The computed tomography imaging of a local region inside a sample with a size larger than the field of view is particularly important for synchrotron X-ray imaging.In this letter,an improved algorithm is proposed to reconstruct the local structure inside a sample using almost completely local data.The algorithm significantly reduces the X-ray radiation dose and improves computational efficiency.Simulation results show that the new algorithm works well and has a higher reconstruction precision than previous methods,as confirmed by experimental results carried out at the Shanghai Synchrotron Radiation Facility.
Matrix metalloproteinase-9（MMP-9） plays a beneficial role in the sub-acute phase after ischemic stroke.However,unrestrained MMP-9 may disrupt the blood-brain barrier（BBB）,which has limited its use for the treatment of brain ischemia.In the present study,we constructed lentivirus mediated hypoxiacontrolled MMP-9 expression and explored its role after stroke.Hypoxia response element（HRE）was used to confine MMP-9 expression only to the hypoxic region of mouse brain after 120-min transient middle cerebral artery occlusion.Lentiviruses were injected into the peri-infarct area on day 7 after transient ischemia.We found hyperexpression of exogenous HRE-MMP-9 under the control of hypoxia,and its expression was mainly located in neurons and astrocytes without aggravation of BBB damage compared to the CMV group.Furthermore,mice in the HRE-MMP-9 group showed the best behavioral recovery compared with the normal saline,GFP,and SB-3CT groups.Therefore,hypoxia-controlled MMP-9 hyperexpression during the sub-acute phase of ischemia may provide a novel promising approach of gene therapy for stroke.
We report a design for one nanometer X-ray focusing by a complex refractive lens, which is capable of focusing 20 keV X-rays down to a lateral size of 0.92 nm （full-width at half-maximum （FWHM）） and an axial size of 98 nm （FWHM） with intensity gain of 49050. This complex refractive lens is comprised of a series of kinoform lenses, whose aperture is gradually matched to the converging trace of the X-ray beam so as to increase the numerical aperture （NA）. The theoretical principle of the proposed complex refractive lens is presented. The NAs of these lenses are calculated. The numerical simulation results demonstrate that the proposed design can focus the X-ray beam into sub-nanometer while remaining high gain.
Kinoform单透镜可以高效聚焦硬X射线至纳米量级,在X射线纳米显微学和纳米光谱学领域有着重要的应用前景.基于衍射光学和傅里叶光学理论,给出了X射线经由Kinoform单透镜聚焦的物理模型,基于数值模拟,研究了不同材料、光子能量、台阶数量和顶点曲率半径对Kinoform单透镜聚焦性能的影响.结果表明,孔径为1 mm的Kinoform单透镜对30 ke V的X射线聚焦,可以得到14 nm焦斑、62μm焦深,且可实现4个量级的光强增益和大于30%的光强透过率.
