Hyperspectral Imaging during Normothermic Machine Perfusion-A Functional Classification of Ex Vivo Kidneys Based on Convolutional Neural Networks.

Facing an ongoing organ shortage in transplant medicine, strategies to increase the use of organs from marginal donors by objective organ assessment are being fostered. In this context, normothermic machine perfusion provides a platform for ex vivo organ evaluation during preservation. Consequently, analytical tools are emerging to determine organ quality. In this study, hyperspectral imaging (HSI) in the wavelength range of 550-995 nm was applied. Classification of 26 kidneys based on HSI was established using KidneyResNet, a convolutional neural network (CNN) based on the ResNet-18 architecture, to predict inulin clearance behavior. HSI preprocessing steps were implemented, including automated region of interest (ROI) selection, before executing the KidneyResNet algorithm. Training parameters and augmentation methods were investigated concerning their influence on the prediction. When classifying individual ROIs, the optimized KidneyResNet model achieved 84% and 62% accuracy in the validation and test set, respectively. With a majority decision on all ROIs of a kidney, the accuracy increased to 96% (validation set) and 100% (test set). These results demonstrate the feasibility of HSI in combination with KidneyResNet for non-invasive prediction of ex vivo kidney function. This knowledge of preoperative renal quality may support the organ acceptance decision.

Inulin Clearance During Ex vivo Normothermic Machine Perfusion as a Marker of Renal Function.

Normothermic machine perfusion (NMP) offers a unique opportunity to objectively assess donor organ quality. This study describes the evaluation of inulin clearance as a potential marker for the ex vivo function of porcine kidneys during NMP. The function assessment was performed in both kidneys from slaughterhouse pigs (n = 20) and kidneys from pigs in a laboratory setting (n = 28). The kidneys were exposed to different warm ischemia times (WIT). After a period of static cold storage, the kidneys underwent a 4-hour NMP with autologous whole blood. Inulin clearance, hemodynamic parameters, and urine output were measured. Based on the inulin excretion behavior laboratory pig kidneys were assigned to three classes (functional, limited functional, and nonfunctional), slaughterhouse pig kidneys to two classes (limited functional and nonfunctional), respectively. Contrary to the marginal kidneys of the slaughterhouse pigs, the functional variation of kidneys of the laboratory pigs was associated with the WIT. A correlation between functional kidneys and a WIT less than 25 min was shown. Because none of the slaughterhouse pig kidneys could be assigned to the functional class, only the laboratory pig kidneys were used for examinations with functional markers. Renal blood flow and urine output during NMP correlated significantly ( p < 0.01) with ex vivo kidney function. This study demonstrated that inulin is a marker of high quality for the evaluation of suggested kidney function after NMP with whole blood. Furthermore, surrogate markers measured during NMP can be used to describe and predict the physiologic behavior of kidneys before transplantation.

Algorithms for mapping kidney tissue oxygenation during normothermic machine perfusion using hyperspectral imaging.

The lack of donor grafts is a severe problem in transplantation medicine. Hence, the improved preservation of existing and the usage of organs that were deemed untransplantable is as urgent as ever. The development of novel preservation techniques has come into focus. A promising alternative to traditional cold storage is normothermic machine perfusion (NMP), which provides the benefit of improving the organs' viability and of assessing the organs' status under physiological conditions. For this purpose, methods for evaluating organ parameters have yet to be developed. In a previous study, we determined the tissue oxygen saturation (StO2) of kidneys during NMP with hyperspectral imaging (HSI) based on a discrete wavelength (DW) algorithm. The aim of the current study was to identify a more accurate algorithm for StO2 calculation. A literature search revealed three candidates to test: a DW algorithm and two full spectral algorithms - area under a curve and partial least square regression (PLSR). After obtaining suitable calibration data to train each algorithm, they were evaluated during NMP. The wavelength range from 590 to 800 nm was found to be appropriate for analyzing StO2 of kidneys during NMP. The PLSR method shows good results in analyzing the tissues' oxygen status in perfusion experiments.

Oxygenation and perfusion monitoring with a hyperspectral camera system for chemical based tissue analysis of skin and organs.

The monitoring of free flaps, free transplants or organs for transplantation still poses a problem in medicine. Available systems for the measurement of perfusion and oxygenation can only perform localized measurements and usually need contact with the tissue. Contact free hyperspectral imaging and near-infrared spectroscopy (NIRS) for the analysis of tissue oxygenation and perfusion have been used in many scientific studies with good results. But up to now the clinical and scientific application of this technology has been hindered by the lack of hyperspectral measurement systems usable in clinical practice. We will introduce the application of a new hyperspectral camera system for the quick and robust recording of remission spectra in the combined VIS and NIR spectral range with high spectral and spatial resolution. This new system can be applied for the clinical monitoring of free flaps and organs providing high quality oxygenation and perfusion images.

Indocyanine green R15 ratio depends directly on liver perfusion flow rate.

BACKGROUND: Indocyanine green (ICG) is a synthetic dye that is widely used to evaluate liver function in critically ill patients, before liver resection or after liver transplantation. Controversy still exists about the impact exerted on the ICG ratio after 15 min (ICG R15) by differences in liver perfusion rates, hyperdynamic states, or patient cardiac output. We studied the role of different liver perfusion rates on the ICG R15 ratio in a normothermic extracorporeal liver perfusion system under standardized conditions. METHODS: Livers from landrace pigs (40-50 kg) were perfused with fresh porcine blood. Normal and high perfusion rates were defined as 1 ml and 2 ml/g liver/min, respectively. Perfusate pressure of the hepatic artery and portal vein were within the physiological range in both groups. According to manufacturer's instructions, 0.5 mg of ICG per kg was applied and the ICG R15 was calculated. Calculations were based on fifteen experiments in five liver perfusions. Bile production, liver function and histology were analyzed. RESULTS: All perfusions were characterized by physiological bile production, lack of hepatocellular damage and normal histology. ICG R15 ratio in group I, perfused with 1 ml/g liver, was 18.9 +/- 6%. In group II, perfused with 2 ml/g liver, the ICG R15 ratio was 7.2 +/- 3%. The difference between groups 1 and 2 was statistically significant (p < 0.05). CONCLUSION: ICG R15 is reliable within one group at defined perfusion rates. Doubled perfusion rates contribute to higher ICG clearance. For clinical application we would like to suggest considering cardiac output of the patient for interpretation of ICG ratios.