Automatic plaque removal by dual energy CTA: assessment of effectiveness and impact on quantification of stenosis – a phantom study
The following abstract was presented during the 89th German Congress of Roentgenology in Berlin (May 2008, 20th – 23th)
Purpose: Dual energy CT allows automatic removal of calcified plaques from vessel lumen based on different absorption properties of calcium and iodine. The purpose of this phantom study was to evaluate the accuracy of dual energy CT with automatic plaque removal for grading of stenoses.
Materials and Methods: Vessel phantoms of different diameters (3mm-8mm), degrees of stenoses (25-75%), luminal contrast densities (150-450HU) and calcium plaque densities (300-720HU) were scanned using a Somatom Definition (Siemens) at 80 and 140kV. Separate datasets were calculated per voltage and used to generate plaque-subtracted images. Effectiveness of plaque removal, luminal integrity and degree of stenoses were assessed.
Results: A total of 405 measurements were performed. Plaque removal was effective in all cases except for the lowest plaque and lumen densities in 3 mm vessels. Luminal integrity was interrupted falsely suggesting occlusion in 20%. This occurred most frequently at low contrast concentration (lumen density 150HU, 37%) and least commonly at high contrast concentration (lumen 450 HU, 11%). Furthermore, false positive occlusions were most frequently seen in 75% stenoses (46%). Correlation between measured and real degree of stenoses increased with plaque and contrast density and vessel diameter from poor for 300HU-plaque/150HU-blood (R²=0,24) to excellent for 720HU-plaque/450HU-blood (R²=0.992; 8mm vessel).
Conclusion: In our phantom study, automatic plaque removal with dual energy CT worked well for strongly calcified plaques and high luminal contrast concentrations. Its accuracy is limited in stenoses with less calcium and lower luminal contrast enhancement and in high grade stenoses of vessels under 5mm diameter.
Authors: T. Werncke, B. Meyer, K.-J. Wolf, T. Albrecht
