New formula for quantification of pleural effusions from computed tomography

The authors develop a method to accurately and easily estimate the volume o f pleural effusions with computed tomography (CT). In 15 patients with eith er simple or loculated pleural effusions (14 right-sided and 11 left-sided) , routine helical CT examinations of the thorax were obtained. Two experien ced radiologists visually estimated the volume of the effusions. Three-dime nsional reconstructions of the pleural effusions were performed from the he lical CT examinations, and the volumes of the effusions were calculated. Ef fusion volumes were also estimated using the formula d(2) x l (d = greatest depth of the effusion on a single CT image, l = greatest length of the eff usion). The computer calculated the estimated Volumes and they were then st atistically compared. The coefficient of correlation between the estimation by measurement and calculated volumes of all effusions was 0.908 (p < 0.00 01) for the right side, and 0.849 for the left side (p < 0.002). Excluding the loculated effusions, the coefficient of correlation was 0.969 for the r ight side and 0.949 for the left side (p < 0.001). The volume estimation by visual inspection was also correlated to the calculated volumes (0.84 on t he left and 0.85 on the right, p < 0.008), but resulted in a consistent ove restimation by 300 ml to 500 ml. Although pleural effusion volumes can be e stimated by visual inspection with good correlation, some overestimation is consistently seen. Use of the formula d(2) x l readily enables estimation of pleural effusion volume from CT, from two simple measurements. This form ula-based method of volume estimation provides an accurate and easily measu red means of estimation that is readily obtained from routine CT of the che st.