Optical imaging and measuring methods to assess porcine kidney microcirculation during normothermic machine perfusion

A comparative proof-of-concept study

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OBJECTIVE This study aims to compare non-invasive real-time optical imaging and measuring methods for the quantification of microcirculation of organs during normothermic machine perfusion (NMP). This could help to determine which method is most promising for further development towards a clinical objective transplantability assessment tool.
BACKGROUND In organ transplantation, microvascular damage due to an ischemic period and reperfusion is inevitable. Evidence suggests a correlation between microcirculation during reperfusion and post-implantation organ functionality. Optical methods can measure the organ microcirculation in real-time in-vivo. Laser Speckle Contrast Imaging (LSCI), Near Infrared Spectroscopy (NIRS) and Sidestream Dark Field Imaging (SDFI) were evaluated on this purpose during NMP of porcine slaughterhouse kidneys.
METHODS An experiment consisting of steady-state NMP and intervention phases was designed. In the intervention phases, the pressure control was decreased and increased in steps and a main branch of the arteria renalis was clamped for three periods with each a consecutive reperfusion phase. Moreover, conventional functionality assessments, such as perfusate analysis, were performed. The microcirculations of the kidneys were imaged or measured with one of the optical methods throughout the experiment.
RESULTS Consistent responses to the interventions were observed in the LSCI signals. Moreover, some significant correlation was found between these signals and conventional functionality assessments. The signals measured with NIRS showed some trend in response to the interventions. However, these were not as consistent as in the LSCI signals. SDFI recordings were blurred and did not show any response to the interventions.
CONCLUSIONS From comprehension of the methods by (semi-)objective metrics, it can be concluded that LSCI is the most promising method for further development towards a clinical objective transplantability assessment tool. Significant correlations that were found between the LSCI signals and conventional functionality assessments were considered not clinically relevant due to the small sample size and limited comprehension between different experiments.