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.
Reconstructed depth-resolved optic axis orientation obtained by catheter based PSOCT in a tissue volume informs on the orientation of the white matter fiber bundles in the brain, owing to the birefringence of myelinated axons. The physical organization of white matter also leads to anisotropic diffusion of water molecules, which is the basis of dMRI for non-invasive imaging of the three-dimensional orientation of white matter fiber bundles. Having access to fiber orientation in both imaging modalities, we are trying to map the depth-resolved birefringence and optic axis orientation to the larger scale dMRI as well as an atlas of brain anatomy.
SignificanceTypical light sheet microscopes suffer from artifacts related to the geometry of the light sheet. One main inconvenience is the non-uniform thickness of the light sheet obtained with a Gaussian laser beam.AimWe developed a two-photon light sheet microscope that takes advantage of a thin and long Bessel-Gauss beam illumination to increase the sheet extent without compromising the resolution.ApproachWe use an axicon lens placed directly at the output of an amplified femtosecond laser to produce a long Bessel-Gauss beam on the sample. We studied the dopaminergic system and its projections in a whole cleared mouse brain.ResultsOur light sheet microscope allows an isotropic resolution of 2.4 μm in all three axes of the scanned volume while keeping a millimetric-sized field of view, and a fast acquisition rate of up to 34 mm2 / s. With slight modifications to the optical setup, the sheet extent can be increased to 6 mm.ConclusionThe proposed system’s sheet extent and resolution surpass currently available systems, enabling the fast imaging of large specimens.
The purpose is to determine whether diffuse reflectance spectroscopy (DRS) can provide optical guidance during deep brain stimulation (DBS) surgery. Experiments on monkey ex vivo brains have been performed to ensure DRS methods could differentiate white and gray matter. In this study, we use principal component analysis (PCA) to determine the composition of tissue in front of the stimulation electrode. Furthermore, our work tackles the mechanical consequences of implementing an optical probe in a DBS electrode. This multidisciplinary project shows that DRS can be used as a non-invasive, cost-effective and real-time tissue characterization.
We introduce the GRIN-axicon, a new low-cost optical component that is easy to manufacture and could replace the axicon in various setups such as a two-photon microscope. In neuroscience, the imaging of in vivo samples requires high temporal resolution in order to capture the interactions between neurons located at different depths in the tissue. To achieve this, the use of an axicon lens increases the depth of field of the microscope and reduces the number of scans to be performed. However, the axicon is difficult to manufacture and generally has defects on the tip of the cone, thus degrading the quality of the resultant Bessel-Gauss beam.
We propose a method to compute the axial distribution of non-diffracting beams. The approach stands on simple ray tracing and energy conservation principles. The proposed method is applied for four different Bessel beam generators, such as the refractive axicon, to compute the output axial intensity profile for a given input beam. We show great agreement between the results and the CODE V diffractional simulations. The method can also be used to calculate analytically the incident illumination pattern needed for a target output profile or to design an optical element surface to reach the same goal.
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