[Evaluation of helical scan CT in the detection of lung nodules of pulmonary metastasis].

The purpose of this study was to evaluate the diagnostic capability of helical scan CT (HS-CT). We investigated the ability of HS-CT to detect lesions by scanning 129 small nodular lesions in the lung field in six cases of pulmonary metastasis. HS-CT was then employed to scan the same regions at table slide speeds of 20 mm/sec and 25 mm/sec. The acquired images were recorded on film and a video tape recorder (VTR), using axial multiplanar reconstruction. We then compared the various images to evaluate the effectiveness of conventional CT (slice thickness: 10 mm, table slide pitch: 10 mm) and HS-CT in visualizing the lesions. HS-CT images acquired at 20 mm/sec and at 25 mm/sec were equally effective in visualizing the lesions. Diagnostic capability was significantly lower in the apical area than in the middle and subdiaphragmatic areas. VTR images were better than film images in terms of diagnostic capability. The disadvantage of VTR images was that VTR processing required much time and labor, and thus is not practical at present. In conclusion, HS-CT is useful in detecting small nodular lesions in the lung field. However, the scanning conditions of HS-CT and interpretation of images, especially in the apical area, require further improvement.