Detection of nodular lesions in the lung using helical computed tomography: comparison of fast couch speed technique with conventional computed tomography.

The present study assessed the ability of helical CT performed at fast couch speeds (20 mm or 25 mm/sec), sufficient to cover the entire lung field during a single breath hold, compared with conventional CT for detecting pulmonary nodules in patients with metastatic lung disease. The subjects were seven consecutive patients with metastatic lung tumors in whom 152 lesions were detected by conventional CT. The average diameter of the nodules was 8.3 (range 2-23 mm). To scan the entire lung, we first employed conventional CT (10-mm slice thickness, 10 mm couchtop slide). We then used helical CT with couchtop speeds of 20 and 25 mm/sec, permitting easy scanning of the entire lung field during a single breath hold (images of reconstruction intervals; 25, 20, 12.5 and 10 mm). We assessed each image to compare detection capabilities in the lung. The detection capabilities for each reconstruction interval were 78, 83, 91 and 97%, respectively. The detection of nodules was superior for 12.5 and 10 mm images than for 25 and 20 mm images (P < 0.01). In 25 and 20 mm images, the detection capability was significantly lower in the apical area than in the middle area (P < 0.01). For nodules 5 mm in diameter, 10 mm images permitted complete detection. Helical CT fast couch speeds (20 or 25 mm/sec), which allow imaging of the entire lung during a single breath hold, may be useful in detecting metastatic pulmonary nodules, and helical CT is expected to be a useful method for lung screening.