Hyperspectral imaging system for monitoring laser-induced thermal damage in gastric mucosa

Minimally invasive techniques are gaining a major role in treating superficial gastrointestinal cancers. Energy-based approaches have been investigated as potential alternative to the gold-standard techniques (e.g., Endoscopic Submucosal Dissection). Among these techniques, the laser has been studied for achieving a selective ablation of the gastric mucosa. Together with the optimization of the laser settings for avoiding tissue perforation or insufficient ablation, a tool providing quantitative information about the intraoperative tissue state can support the treatment guidance. This work aims at providing a novel non-invasive approach based on the use of hyperspectral imaging (HSI) for monitoring ablative therapy in in vivo gastric mucosa. The three-dimensional datasets generated by the HSI provide spatial and spectral information of the scene, thus collecting tissue optical features during the ablation therapy in each pixel of the images. The operation of a diode laser focused on the porcine gastric mucosa was controlled in accordance with chosen temperature thresholds (i.e., 36, 60, 70, 80, 100, 110 °C), measured with a thermographic camera. HSIs of the living gastric mucosa undergoing laser procedure hold diagnostic information about the thermal outcome. Two tests have been performed, and the temperature dependence of three characteristic spectral wavelengths have been analysed: oxyhemoglobin (Hb02) in the visible range 500-600 nm, methemoglobin (metHb) around 630 nm, and deoxyhemoglobin (Hb) at 760 nm. The data have been processed in terms of absorbance at the set temperature relative to the absorbance at initial body temperature (36 °C). After 60 °C the percentage relative absorbance of metHb increased significantly in both tests (i.e., 92.3±1.9 % at 70 °C and 229.4±4.7% at 100 °C in Test2); regarding the Hb at 110 °C, Test1 reported an increase of 43.8±1.7 %, versus 127.2±3.8% in the Test2. On the other hand, HbO2 chromophore experiences an increase only for the first stages of heating later decreasing in favour of metHb and Hb formation.In both tests, similar trends for characteristic wavelengths are found, thus demonstrating the potential of the HSI measurement in laser-induced thermal damage monitoring. Although optical response show dependence on the tissue type and condition, this finding encourages future studies to standardize this promising technique.