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 (Cf) angiography wit h shaded surface display (SSD). Materials and Methods. A dedicated phantom was developed with an 8-mm lumin al diameter. Each of 19 vessels had stenoses ranging from 0% to 93.8%. Five blinded, experienced reviewers separately measured each vessel by using SS D 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 thres hold remained 100 HU, but this threshold was significantly less accurate th an 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 th is still produced measurements significantly less accurate than the gold st andard (P = .036) and one false occlusion in 15 vessels. Conclusion. CT angiography with SSD and an optimized threshold value is a u seful technique in vessels 1 mm and larger.