Pulmonary nodule enhancement in subtraction CT and dual-energy CT: A comparison study

Objective: To compare nodule enhancement on subtraction CT iodine maps to that on dual-energy CT iodine maps using CT datasets acquired simultaneously. Methods: A previously-acquired set of lung subtraction and dual-energy CT maps consisting of thirty patients with 95 solid pulmonary nodules (>=4 mm diameter, 72 malignant) was used. Nodules were annotated and segmented on CT angiography, and mean nodule enhancement in the iodine maps calculated. Three radiologists scored nodule visibility with both techniques on a 4-point scale. Results: Mean nodule enhancement was higher (p < 0.001) at subtraction CT (34.9 +- 12.9HU) than at dual-energy CT (25.4 +- 21.0HU). Nodule enhancement at subtraction CT was judged more often to be "highly visible" for each observers (p < 0.001) with an area under the curve of 0.81. Conclusions: Subtraction CT is able to depict iodine enhancement in pulmonary nodules better than dual-energy CT.