Straightforward method for quantifying pleural effusion volume from CT scans

Objective: To explore a mathematical calculation based on CT to quantitative assessment of free pleural effusion volume. Methods: Forty adult free pleural effusion patients were enrolled. The volume (V) of free pleural effusion was calculated by Philips EBW workstation. Planar measurements were made on CT scans such as liquid level to the chest distance (a), liquid length (c) and width (b). Individual planar measurements a, b, c, a×c, a×b, a×b×c were statistically calculated with the detected volume of pleural effusion by SPSS 19.0. A mathematical calculation of the expression measurement was created. Results: Nine kinds of functions to calculate were used. The equation about a was preferable (R²=0.847, P<0.005), the regression equation of single value of a was V=-195.672+36.150a-1.064a²+0.013a³. The most accurate correlation between the volume and planar measurements was found in the a×c (R²=0.937, P<0.005). Conversion of the measurement to the appropriate volume was possible by regression equation V=-139.325+0.126(a×c)-1.269(E-5)×(a×c)²+5.720(E-10)×(a×c)². Conclusion: Both a and a×c equations are enough for calculation pleural effusion volume. The pleural effusion volume with an equation can be obtained by a single value a, which can be also obtained by a×c. Devised a method of conversion of planar measurements on CT scan to the volume of free pleural effusion may be easily and effectively used in routine practice.