Figure 4. Relationship between tumour size and the difference in CT values between the tumour and its surrounding lung parenchyma (CT) in visible and invisible tumours in cases detected on CT screening and those detected clinically. The detection rates onchest radiographs were 18% (4/22) for tumours 10 mm in diameter and 66% (27/41) for tumours 11–20 mm in diameter, and 8% (2/24) fortumours 400 HU CT and 74% (29/39) fortumours >400 HU CT. , Invisible tumour in CT screening group; , visible tumour in CT screening group; , invisible tumour in clinical group; •, visible tumour in clinical group.