Quantitative Ultrasound Analysis of Gas Embolic Disease in Bycaught Sea Turtles

Abstract

ObjectivesBycatch-related decompression after forced submersion can result in severe gas embolic disease in sea turtles. This work used qualitative and quantitative ultrasound analyses, including gas grading, brightness analysis, and texture feature extraction, to investigate organ-specific gas burden and temporal evolution in the hearts, kidneys, and livers of bycaught sea turtles. Materials and MethodsUltrasound imaging of the hearts, kidneys, and livers of bycaught turtles was performed as part of veterinary evaluation either onboard fishing vessels immediately after surfacing (boat group, n=47) or after longer periods at shore-based facilities (shore group, n=30). Gas burden in each ultrasound scan was graded on an ordinal scale from 0 (no gas) to 5 (gas completely shadowing organ anatomy). Temporal differences in gas burden were compared between the shore and boat groups. Quantitative brightness and texture features were extracted from all organs, including contrast, correlation, homogeneity, and energy from liver and kidney data. A multivariate logistic regression model with leave-one-out cross-validation was conducted, with shore versus boat as a binary outcome (surrogate of post-surfacing decompression state) and ultrasound texture metrics as independent variables. ResultsMedian grades from the first ultrasound scan were significantly higher in the boat group than in the shore group for the liver, kidney, and heart (3, 3, and 3 vs 1, 1, and 0, respectively). This pattern coincided with a difference in the mean duration until the first scan which was conducted being 54 min for the onboard studies vs 330 minutes in the shore group. Mean pixel brightness within cardiac and liver regions of interest increased with rising bubble grade before decreasing at the highest grades, consistent with acoustic shadowing at severe gas burden. Texture features demonstrated significant organ-specific changes with increasing gas burden, and the regression models achieved areas under the receiver operating characteristic curve of 0.92 for liver texture features and 0.83 for kidney texture features. ConclusionsThese findings demonstrate organ-specific differences in gas evolution over time. Quantitative ultrasound features were associated with gas burden and post-surfacing interval in bycaught sea turtles. These findings support the feasibility of quantitative ultrasound biomarkers for assessment of decompression-related gas burden.