DETECTION OF NODULAR LESIONS IN THE LUNG USING HELICAL COMPUTED-TOMOGRAPHY - COMPARISON BETWEEN 360-DEGREES AND 180-DEGREES RECONSTRUCTION ALGORITHMS

The present study has evaluated helical computed tomography (HS-CT) pe rformed at a fast couch-top sliding speed (20 mm/sec, sufficient to co ver the entire lung field during the holding of a single breath) with regard to its ability to detect pulmonary nodules in patients with met astatic lung disease. The detectability of lesions by HS-CT was compar ed between 360 degrees and 180 degrees reconstruction algorithms. The subjects were eight consecutive patients with metastatic lung tumors, in whom 214 lesions had been detected by conventional CT. The average diameter of the nodules detected was 7.7 mm (2-22 mm). To scan the ent ire lung, we first used conventional CT (10-mm slice thickness, 10-mm stepping) and then HS-CT with a couch-top speed of 20 mm/sec and a tub e current of 50 mA. Both 360 degrees and 180 degrees algorithms were u sed to reconstruct images at intervals of 20 and 10 mm from HS-CT data . Detection rates of 79% for 20-mm images and 94% for 10-mm images wer e achieved with the 360 degrees algorithm. Detection rates of 81% for 20-mm images and 99% for 10-mm images were achieved with the 180 degre es algorithm. The detection of nodules was greater for 10-mm images th an 20-mm images (P<0.01). There was no significant difference between the 360 degrees and 180 degrees algorithms. Images acquired using the 180 degrees algorithm, however, depicted lesions with greater sharpnes s than those acquired using the 360 degrees algorithm. It is presumed that they indirectly show the superiority of the 180 degrees algorithm over the 360 degrees algorithm. HS-CT should prove a useful screening technique for lesions in the lung field.