Laser Speckle Contrast Imaging (LSCI) has emerged as a promising imaging modality that offers full field, real time, continuous and agent free monitoring of cerebral blood flow during neurosurgery. Since LSCI does not require the injection of a contrast agent, it has the potential to complement fluorescence-based modalities by providing continuous and dynamic changes in blood flow during critical moments of neurosurgery. We performed a clinical study with LSCI to investigate the clinical utility of the technique intraoperatively. A commercially available Zeiss Pentero 900® microscope was equipped with a λ=785nm laser diode attached to a customized mount. The backscattered laser light was collected by the microscope, producing a laser speckle image on the external camera which was mounted on the microscope side-port. Custom software collected laser speckle images, computed, and then displayed the speckle contrast images in real time throughout the surgery onto the operating room monitors. The images were displayed with custom color maps and thresholding. The robust integration in the surgical workflow of the technology enabled the investigation of the need for dynamic vessel-flow characterization in 20-patients at the Inselspital in Bern, Switzerland. We assessed vessel flow during key time points in the surgery and provided real time and continuous measurements to the surgeon.
We use a wide field imaging Mueller polarimeter to visualize the fiber tracts of healthy brain in the retardance maps for the detection of tumor borders. The results of ex-vivo polarimetric studies of thick sections of brain tissue are presented.
The accurate detection of brain tumor border during neurosurgery is crucial for the safe and complete tumor resection, but it is often difficult to differentiate solid tumor tissue from infiltrated white matter. To address this problem we suggest detecting optical anisotropy of brain white matter which consists of bundles of axons (or fiber tracts). Tumor growth erases this optical anisotropy of healthy brain. We used a wide-field imaging Mueller polarimeter to measure thick fixed human and fresh animal brain sections in reflection. The maps of azimuth of fast optical axis of linear birefringent medium obtained from Lu-Chipman decomposition of the experimental Mueller matrices showed a compelling correlation with the fiber tracts directions on histology image of thin whole mount silver-stained brain tissue section.
The crucial problem of brain tumor surgery is the accurate detection the tumor border for safe and complete tumor resection. Whereas it is quite easy to identify brain tumor in preoperative magnetic resonance imaging, it is often difficult to differentiate solid tumor tissue from infiltrated white matter during surgery with conventional surgical intra-operative microscope. To address this problem we suggest exploring the optical anisotropy of healthy brain white matter which represents a highly ordered structure consisting of axons that are joined together in fiber tracts. Tumor cells grow chaotically and erase the optical anisotropy of healthy brain. Instead of detecting the tumor itself, we suggest to visualize healthy white matter by means of its fiber tracts by detecting the optical anisotropy of brain tissue. For this purpose we used a wide-field imaging Mueller polarimetric system operating in the visible wavelength range in backscattering configuration. The Mueller matrix images of the thick (~1cm) fixed human brain specimen and thick (~1cm) fresh veal brain specimen were measured at 633 nm in reflection. Lu Chipman decomposition was applied pixel-wise to the experimental Mueller matrices. The maps of azimuth of fast optical axis of linear birefringent medium showed a compelling correlation with the fiber tracts directions on histology image of thin whole mount silver-stained brain tissue section, that is gold standard for ex-vivo brain fiber tract visualization. Thus, label-free non-contact imaging Mueller polarimetry shows potential for the intra-operative visualization of brain white matter fiber tracts. Further studies are ongoing.
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