CT OF THE CHEST AND ABDOMEN IN PATIENTS ON MECHANICAL PULMONARY VENTILATORS - QUALITY OF IMAGES MADE AT 0.6-SEC VS 1.0-SEC

OBJECTIVE. Chest and abdominal CT scans using 1.0-sec scan times are o ften limited by motion in patients who are unable to hold their breath . With our scanner we can obtain images in 0.6 sec (partial scan) that use data from 225 degrees instead of the 360 degrees used for 1.0-sec scans. The purpose of this study was to assess whether the quality of images of the chest and abdomen in patients on mechanical pulmonary v entilators who could not breath-hold could be improved if images were taken using a scan time of 0.6 sec rather than 1.0 sec. MATERIALS AND METHODS. Thirty patients who were being treated with mechanical pulmon ary ventilation with indications for chest or abdominal CT or both wer e scanned with a scan time of 1.0 sec. At the end of the examination, additional 0.6-sec images were taken at three or four levels. Images o btained with these two scan times were filmed at similar levels and wi ndows, and anatomically matched levels were compared. The images were masked and independently evaluated by three radiologists for motion, n oise, artifact, and overall image quality. Each parameter was rated us ing a scale of 1 to 4. Using Kendall's tau correlation, there was no s ignificant difference between the radiologists in the grading of indiv idual parameters or of overall image quality. Therefore, the average o f the scores of the three radiologists was used. Statistical analysis was done using repeated measures multivariate analysis of variance. RE SULTS. Images obtained in 0.6 sec had significantly less motion (p < . 001) but more noise (p < .001) than those obtained in 1.0 sec. We foun d no statistically significant difference in artifacts between the two scan times. Overall image quality was judged to be significantly bett er on scans obtained in 0.6 sec than on scans obtained at 1.0 sec (p < .001), in spite of the greater noise on 0.6-sec images. The higher qu ality of 0.6-sec images was most noticeable for lung window settings. CONCLUSION. Our results indicate that scans taken in 0.6 sec (partial scans) provide better quality images than those obtained in 1.0 sec in patients being treated with mechanical pulmonary ventilation who cann ot breath-hold. This technique may be useful not only in this populati on but in all patients who are unable to cooperate with breath-holding instructions.