PURPOSE: Characterization of pleural effusions into transudates and exudates requires an invasive diagnostic procedure and the measurement of lactate dehydrogenase, protein, or albumin. Non-invasive characterization of pleural effusions in vivo using ultrasonography has been performed. Sonographic features including complex nonseptated, complex septated, and homogenously echogenic are specific for exudative pleural effusions. Unfortunately, the sensitivity of these findings is low. We hypothesized that the acoustic attenuation coefficient of exudative pleural effusions is higher than that of transudates. We sought to determine the viscosity and acoustic attenuation coefficient of increasing concentrations of albumin solutions.
METHODS: Solutions containing 0.9% sodium chloride and 0-6 gram/deciliter (gm/dl) of purified bovine albumin were prepared. Viscosity of each solution was determined using a size 50 Cannon-Fenske viscometer (Cannon Instrument Company, State College, PA) at 36.56 ± 0.021 degrees C. Samples of each solution were then placed in a custom ultrasound chamber and interrogated at 35.64 ± 0.134 degrees C with a broadband ultrasonic pulse generated by a V382 transducer and 5072PR pulser-receiver (Panametrics-NDT, Waltham, MA) operating in pulse-echo mode. The acoustic attenuation coefficient at 3.54 MHz, the center frequency of the transducer, was then determined.
RESULTS: The mean viscosities of the solutions containing 0-6 gm/dl of albumin were 0.724 ± 0.002, 0.745 ± 0.000, 0.778 ± 0.004, 0.811 ± 0.005, 0.847 ± 0.005, 0.890 ± 0.005, and 0.928 ± 0.010 centistokes, respectively. The mean attenuation coefficients at 3.54 MHz for the 0-6 gm/dl albumin solutions were −0.032 ± 0.021, 0.091 ± 0.128, 0.212 ± 0.092, 0.179 ± 0.076, 0.380 ± 0.065, 0.398 ± 0.042 and 0.912 ± 0.147 decibels/cm, respectively.
CONCLUSION: Viscosity increased linearly with increasing concentrations of albumin. There was a trend for increased acoustic attenuation with higher albumin concentrations; variations from linearity were thought to result from variations in temperature during measurement of the acoustic attenuation coefficient.
CLINICAL IMPLICATIONS: Use of viscosity and acoustic attenuation coefficients to characterize pleural effusions may allow non-invasive discrimination between transudates and exudates. Further investigation is currently underway.
DISCLOSURE: Steven Leh, None.