Purpose A precise resection of the entire tumor tissue during surgery for brain metastases is essential to reduce local recurrence. Conventional intraoperative imaging techniques all have limitations in detecting tumor remnants. Therefore, there is a need for innovative new imaging methods such as optical coherence tomography (OCT). The purpose of this study is to discriminate brain metastases from healthy brain tissue in an ex vivo setting by applying texture analysis and machine learning algorithms for tissue classification to OCT images. Methods Tumor and healthy tissue samples were collected during resection of brain metastases. Samples were imaged using OCT. Texture features were extracted from B-scans. Then, a machine learning algorithm using principal component analysis (PCA) and support vector machines (SVM) was applied to the OCT scans for classification. As a gold standard, an experienced pathologist examined the tissue samples histologically and determined the percentage of vital tumor, necrosis and healthy tissue of each sample. A total of 14.336 B-scans from 14 tissue samples were included in the classification analysis. Results We were able to discriminate vital tumor from healthy brain tissue with an accuracy of 95.75%. By comparing necrotic tissue and healthy tissue, a classification accuracy of 99.10% was obtained. A generalized classification between brain metastases (vital tumor and necrosis) and healthy tissue was achieved with an accuracy of 96.83%. Conclusions An automated classification of brain metastases and healthy brain tissue is feasible using OCT imaging, extracted texture features and machine learning with PCA and SVM. The established approach can prospectively provide the surgeon with additional information about the tissue, thus optimizing the extent of tumor resection and minimizing the risk of local recurrences.

OBJECTIVEOptical coherence tomography (OCT) is an imaging technique that uses the light-backscattering properties of different tissue types to generate an image. In an earlier feasibility study the authors showed that it can be applied to visualize human peripheral nerves. As a follow-up, this paper focuses on the interpretation of the images obtained.METHODSTen different short peripheral nerve specimens were retained following surgery. In a first step they were examined by OCT during, or directly after, surgery. In a second step the nerve specimens were subjected to histological examination. Various steps of image processing were applied to the OCT raw data acquired. The improved OCT images were compared with the sections stained by H & E. The authors assigned the structures in the images to the various nerve components including perineurium, fascicles, and intrafascicular microstructures.RESULTSThe results show that OCT is able to resolve the myelinated axons. A weighted averaging filter helps in identifying the borders of structural features and reduces artifacts at the same time. Tissue-remodeling processes due to injury (perineural fibrosis or neuroma) led to more homogeneous light backscattering. Anterograde axonal degeneration due to sharp injury led to a loss of visible axons and to an increase of light-backscattering tissue as well. However, the depth of light penetration is too small to allow generation of a complete picture of the nerve.CONCLUSIONSOCT is the first in vivo imaging technique that is able to resolve a nerve’s structures down to the level of myelinated axons. It can yield information about focal and segmental pathologies.

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Various methods of lumbosacral fusions for the treatment of degenerative spinal diseases are used clinically. Results vary greatly depending on indication, type of fusion, implants, and method of evaluation. In a retrospective clinical and radiological examination after an average follow-up time of 3.9 years this study reports on the outcome of lumbosacral distraction spondylodesis (LSDS) in a consecutive series of 147 patients being fused for the treatment of spondylolisthesis, failed-back syndrome, or lumbar instability. LSDS consists of a posterolateral fusion together with an autologous corticocancellous H-graft wedged under distraction between the spinous processes of L4 and S1. With 81.0% good and excellent results this noninstrumented fusion technique showed the best outcome in patients with spondylolisthesis, while in cases with a failed-back syndrome or lumbar instability only 62.3% excellent to satisfying outcomes were noted. The rate of pseudarthrosis was 13.6% in the whole patient group; no major complications such as nerve root damage, postoperative neurological deficits, or spinal stenosis were found.

The occipito-atlanto-axial joint is the most complex one of the human spine. Traumatic or inflammatory lesions in this region may lead to instability and neurological symptoms of clinical importance. This study reports the results of anatomical and biomechanical examination of 13 human upper cervical spine specimens and focuses on the viscoelastic behavior of the alar and transverse ligaments. Non-destructive tensile testing was performed on a uniaxial testing machine with 25 alar and 11 transverse ligaments at three different load rates of 0.1 mm/s, 1.0 mm/s, and 10.0 mm/s. The ligaments were further tested for relaxation over 300s. Each ligament exhibited an initial neutral zone in which no tensile force could be measured during cyclic testing. This neutral zone was more significant in the alar ligaments than in the transverse ligaments with respect to the measured in situ length of the ligaments (11.2 vs 18.1 mm on average). Increasing axial deformation led to increased load in all ligaments. Hysteresis, i.e., the energy loss exhibited by viscoelastic material subjected to loading and unloading cycles, increased with higher displacement rates and higher tensile forces. In neutral position the alar ligaments were lax in all specimens. During axial rotation both alars tightened. Ligamentous resistance increased as the end of the range of motion (ROM) was approchaed during rotation. The neutral zone explains the laxity of the ligaments in midposition and allows mobility of the upper cervical spine with minimum expenditure of muscular energy. The ligaments become stiffer under higher loads and therefore contribute to a limitation of the ROM in the occipitio-atlanto-axial joint.