Development and testing of a CW-EPR apparatus for imaging of short-lifetime nitroxyl radicals in mouse head

This article describes a method for reducing the acquisition time in three-dimensional (3D) continuous-wave electron paramagnetic resonance (CW-EPR) imaging. To visualize nitroxyl spin probes, which have a short lifetime in living organisms, the acquisition time for a data set of spectral projections should be shorter than the lifetime of the spin probes. To decrease the total time required for data acquisition, the duration of magnetic field scanning was reduced to 0.5 s. Moreover, the number of projections was decreased by using the concept of a uniform distribution. To demonstrate this faster data acquisition, two kinds of nitroxyl radicals with different decay rates were measured in mice. 3D EPR imaging of 4-hydroxy-2,2,6,6-tetramethylpiperidine-d₁₇-1-¹⁵N-1-oxyl in mouse head was successfully carried out. 3D EPR imaging of nitroxyl spin probes with a half-life of a few minutes was achieved for the first time in live animals.     

In vivo temporal EPR imaging of the brain of rats by using two types of blood-brain barrier-permeable nitroxide radicals

In vivo temporal EPR imaging was conducted on the brain of rats that received one of two kinds of blood-brain barrier-permeable nitroxide radicals via the tail vein-one is a water-soluble 3-hydroxymethyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (hydroxymethyl-PROXYL); and the other is a non-water-soluble 3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (PCAM). From temporal EPR imaging data, temporal changes in the distribution of the nitroxide radical in the cerebral cortex, striatum, and hippocampus in the brain were investigated. It was found that the half-lives of the three parts in the brain of hydroxymethyl-PROXYL are longer and their EPR signal intensities are greater than those of PCAM.     

Two-dimensional imaging by the continuous-wave EPR

To be able to perform a two-dimensional study of free radical distribution by the continuous-wave electron paramagnetic resonance method in the X-band, special coils producing a magnetic gradient of 8 G/mm have been designed and constructed. The EPR spectra recorded for this gradient were subjected to the procedure of deconvolution in order to elicit information on the concentration of the radical distribution. The data obtained were used as the source file of the program reconstructing the image. The reconstruction was based on the iterative simultaneous algebraic reconstruction technique (Andersen A.H., Kak A.C.: Ultrason. Imag. 6, 81–94, 1984). The quality of the generated images depends on the angle of the sample axis to the gradient direction set by a goniometer and on the deconvolution procedures applied. The first tests on artificially generated phantoms indicated a dependence of the obtained images on the magnetic field gradients applied. The determined spatial distribution of radicals has confirmed their uniform distribution in the sample. The preliminary tests were performed for diphenyl-picrylhydrazyl. Having proved the reliability of the method, analogous measurements were also performed for plyphenylene sulphide PPS-V1 and indicated a homogeneous distribution of radicals in the whole volume of the sample. The images obtained confirmed the uniform distribution of the radicals.     

Analysis of time-resolved CW-EPR spectra of short-lived radicals at different times after laser excitation

Laser excitation combined with time-resolved CW-EPR spectroscopy of a carotenoid-porphyrin-diquinone tetrad (1), observes polarized spectra of the end quinone radical anion, Q·_B ^?. These spectra strongly depend on the time interval between the laser pulse and the position of the detection window of the transient magnetization profile, and may lead to misinterpretation of the radical intermediates participating in the reaction route. Spectral distortions arise from small hyperfine splittings and narrow line widths, resulting in the appearance of Torrey wiggles at off-resonance fields. The correct spectrum, however, and its line shape appear at times above 1 μs after the laser pulse, and is in complete agreement with the Fourier transform EPR spectrum. Analysis and reconstruction of the transient spectra is carried out in Fourier conjugate space. The experimental spectra are shown to be the Fourier transform of the free-induction decay (FID) multiplied by an appropriate windowing function. The changes in the spectra taken at t<1 μs are due to line distortions and not to chemical processes. This treatment is of general applicability in the spectral analysis of time-resolved CW-EPR spectra.     

Characterization of ancient and modern papers by CW-EPR spectroscopy

Several old (15th to 18th century), new (1900–1950) and recently produced (after 1990) papers have been investigated by X-band continuous-wave electron paramagnetic resonance (EPR) spectroscopy. Signals from Cu(II), Fe(III), Mn(II) and radicals are apparent. A clear-cut distinction is observed between recently produced papers and the other samples: recent papers show just EPR signals from Mn(II) and sometimes small signals from Fe(III) in rhombic site, while the older samples show usually strong signals from Fe(III), Mn(II), Cu(II) and radicals. Furthermore, Mn(II) EPR signals from recent papers are characterized by small zero-field splitting (ZFS) parameters, indicating Mn(II) in high-symmetry sites, while older samples show broader Mn(II) EPR signals, typical for Mn(II) in low-symmetry sites (increased ZFS parameters).     

Two-dimensional visualization of the flame front in an internal combustion engine by laser-induced fluorescence of OH radicals

Two-dimensional laser-induced fluorescence (2D-LIF) imaging of OH radicals, excited at 308 nm, has been employed to visualize the flame front in an internal combustion engine burning air/propane mixtures. Light sheet thicknesses down to 70 m have been attained for excitation. Hydroxyl radicals were detected up to pressures of 7.5 bar at engine speeds of 500 rpm. An upper limit of 300 m for the flame front thickness was obtained from line intensity profiles.     

H2O温度二维分布的滤波反投影重建

利用可调谐半导体吸收光谱技术实现燃烧场温度二维分布重建。设计H2O模型温度分布范围为300~1300 K,高斯型分布,利用Radon变换模拟实验测量结果。采用滤波反投影算法重建了两条吸收谱线强度场,进而得到气体温度二维分布,重建结果与模型符合较好。研究了不同投影数目和随机噪声对重建结果的影响,结果表明:随着投影数目的减少和噪声幅值的增加,重建温度分布均方误差增大,图像重建效果变差。当投影数目减小到4个,重建温度场已不能完全反映原始温度场信息。     

A CW-EPR and ESEEM spectroscopic study of the dithiadiazolyl radicals p-XC6F4CNSSN (X = CN, Br)

Two dithiadiazolyl radicals, p-NCC₆F₄CNSSN and p-BrC₆F₄CNSSN, have recently been found to be paramagnetic in the solid state. While the β-phase of the first one exhibits spontaneous magnetization below 36 K, the second one shows a paramagnetic character in the solid state. The spin density distribution in these radicals is examined through continuous-wave electron paramagnetic resonance and electron spin echo envelope modulation spectroscopies. Hyperfine correlation sublevel spectroscopy provides information about the interaction of the unpaired spin with F and N nuclei. A signal coming from the interaction with Br nucleus is also detected. The superhyperfme coupling constants of the unpaired electron with the magnetic nuclei are obtained and values of the corresponding spin densities, ?_s and ?_σ - ?_π, can be estimated in the isolated radicals. Spin density distribution has also been calculated in both molecules with density functional theory, being in excellent agreement with those determined from the spectra. The spin density is mainly concentrated in the dithiadiazolyl ring, but some spin density is observed on the fluorinated aromatic rings. They also provide a strong basis to understand the differences of the magnetic behavior of both molecules in terms of their respective packing in the solid state.     

H2O温度二维分布的滤波反投影重建

利用可调谐半导体吸收光谱技术实现燃烧场温度二维分布重建。设计H2O模型温度分布范围为300~1300 K,高斯型分布,利用Radon变换模拟实验测量结果。采用滤波反投影算法重建了两条吸收谱线强度场,进而得到气体温度二维分布,重建结果与模型符合较好。研究了不同投影数目和随机噪声对重建结果的影响,结果表明：随着投影数目的减少和噪声幅值的增加,重建温度分布均方误差增大,图像重建效果变差。当投影数目减小到4个,重建温度场已不能完全反映原始温度场信息。     

Two-dimensional synthetic aperture imaging in the optical domain

In scan-mode synthetic aperture imaging radar, spatial resolution in a range is given by a frequency-swept waveform, whereas resolution in the orthogonal direction is derived from the record of phase as the beam footprint executes linear motion over the object. We demonstrate here what is to our knowledge the first two-dimensional imaging that uses exactly this process in the optical domain for a 1 cm x 1 cm object with 90 mumx170 mum resolution.     

Different magnetic resonance imaging features in two types of nontraumatic rabbit osteonecrosis models

A single injection of high-dose steroid (20 mg/kg) has been reported to induce necrotic lesions in the proximal metaphysis and diaphysis of the rabbit femur. In the rabbit osteonecrosis (ON) model induced by two-dose horse serum injections, contrast-enhanced magnetic resonance imaging (MRI) and T2*-weighted dynamic MRI have been reported to detect necrotic lesions at 3 days after the second serum injection sensitively. The purpose of the present study was to determine whether contrast-enhanced MRI and T2*-weighted dynamic MRI could detect early development of necrotic lesions in the rabbit proximal femora after a single high-dose steroid injection and compare MRI features of the two types of nontraumatic rabbit ON models. We performed nonenhanced MRI, contrast-enhanced MRI and T2*-weighted dynamic MRI of bilateral proximal femora 3 days (10 femora), 1 week (10 femora), 3 weeks (10 femora), 6 weeks (18 femora) and 9 weeks (18 femora) after a single 20 mg/kg steroid injection. Femoral signal intensity of each T2*-weighted dynamic MRI was measured from a 1-cm(2) region of interest in the proximal metaphysis and diaphysis. As a control, MRI was performed in untreated animals (six femora). Histologically, no necrotic lesions were observed in the proximal femora at 3 days and 1 week. Bone marrow necrosis was observed in four (40%) femora at 3 weeks, two (11.1%) femora at 6 weeks and six (33.3%) femora at 9 weeks. Bone marrow lesion completely replaced by granulation tissue was observed in one femur at 6 weeks and one femur at 9 weeks. Histologic evidence of repair tissue surrounding bone marrow necrosis was seen after 6 weeks. Average lesion area including repair tissue was 4.40 mm(2) (range, 0.32 to 20.2 mm(2)). At 9 weeks, contrast-enhanced MRI could detect four (66.7%) femora with bone marrow necrosis of more than 4 mm(2) in the lesion area, while T2*-weighted dynamic images showed a finding of complete ischemia in only one of these four femora. In conclusion, neither contrast-enhanced MRI nor T2*-weighted dynamic MRI could detect early development of necrotic lesions in the single-dose steroid ON model. These results indicated that development of necrotic lesions in the single-dose steroid ON model was not accompanied by as diffuse a femoral hemodynamic change as the two-dose horse serum ON model.     

激光干涉结晶技术制备二维有序分布纳米硅阵列

利用结合移相光栅掩模 (PSGM) 的激光结晶技术在超薄a-SiN_x/a-Si:H/ a-SiN _x三明治结构样品中制备出二维有序分布的纳米硅阵列.原始样品是用等离子体 增强化学气相淀积法生长.a-Si:H层厚为10nm，a-SiN_x 为50nm，衬底材料为SiO ₂/Si或 熔凝石英.原子力显微镜、剖面透射电子显微镜、高分辨透射电子显微镜对样品表面形貌和 微结构的观测结果表明，采用该方法可以在原始淀积的a-Si:H层中得到位置可控的晶化区域 ：每个晶化区域直径约250nm，具有同PSGM一致的2μm周期；晶化区域内形成的纳米硅 颗粒尺寸接近原始淀积的a-Si:H层厚，且晶粒的择优取向为<111>. 关键词： 纳米硅 激光结晶 定域晶化 移相光栅     

Two-dimensional birefringence imaging in biological tissue by polarization-sensitive optical coherence tomography

Using a low-coherence Michelson interferometer, we measure two-dimensional images of optical birefringence in bovine tendon as a function of depth. Polarization-sensitive detection of the signal formed by interference of backscattered light from the sample and a mirror in the reference arm give the optical phase delay between light that is propagating along the fast and slow axes of the birefringent tendon. Images showing the change in birefringence in response to laser irradiation are presented. The technique permits rapid noncontact investigation of tissue structural properties through two-dimensional imaging of birefringence.     

Two-dimensional coherent detection imaging in multiple scattering media based on the directional resolution capability of the optical heterodyne method

This paper describes a new application of optical heterodyne detection using a laser beam for two-dimensional imaging of the internal structure of strongly scattering media in which the structure is completely obstructed from normal visual observation. The directional resolution capability for image formation due to the excellent antenna properties of the heterodyne technique is verified experimentally using a ground glass to cause strong scattering of the signal beam. Successful image detection of a test target placed in a highly scattering absorptive medium, with spatial resolution better than 400 m in the case of our experiments, demonstrates that this Coherent Detection Imaging (CDI) method can overcome the diffuse nature of images in media such as those of biomedical interest and others to achieve scanning and tomographic imaging.     

Two-dimensional imaging of the current-density distribution in superconducting tunnel junctions

Using a scanning electron microscope equipped with a low-temperature stage, we show that under the electron irradiation a superconducting tunnel junction can operate regularly. The electron beam generates a voltage signal across the current-biased junction. By recording the small voltage change synchronously with the coordinate irradiated by the beam, a two-dimensional “voltage image” of the density distribution of the junction tunneling current can be obtained. The distributions are in agreement with the magnetic interference patterns of the dc-Josephson currents in the junctions.     

Two-dimensional imaging of gauge fields in optical lattices

We propose a scheme to generate an arbitrary Abelian vector potential for atoms trapped in a two-dimensional optical lattice. By making the optical lattice potential dependent on the atomic state, we transform the problem into that of a two-dimensional imaging. It is shown that an arbitrarily fine pattern of the gauge field in the lattice can be realized without need of diffraction-limited imaging.     

Two-dimensional multispecies imaging of a supersonic nozzle flow

Raman imaging is shown to be a very suitable technique for simultaneous density mapping of different species in dry air and N(2) supersonic nozzle flows. The salient features of Raman scattering are its molecular sensitivity and the fact that it can be spectrally separated from strong reflections and Mie scattering. We collected Raman images of both N(2) and O(2) concurrently by imaging the flow through an imaging spectrograph with a broad entrance slit onto a CCD camera. The main advantage of this method is that different species can be imaged under exactly the same flow conditions.     

Statistical mechanics of melting mediated by two types of defects

We propose a defect-mediated melting theory based on the statistics of two types of lattice defects, the point defects and dislocation pairs. The model predicts a first-order phase transition. Based on the model, phase transition temperature, latent heat and other thermodynamic functions are derived. Melting occurs due to discontinuous growth of point defects into dislocation pairs. The calculated phase transition temperature for five alkali metallic crystals are in fair agreement with measured melting temperatures, and the Richards' rule is derived by the model also.     

Two-dimensional measurements of velocity using two rotating gratings

A two-dimensional vector velocimeter is proposed on the basis of the time-varying spatial filtering method using a rotating disk with two transmission gratings. The filtering characteristics of the spatial filter used in the velocimeter were studied theoretically. A preliminary experiment was performed to measure the velocity vector of a rotating random pattern. The experimental results show the usefulness of the present velocimeter for measurements of the velocity.     

Two-dimensional quantitative imaging of multicomponent samples using polychromatic X-rays

We present the theoretical formalism and an experimental demonstration of a technique for two-dimensional quantitative imaging of two-component samples using polychromatic X-rays. The technique takes into account the full spectral information of the incident polychromatic beam to quantify the total X-ray attenuation, due to each component presented in the sample, as functions of both energy and thickness. As a result, this technique is able to effectively ameliorate the effects of beam hardening. Here, we demonstrate the application of this technique to a two-component sample. The technique makes it possible for laboratory-based polychromatic X-ray sources to be used for critical quantitative purposes.