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AJNR - American Journal of Neuroradiology

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Measurement Error of Percent Diameter Carotid Stenosis Determined by Conventional Angiography: Implications for Noninvasive Evaluation

Joseph E. Heiserman^a

^a From the Division of Neuroradiology, Barrow Neurological Institute, Phoenix, AZ 85013

View larger version (33K): [in a new window]   FIG 1. Graphs show summary of 500 randomly selected measurements from the simulation run. In A, differences between 2 simulated measurements are plotted versus mean value of s, the fractional residual lumen. B displays absolute difference versus mean for the same data. The line in B represents the linear regression fit. Although not strictly valid because the standard deviation is derived from a half-normal distribution, 95% limits of agreement (21) are indicated in A for reference. These plots illustrate the range of error as well as the mild dependence of standard deviation on stenosis grade in the simulation. The standard deviation tends to decrease for higher percentage diameter stenosis.

View larger version (12K): [in a new window]   FIG 2. Analysis of 1000 individuals evaluated for 60% diameter carotid stenosis using carotid angiography, is from data generated using the simulation described in the text. Prevalence is taken to be 30%, and the data from Table 3 are used to estimate outcomes, assuming these data are independent of prevalence. Of the 300 individuals with stenosis, 24 (8%) were false-negative (FN), and of the 700 individuals without stenosis, 21 (3%) were false-positive (FP). The overall misclassification rate is approximately 4%. TP indicates, true-positive; TN, indicates true-negative.