Pulmonary nodules with ground-glass opacity can be reliably measured with low-dose techniques regardless of iterative reconstruction: results of a phantom study.

Abstract

Pulmonary nodules of ground-glass opacity represent one imaging manifestation of a slow-growing variant of lung cancer. The objective of this phantom study was to quantify the effect of the radiation dose used for the examination (volume CT dose index [CTDI(vol)]), type of reconstruction algorithm, and choice of postreconstruction enhancement algorithms on the measurement error when assessing the volume of simulated lung nodules with CT, focusing on two radiodensity levels. Twelve synthetic nodules of two radiodensities (-630 and -10 HU), three shapes (spherical, lobulated, and spiculated), and two sizes (nominal diameters of 5 and 10 mm) were inserted into an anthropomorphic chest phantom and scanned with techniques varying in CTDI(vol) (from subscreening dose [0.8 mGy] to diagnostic levels [6.5 mGy]), reconstruction algorithms (iterative reconstruction and filtered back projection), and different postreconstruction enhancement algorithms. Nodule volume was measured from the resulting reconstructed CT images with a matched filter estimator. No significant over- or underestimation of nodule volume was observed across individual variables, with low percentage error overall (-1.4%) and for individual variables (range, -3.4% to 0.4%). The magnitude of percentage error was also low (overall average percentage error < 6% and SD values < 4.5%) and for individual variables (absolute percentage error range 3.3-5.6%). No clinically significant differences were observed between different levels of CTDI(vol), use of iterative reconstruction algorithms, or use of different postreconstruction enhancement algorithms. These results indicate that, if validated for other measurement tools and scanners, lung nodule volume measurements from scans acquired and reconstructed with significantly different acquisition and reconstruction techniques can be reliably compared.