In vivo assessment of pulmonary edema in rats using the backscatter coefficient and envelope statistics

Abstract

Ultrasound could be used as a convenient, non-ionizing method for monitoring pulmonary edema. In this study, the ability of backscatter coefficient (BSC) and envelope statistical quantitative ultrasound (QUS) parameters to evaluate edema in rat lungs was investigated. Ultrasound data were acquired from six healthy rats and six with pulmonary edema using a Verasonics Vantage ultrasound scanner. After ultrasound data acquisition, a piece of the lung was excised and immediately weighed (wet weight), before being dried in an oven and weighed again (dry weight). The wet and dry weight were used to compute the wet-to-dry (W/D) weight ratio, used as the gold standard for pulmonary edema severity. BSC and envelope statistical parameters were computed in overlapping time gates over the lung ultrasound data. The average and standard deviation of each parameter, along with the slope and intercept of a linear function fit to each parameter over acoustic propagation time, were obtained. Each QUS parameter was correlated with the W/D ratio. The strongest correlation was achieved by the standard deviation of spectral intercept and by the average homodyned K structure parameter, both with a 0.78 correlation coefficient magnitude. Therefore, BSC and envelope statistical parameters have the potential to improve monitoring of pulmonary edema.