High resolution 3D x-ray diffraction microscopy

We have imaged a 2D buried Ni nanostructure at 8 nm resolution using coherent x-ray diffraction and the oversampling phasing method. By employing a 3D imaging reconstruction algorithm, for the first time we have experimentally determined the 3D structure of a noncrystalline nanostructured material at 50 nm resolution. The 2D and 3D imaging resolution is currently limited by the exposure time and the computing power, while the ultimate resolution is limited by the x-ray wavelengths. We believe these results pave the way for the development of atomic resolution 3D x-ray diffraction microscopy.     

Superiority of 3D wavelet-packet denoising in MR microscopy

Three dimensional Magnetic Resonance Imaging (MRI) datasets are becoming increasingly important in clinical and research applications because of their inherent signal to noise (SNR) advantages, high resolution and isotropic voxels. Despite SNR advantages, some 3D acquisitions may be SNR-limited, particularly in MR microscopy. Historically, both classic filtering and wavelet-based denoising techniques have been performed on a slice-by-slice basis. In principle, adaptive techniques such as best- basis wavelet-packet denoising might offer inherent advantages when performed in 3D, instead of 2D, by tracking through plane "structure" and suppressing noise "pseudostructure." This hypothesis was tested in 10 volumetric MR microscopy datasets from several different MR microscopy atlas projects. 3D wavelet-packet denoised images consistently yielded lower minimum mean-square error and subjectively perceived noise power than corresponding 2D denoised images using otherwise identical algorithms and parameters. MR microscopy researchers preferred the denoised images to the unprocessed images for their atlas projects.     

Fluorescence microscopy with 3D resolution in the 100 nm range

We propose a combination of 4Pi and Theta microscopies to improve the resolution of fluorescence microscopy by using six microscope objectives in a configuration we call Multiple Objective Microscopy (MOM). A resolution in the 100 nm range is obtained in the three dimensions using low numerical aperture, long working distance objectives. The obtained results not only show that high resolution is not restricted to high numerical aperture objectives, but also open the possibility of exploring large volumes with a very good resolution.     

Development of high resolution 3D hyperpolarized carbon-13 MR molecular imaging techniques

The goal of this project was to develop and apply techniques for T₂ mapping and 3D high resolution (1.5 mm isotropic; 0.003 cm³) ¹³C imaging of hyperpolarized (HP) probes [1-¹³C]lactate, [1-¹³C]pyruvate, [2-¹³C]pyruvate, and [¹³C,¹⁵N₂]urea in vivo. A specialized 2D bSSFP sequence was implemented on a clinical 3T scanner and used to obtain the first high resolution T₂ maps of these different hyperpolarized compounds in both rats and tumor-bearing mice. These maps were first used to optimize timings for highest SNR for single time-point 3D bSSFP acquisitions with a 1.5 mm isotropic spatial resolution of normal rats. This 3D acquisition approach was extended to serial dynamic imaging with 2-fold compressed sensing acceleration without changing spatial resolution. The T₂ mapping experiments yielded measurements of T₂ values of > 1 s for all compounds within rat kidneys/vasculature and TRAMP tumors, except for [2-¹³C]pyruvate which was ~ 730 ms and ~ 320 ms, respectively. The high resolution 3D imaging enabled visualization the biodistribution of [1-¹³C]lactate, [1-¹³C]pyruvate, and [2-¹³C]pyruvate within different kidney compartments as well as in the vasculature. While the mouse anatomy is smaller, the resolution was also sufficient to image the distribution of all compounds within kidney, vasculature, and tumor. The development of the specialized 3D sequence with compressed sensing provided improved structural and functional assessments at a high (0.003 cm³) spatial and 2 s temporal resolution in vivo utilizing HP ¹³C substrates by exploiting their long T₂ values. This 1.5 mm isotropic resolution is comparable to ¹H imaging and application of this approach could be extended to future studies of uptake, metabolism, and perfusion in cancer and other disease models and may ultimately be of value for clinical imaging.     

Three-dimensional snow images by MR microscopy

MR microscopy technique was introduced to visualize and quantify the three-dimensional structure of snowpack. Since the NMR signal from the ice was week, we looked at the air space instead filling with dodecane or aniline doped with iron acetylacetonate. Four types of snow were tested: ice spheres, large rounded poly crystals, small rounded mono-crystals and depth hoar crystals. A specific specimen-cooling system was developed to keep the temperature below 0 degrees C. In the experiments 0.5 to 2 h were necessary to accumulate the signals enough to obtain a 3D micro-image; the image matrix 128(3), voxel size (200 microm)3 or 256(3) (120 microm)3. Comparison with the 2D data using the conventional section plane method was also carried out and MR microscopy is proved to be a very useful method to visualize the microstructure of snowpack.     

Jet fuel toxicity: skin damage measured by 900-MHz MRI skin microscopy and visualization by 3D MR image processing

The toxicity of jet fuels was measured using noninvasive magnetic resonance microimaging (MRM) at 900-MHz magnetic field. The hypothesis was that MRM can visualize and measure the epidermis exfoliation and hair follicle size of rat skin tissue due to toxic skin irritation after skin exposure to jet fuels. High-resolution 900-MHz MRM was used to measure the change in size of hair follicle, epidermis thickening and dermis in the skin after jet fuel exposure. A number of imaging techniques utilized included magnetization transfer contrast (MTC), spin-lattice relaxation constant (T1-weighting), combination of T2-weighting with magnetic field inhomogeneity (T2*-weighting), magnetization transfer weighting, diffusion tensor weighting and chemical shift weighting. These techniques were used to obtain 2D slices and 3D multislice–multiecho images with high-contrast resolution and high magnetic resonance signal with better skin details. The segmented color-coded feature spaces after image processing of the epidermis and hair follicle structures were used to compare the toxic exposure to tetradecane, dodecane, hexadecane and JP-8 jet fuels. Jet fuel exposure caused skin damage (erythema) at high temperature in addition to chemical intoxication. Erythema scores of the skin were distinct for jet fuels. The multicontrast enhancement at optimized TE and TR parameters generated high MRM signal of different skin structures. The multiple contrast approach made visible details of skin structures by combining specific information achieved from each of the microimaging techniques. At short echo time, MRM images and digitized histological sections confirmed exfoliated epidermis, dermis thickening and hair follicle atrophy after exposure to jet fuels. MRM data showed correlation with the histopathology data for epidermis thickness (R²=0.9052, P<.0002) and hair root area (R²=0.88, P<.0002). The toxicity of jet fuels on skin structures was in the order of tetradecane>hexadecane>dodecane. The method showed a sensitivity of 87.5% and a specificity of 75%. By MR image processing, different color-coded skin structures were extracted and 3D shapes of the epidermis and hair follicle size were compared. In conclusion, high-resolution MRM measured the change in skin epidermis and hair follicle size due to toxicity of jet fuels. MRM offers a three-dimensional spatial visualization of the change in skin structures as a method of toxicity evaluation and for comparison of jet fuels.     

Improved spectral quality for 3D MR spectroscopic imaging using a high spatial resolution acquisition strategy

Spectral quality in (1)H MR spectroscopic imaging (MRSI) of the brain is often significantly degraded in regions subject to local magnetic susceptibility variations, which results in broadened and distorted spectral lineshapes. In this report, a modified acquisition strategy for volumetric echo-planar spectroscopic imaging (3D EPSI) is presented that extends the region of the brain that can be observed. The data are sampled at higher spatial resolution, then corrected for local B(0) shifts and reconstructed such that the final spatial resolution matches that of 3D EPSI data acquired with the conventional lower spatial resolution. Comparison of in vivo data obtained at 1.5 T with these two acquisition schemes shows that the high spatial resolution acquisition provides considerable reduction of spectral linewidths in many problematic brain regions, though with a reduction in signal-to-noise ratio by a factor of approximately 1.4 to 1.6 for the matrix sizes used in this study. However, the effect of the increased noise was largely offset by the improved spectral quality, leading to an overall improvement of the metabolite image quality obtained using automated spectral analysis.     

Fringe projection based quantitative 3D microscopy

A fringe projection based quantitative three-dimensional microscopy (FP-3DM) is presented. The image formation for FP-3DM is formulated based on a concept of active micro stereovision. The problem of point correspondences in active stereo imaging can be solved with help of the phase measuring technique. A prototype of the FP-3DM is also established and calibration strategy for proposed FP-3DM is suggested. Some preliminary experiment results are also presented to verify this approach. The FP-3DM can provide quantitative 3D micro imaging especially for quantitative characterization of 3D microstructures.     

Photoselective laser photo-ion microscopy with 5 nm resolution

Spectral selectivity has been attained in the method of field-ion microscopy with a spatial resolution of about 5 nm and time-of-flight determination of the photo-ion masses. Light-absorbing CdS_xSe_1−x nanocrystals in a transparent glass matrix are detected by irradiating field tips made from red light filters with copper-vapor laser radiation. The nanocrystals appeared in the photo-ion images as bright spots on a dark background. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 7, 450–454 (10 April 1998)     

Color lensless digital holographic microscopy with micrometer resolution

Color digital lensless holographic microscopy with micrometer resolution is presented. Multiwavelength illumination of a biological sample and a posteriori color composition of the amplitude images individually reconstructed are used to obtain full-color representation of the microscopic specimen. To match the sizes of the reconstructed holograms for each wavelength, a reconstruction algorithm that allows for choosing the pixel size at the reconstruction plane independently of the wavelength and the reconstruction distance is used. The method is illustrated with experimental results.     

Saturated structured confocal microscopy with theoretically unlimited resolution

The resolution of fluorescence microscopes is limited by diffraction, which determines the extension of their point spread functions. We propose and study numerically a simple method, based on a combination of subtraction microscopy with regular and annular excitation beams, which permits to double the resolution compared to wide field microscopy. When combined with the fluorescence saturation phenomenon, this approach would be able to deliver a resolution of a few tens of nanometers.     

Lattice imaging of close-packed structures by high resolution electron microscopy: ABO3 perovskite polytypes

Lattice imaging technique of high resolution electron microscopy has been employed to examine 4H, 6H and 9R ABO₃ perovskite polytypes. The lattice images can be correlated with the lattice periodicity and the stacking sequence of AO₃ layers and BO₆ octahedra. The study shows the utility and validity of the lattice imaging technique for the study of relatively close-packed systems. Commonwealth Visiting Professor, University of Oxford (1974–75).     

Three-dimensional resolution enhancement in fluorescence microscopy by harmonic excitation

A method for increasing lateral as well as axial resolution in fluorescence microscopy is presented. A passband with a high cutoff frequency throughout reciprocal space can be achieved by illumination of the object with spatially harmonic excitation patterns generated by the interference of two collimated laser beams. Theoretical calculations show an almost isotropic point-spread function with a FWHM near 100 nm.     

Noninvasive 3D MR microscopy as a tool in pharmacological research: Application to a model of rheumatoid arthritis

Magnetic resonance microscopy (MRM) was applied to noninvasively image skeletal structures in the hindpaw of the live rat to characterize the progression of a heterologous type II collagen-induced arthritic process. Using a resonator, with optimized filling factor, three-dimensional (3D) gradient-echo images with voxel dimensions of 94 × 81 × 60 μm³ were acquired in 54.6 min. Three-dimensional MRM reduces the slice positioning problem, which is critical in longitudinal studies. Moreover, due to the much smaller slice thickness of images derived from 3D data sets, partial volume effects are less pronounced than in corresponding 2D images. Distinct pathomorphological changes associated with the collagen-induced arthritic process (e.g., increase of metatarsophalangeal joint space, and bone and cartilage erosion) could thus be analyzed under in vivo conditions.     

MR image reconstruction of sparsely sampled 3D k-space data by projection-onto-convex sets

In many rapid three-dimensional (3D) magnetic resonance (MR) imaging applications, such as when following a contrast bolus in the vasculature using a moving table technique, the desired k-space data cannot be fully acquired due to scan time limitations. One solution to this problem is to sparsely sample the data space. Typically, the central zone of k-space is fully sampled, but the peripheral zone is partially sampled. We have experimentally evaluated the application of the projection-onto-convex sets (POCS) and zero-filling (ZF) algorithms for the reconstruction of sparsely sampled 3D k-space data. Both a subjective assessment (by direct image visualization) and an objective analysis [using standard image quality parameters such as global and local performance error and signal-to-noise ratio (SNR)] were employed. Compared to ZF, the POCS algorithm was found to be a powerful and robust method for reconstructing images from sparsely sampled 3D k-space data, a practical strategy for greatly reducing scan time. The POCS algorithm reconstructed a faithful representation of the true image and improved image quality with regard to global and local performance error, with respect to the ZF images. SNR, however, was superior to ZF only when more than 20% of the data were sparsely sampled. POCS-based methods show potential for reconstructing fast 3D MR images obtained by sparse sampling.     

Lateral resolution improvement in two-photon excitation microscopy by aperture engineering

A technique for resolution improvement in two-photon excitation (2PE) fluorescence microscopy based on radially-symmetric annular binary filter (consist of central circular aperture and a concentric peripheral annulus) is proposed. Resolution improvement is achieved by engineering the aperture of the objective lens in a way so as to enhance high spatial frequencies. The structure of the electromagnetic field in the regions of focus and nearby regions are determined. The central lobe of the time-averaged electric energy density is considerably reduced for both linearly- and circularly-polarized illuminated light. An impressive combined comparative percentage improvement of 40% and 53.71% both at low (α = 30) and high (α = 60) aperture angle is obtained for linearly-polarized light. Proposed aperture engineering technique complements conventional, confocal, two-photon fluorescence microscopy, and may facilitate working at low-to-medium magnifications and large free-working distances.     

Investigation of resolution of the stereoscopic 3D images

Evaluation of 3D images is an important part of 3D display developments. In this paper, we propose an evaluation method which can reflect the characteristics of the stereoscopic 3D images in the depth direction. Perception of the depth planes is verified using a subjective evaluation method. Resolution of the stereoscopic 3D images which represents the distribution of the 3D images in the depth direction quantitatively is calculated and analyzed.     

Field emission patterns with atomic resolution of single-walled carbon nanotubes by field emission microscopy

Electron emission properties of single-walled carbon nanotubes (SWCNTs) assembled on a tungsten tip were investigated using field emission microscopy (FEM). The transmission electron microscopy (TEM) micrograph confirmed the existence of an SWCNT bundle on the W tip. Under appropriate experimental conditions,a series of FEM patterns with atomic resolution were obtained. These patterns arose possibly from the field emission of the open end of an individual (16,0) SWCNT protruding from the SWCNT bundle. The magnification factor and the resolution under our experimental conditions were calculated theoretically. If the value of the compression factor β was set at β= 1.76, the calculated value of the magnification factor was in agreement with the measured value. The resolving powerof FEM was determined by the resolution equation given by Gomer. The resolutionof 0.277 nm could be achieved under the typical electric field of 5.0×107 V/cm, which was close to the interatomic separation 0.246 nm between carbon atoms along the zigzag edge at the open end for the (16, 0) SWCNT. Consequently, our experimental results were further supported by our theoretical calculation.     

Contrast-enhanced 3D MR voiding urethrography: preliminary results

Contrast-enhanced 3D MR voiding urethrography (CE 3D MRVU) was performed on 5 healthy volunteers and 18 patients with urethral disease. After intravenous injection of 0.3 ml/kg gadolinium, the images of the three consecutive acquisitions of the 3D MRVU technique were obtained during voiding. The raw data were reconstructed on all patients for visual analysis. The image quality of the volunteers was technically sufficient to demonstrate normal urethral anatomy. Contrast-enhanced 3D MR voiding urethrography of the urethral strictures was compared with conventional retrograde urethrography (n = 10) and urethroscopy (n = 12). The urethral pathologies including strictures and other obstructive causes of impaired urethral flow were correctly identified on CE 3D MRVU.