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CT Angiographic Measurement of the Carotid Artery: Optimizing Visualization by Manipulating Window and Level Settings and Contrast Material Attenuation¹

¹ From the Departments of Radiology (Y.L., K.D.H.) and Health Evaluation Sciences (D.T.M.) and the College of Medicine (K.A.A.), Penn State University, PO Box 850, Hershey, PA 17033; and the Department of Radiology, Hua Dong Hospital, Shanghai, China (Y.L.). Received May 18, 1999; revision requested July 14; revision received January 24, 2000; accepted February 21. Address correspondence to K.D.H. (e-mail: khopper@psu.edu).

PURPOSE: To evaluate a broad range of window and level settings for various contrast material attenuation coefficients and degrees of vascular stenosis to obtain the most accurate computed tomographic (CT) angiographic measurements.

MATERIALS AND METHODS: A total of 25,480 measurements were made transversely (perpendicular to the lumen) and by means of maximum intensity projection (MIP) in a phantom with stenoses of 0%–100%, contrast material with attenuation coefficients of 150–350 HU, and 14 window and 13 level settings. Edge definition was also evaluated.

RESULTS: There was an inherent relationship between the contrast material attenuation coefficient and the optimal window and level settings in the measurement of stenoses at both transverse and MIP CT angiography. This relationship between the contrast material attenuation coefficient D and the optimal settings for window W and level L was represented by the following simple equations: W/D = [-2 x (L/D)] + 1.3, where -0.2 < L/D < 0.5, and W/D = [3.3 x (L/D)] - 1.3, where 0.5 < L/D < 1.0. With a vascular contrast material attenuation coefficient of 250–350 HU, the best transverse and MIP display settings for the window and level were 96 and 150 HU, respectively.

CONCLUSION: The use of optimized window and level settings at CT angiography reduces measurement variability.

Index terms: Carotid arteries, angiography, 172.129116 • Carotid arteries, CT, 172.129116 • Carotid arteries, stenosis or obstruction, 172.721 • Computed tomography (CT), maximum intensity projection, 172.129119 • Contrast media, experimental studies • Phantoms

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