High-resolution spectroscopic imaging of the Sun with a universal birefringent filter and a Fabry-Perot Interferometer

Summary We describe an optical device consisting of a Universal Birefringent Filter and a Fabry-Perot interferometer used in tandem to obtain monochromatic images of the Sun in the visible spectrum (between 4200 and 7000 ?). The spectral resolving power is about 300000 and the wavelength stability might reach 0.02 m? at 5000 ? (≈1.2 m/s) with an integration time of 1 s. The image is recorded by a CCD camera based on a Thomson THX31159 device with 512×512 square pixels 19 μm in size. A prototype of this instrument was tested at the G. B. Donati Solar Tower of the Arcetri Astrophysical Observatory by obtaining, at fixed time intervals, several series of full disk monochromatic images of the Sun at different wavelengths inside the Fe I 5905.7 ? photospheric line. In this paper we describe the instrument and its characteristics and we give an cccount of the preliminary results obtained by measuring the global velocity field on the solar photosphere. These results show that the instrument is well suited for global oscillation measurements. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

High-resolution 3D MR spectroscopic imaging of the prostate at 3 T with the MLEV-PRESS sequence

A 3 T MLEV-point-resolved spectroscopy (PRESS) sequence employing optimized spectral-spatial and very selective outer-voxel suppression pulses was tested in 25 prostate cancer patients. At an echo time of 85 ms, the MLEV-PRESS sequence resulted in maximally upright inner resonances and minimal outer resonances of the citrate doublet of doublets. Magnetic resonance spectroscopic imaging (MRSI) exams performed at both 3 and 1.5 T for 10 patients demonstrated a 2.08+/-0.36-fold increase in signal-to-noise ratio (SNR) at 3 T as compared with 1.5 T for the center citrate resonances. This permitted the acquisition of MRSI data with a nominal spatial resolution of 0.16 cm3 at 3 T with similar SNR as the 0.34-cm3 data acquired at 1.5 T. Due to the twofold increase in spectral resolution at 3 T and the improved magnetic field homogeneity provided by susceptibility-matched endorectal coils, the choline resonance was better resolved from polyamine and creatine resonances as compared with 1.5 T spectra. In prostate cancer patients, the elevation of choline and the reduction of polyamines were more clearly observed at 3 T, as compared with 1.5 T MRSI. The increased SNR and corresponding spatial resolution obtainable at 3 T reduced partial volume effects and allowed improved detection of the presence and extent of abnormal metabolite levels in prostate cancer patients, as compared with 1.5 T MRSI.     

In vivo 31P echo-planar spectroscopic imaging of human calf muscle

Localized phosphorus-31 NMR spectra of human calf muscle in vivo were obtained by means of echo-planar spectroscopic imaging (EPSI) with a 1.5-T whole-body scanner. The technique permits the measurement of two-dimensional 31P SI data at a minimum acquisition time of 2.4 s (8x8 voxels, TR=300 ms). With 9.4 min measurement time (TR=1100 ms, 64 averages) and 25x25x40 mm spatial resolution in vivo the 31P NMR signal-to-noise ratio (S/N) of the phosphocreatine (PCr) resonance was about 45; the multiplets of nucleoside 5'-triphosphates were resolved. Spectral quality permits quantitative assessment of the PCr signal in a measurement time that is shorter by a factor of 2 or more than the minimum measurement time feasible with chemical-shift imaging. In a functional EPSI study with a time resolution of 20.5 s on the calf muscle of volunteers, spectra showed a 40% decrease of the PCr signal intensity (at rest: S/N congruent with12) upon exertion of the muscle.     

Determination of human skin optical properties in vivo from reflectance spectroscopic measurements

A novel approach has been proved to quickly and non-invasively determine the optical properties of human skin in vivo. It is based on the diffuse reflectance approximation model and subjected to the well established library of absorption spectra of water and hemoglobin. Under the nonlinear least-square algorithm, fitting the measured spectra in the range of 400-1000 nm to the diffusion approximation model, the reduced scattering coefficient and absorption coefficient of skin tissue can be quickly determined in vivo. The results show that this method is convenient and suitable for the real-time clinical application.     

High-resolution imaging using Hadamard encoding

High-resolution imaging techniques using noninvasive modalities such as magnetic resonance (MR) imaging are being pursued as in vivo cancer screening techniques in an attempt to eliminate the invasive nature of surgical biopsy. When acquiring high-resolution MR images for tissue screening, image fields of view have in the past been limited by the matrix sizes available in conventional MR scanners. We present here a technique that uses aliasing to produce high resolution images with larger matrix sizes than are currently available. The image is allowed to alias in both the frequency encoding and phase encoding dimensions, and the individual, aliased fields of view are recovered by Hadamard encoding methods. These fields may then be tiled to obtain a composite image with high spatial resolution and a large field of view. The technique is demonstrated using two-dimensional and three-dimensional in vivo imaging of the human brain and breast.     

High-resolution diffusion imaging using phase-corrected segmented echo-planar imaging

Diffusion magnetic resonance imaging (MRI) was performed with a high-resolution segmented echo-planar imaging technique, which provided images with substantially less susceptibility artifacts than images obtained with single-shot echo-planar imaging (EPI). Diffusion imaging performed with any multishot pulse sequence is inherently sensitive to motion artifacts and in order to reduce motion artifacts, the presented method utilizes navigator echo phase corrections, performed after a one-dimensional Fourier transform along the frequency-encoding direction. Navigator echo phases were fitted to a straight line prior to phase correction to avoid errors from internal motion. In vivo imaging was performed using electro cardiographic (ECG) triggering. Apparent diffusion coefficient (ADC) maps were calculated on a pixel-by-pixel basis using up to seven diffusion sensitivities, ranging from b = 0 to 1129 x 10(6) s/m(2).     

Possibilities for human skin characterization based on strongly reduced Raman spectroscopic information

Loss‐of‐function mutations in the gene coding for filaggrin are the single most important risk factor for development of atopic dermatitis and associated allergic rhinitis and asthma. Filaggrin is enzymatically degraded to natural moisturizing factor (NMF) in the stratum corneum (SC). In vivo Raman spectra of human skin can be used to quantify the NMF concentration in SC and thereby identify carriers of a loss‐of‐function mutation in the gene coding for filaggrin, which results in decreased NMF content. Here, we demonstrate that strongly reduced Raman spectral information is sufficient to make this differentiation. This is an important step towards development of a dedicated diagnostic device of reduced complexity, size and cost as compared to current state‐of‐the‐art Raman equipment. A genetic algorithm was used to select the spectral regions needed to classify skin based on normal or reduced NMF content in SC. Using the NMF content based on full spectral information as gold standard, only four Raman regions were required to create a linear discriminant analysis model that can differentiate between skin with low NMF and skin with normal NMF with a prediction accuracy of 93 %. Copyright © 2013 John Wiley & Sons, Ltd.     

Phase-difference and spectroscopic imaging for monitoring of human brain temperature during cooling

Decrease of the human brain temperature was induced by intranasal cooling. The main purpose of this study was to compare the two magnetic resonance methods for monitoring brain temperature changes during cooling: phase-difference and magnetic resonance spectroscopic imaging (MRSI) with high spatial resolution. Ten healthy volunteers were measured. Selective brain cooling was performed through nasal cavities using saline-cooled balloon catheters. MRSI was based on a radiofrequency spoiled gradient echo sequence. The spectral information was encoded by incrementing the echo time of the subsequent eight image records. Reconstructed voxel size was 1×1×5 mm³. Relative brain temperature was computed from the positions of water spectral lines. Phase maps were obtained from the first image record of the MRSI sequence. Mild hypothermia was achieved in 15–20 min. Mean brain temperature reduction varied in the interval <−3.0; − 0.6>°C and <−2.7; − 0.7>°C as measured by the MRSI and phase-difference methods, respectively. Very good correlation was found in all locations between the temperatures measured by both techniques except in the frontal lobe. Measurements in the transversal slices were more robust to the movement artifacts than those in the sagittal planes. Good agreement was found between the MRSI and phase-difference techniques.     

3D phase encoding 1H spectroscopic imaging of human brain.

A three-dimensional (3D) phase-encoding proton spectroscopic imaging method is presented for a whole body MRI/MRS system. Metabolite images at 2 T of choline, creatine, and N-acetyl aspartate (NAA) of normal brain were obtained with a spatial resolution of 1.5 cc. With PRESS volume preselection and outer volume suppression pulses, brain regions close to the skull could be studied without significant contamination by lipid and water signals.     

高分辨率405 nm激光显微成像系统研究

 研究了405 nm短波长激光作为照明光源、数值孔径0.65显微物镜组成的显微成像系统。采用该系统对CD-R及DVD-R盘片进行了显微成像,并对激光成像散斑进行了消除,同时利用CCD图像传感技术和图像采集技术对显微图像进行实时观察与存储,与卤素灯白光作为照明光源时的显微图像进行了比较。结果表明：该系统在卤素灯白光作为照明光源时对CD-R盘片信息点可清晰分辨,但对DVD-R盘片信息点的图像不可分辨;而在405 nm激光照明时信息点均可清晰分辨,系统分辨优于400 nm,明显高于普通卤素灯白光照明系统。     

CDSD-4000: High-resolution, high-temperature carbon dioxide spectroscopic databank

We present a high-resolution, high-temperature version of the Carbon Dioxide Spectroscopic Databank called CDSD-4000. The databank contains the line parameters (positions, intensities, air- and self-broadened half-widths, coefficients of temperature dependence of air- and self-broadened half-widths, and air-broadened pressure shifts) of the four most abundant isotopologues of CO₂. A reference temperature is 296 K and an intensity cutoff is 10⁻²⁷ cm⁻¹/molecule cm⁻² at 4000 K. The databank has 628,324,454 entries, covers the 226-8310 cm⁻¹ spectral range and designed for the temperature range 2500-5000 K. Format of CDSD-4000 is similar to that of HITRAN-2008. The databank has been generated within the framework of the method of effective operators and based on the global fittings of spectroscopic parameters (parameters of the effective Hamiltonians and effective dipole moment operators) to observed data collected from the literature. The databank is useful for studying high-temperature radiative properties of CO₂, including exoplanets atmospheres, aerothemal modeling for Mars entry missions, high-temperature laboratory spectra, and industrial applications. CDSD-4000 is freely accessible via the Internet site ftp://ftp.iao.ru/pub/CDSD-4000.     

One-dimensional spectroscopic imaging with stimulated echoes: phantom and human leg studies

One-dimensional phase encoding was incorporated in the stimulated echo single voxel localization sequence for in vivo proton spectroscopic studies. Phantom studies were performed to assess the effect of the number of phase encoding steps on the spectral contamination from the adjacent volumes. Both water suppressed and unsuppressed spectra were obtained in reasonable acquisition times from various regions in the human leg with a spatial resolution of around 1.1 cm3.     

In vivo video rate multiphoton microscopy imaging of human skin

We present a multiphoton microscopy instrument specially designed for in vivo dermatological use that is capable of imaging human skin at 27 frames per second with 256 pixels × 256 pixels resolution without the use of exogenous contrast agents. Imaging at fast frame rates is critical to reducing image blurring due to patient motion and to providing practically short clinical measurement times. Second harmonic generation and two-photon fluorescence images and videos acquired at optimized wavelengths are presented showing cellular and tissue structures from the skin surface down to the reticular dermis.     

Application of spectroscopic imaging in epilepsy

Functional and anatomical neuroimaging has had a dramatic effect on the evaluation of patients for seizure surgery. The demonstration by PET that the epileptogenic focus has interictal metabolic abnormalities has allowed a greater number of patients to come to seizure surgery, with fewer of these patients requiring intracranial electrode evaluations. Metabolic changes have also been demonstrated utilizing single voxel and whole brain ¹H and ³¹P MRS imaging techniques with the interictal focus characterized by increased Pi, pH, and decreased PME and NAA. These findings can be used to accurately lateralize temporal lobe as well as frontal lobe epilepsy. Furthermore, there is evidence that these findings can be used to localize the seizure focus with the changes specific for the epileptogenic region; although, more diffuse changes both ipsilaterally and contralaterally have been seen. In patients with anterior hippocampal seizure foci the pH is significantly alkaline only in the ipsilateral hippocampus, whereas the increased Pi and decreased PME can be seen throughout the ipsilateral temporal lobe. When compared to controls the contralateral hemisphere is acidotic. Decreased NAA concentrations as well as NAA/Cr ratios have been demonstrated in the epileptogenic region in temporal and frontal lobe epilepsy. The decreased NAA has been correlated with the severity of cell loss, and may be a more sensitive measure than qualitative or quantitative measures of the hippocampal atrophy; however, the NAA decrease is more widespread than just the epileptogenic focus but may be maximal at the site of seizure initiation. In preliminary work, NAA maps of deviation from normality have suggested the maximal change to coincide with the epileptogenic region. These results suggest that in focal epilepsy there is abnormal metabolic activity throughout the brain detectable by MRS, with patterns of metabolic asymmetry that are useful for seizure localization.     

Three-dimensional fourier transform NMR imaging. High-resolution chemical-shift-resolved planar imaging

A conventional high-resolution NMR spectrometer has been adapted for a three-dimensional imaging experiment which involves two spatial coordinates plus chemical shift. One dimension has far greater digital resolution than the other two, and when it is used to encode the chemical shifts it is possible to obtain separate slice images showing the distribution of each chemical species within the imaging plane. The method is illustrated using a tube phantom containing ethanol and water, in this case the ethanol gives sufficiently narrow finewidths that it is possible to obtain a separate image from the individual transitions of each multiplet.     

High-resolution transparent x-ray beam location and imaging

We present a high-resolution in situ imaging and localization method of energetic particle beams. Recording of the scattered radiation from a thin featureless foil, placed in the path of the beam, and taken with a pinhole or coded aperture camera arrangement magnifies beam movements at the sensor. At the same time, a magnified image of the beam is available with an exceptional signal-to-noise ratio. We show measurement results of the level of precision that can be achieved and compare them to theoretical limits based on the signal-to-noise levels.     

高分辨率中红外温度自适应夜视成像系统

针对现代最先进的像元尺寸为15 m、像元数640480的中红外焦平面大面阵探测器,设计了一种全球面轻小型高分辨率温度自适应夜视成像系统,系统工作波段为3~5 m,全视场角为8.58,相对孔径为1/2,焦距为80 mm,四片式结构,使用锗、硒化锌和硅三种材料,系统采用全球面结构,避免了以往该种系统中使用衍射面或非球面,大大降低了加工检测难度且成本低。设计结果表明,该高分辨率温度自适应夜视成像系统具有结构简单、体积小、分辨率高、成像质量高等特点,满足设计要求,可用于机载光电探测和跟踪系统。     

High-resolution magnetic imaging by local tunneling magnetoresistance

We give an overview over our recent efforts of high-resolution magnetic imaging using scanning tunneling microscopy with a ferromagnetic tip. Magnetic sensitivity is obtained on the basis of local tunneling magnetoresistance between a soft magnetic tip and the sample. The magnetisation of the tip is switched periodically with a small coil, leading to variations of the tunneling current due to the tunneling magnetoresistance effect. These variations are detected with a lock-in amplifier to separate spin-dependent parts from the topographic parts of the tunneling current such that the topography and the magnetic structure of the sample can be recorded simultaneously. Crucial for this method is to avoid mechanical vibrations of the tip, that may also lead to variations in the tunneling current. Exemplary studies of polycrystalline Ni and the closure domain pattern of Co(0001) are presented, showing high contrast at acquisition times as low as 3 ms/pixel and a lateral resolution of the order of 1 nm. Further it is demonstrated that besides topography and magnetisation, also local information about the magnetic susceptibility can be obtained. Received: 28 April 2000 / Accepted: 15 May 2000 / Published online: 7 March 2001