Optimized Scanning Conditions of High Resolution CT in the Follow-Up of Pulmonary Emphysema

PURPOSE: To address the optimal scanning condition of high resolution computerized tomography from the perspective of minimizing exposed dose. METHOD: The influence of the electric current, the slice number, and the slice thickness on precise percent ratio of the low attenuation area to whole lung field (LAA%) of chronic obstructive pulmonary disease patients was examined. The standard conditions were 250 mA, 3 slices, 2 mm slice thickness, and a varied parameter. RESULTS: In cases showing an LAA% less than 30, LAA% obtained by < or =150 mA were significantly larger than those by 250 mA. The mean LAA% with 3 and 10 slices were well correlated and the correlation with lung function was similar. The correlation of LAA% with lung function was approximately the same between the 2 and 5 mm slice thicknesses. CONCLUSION: The electrical current must be > or =200 mA, and 3 slices and 2 mm slice thickness are appropriate.