnerability 63,64 . In fact, lipid-rich plaque core is seen in the DU as echolucent, and fibrotic components as echogenic.…”

Current Strategies and Possible Perspectives of Ultrasonic Risk Stratification of Ischemic Stroke in Internal Carotid Artery Disease

“…The GSM scale (grayscale median) describes the distribution of grayscale values on a scale from 0 -255. By means of digital processing of stored ultrasound pictures, it is relatively simple to perform normalization based on reference tissue like adventitia (GSM 185 -195) or blood (GSM 0 -5), thereby achieving better reproducibility of the data [22]. It has been demonstrated that the "normalized" GSM values acquired in this way consistently correlate with clinical events, i. e., they describe the risk of stroke connected to the morphological changes of the plaque [23,24].…”