Quantitative assessment of sciatic nerve changes in Charcot-Marie-Tooth type 1A patients using magnetic resonance neurography.

BACKGROUND AND PURPOSE: Nerve tissue alterations have rarely been quantified in Charcot-Marie-Tooth type 1A (CMT1A) patients. The aim of the present study was to quantitatively assess the magnetic resonance imaging (MRI) anomalies of the sciatic and tibial nerves in CMT1A disease using quantitative neurography MRI. It was also intended to seek for correlations with clinical variables. METHODS: Quantitative neurography MRI was used in order to assess differences in nerve volume, proton density and magnetization transfer ratio in the lower limbs of CMT1A patients and healthy controls. Disease severity was evaluated using the Charcot-Marie-Tooth Neuropathy Score version 2, Charcot-Marie-Tooth examination scores and Overall Neuropathy Limitations Scale scores. Electrophysiological measurements were performed in order to assess the compound motor action potential and the Motor Unit Number Index. Clinical impairment was evaluated using muscle strength measurements and Charcot-Marie-Tooth examination scores. RESULTS: A total of 32 CMT1A patients were enrolled and compared to 13 healthy subjects. The 3D nerve volume, magnetization transfer ratio and proton density were significantly different in CMT1A patients for the whole sciatic and tibial nerve volume. The sciatic nerve volume was significantly correlated with the whole set of clinical scores whereas no correlation was found between the tibial nerve volume and the clinical scores. CONCLUSION: Nerve injury could be quantified in vivo using quantitative neurography MRI and the corresponding biomarkers were correlated with clinical disability in CMT1A patients. The sensitivity of the selected metrics will have to be assessed through repeated measurements over time during longitudinal studies to evaluate structural nerve changes under treatment.

Microscale mechanical and mineral heterogeneity of human cortical bone governs osteoclast activity.

Human cortical bone permanently remodels itself resulting in a haversian microstructure with heterogeneous mechanical and mineral properties. Remodeling is carried out by a subtle equilibrium between bone formation by osteoblasts and bone degradation by osteoclasts. The mechanisms regulating osteoclast activity were studied using easy access supports whose homogeneous microstructures differ from human bone microstructure. In the current study, we show that human osteoclasts resorb human cortical bone non-randomly with respect to this specific human bone microstructural heterogeneity. The characterization of this new resorption profile demonstrates that osteoclasts preferentially resorb particular osteons that have weak mechanical properties and mineral contents and that contain small hydroxyapatite crystals with a high carbonate content. Therefore, the influence of human bone microstructure heterogeneity on osteoclast activity could be a key parameter for osteoclast behaviour, for both in vitro and clinical studies.

Reaction of bone nanostructure to a biodegrading Magnesium WZ21 implant - A scanning small-angle X-ray scattering time study.

Understanding the implant-bone interaction is of prime interest for the development of novel biodegrading implants. Magnesium is a very promising material in the class of biodegrading metallic implants, owing to its mechanical properties and excellent immunologic response during healing. However, the influence of degrading Mg implants on the bone nanostructure is still an open question of crucial importance for the design of novel Mg implant alloys. This study investigates the changes in the nanostructure of bone following the application of a degrading WZ21 Mg implant (2wt% Y, 1wt% Zn, 0.25wt% Ca and 0.15wt% Mn) in a murine model system over the course of 15months by small angle X-ray scattering. Our investigations showed a direct response of the bone nanostructure after as little as 1month with a realignment of nano-sized bone mineral platelets along the bone-implant interface. The growth of new bone tissue after implant resorption is characterized by zones of lower mineral platelet thickness and slightly decreased order in the stacking of the platelets. The preferential orientation of the mineral platelets strongly deviates from the normal orientation along the shaft and still roughly follows the implant direction after 15months. We explain our findings by considering geometrical, mechanical and chemical factors during the process of implant resorption. STATEMENT OF SIGNIFICANCE: The advancement of surgical techniques and the increased life expectancy have caused a growing demand for improved bone implants. Ideally, they should be bio-resorbable, support bone as long as necessary and then be replaced by healthy bone tissue. Magnesium is a promising candidate for this purpose. Various studies have demonstrated its excellent mechanical performance, degradation behaviour and immunologic properties. The structural response of bone, however, is not well known. On the nanometer scale, the arrangement of collagen fibers and calcium mineral platelets is an important indicator of structural integrity. The present study provides insight into nanostructural changes in rat bone at different times after implant placement and different implant degradation states. The results are useful for further improved magnesium alloys.

Bias image correction via stationarity maximization.

Automated acquisitions in microscopy may come along with strong illumination artifacts due to poor physical imaging conditions. Such artifacts obviously have direct consequences on the efficiency of an image analysis algorithm and on the quantitative measures. In this paper, we propose a method to correct illumination artifacts on biological images. This correction is based on orthogonal polynomial modeling, combined with stationary maximization criteria. To validate the proposed method we show that we improve particle detection algorithm.