Differentiation between nerve and adipose tissue using wide‐band spectroscopy 129 Introduction The ability to visually distinguish vital anatomy, such as nerve tissue, is of great importance during all surgical procedures. There is a wide variety of procedures with a realistic chance of peroperative nerve injury that may result in temporary or permanent dysfunction of motor or sensory nerves. Extra caution is, for example, required during complicated surgical procedures like thyroidectomy1 and total mesorectal excision2,3, but also during less difficult procedures such as inguinal hernia repair4. When spatial perception from direct sight and haptic feedback from direct touch are lacking (e.g. during minimally invasive surgery) nerve identification can be even more challenging than during delicate open surgery. Therefore, a reliable tool to enhance the contrast of nerve tissue from its surroundings is desirable for improved intraoperative nerve detection and preservation. Exploring optical spectroscopy techniques might offer a roadmap towards such a tool. Aerospace science combines hyperspectral camera technology, with pre‐acquired library spectra recorded on the earth surface, to generate satellite images for discovering places of interest for e.g. agricultural purposes5,6 and military and homeland security applications7. Furthermore, hyperspectral imaging incorporates potential to facilitate image‐guided surgery8. It has, for example, been investigated for noninvasive intraoperative assessment of renal oxygenation (i.e., tissue oxygen saturation) during partial nephrectomy9,10, for intraoperative enhancement of biliary imaging (i.e., anatomical imaging) during laparoscopic cholecystectomy11 and for intraoperative assessment of resection margins for residual tumor tissue (i.e., tumor detection) in breast cancer surgery12. Arrays of Charge‐Coupled Devices (CCD) and Complementary Metal Oxide Semiconductors (CMOS) are the most commonly used detectors (camera chips) in medical hyperspectral imaging systems, which can be composed of silicon (Si) and indium gallium arsenide (InGaAs) sensors. Si sensors cover the wavelength range of 400 – 1000 nm, whereas InGaAs sensors are typically sensitive in the 900 – 1700 nm wavelength region and depending on the amount of Indium‐doping the longer wavelength boundary can shift up to 2500 nm8. Intraoperative recurrent laryngeal nerve (RLN) identification before removal of the thyroid gland is of great importance. The RLN diameter is on average 2 mm13. In a retrospective analysis of 5104 primary and 685 secondary thyroidectomies, transient vocal problems as a consequence of RLN palsy occurred in respectively 2% and 1% of cases (permanent in 0.5% and 1.5%). Furthermore the rate of permanent complications was found to be significantly higher in reoperative surgery14. Routine visual RLN identification currently remains the gold standard for preventing iatrogenic nerve injury
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