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.
