A multispectral fluorescence imaging system: Design and initial clinical tests in intra‐operative Photofrin‐photodynamic therapy of brain tumors

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Abstract
Background and Objectives Intra‐operative identification of tumor by fluorescence may improve surgical resection or photodynamic therapy (PDT). A novel instrument was designed, constructed, and tested for this purpose. Study Design/Materials and Methods The instrument was designed to provide high‐resolution, multi‐spectral (five band) fluorescence imaging, and non‐contact point spectroscopy, with long working distance (∼50 cm), large field‐of‐view (∼3 cm diameter), large depth of view (∼2 cm), and ‘point‐and‐shoot’ operation. Its performance was determined in tissue‐simulating phantoms and in pilot studies in brain tumor resection patients, with or without intra‐operative Photofrin‐PDT. Results In phantoms the imaging resolution was ∼150 μm, while Photofrin concentrations as low as 0.05 or 0.1 μg/g could be detected at the tissue surface or at 0.5 mm depth, respectively. Red Photofrin fluorescence could be clearly visualized post radical resection in all PDT patients, with biopsy confirmation of residual tumor tissue in regions that were not seen as tumor under white light. Photobleaching of Photofrin during PDT was also demonstrated. Conclusions The system performed to specification under realistic operating conditions and could reveal unresected residual tumor tissue. It may be used for either PDT dosimetry/monitoring and/or for surgical guidance. Lasers Surg. Med. 32:224–232, 2003.