Optical signature of nerve tissue—Exploratory ex vivo study comparing optical, histological, and molecular characteristics of different adipose and nerve tissues

Abstract

BackgroundDuring several anesthesiological procedures, needles are inserted through the skin of a patient to target nerves. In most cases, the needle traverses several tissues—skin, subcutaneous adipose tissue, muscles, nerves, and blood vessels—to reach the target nerve. A clear identification of the target nerve can improve the success of the nerve block and reduce the rate of complications. This may be accomplished with diffuse reflectance spectroscopy (DRS) which can provide a quantitative measure of the tissue composition. The goal of the current study was to further explore the morphological, biological, chemical, and optical characteristics of the tissues encountered during needle insertion to improve future DRS classification algorithms.MethodsTo compare characteristics of nerve tissue (sciatic nerve) and adipose tissues, the following techniques were used: histology, DRS, absorption spectrophotometry, high‐resolution magic‐angle spinning nuclear magnetic resonance (HR‐MAS NMR) spectroscopy, and solution 2D 13C‐1H heteronuclear single‐quantum coherence spectroscopy. Tissues from five human freshly frozen cadavers were examined.ResultsHistology clearly highlights a higher density of cellular nuclei, collagen, and cytoplasm in fascicular nerve tissue (IFAS). IFAS showed lower absorption of light around 1200 nm and 1750 nm, higher absorption around 1500 nm and 2000 nm, and a shift in the peak observed around 1000 nm. DRS measurements showed a higher water percentage and collagen concentration in IFAS and a lower fat percentage compared to all other tissues. The scattering parameter (b) was highest in IFAS. The HR‐MAS NMR data showed three extra chemical peak shifts in IFAS tissue.ConclusionCollagen, water, and cellular nuclei concentration are clearly different between nerve fascicular tissue and other adipose tissue and explain some of the differences observed in the optical absorption, DRS, and HR‐NMR spectra of these tissues. Some differences observed between fascicular nerve tissue and adipose tissues cannot yet be explained but may be helpful in improving the discriminatory capabilities of DRS in anesthesiology procedures. Lasers Surg. Med. 50:948–960, 2018. © 2018 The Authors. Lasers in Surgery and Medicine Published by Wiley Periodicals, Inc.

Model-based characterization platform of fiber optic extended-wavelength diffuse reflectance spectroscopy for identification of neurovascular bundles

“…SMLR classification of EWDRS spectra utilized a set of spectral features in both the VIS/NIR and SWIR spectral ranges, including features at 523, 597, 606, 625, 850, 985 1185 to 1205, 1260, and 1306 nm, which were similar to those spectral bands utilized in analytical approaches published in prior human subjects studies. 38,39,42,43 A number of studies have previously demonstrated successful classification of nerve versus surrounding tissues using the k-nearest neighbor principle, partial least squares discriminant analysis, support vector machine, and classification and regression trees analysis, combined with principal component analysis to reduce the spectral features or defined parameters associated with specific chromophores, and regardless of the specific technique, overall classification accuracies between 82% and 91%, [38][39][40][41][42][43] similar to the current study, were reported. Moreover, the relative improvement in identification of nerves when using the full EWDRS spectrum is in general agreement with prior studies which directly compared VIS/NIR versus VIS/NIR/SWIR spectral bands for tissue classification.…”

“…Calculations of the mean spectral ratios for blood-related ( ) and lipid-related ( ) composition are shown in Table S1 in the Supplemental Material and are representative of prior reports in human tissues. 38 – 43 …”

“…Calculations of the mean spectral ratios for blood-related (575∕610 nm) and lipid-related (1210∕1270 nm) composition are shown in Table S1 in the Supplemental Material and are representative of prior reports in human tissues. [38][39][40][41][42][43] Classification of nerve and NVB versus all other tissues (including skin, muscle, vessels, and connective tissues) was performed using SMLR, using spectra collected across the full EWDRS range as well as with spectra collected with the VIS/NIR spectral channel alone (Table 1). The overall accuracy of VIS/NIR spectra was 89%, with nine spectra misclassified, including five spectra collected from nerve and NVB.…”

“… 20 – 37 A particularly valuable application of EWDRS configurations is the detection of nerves and neurovascular bundles (NVB). 38 – 43 NVB are a multilayered structure and can contain multiple nerves and vessels surrounded by fat and connective tissues and can be difficult to identify visually due to the range of sizes and scenarios with which they present during surgery. 44 – 50 EWDRS technologies targeting this challenge have demonstrated the ability to identify peripheral nerve bundles from surrounding tissues in open surgeries using a handheld probe 42 and also show the ability of EWDRS and fluorescence spectroscopy in combination to identify nerves during head and neck surgeries using a needle-shaped probe.…”

Methods for standardizing and enhancing Biomedical Fluorescence Imaging

“…Cancerous breast tissue has shown higher hemoglobin concentration, as long as higher scattering and refractive index increase in comparison to healthy breast tissue [75], [76]. Encouraging results have also been shown to differentiate colon cancer [77] and nerves [78] from other tissues.…”