Post-mortem Tissue Degassing Using Positive Pressure Is Superior to Negative Pressure

Abstract

ObjectiveTo compare the effectiveness of positive pressure (PP) and negative pressure (NP) for reducing gas inclusions in biological tissues in preparation for acoustic imaging. MethodsEighteen pieces of porcine liver in degassed saline were included in this study. For the PP group (n = 9 samples), a wristwatch waterproof tester was used to pressurize samples to 0.41 MPa (59 psi) for 10 min. For the NP group (n = 9 samples), a desiccator at −0.08 MPa (−12 psi) was used for 30 min. Backscatter coefficients (BSCs) were calculated over the central frequency range of the backscattered spectra and paired-samples t-tests were performed. ResultsUtilization of PP resulted in a decrease in BSC for all samples, indicating less gas post-PP (pre-PP −13.0 ± 4.3 dB [mean ± SD], post-PP −18.9 ± 5.0 dB, p = .001). Utilization of NP resulted in an increase in BSC for the majority of samples (pre-NP −14.6 ± 6.0 dB, post-NP −13.1 ± 5.3 dB, p = .177). ConclusionUtilization of a simple PP chamber consistently resulted in a decrease in tissue gas, at lower pressures than previously reported. The vacuum method is ineffective, may result in a paradoxical increase in tissue gas, and may not be recommended for tissue degassing.