Diagnostic Potential of Autofluorescence for an Assisted Intraoperative Delineation of Glioblastoma Resection Margins¶

Mesoscopic fluorescence lifetime imaging: Fundamental principles, clinical applications and future directions

Fluorescence lifetime imaging (FLIm) is an optical spectroscopic imaging technique capable of real-time assessments of tissue properties in clinical settings. Label-free FLIm is sensitive to changes in tissue structure and biochemistry resulting from pathological conditions, thus providing optical contrast to identify and monitor the progression of disease. Technical and methodological advances over the last two decades have enabled the development of FLIm instrumentation for real-time, in situ, mesoscopic imaging compatible with standard clinical workflows. Herein, we review the fundamental working principles of mesoscopic FLIm, discuss the technical characteristics of current clinical FLIm instrumentation, highlight the most commonly used analytical methods to interpret fluorescence lifetime data and discuss the recent applications of FLIm in surgical oncology and cardiovascular diagnostics. Finally, we conclude with an outlook on the future directions of clinical FLIm.

Quantitative assessment of microenvironment characteristics and metabolic activity in glioma via multiphoton microscopy

Tumor microenvironment and metabolic activity in gliomas are the important biomarkers to evaluate the progression of gliomas. Many evidences have suggested that the targeting of metabolic activity and tumor microenvironment simultaneously can be more effective to take the tumor therapy. Therefore, the noninvasive, accurate assessment of tumor microenvironment and metabolic activity is quite important in clinical practice. Multiphoton microscopy (MPM), based on two-photon-excited fluorescence and second harmonic generation was performed on unstained glioma tissues. With our combined image analysis approaches, our research findings indicate that MPM is able to qualitatively and quantitatively describe the microenvironment characteristics in gliomas, such as collage deposition in extracellular matrix, lymphocyte infiltration and tumor angiogenesis, etc. Meanwhile, the metabolic activity can also be quantitatively evaluated by optical redox ratio, NADH and FAD intensity. With the microendoscope and fiberscope are portable, MPM technique can be used to perform in-vivo studies and clinical examinations in gliomas.

Multimodal imaging to explore endogenous fluorescence of fresh and fixed human healthy and tumor brain tissues

To complement a project toward label-free optical biopsy and enhanced resection which the overall goal is to develop a multimodal nonlinear endomicroscope, this multimodal approach aims to enhance the accuracy in classifying brain tissue into solid tumor, infiltration and normal tissue intraoperatively. Multiple optical measurements based on one- and two-photon spectral and lifetime autofluorescence, including second harmonic generation imaging, were acquired. As a prerequisite, studying the effect of the time of measurement postexcision on tissue's spectral/lifetime fluorescence properties was warranted, so spectral and lifetime fluorescences of fresh brain tissues were measured using a point-based linear endoscope. Additionally, a comparative study on tissue's optical properties obtained by multimodal nonlinear optical imaging microscope from fresh and fixed tissue was necessary to test whether clinical validation of the nonlinear endomicroscope is feasible by extracting optical signatures from fixed tissue rather than from freshly excised samples. The former is generally chosen for convenience. Results of this study suggest that an hour is necessary postexcision to have consistent fluorescence intensities\lifetimes. The fresh (a,b,c) vs fixed (d,e,f) tissue study indicates that while all optical signals differ after fixation. The characteristic features extracted from one- and two-photon excitation still discriminate normal brain (a,d) cortical tissue, glioblastoma (GBM) (b,e) and metastases (c,f).

Nanoimaging and neurological surgery

Over 32 million surgical procedures are performed in the United States each year. Increasingly, image guidance is used in order to aid in the surgical localization of pathology, minimization of incisions, and improvement of surgical intervention outcomes. A variety of imaging modalities using different portions of the electromagnetic spectrum are used in neurological surgery. These include wavelengths used in ultrasonography, optical, infrared, ionizing radiation, and magnetic resonance. The use of currently available image-guidance tools for neurological surgery is reviewed. Advances in nanoparticulates and their integration into the neurosurgical operating room environment are discussed.