A PHANTOM STUDY - EVALUATION OF RENAL-ARTERY STENOSIS USING HELICAL CT AND 3D RECONSTRUCTIONS

Purpose: We studied which set of CT parameters and modeling parameters yielded accurate measurements of three graded artificial renal artery stenoses. Method: An acrylic phantom resembling the abdominal aorta a nd renal arteries was constructed. Stenotic segments had diameters of 1.8, 3.2, and 4.8 mm; nonstenotic segment diameter was 6.3 mm. Helical scans were done using 1 and 3 mm collimation at pitches of 1, 1.5, an d 2. 3D renderings were produced and measured. Multifactorial and regr ession tree analysis were used to determine the accuracy of the 3D ren derings. Mean squared error (MSE) was used to compare true diameter wi th measured diameter. Results: Collimation of I mm produced an MSE of 0.55 versus an MSE of 1.35 for 3 mm collimation. Stenosis grade was th e next most important parameter in the 1 mm subgroup and viewing direc tion in the 3 mm collimation subgroup. In the 1 mm subgroup, high and mid grade stenoses had an MSE of 0.52 versus low grade stenosis that h ad an MSE of 0.61, Pitch was a fourth-order effect. Conclusion: Collim ation of 1 mm combined with a pitch ratio as high as 2:1 is superior t o 3 mm collimation. Shaded surface modeling was the single best choice . for rendering 3D data. Stenosis grade interacted strongly with user- controllable parameters.