Optimization of shaded surface display for CT angiography.

RATIONALE AND OBJECTIVES: The authors performed this study to determine the optimum threshold for performing computed tomographic (CT) angiography with shaded surface display (SSD). MATERIALS AND METHODS: A dedicated phantom was developed with an 8-mm luminal diameter. Each of 19 vessels had stenoses ranging from 0% to 93.8%. Five blinded, experienced reviewers separately measured each vessel by using SSD with display thresholds of 50, 100, 150, and 200 HU. RESULTS: For vessel diameters of 2 mm and larger, the best threshold value was 100 HU. This yielded measurements within 2% of the actual diameter and produced no false occlusions. For vessels 1 mm in diameter, the best threshold remained 100 HU, but this threshold was significantly less accurate than the standard (P = .0001) and produced two false occlusions in 15 vessels. For vessels 0.5 mm in diameter, the best threshold was 50 HU, although this still produced measurements significantly less accurate than the gold standard (P = .036) and one false occlusion in 15 vessels. CONCLUSION: CT angiography with SSD and an optimized threshold value is a useful technique in vessels 1 mm and larger.

CT angiography: in vitro comparison of five reconstruction methods.

OBJECTIVE: Five image reconstruction techniques have been used with CT angiography: axial (cross-sectional), maximum intensity projection (MIP), curved multiplanar reconstruction (MPR), shaded-surface display, and volume rendering. This study used a phantom to compare the accuracy of these techniques for measuring stenosis. SUBJECTS AND METHODS: A 19-vessel phantom containing various grades of concentric stenoses (0-100%) and three lengths (5, 7.5, and 10 mm) of stenoses was used for this study. Scans were obtained with a slice thickness of 2.0 mm, slice interval of 1.0 mm, pitch of 1.0, 120 kVp, 200 mA, and with the vessels oriented parallel to the z-axis and opacified with nonionic contrast material. CT angiography images were produced using five optimized techniques: axial, MIP, MPR, shaded-surface display, and volume rendering; and measurements were made with an electronic cursor in the normal lumen and mid stenosis by five separate investigators who were unaware of vessel and stenosis diameters. Each of the techniques was first optimized according to the radiology literature and our own preliminary testing. RESULTS: For vessels greater than 4 mm in diameter, axial, MIP, MPR, shaded-surface display, and volume-rendering CT angiography techniques all had a measurement error of less than 2.5%. However, axial, MIP, MPR, and shaded-surface display techniques were less accurate in estimating smaller (

CT angiographic measurement of the carotid artery: optimizing visualization by manipulating window and level settings and contrast material attenuation.

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.