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 (<or=4 mm) diameters. Volume rendering tended to be more accurate in the measurement of vessels with a 2.0- to 4.0-mm diameter and was statistically more accurate for diameters of 0.5-1.0 mm (p < 0.001).
Conclusion: All five CT angiography display techniques (axial, MIP, MPR, shaded-surface display, and volume rendering) accurately display vessels and stenoses greater than 4 mm in diameter. However, volume rendering tends to be more accurate for stenoses of 2-4 mm and was statistically better in the measurement of diameters of 0.5-1.0 mm (p < 0.001). Volume rendering is an accurate method for evaluating all grades of stenoses.