A phantom study investigating the relationship between ground‐glass opacity visibility and physical detectability index in low‐dose chest computed tomography

In this study, the relationship between ground‐glass opacity (GGO) visibility and physical detectability index in low‐dose computed tomography (LDCT) for lung cancer screening was investigated. An anthropomorphic chest phantom that included synthetic GGOs with CT numbers of [Formula: see text] Hounsfield units (HU; high attenuation GGO: HGGO) and [Formula: see text] HU (low attenuation GGO: LGGO), and three phantoms for physical measurements were employed. The phantoms were scanned using 12 CT systems located in 11 screening centers in Japan. The slice thicknesses and CT dose indices ([Formula: see text]) varied over 1.0–5.0 mm and 0.85–3.30 mGy, respectively, and several reconstruction kernels were used. Physical detectability index values were calculated from measurements of resolution, noise, and slice thickness properties for all image sets. Five radiologists and one thoracic surgeon, blind to one another's observations, evaluated GGO visibility using a five‐point scoring system. The physical detectability index correlated reasonably well with the GGO visibility ([Formula: see text] for 6 mm HGGO and [Formula: see text] for 10 mm LGGO), and was nearly proportional to the CTDI(vol). Consequently, the [Formula: see text] also correlated reasonably well with the GGO visibility ([Formula: see text] for 6 mm HGGO and [Formula: see text] for 10 mm LGGO). As a result, the [Formula: see text] was nearly dominant in the GGO visibility for image sets with different reconstruction kernels and slice thicknesses, used in this study. PACS numbers: 81.70.Tx, 87.57.Q‐