CT densitometry of pulmonary nodules: a phantom study.

Density determinations by computed tomography (CT) have been used to distinguish benign from malignant pulmonary nodules. Unfortunately, clinical scanning of pulmonary nodules frequently yields artifactually low CT numbers because of partial volume artifacts from the surrounding aerated lung. In order to determine the best performance that can be expected from a CT scanner in providing CT numbers for pulmonary nodules free of partial volume artifacts, we scanned a phantom containing plastic spheres surrounded by air to simulate nodules in aerated lung. The relations among size of the sphere, slice thickness (collimation), and centering of the CT slice critically affected the number of accurate voxel values. A simple computer model accurately duplicated the experimental findings. These data enable us to define the basic geometric requirements for accurate CT densitometry of pulmonary nodules.