Donor organ quality is pivotal for successful organ transplantation. Prolonged ischemia puts the organ at risk. Near infrared spectroscopy (NIRS) is a non-destructive and fast method to evaluate tissue and organ characteristics [1–3]. One of the most important factors reducing organ quality in organ transplantation is the unavoidable ischemic reperfusion injury (IRI). The aim of our study was to evaluate whether NIRS correlates with the duration of the ischemia time and could be potentially useful to assess organ quality.
2 Materials and methods
We analysed livers of three male lewis rats (age 4.5 months, weight 433 – 445 g, Charles River, Sulzfeld, Germany)in vivo . Ischemia was induced by selectively clamping all supplying vessels of 70% of the liver as shown in Figure 1. Measurements were taken on three points per lobe before clamping and in intervals of 10 minutes within one hour after clamping in clamped and unclamped liver lobes (see Figure 2). All procedures and housing of the animals were strictly carried out according to theGerman animalwelfare legislation.
Our measurement setup consisted of a Zeiss MCS611 spectrometer system, containing a VIS and a NIR spectrometer cassette, and a fibre probe attached to light source and both spectrometer cassettes. Reflection of Accuflect was used as optical reference. The fibre probe was set on the measurement point by the surgeon and one spectrum per point was recorded. A total of n = 252 spectra at four lobes per rat were taken and the absorbance was calculated.
To achieve optimal calibration results, appropriate wavelength range(s) and data preprocessing had to be chosen. In an iterative approach we combined varying wavelength ranges in visible and near infrared light with the following options for data preprocessing:
– no data preprocessing
– subtraction of a constant offset,
– subtraction of a line,
– vector normalisation (snv),
– first derivation,
– second derivation,
– first derivation and subtraction of a line and
– first derivation and vector normalisation (snv).
During this iterative procedure the parameters of quality (coefficient of determination R2, root mean square error of cross validation RMSECV, residual prediction deviation RPD) were evaluated and consequently the best calibrations chosen.
We identified three wavelength ranges within visible and near infrared light, that were appropriate for the prediction of ischemia time. The optimal wavelength ranges and the parameters of quality are shown in Table 1.
The scatterplot of the calibration using only visible light (310 – 560 nm) is shown in Figure 3, while the calibration using visible and near infrared light (480 – 540 and 740 – 1150 nm) is shown in Figure 4, and the calibration using only near infrared light (900 – 1300 and 1400 – 1700 nm) is shown in Figure 5.
This study shows that NIRS is suitable for prediction of ischemia time with a precision of time ±6.3 minutes within one hour. NIR is better suited for prediction than visible light. Since the point in time of donor organ explantation is documented the duration of ischemia is clinically less relevant. Therefore further approaches aim at translating our results into clinical use by developing a tool capable of assessing severity and extent of IRI after extensive liver surgery.
This study was funded by the German Federal Ministry for Economic Affairs and Energy (VF130008) on the basis of a decision by the German Bundestag.
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About the article
Published Online: 2015-09-12
Published in Print: 2015-09-01
Conflict of interest: Authors state no conflict of interest. Material and Methods: Informed consent: Informed consent has been obtained from all individuals included in this study. Ethical approval: The research related to human use has been complied with all the relevant national regulations, institutional policies and in accordance the tenets of the Helsinki Declaration, and has been approved by the authors’ institutional review board or equivalent committee.