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Optimal Peak Systolic Velocity Threshold at Duplex US for Determining the Need for Carotid Endarterectomy: A Decision Analytic Approach¹

¹ From the Program for the Assessment of Radiological Technology (ART Program), Department of Epidemiology & Biostatistics, and Dept of Radiology, Erasmus MC-Univ Medical Center Rotterdam, EE21-40b, Dr Molewaterplein 50, 3015 GE Rotterdam, the Netherlands (M.H.H., M.G.M.H.); Department of Neurology, Academic Medical Center, Amsterdam, the Netherlands (P.J.N.); Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht, the Netherlands (E.B., Y.v.d.G.); and Department of Health Policy and Management, Harvard School of Public Health, Boston, Mass (M.G.M.H.). Received June 18, 2004; revision requested August 26; revision received March 7, 2005; accepted April 4; final version accepted May 4. Supported by program grant 904-66-091 from the Netherlands Organization for Scientific Research. Address correspondence to M.H.H. (e-mail: m.heijenbrok{at}erasmusmc.nl).

View larger version (32K): [in a new window]   Figure 1a: Scatterplots of absolute PSV measurements and angiographic stenosis measurements. PSV thresholds for referring patients with (a) 70%–99% stenosis (220 cm/sec) and (b) 50%–99% stenosis (180 cm/sec) for carotid endarterectomy are shown. Increasing the PSV threshold reduces the number of false-positive (FP) cases (higher specificity) at the expense of a higher number of false-negative (FN) cases (lower sensitivity). TN = true-negative cases, TP = true-positive cases.

View larger version (32K): [in a new window]   Figure 1b: Scatterplots of absolute PSV measurements and angiographic stenosis measurements. PSV thresholds for referring patients with (a) 70%–99% stenosis (220 cm/sec) and (b) 50%–99% stenosis (180 cm/sec) for carotid endarterectomy are shown. Increasing the PSV threshold reduces the number of false-positive (FP) cases (higher specificity) at the expense of a higher number of false-negative (FN) cases (lower sensitivity). TN = true-negative cases, TP = true-positive cases.

View larger version (29K): [in a new window]   Figure 2a: Observed (ie, original) and smooth ROC curves for indications of (a) 70%–99% and (b) 50%–99% stenoses. The optimal likelihood ratio (LR)—that is, the slope of the ROC curve—derived at cost-effectiveness analysis is indicated with the associated sensitivity, specificity, and optimal PSV threshold. These data show that the optimal operating point on the ROC curve based on cost-effectiveness analysis results is different from the point on the curve that is closest to the upper left corner in ROC space, which is based on maximal accuracy.

View larger version (30K): [in a new window]   Figure 2b: Observed (ie, original) and smooth ROC curves for indications of (a) 70%–99% and (b) 50%–99% stenoses. The optimal likelihood ratio (LR)—that is, the slope of the ROC curve—derived at cost-effectiveness analysis is indicated with the associated sensitivity, specificity, and optimal PSV threshold. These data show that the optimal operating point on the ROC curve based on cost-effectiveness analysis results is different from the point on the curve that is closest to the upper left corner in ROC space, which is based on maximal accuracy.