## 3 Results and Discussion  
The FS spectra obtained during the measurements were normalized by the level of backscattered excitation radiation. The results of averaging these spectra are shown in Figure 2.  
The main feature of the collected data is a high variability of fluorescence intensities. It is assumed that this is caused by both individual variability and different factors, such as, the state and nature  
Figure 2: Averaged normalized fluorescence spectra under excitation wavelengths 365 nm (**a**) and 450 nm (**b**). of changes in tissues, the phase development of pathological processes as well as ongoing treatment. In some patients, it was difficult to register fluorescence spectra with sufficient level of signal to noise ratio, which may be due to the presence of bile, blood and pus, which absorbed major part of fluorescence emission [20]. The components of blood, especially haemoglobin, are good absorbers of optical radiation and one of possible measures to reduce this effect is applying to the probe a moderate pressure. This technique allows one to decrease the blood content in the tissue as well as alleviate the attenuation effect of blood on the fluorescence spectrum [21]. However, in surgery in many cases the pressure applied to the end of optical probe can have negative effects on the soft tissues under study. The problem of accurate measurements requires an appropriate solution. The use of additional optical methods (e.g., diffuse reflectance spectroscopy) can be considered. Extending the number of implemented modalities allows for obtaining the data, which can be used to compensate the influence of blood on recorded fluorescence spectra [22]. If the blood content of the living tissue is to be kept unaffected, then to eliminate the probe pressure, an embedded in the probe noncontact distance measurements with subsequent automation of the recording procedure at a fixed optimal distance can be one of the possible solutions. Moreover, another measure to increase the level of signal to noise ratio is automation of mucus, pus and blood removal from the surface of optical probe during the procedure with minimal impact on the surface of biological tissue. Obtained spectral data were compared and assessed for statistically significant differences using one-way analysis of variance (ANOVA). Statistically significant difference between averaged levels of peak fluorescence intensity in the types of areas under study was observed (Figure 3). It was noted that the normalized values of fluorescence intensities are higher in common bile duct walls compared with the data obtained in the other areas. Normalized fluorescence intensities under 450 nm excitation wavelength was higher than the ones under 365 nm. The significant differences between fluorescence maxima in gallbladder and liver abscess with excitation at 450 nm were noticed as well (Table 1). This can be related to the pathological changes in the tissues including acute inflammatory process in abscess formation. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Area**} & \multicolumn{2}{c}{**Mean**} & \multicolumn{2}{c}{**Standard Deviation**} \\ \cline{2-5}  & **365 nm** & **450 nm** & **365 nm** & **450 nm** \\ \hline Common bile duct & 0.90 & 1.43 & 0.36 & 0.61 \\ Gallbladder & 0.66 & 0.93 & 0.34 & 0.49 \\ Liver & 0.67 & 0.63 & 0.45 & 0.39 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Averaged fluorescence intensity maxima. Figure 3: Box-Whisker diagrams of fluorescence intensity maxima under excitation wavelengths 365 nm (**a**) and 450 nm (**b**). \({}^{*}\) Confirmed statistically significant differences. The level of significance was estimated using a one-way analysis of variance (\(p<0.05\))  
Examples of LDF signals recorded in the different areas of interest are shown in Figure 4a.