LOW-DOSE SPIRAL COMPUTED-TOMOGRAPHY OF THE THORAX - COMPARISON WITH THE STANDARD-DOSE TECHNIQUE

RATIONALE AND OBJECTIVES. This study was conducted to determine whethe r significant reduction in radiation dose (250 mAs - 50 mAs), in chest computed tomography (CT) using volume acquisition affects image quali ty or the detectability of pathologic findings in the lung and mediast inum. METHODS. Phantom studies tr ere conducted to evaluate resolution and noise level, then a patient study was then done, Fifty consecutiv e patients (10 normal and 40 abnormal) cases were examined. After a sc an (250 mAs, 120kVp) of the entire thorax, five additional slices (50 mAs, 120kVp) at the level of the abnormality were obtained. Three inde pendent observers evaluated the visibility of normal lung and mediasti nal structures, as well as image noise. The mean score was compared be tween the standard and low doses. In a second study, an independent ev aluation of the presence or absence of pathologic findings was made by four observers. RESULTS. Lucite phantom studies demonstrated diminish ed low-contrast resolution and increased noise level for the low-dose technique, Observers assessed more noise in the low-dose images (P < 0 .001). The normal structures were judged to be more visible with stand ard dose (P < 0.01), but the magnitude of the judged differences was s mall especially in the lung. No differences were found in the detectio n of lung and mediastinal abnormalities (P > 0.10). CONCLUSIONS. The l ow-dose technique was effective in demonstrating pathologic findings f or the lung and mediastinum. Low-dose spiral CT should be considered a s a viable alternative to standard-dose spiral CT.