September 1, 2000Open Access
View Full PaperReproducibility of Computer-Quantified Carotid Plaque Echogenicity
Key Result
Carotid plaques associated with ipsilateral silent brain infarcts had a significantly lower median gray scale median (GSM) compared to plaques without such infarcts (14 vs 30; P=0.003).
Study Design
Type
Observational (n=232)
Structured PICO
Does normalized computer-quantified carotid plaque echogenicity reproducibly identify plaques associated with silent brain infarcts in asymptomatic patients with 60-99% stenosis?
P
Population
232 asymptomatic carotid plaques causing 60% to 99% stenosis evaluated for echogenicity in relation to ipsilateral CT-demonstrated brain infarcts.
E
Exposure
Quantitative assessment of carotid plaque echogenicity using normalized gray scale median (GSM)
C
Comparator
Assessment before normalization; plaques not associated with silent brain infarcts
O
Outcome
Variability between storage media, magnification, and probes; interobserver agreement; association with ipsilateral CT-demonstrated brain infarctssurrogate
A computer-quantified method using normalized gray scale median improves the reproducibility of carotid plaque echogenicity assessment and can distinguish plaques associated with silent brain infarcts.
Main Result
Absolute Event Rate: 14% vs 30%
p-value: p=0.003
Limitations
- The method does not decrease the variability between degrees of magnification.
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 -14.5 and -0.12, 2.24 and 1.68, and -8.3 and -0.7, 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 (P:=0.003). The interobserver GSM difference was -0.05 (95% CI, -1.7 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.