Hyperspectral Imaging and Machine Perfusion in Solid Organ Transplantation: Clinical Potentials of Combining Two Novel Technologies

Abstract

Organ transplantation survival rates have continued to improve over the last decades, mostly due to reduction of mortality early after transplantation. The advancement of the field is facilitating a liberalization of the access to organ transplantation with more patients with higher risk profile being added to the waiting list. At the same time, the persisting organ shortage fosters strategies to rescue organs of marginal donors. In this regard, hypothermic and normothermic machine perfusion are recognized as one of the most important developments in the modern era. Owing to these developments, novel non-invasive tools for the assessment of organ quality are on the horizon. Hyperspectral imaging represents a potentially suitable method capable of evaluating tissue morphology and organ perfusion prior to transplantation. Considering the changing environment, we here discuss the hypothetical combination of organ machine perfusion and hyperspectral imaging as a prospective feasibility concept in organ transplantation.

Keywords: hyperspectral imaging; machine perfusion; organ transplantation.

Figure 1

Hyperspectral imaging (HSI) applied on porcine kidneys after 3 h and 6 h NMP in an experimental setting; representative intraoperative (a) RBG image, corresponding HSI generated color coded, (b) tissue hemoglobin index (THI), (c) oxygen saturation index (StO2%), (d) near-infrared perfusion index (NIR), (e) tissue water index (TWI). Four standardized markers were placed on upper pole, corticomedullary boundary, lower pole, and ureter. Intraoperative images were acquired using the TIVITA^® Tissue HSI system (Diaspective Vision, Germany). For undisturbed image acquisition and data generation, the ambient light in the operating room had to be dimmed. The camera system incorporates a high number of spectrally differentiated channels, and acquires pictures with a high spectral resolution (5 nm) in the visible and near-infrared range (500–1000 nm). This scanner is mounted on a moving arm, which is brought to the organ. Using a 25 mm focal lens, a constant distance of 50 cm between the object and camera has to be retained during image acquisition. The HSI camera subsequently takes an RGB picture and in parallel computes a pseudo-color image, which represents physiologic parameters such as oxygen saturation, near-infrared perfusion, tissue hemoglobin, and tissue water of the recorded area. The maximum relative penetration depth of this HSI system is 6 mm. Quantitative StO2% measurements can either be performed at a depth of up to 1 mm for superficial microcirculation evaluation as well as at a depth of 4–6 mm, which corresponds to wavelengths recorded within the near-infrared spectrum. HSI can be applied almost “real time” and the acquisition for the hyperspectral image takes less than ten seconds. All images are stored, and further analysis of the hyperspectral data can be performed on the system with the TIVITA^® Suite software. HSI: hyperspectral imaging; NMP: normothermic machine perfusion; RGB: red-green-blue image; THI: tissue hemoglobin index; StO2%: oxygen saturation index; NIR: near infrared perfusion index; TWI: tissue water index.

Figure 2

Hyperspectral imaging (HSI) applied on human livers after 22 h, 44 h, and 55 h NMP in an experimental setting; representative intraoperative (a) RBG image, corresponding HSI generated color coded, (b) tissue hemoglobin index (THI), (c) oxygen saturation index (StO2%), (d) near-infrared perfusion index (NIR), (e) tissue water index (TWI). Three standardized markers were placed on peripheral (right/left lobe) and central compartments. Intraoperative images were acquired using the TIVITA^® Tissue HSI system (Diaspective Vision, Germany). For undisturbed image acquisition and data generation, the ambient light in the operating room had to be dimmed. The camera system incorporates a high number of spectrally differentiated channels which acquires pictures with a high spectral resolution (5 nm) in the visible and near-infrared range (500–1000 nm). This scanner is mounted on a moving arm which is brought to the organ. Using a 25 mm focal lens, a constant distance of 50 cm between the object and camera has to be retained during image acquisition. The HSI camera subsequently takes an RGB picture and in parallel computes a pseudo-color image, which represents physiologic parameters such as oxygen saturation, near-infrared perfusion, tissue hemoglobin, and tissue water of the recorded area. The maximum relative penetration depth of this HSI system is 6 mm. Quantitative StO2% measurements can either be performed at a depth of up to 1 mm for superficial microcirculation evaluation as well as at a depth of 4–6 mm,, which corresponds to wavelengths recorded within the near-infrared spectrum. HSI can be applied almost “real time” and the acquisition for the hyperspectral image takes less than 10 s. All images are stored, and further analysis of the hyperspectral data can be performed on the system with the TIVITA^® Suite software. HSI: hyperspectral imaging; NMP: normothermic machine perfusion; RGB: red-green-blue image; THI: tissue hemoglobin index; StO2%: oxygen saturation index; NIR: near infrared perfusion index; TWI: tissue water index.

Figure 3

Courses of hyperspectral imaging (HSI) indices during normothermic machine perfusion (NMP) applied on human livers (a) Dynamics of tissue oxygen saturation index (StO2%), (b) tissue hemoglobin index (THI), (c) near-infrared perfusion index (NIR), and (d) tissue water index (TWI) during NMP of human livers (n = 10) in a clinical setting. NMP time was extended to a maximum of 24 h. HSI measurements were performed before starting NMP, after 1 h NMP, 6–12 h NMP, and 12–24 h NMP. In a retrospective analysis, markers representing the region of interest were inserted into the pseudo-colored images, and the index averages from the values inside the region of interest were calculated. Applied statistic test: Friedman Test, p values < 0.05 were considered significant. HSI: hyperspectral imaging; THI: tissue hemoglobin index; StO2%: oxygen saturation index; NIR: near infrared perfusion index; TWI: tissue water index; NMP: normothermic machine perfusion.