Chapter 9 supported by previously reported data on composition of nerve and adipose tissue23,34,35. In essence, nerve tissue contains 20% lipid and 80% protein34, while adipose tissue contains 61–87% lipid, 8% protein and 11–31% water35. The reflectance spectra, which were the basis to extract gradient and amplitude difference features, originate from intrinsic tissue properties (endogenous contrasts) that do not require preoperative contrast administration. Consequently there are no problems with potential toxicity or allergy to a contrast agent. Regarding exogenous contrast‐based optical techniques, in vivo optical imaging of peripheral nerves using systemically administered myelin‐selective fluorescent dyes36 or nerve‐highlighting fluorescent peptides37 has been reported. Development of a new NIR fluorescent dye for use in the design of nerve‐targeted optical imaging probes has also been described38. The LOO cross‐validation method inherently produces relatively optimistic classification results (therefore we additionally applied the TT cross‐validation method). External validation remains essential before classification models can be implemented in clinical practice39. Such validation would need to be performed on newly acquired data. Additional data acquired in a multi‐center study would also be needed. The choice to use a limited set of pre‐known spectral regions of interest for water, fat and hemoglobin was made based upon the limited number of spectra included in our data set. Differentiation based on completely automatically extracted features from a larger data set might achieve better results, and could be explored in future work. The identified reflectance spectra are specific to the probe geometry used in this study. To extend this study even further, translation of these reflectance spectra to in vivo biological parameters is needed. Such an approach would yield information about the optical tissue properties, and provide a better understanding of the nature of discrimination performance, i.e. whether nerves can be optically distinguished from surrounding (adipose) tissues based on differences in light scattering behaviour (related to structural differences) or due to differences in absorption behaviour (related to chromophore concentrations such as blood, water and fat). Such an approach would also be tissue‐specific and robust to inter‐patient and multi‐center variability. The “gold standard” used in this study was the surgeons’ visual judgment. This judgment is not solely based on color (spectral) information, but also relies on the recognition of spatial anatomical position of a specific tissue. Therefore, this study needs extension from spot‐wise probe‐measurements to imaging of the whole surgical field. In contrast to our previous ex vivo experiments using wide band diffuse reflectance spectroscopy24, the current measurements were performed during surgery. In vivo circumstances as vascular filling and oxygenation were not disrupted. Using diffuse 140
proefschrift_Schols_SLV
To see the actual publication please follow the link above