We applied helical CT to examinations of the abdomen and thorax. Scann
ing was performed continuously while the couchtop of the CT scanner wa
s shifted at a constant speed. The entire lung field could be scanned
during a single holding of the breath when the couchtop speed was 20 m
m/s. Tumors as small as 3 mm were detected. The diagnostic detectabili
ty and accuracy of helical CT were far superior to those of convention
al chest radiography. During abdominal examination, the target organ c
ould be scanned at any specified phase (preferably arterial) during th
e injection of contrast medium. We detected very small hepatic tumors
which could not be detected by conventional CT. Helical CT produced co
ntinuous data, which was reconstructed to display three-dimensional im
ages. Helical CT could be used in mass screening for the detection of
early lung cancer and in computer-aided diagnosis.