Wei-Chiang Lin

In Vivo Brain Tumor Demarcation Using Optical Spectroscopy

Abstract The applicability of optical spectroscopy for intraoperative detection of brain tumors/tumor margins was investigated in a pilot clinical trial consisting of 26 brain tumor patients. The results of this clinical trial suggest that brain tumors and infiltrating tumor margins (ITM) can be effectively separated from normal brain tissues in vivo using combined autofluorescence and diffuse-reflectance spectroscopy. A two-step empirical discrimination algorithm based on autofluorescence and diffuse reflectance at 460 and 625 nm was developed. This algorithm yields a sensitivity and specificity of 100 and 76%, respectively, in differentiating ITM from normal brain tissues. Blood contamination was found to be a major obstacle that attenuates the accuracy of brain tumor demarcation using optical spectroscopy. Overall, this study indicates that optical spectroscopy has the potential to guide brain tumor resection intraoperatively with high sensitivity.

Intraoperative optical spectroscopy identifies infiltrating glioma margins with high sensitivity.

OBJECTIVE Adult gliomas have indistinct borders. As the ratio of neoplastic cells to normal cells becomes lower, the ability to detect these cells diminishes. We describe a device designed to augment intraoperative identification of both solid tumor and infiltrating tumor margins. METHODS A novel, intraoperative, optical spectroscopic tool, using both white light reflectance and 337-nm excitation fluorescence spectroscopy, is described. Discrimination algorithms have been developed to segregate neoplastic tissues from normal glial and neuronal elements. The spectroscopy device was used to measure 5 to 10 locations during glioma resection. Beneath the tool, a biopsy sample was obtained and the pathological results were reviewed in a blinded fashion. Samples were classified as solid tumor, infiltrating tumor, or normal gray or white matter. Comparisons were made between the optical spectra and the histopathological results of sampled areas in evaluating the sensitivity and specificity of the tool for tissue discrimination. RESULTS Spectral data were obtained from 24 patients with glioma and from 11 patients with temporal lobe epilepsy. A sensitivity of 80% and a specificity of 89% in discriminating solid tumor from normal tissues were obtained. In addition, infiltrating tumor margins were distinguished from normal tissues with a sensitivity of 94% and a specificity of 93%. CONCLUSION We have developed a handheld, optical spectroscopic device that may be used rapidly and in near real time with high sensitivity and reproducibility as an optical tissue discrimination tool in glioma surgery.

Brain tumor demarcation using optical spectroscopy; an in vitro study

Optical spectroscopy for brain tumor demarcation was investigated in this study. Fluorescence and diffuse reflectance spectra were measured from normal and tumorous human brain tissues in vitro. A fluorescence peak was consistently observed around 460 nm (+/- 10 nm) emission from both normal and tumorous brain tissues using 337 nm excitation. Intensity of this fluorescence peak (F460) from normal brain tissues was greater than that from primary brain tumorous tissues. In addition, diffuse reflectance (Rd) between 650 and 800 nm from white matter was significantly stronger than that from primary and secondary brain tumors. A good separation between gray matter and brain tumors was found using the ratio of F460 and Rd at 460 nm (Rd460). Two empirical discrimination algorithms based on F460, Rd625, and F460/Rd460 were developed. These algorithms yielded an average sensitivity and specificity of 96% and 93%, respectively.

In vitro determination of normal and neoplastic human brain tissue optical properties using inverse adding-doubling

To complement a project towards the development of real-time optical biopsy for brain tissue discrimination and surgical resection guidance, the optical properties of various brain tissues were measured in vitro and correlated to features within clinical diffuse reflectance tissue spectra measured in vivo. Reflectance and transmission spectra of in vitro brain tissue samples were measured with a single-integrating-sphere spectrometer for wavelengths 400-1300 nm and converted to absorption and reduced scattering spectra using an inverse adding-doubling technique. Optical property spectra were classified as deriving from white matter, grey matter or glioma tissue according to histopathologic diagnosis, and mean absorption and reduced scattering spectra were calculated for the three tissue categories. Absolute reduced scattering and absorption values and their relative differences between histopathological groups agreed with previously reported results with the exception that absorption coefficients were often overestimated, most likely due to biologic variability or unaccounted light loss during reflectance/transmission measurement. Absorption spectra for the three tissue classes were dominated by haemoglobin absorption below 600 nm and water absorption above 900 nm and generally determined the shape of corresponding clinical diffuse reflectance spectra. Reduced scattering spectral shapes followed the power curve predicted by the Rayleigh limit of Mie scattering theory. While tissue absorption governed the shape of clinical diffuse reflectance spectra, reduced scattering determined their relative emission intensities between the three tissue categories.

Dynamics of tissue optics during laser heating of turbid media

The dynamics of the optical behavior of tissue during the photothermal interaction of laser radiation with tissue could significantly affect the optimization of light doses for effective and safe applications of lasers in medicine. Characterization of the dynamics of tissue optics during laser heating was performed by means of simultaneous measurements of the total transmittance, diffuse reflectance, and surface temperature of fresh and thermally coagulated human skin and canine aorta during long-pulsed Nd:YAG laser heating with a double integrating-sphere system and an infrared camera. Thermally induced changes in the optical properties of tissue caused a decrease in the total transmittance and an increase in the diffuse reflectance of both fresh and precoagulated skin and aorta samples. For fresh tissue, these changes were primarily reversible until photocoagulation occurred, then both the reversible, as well as the irreversible, changes were observed. However, for precoagulated tissue the reversible changes in the optical properties were dominant, whereas the irreversible changes were insignificant. Results from this study indicate the existence of the nonlinear behavior in the optics of turbid biological media during pulsed laser heating. Possible mechanisms responsible for this nonlinear optical behavior are discussed.

In vivo assessment of thermal damage in the liver using optical spectroscopy

Resection is not a viable treatment option for the majority of liver cancer patients. Alternatives to resection include thermotherapies such as radio-frequency ablation; however, these therapies lack adequate intraoperative feedback regarding the degree and margins of tissue thermal damage. In this proof of principle study, we test the ability of fluorescence and diffuse reflectance spectroscopy to assess local thermal damage in vivo. Spectra were acquired in vivo from healthy canine liver tissue undergoing radio-frequency ablation using a portable fiber-optic-based spectroscopic system. The major observed spectral alterations on thermal coagulation were a red shift in the fluorescence emission peak at 480 nm, a decrease in the overall fluorescence intensity, and an increase in the diffuse reflectance from 450 to 750 nm. Spectral changes were quantified and correlated to tissue histology. We found a good correlation between the proposed spectral correlates of thermal damage and histology. The results of this study suggest that fluorescence and diffuse reflectance spectroscopy show strong potential as tools to monitor liver tissue thermal damage intraoperatively.

Feasibility study using surface-enhanced Raman spectroscopy for the quantitative detection of excitatory amino acids

The release of excitatory amino acids (EAAs) from injured neurons has been associated with secondary injury following head trauma. The development of a rapid and sensitive method for the quantification of EAAs may provide a means for clinical management of patients affected by head trauma. We explore the potential application of surface-enhanced Raman spectroscopy (SERS) for rapid quantification of the concentration of EAAs in aqueous silver colloids. The EAAs glutamate (Glu) and aspartate (Asp) are released following head injury and have been observed to exhibit SERS spectra that should enable them to be distinguished in a complex aqueous media. Of the two EAAs, the concentration of Glu has been shown to be more indicative of injury to the central nervous system. Using 30-s scans and a 50-mW argon laser, aqueous Glu is quantifiable from 0.4 to 5 micromol/L and is spectrally distinguishable from Asp. In addition, initial in vivo microdialysis experiments suggest that this SERS system is capable of measuring chemical changes following head trauma in the rat brain. Compared with current high-performance liquid chromatography (HPLC) techniques for amino acid detection, the short scanning and processing time associated with the SERS approach enables measurement on a near-real-time basis, providing clinical information in anticipation of pharmaceutical intervention.

Intraoperative application of optical spectroscopy in the presence of blood

A simple but effective method of spectral processing was developed to minimize or remove the effects of the presence of superficial blood on tissue optical spectra and, hence, enhance the performance of optical-spectroscopic-based in vivo tissue diagnosis and surgical guidance. This spectral-processing algorithm was developed using the principles of absorption-induced light attenuation wherein the ratio of fluorescence intensity (F) and the hth power of diffuse reflectance intensity (Rd) at a given emission wavelength /spl lambda//sub m/ is immune to spectral distortions induced by the presence of blood on the tissue surface. Here, the exponent h is determined by the absorption coefficients of whole blood at the excitation and emission wavelengths. The theoretical basis of this spectral processing was verified using simulations and was experimentally validated. Furthermore, the optical spectra of brain tissues collected in vivo was processed using this algorithm to evaluate its impact on brain tissue differentiation using combined fluorescence and diffuse reflectance spectroscopy. Based on the simulation, as well as experimental results, it was observed that using F/Rd/sup h/ h can effectively reduce or remove spectral distortions induced by superficial blood contamination on tissue optical spectra. Thus, optical spectroscopy can also be used intraoperatively for applications such as surgical guidance of tumor resection.

A probability-based spectroscopic diagnostic algorithm for simultaneous discrimination of brain tumor and tumor margins from normal brain tissue.

This paper reports the development of a probability-based spectroscopic diagnostic algorithm capable of simultaneously discriminating tumor core and tumor margins from normal human brain tissues. The algorithm uses a nonlinear method for feature extraction based on maximum representation and discrimination feature (MRDF) and a Bayesian method for classification based on sparse multinomial logistic regression (SMLR). Both the autofluorescence and the diffuse-reflectance spectra acquired in vivo from patients undergoing craniotomy or temporal lobectomy at the Vanderbilt University Medical Center were used to train and validate the algorithm. The classification accuracy was observed to be approximately 96%, 80%, and 97% for the tumor, tumor margin, and normal brain tissues, respectively, for the training data set and approximately 96%, 94%, and 100%, respectively, for the corresponding tissue types in an independent validation data set. The inherently multi-class nature of the algorithm facilitates a rapid and simultaneous classification of tissue spectra into various tissue categories without the need for a hierarchical multi-step binary classification scheme. Further, the probabilistic nature of the algorithm makes it possible to quantitatively assess the certainty of the classification and recheck the samples that are classified with higher relative uncertainty.

Neuro-oncological applications of optical spectroscopy.

Advances in optics and molecular imaging have occurred rapidly in the past decade. One technique poised to take advantage of these developments is optical spectroscopy (OS). All optical spectroscopic techniques have in common tissue interrogation with light sources ranging from the ultraviolet (UV) to the infrared (IR) ranges of the spectrum, and collection of information on light reflected (reflectance spectroscopy) or light interactions with tissue and emergence at different wavelengths (fluorescence and Raman spectroscopy). OS can provide information regarding intrinsic tissue optical properties such as tissue structure, nuclear density, and the presence or absence of endogenous or exogenous fluorophores. Among other applications, this information has been used to distinguish tumor from normal brain tissues, to detect tumor margins in intrinsic, infiltrating gliomas, to identify radiation damage to tissues, and to assess tissue viability and predict the onset of apoptosis in vitro and in vivo. Potential applications of OS include detection of specific central nervous system (CNS) structures, such as brain nuclei, identification of cell types by the presence of specific neurotransmitters, and the detection of optically labeled cells or drugs during therapeutic interventions. All have potential utility in neuro-oncology, have been investigated in our laboratories, and will be the subject of this review.