Radiation exposure and image quality in chest CT examinations

OBJECTIVE. The purpose of this study was to determine how changes in radiog raphic tube current affect patient dose and image quality in unenhanced che st CT examinations. SUBJECTS AND METHODS. Ten sets of CT images were obtained from patients und ergoing CT-guided chest biopsies. For each patient, six images of the same region were obtained at settings between 40 and 280 mAs. CT data were used to reconstruct tomographic sections with a field of view limited to the nor mal contralateral lung. Images were printed using lung and mediastinal imag e display settings. Image quality was determined by asking radiologists to assess the perceived level of mottle in CT images. Five chest radiologists ranked the relative image quality of six images. Patient effective doses we re computed for chest CT examinations performed at each milliampere-second setting, Radiologists indicated whether any perceived improvement of image quality at the higher radiation exposures was worth the additional radiatio n dose. RESULTS. The differences in quality of chest CT images generated at greater than or equal to 160 mAs were negligible. Reducing the radiographic techni que factor below 160 mAs resulted in a perceptible reduction in image quali ty. Differences in CT image quality for radiographic techniques between 120 and 280 mAs were deemed to be insufficient to justify any additional patie nt exposure. However, the use of 40 mAs results in an inferior image qualit y that would justify increased patient exposure. CONCLUSION. Radiographic techniques for unenhanced chest CT examinations ca n be reduced from 280 to 120 mAs without compromising image quality.