CT angiography: In vitro comparison of five reconstruction methods

OBJECTIVE. Five image reconstruction techniques have been used with CT angi ography: axial (cross-sectional), maximum intensity projection (MIP), curve d multiplanar reconstruction (MPR), shaded-surface display, and volume rend ering. This study used a phantom to compare the accuracy of these technique s for measuring stenosis. SUBJECTS AND METHODS. A 19-vessel phantom containing various grades of conc entric 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 v essels oriented parallel to the z-axis and opacified with nonionic contrast material. CT angiography images were produced using five optimized techniq ues: axial, MIR MPR, shaded-surface display, and volume rendering; and meas urements were made with an electronic cursor in the normal lumen and mid st enosis by five separate investigators who were unaware of vessel and stenos is diameters. Each of the techniques was first optimized according to the r adiology literature and our own preliminary testing. RESULTS. For vessels greater than 4 mm in diameter, axial, MIP, WR, shaded- surface display, and volume-rendering CT angiography techniques all had a m easurement error of less than 2.5%. However. axial, MIF, MPR, and shaded-su rface display techniques were less accurate in estimating smaller (less tha n or equal to 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 statis tically more accurate for diameters of 0.5-1.0 mm (p < 0.001). CONCLUSION. All five CT angiography display techniques (axial, MIR MPR, sha ded-surface display, and volume rendering) accurately display vessels and s tenoses greater than 4 nun in diameter. However, volume rendering tends to be more accurate for stenoses of 2-4 mm. and was statistically better in th e measurement of diameters of 0.5-1.0 mm (p < 0.001). Volume rendering is a n accurate method for evaluating all grades of stenoses.