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Correlation of pleural effusions' grayscale sonographic parameters with fluid's analysis results.

BACKGROUND
Quantitative sonographic methods are used to assess pleural fluid's volume but no validated method exists for the measurement of the fluids' density and other qualitative values. We suggest a quantitative method, based on the pixel density of the pleural effusion's image, in order to evaluate the echogenicity of pleural effusion.


METHODS
Pleural ultrasound (US) was performed in 62 patients with pleural effusion. Five consequent images of the pleural effusion were retrieved through axial view between the 9th and the 10th rib and one from the 10th rib through coronal view and converted into the high-resolution tagged image file format. The mean echo levels of all pixels of the pleural effusion and of the 10th rib were counted, and the hypoechogenicity index (HI) was calculated according to the following formula: HI = mean echo level of all pixels of the rib/mean echo levels of all pixels of pleural effusion. HI greater than 1 indicates pleural effusion's hypoechogenicity. Diagnostic thoracocentesis was performed and biochemical markers were measured.


RESULTS
LDH, Cell Count, pH and Effusion Pixels (Mean) were both significantly correlated and associated with pixel ratio. Conversely, pixel ratio was not correlated with any other ultrasonography-derived parameter or biomarker.


CONCLUSIONS
This study introduced HI as new index, which could demonstrate the inflammation density of pleural effusions. Moreover, when used in combination with classical biomarkers, HI might be a useful adjunct for the discrimination of pleural transudate.