SignificanceWe assess the feasibility of using diffuse reflectance spectroscopy (DRS) and coherent anti-Stokes Raman scattering spectroscopy (CARS) as optical tools for human brain tissue identification during deep brain stimulation (DBS) lead insertion, thereby providing a promising avenue for additional real-time neurosurgical guidance.AimWe developed a system that can acquire CARS and DRS spectra during the DBS surgery procedure to identify the tissue composition along the lead trajectory.ApproachDRS and CARS spectra were acquired using a custom-built optical probe integrated in a commercial DBS lead. The lead was inserted to target three specific regions in each of the brain hemispheres of a human cadaver. Spectra were acquired during the lead insertion at constant position increments. Spectra were analyzed to classify each spectrum as being from white matter (WM) or gray matter (GM). The results were compared with tissue classification performed on histological brain sections.ResultsDRS and CARS spectra obtained using the optical probe can identify WM and GM during DBS lead insertion. The tissue composition along the trajectory toward a specific target is unique and can be differentiated by the optical probe. Moreover, the results obtained with principal component analysis suggest that DRS might be able to detect the presence of blood due to the strong optical absorption of hemoglobin.ConclusionsIt is possible to use optical measurements from the DBS lead during surgery to identify WM and GM and possibly the presence of blood in human brain tissue. The proposed optical tool could inform the surgeon during the lead placement if the lead has reached the target as planned. Our tool could eventually replace microelectrode recordings, which would streamline the process and reduce surgery time. Further developments are required to fully integrate these tools into standard clinical procedures.
Deep brain stimulation (DBS) surgery is performed on patients suffering Parkinson’s disease for whom medication is no longer effective in relieving their motor symptoms. In this surgery, a stimulating electrode is implanted in a specific structure deep within the brain, delivering electrical impulses and thus reducing the motor symptoms. The success of the surgery is highly dependent on placing the electrode accurately in the targeted structure, typically the subthalamic nucleus (STN). We developed a DBS electrode that includes optical fibers to perform coherent anti-Stokes Raman scattering (CARS) spectroscopy and diffuse reflectance spectroscopy (DRS) during the electrode insertion in the brain. We were able to identify white and grey matter using principal component analysis (PCA), showing that spectroscopic measurements could be suitable for neuronavigation.
In this work, quantum cascade laser (QCL) mid-infrared (MIR) reflectance spectroscopy is used to discriminate silicate and carbonate minerals in a standoff measurement setting. The tunable external cavity QCL source that was used allows measurements from 5.2 μm to 13.4 μm wavelength, where the fundamental vibrational bands of silicates and carbonates are observed. Spectra measured from a half-core sample were analyzed using multivariate analysis to extract and identify the end-member spectra from the mixtures. The end-member spectra were compared and validated using the ASTER database spectra and the spectra measured on reference samples with the same QCL MIR reflectance spectroscopy setup. Spectra of minerals commonly found in the mining industry were compared: quartz, microcline, albite, chlorite, muscovite, biotite, calcite and dolomite. MIR reflectance spectroscopy using compact QCL sources allow rapid spectral measurements at standoff distances and high spatial resolution. All these advantages show the potential of QCL MIR reflectance spectroscopy for in-the-field mining applications.
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