Feedback control of liver thermotherapy using optical spectroscopy

Abstract

Thermotherapies such as radio-frequency ablation achieve necrosis of liver tumors through thermal coagulation and are frequently employed when surgical resection is impossible. Currently, thermotherapy procedures suffer from the lack of an adequate feedback control system, making it difficult to know precisely when to terminate therapy. In vitro and in vivo studies were performed on canine liver tissue to determine the feasibility of using fluorescence and diffuse reflectance spectroscopy to provide an objective endpoint for these procedures. The fluorescence and diffuse reflectance spectra of liver tissue exhibited consistent changes over the coagulation process. In vitro results showed a shift in the primary fluorescence peak from 490 nm in the native state to 510 nm in the fully coagulated state; in addition, a three-to four-fold increase in the absolute intensity of the diffuse reflectance spectra was observed upon complete coagulation. Similar spectral alterations were obtained in vivo. Based on our results, fluorescence and diffuse reflectance spectroscopy provide a direct way to assess the biochemical and structural changes associated with tissue thermal damage; hence, they can be developed into a feedback system for thermotherapies.