Quantitative assessment of nonsolid pulmonary nodule volume with computed tomography in a phantom study

Background: To assess the volumetric measurement of small (≤1 cm) nonsolid nodules with computed tomography (CT), focusing on the interaction of state of the art iterative reconstruction (IR) methods and dose with nodule densities, sizes, and shapes. Methods: Twelve synthetic nodules [5 and 10 mm in diameter, densities of −800, −630 and −10 Hounsfield units (HU), spherical and spiculated shapes] were scanned within an anthropomorphic phantom. Dose [computed tomography scan dose index (CTDI vol )] ranged from standard (4.1 mGy) to below screening levels (0.3 mGy). Data was reconstructed using filtered back-projection and two state-of-the-art IR methods (adaptive and model-based). Measurements were extracted with a previously validated matched filter-based estimator. Analysis of accuracy and precision was based on evaluation of percent bias (PB) and the repeatability coefficient (RC) respectively. Results: Density had the most important effect on measurement error followed by the interaction of density with nodule size. The nonsolid −630 HU nodules had high accuracy and precision at levels comparable to solid (−10 HU) nonsolid, regardless of reconstruction method and with CTDI vol as low as 0.6 mGy. PB was Conclusions: Reasonable values of both accuracy and precision were achieved for volumetric measurements of all 10-mm nonsolid nodules, and for the 5-mm nodules with −630 HU or higher density, when derived from scans acquired with below screening dose levels as low as 0.6 mGy and regardless of reconstruction algorithm.