Chapter 2 Furthermore, OCT can be used as an intraoperative optical biopsy method, for example to facilitate regional lymph node staging in the colonic mesentery46. Its feasibility of providing in situ optical tissue biopsy via a NOTES approach has been investigated with promising outcome47. A commercially available probe via the working channel of a gastroscope used as a NOTES peritoneoscope has recently been deployed. By this means, high‐resolution real‐time in vivo images of mesenteric sentinel nodes were obtained in a porcine model and ex vivo images were obtained from human specimen. Diffuse optical spectroscopy Diffuse optical spectroscopy is a non‐invasive technique that can be used to measure the optical properties of physiological tissue, for example for real‐time determination of blood oxygen saturation. This technique is based on a difference in light absorption between deoxyhemoglobin and oxyhemoglobin. This difference is most outspoken in the near‐infrared spectral window of 600‐1000 nm48. The use of spectroscopy for the identification of chemical states is common, but current available systems lack the spatial resolution necessary for video imaging. Applying a spectrophotometric technique during elective laparoscopic and thoracoscopic surgical procedures Curran et al.49 demonstrated that this principle can be used to estimate hemoglobin concentration. The results of their preliminary report are promising, although the investigated device cannot yet be used for real‐time measurements, as the data‐analysis was conducted afterwards. Automated spectral differentiation of essential tissue types encountered during the dissection phase in laparoscopic colorectal surgery (respectively blood vessel, ureter, mesenteric adipose tissue, colonic tissue), was feasible in freshly explanted human colonic specimen, using single point fiber probe measurements50. These results may be used as input for development of multi‐ or hyperspectrally enhanced in vivo laparoscopic surgical imaging. Hyperspectral imaging With hyperspectral imaging (HSI)51 data are captured and analyzed from across the electromagnetic spectrum, hence allowing visualization with visible light and also within the near‐infrared to infrared spectrum. Usually the difference between hyperspectral and multispectral imaging is defined by the number of spectral bands: a hyperspectral image contains hundreds to thousands of bands, a multispectral image contains tens of bands. Zuzak et al.52,53 coupled a surgical laparoscope for conventional minimally invasive surgical procedures with a NIR hyperspectral imaging system to help guide laparoscopic 26
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