meta-DENSE complex acquisition for reduced intravoxel dephasing

Displacement encoding with stimulated echoes (DENSE) with a meta-DENSE readout and RF phase cycling to suppress the STEAM anti-echo is described for reducing intravoxel dephasing signal loss. This RF phase cycling scheme, when combined with existing meta-DENSE suppression of the T1 recovering signal, yields higher quality DENSE myocardial strain maps. Phantom and human images are provided to demonstrate the technique, which is capable of acquiring phase contrast displacement encoded images at low encoding gradient strengths providing better spatial resolution and less signal loss due to intravoxel dephasing than prior methods.     

DENSE with SENSE

Displacement encoding with stimulated echoes (DENSE) with a low encoding strength phase-cycled meta-DENSE readout and a two fold SENSE acceleration (R = 2) is described. This combination reduces total breath-hold times for increased patient comfort during cardiac regional myocardial contractility studies. Images from phantoms, normal volunteers, and a patient are provided to demonstrate the SENSE-DENSE combination of methods. The overall breath-hold time is halved while preserving strain map quality.     

A deep-learning semantic segmentation approach to fully automated MRI-based left-ventricular deformation analysis in cardiotoxicity

Left-ventricular (LV) strain measurements with the Displacement Encoding with Stimulated Echoes (DENSE) MRI sequence provide accurate estimates of cardiotoxicity damage related to breast cancer chemotherapy. This study investigated an automated LV chamber quantification tool via segmentation with a supervised deep convolutional neural network (DCNN) before strain analysis with DENSE images. Segmentation for chamber quantification analysis was conducted with a custom DeepLabV3+ DCNN with ResNet-50 backbone on 42 female breast cancer datasets (22 training-sets, eight validation-sets and 12 independent test-sets). Parameters such as LV end-diastolic diameter (LVEDD) and ejection fraction (LVEF) were quantified, and myocardial strains analyzed with the Radial Point Interpolation Method (RPIM). Myocardial classification was validated against ground-truth with sensitivity-specificity analysis, the metrics of Dice, average perpendicular distance (APD) and Hausdorff-distance. Following segmentation, validation was conducted with the Cronbach's Alpha (C-Alpha) intraclass correlation coefficient between LV chamber quantification results with DENSE and Steady State Free Precession (SSFP) acquisitions and a vendor tool-based method to segment the DENSE data, and similarly for myocardial strain analysis in the chambers. The results of myocardial classification from segmentation of the DENSE data were accuracy = 97%, Dice = 0.89 and APD = 2.4 mm in the test-set. The C-Alpha correlations from comparing chamber quantification results between the segmented DENSE and SSFP data and vendor tool-based method were 0.97 for LVEF (56 ± 7% vs 55 ± 7% vs 55 ± 6%, p = 0.6) and 0.77 for LVEDD (4.6 ± 0.4 cm vs 4.5 ± 0.3 cm vs 4.5 ± 0.3 cm, p = 0.8). The validation metrics against ground-truth and equivalent parameters obtained from the SSFP segmentation and vendor tool-based comparisons show that the DCNN approach is applicable for automated LV chamber quantification and subsequent strain analysis in cardiotoxicity.     

A comprehensive comparison between shortest-path HARP refinement,SinMod, and DENSEanalysis processing tools applied to CSPAMM and DENSE images

We addressed comprehensively the performance of Shortest-Path HARP Refinement (SP-HR), SinMod, and DENSEanalysis using 2D slices of synthetic CSPAMM and DENSE images with realistic contrasts obtained from 3D phantoms. The three motion estimation techniques were interrogated under ideal and no-ideal conditions (with MR induced artifacts, noise, and through-plane motion), considering several resolutions and noise levels. Under noisy conditions, and for isotropic pixel sizes of 1.5 mm and 3.0 mm in CSPAMM and DENSE images respectively, the nRMSE obtained for the circumferential and radial strain components were 10.7 ± 10.8% and 25.5 ± 14.8% using SP-HR, 11.9 ± 2.5% and 29.3 ± 6.5% using SinMod, and 6.4 ± 2.0% and 18.2 ± 4.6% using DENSEanalysis. Overall, the results showed that SP-HR tends to fail for large tissue motions, whereas SinMod and DENSEanalysis gave accurate displacement and strain field estimations, being the last which performed the best.     

High-resolution strain analysis of the human heart with fast-DENSE.

Single breath-hold displacement data from the human heart were acquired with fast-DENSE (fast displacement encoding with stimulated echoes) during systolic contraction at 2.5 x 2.5 mm in-plane resolution. Encoding strengths of 0.86-1.60 mm/pi were utilized in order to extend the dynamic range of the phase measurements and minimize effects of physiologic and instrument noise. The noise level in strain measurements for both contraction and dilation corresponded to a strain value of 2.8%. In the human heart, strain analysis has sufficient resolution to reveal transmural variation across the left ventricular wall. Data processing required minimal user intervention and provided a rapid quantitative feedback. The intrinsic temporal integration of fast-DENSE achieves high accuracy at the expense of temporal resolution.     

Reproducibility of cine displacement encoding with stimulated echoes (DENSE) in human subjects

ObjectivesTo test the hypothesis that two-dimensional (2D) displacement encoding via stimulated echoes (DENSE) is a reproducible technique for the depiction of segmental myocardial motion in human subjects.Materials and methodsFollowing the approval of the institutional review board (IRB), 17 healthy volunteers without documented history of cardiovascular disease were recruited. For each participant, 2D DENSE were performed twice (at different days) and the images were obtained at basal, midventricular and apical levels of the left ventricle (LV) with a short-axis view. The radial thickening strain (Err), circumferential strain (Ecc), twist and torsion were calculated. The intra-, inter-observer and inter-study variations of DENSE-derived myocardial motion indices were evaluated using coefficient of variation (CoV) and intra-class correlation coefficient (ICC).ResultsIn total, there are 272 pairs of myocardial segments (data points) for comparison. There is good intra- and inter-observer reproducibility for all DENSE-derived measures in 17 participants. There is good inter-study reproducibility for peak Ecc (CoV = 19.64%, ICC = 0.8896, p < 0.001), twist (CoV = 33.11%, ICC = 0.9135, p < 0.001) and torsion (CoV = 13.96%, ICC = 0.8684, p < 0.001). There is moderate inter-study reproducibility for Err (CoV = 38.89%, ICC = 0.7022, p < 0.001).ConclusionDENSE is a reproducible technique for characterizing LV regional systolic myocardial motion on a per-segment basis in healthy volunteers.     

微束X射线荧光分析

用能量色散微束X射线荧光分析仪实际测量了微束准直器孔径和X射线强度对微束空间分辨率的影响,在准直器孔径为0.1mm条件下,获得以FWHM定义的空间分辨率最好为0.073mm。通过微束扫描测量出某硫化锰矿微区内的Mn、Fe、Zn、Pb的三维等高线荧光强度分布图和不同小区域内的能谱。     

Velocity and diffusion imaging in dynamic NMR microscopy

The imposition of resolution gradients in a pulsed-gradient spin-echo (PGSE) NMR sequence induces motionally dependent phase and amplitude modulation in the image, a technique which we have termed dynamic NMR microscopy. Fourier analysis of this modulation gives a dynamic displacement profile for each pixel which can then be analyzed to obtain velocity and diffusion maps. The application of this method at high spatial resolution is motivated by a desire to measure vascular flow in living plants and variations in molecular self-diffusion under the influence of velocity shear in narrow capillaries. The theory of dynamic NMR microscopy is presented and potential artifacts discussed, including the effect of slice selection gradients, PGSE gradient nonuniformity, and specific problems associated with the measurement of self-diffusion in the presence of velocity gradients. It is demonstrated that a double-echo PGSE pulse sequence can be used to restore coherent phase shifts associated with steady-state flow, and examples of self-diffusion maps and signed velocity maps from sequences of phase-encoded images obtained by projection reconstruction are given. This method has been applied at 20,um transverse resolution in laminar capillary flow.     

Optical heterodyne grating shearing interferometry for long-range positioning applications

We develop a displacement measurement and positioning system with nanometer resolution over the millimeter traveling range. The method is based on a heterodyne grating shearing interferometry, a homemade lock-in amplifier and a servo control loop for displacement sensing and positioning. The quasi-common optical path configuration of our system provides better immunity against environmental disturbances. The experimental results demonstrate that our system can measure small and long displacement with nanometric resolution. The device achieves a positioning resolution of 2.3 nm over a traveling range of 20 mm.     

A Displacement and Velocity Measurement Technique Using Millimeter-Wave Sensor

In this paper, a millimeter-wave sensor is presented for measurement of displacement and velocity. By using monolithic microwave integrated circuits and digital quadrature sampling signal-processing scheme, the sensor operating at 60 GHz is implemented. Polynomial curve-fitting technique is used for the error correction. Digital quadrature mixer is also configured as a phase-detecting processor, which enables low Doppler frequency to be measured with high resolution. Measured displacement results indicate resolution and maximum error of 10 μm and 30 μm, respectively, and measured speed is as low as 30 mm/s, corresponding to 6.6 Hz in Doppler frequency, with an estimated velocity resolution of 3.3 mm/s. To the best of our knowledge, the attained resolution and maximum error are the best reported results.     

A new laser displacement sensor based on triangulation for gauge real-time measurement

A new laser displacement sensor has been designed, constructed, and used in a train running at a speed of 64 km/h. The laser displacement sensor is insensitive to ambient light and to temperature. The parameters of the laser displacement sensor are as follows: the measurement range is 20 mm, and the laser displacement sensor resolution is 0.3 mm. All the results show that this new displacement sensor meets the requirement for real-time gauge measurement.     

大量程激光位移传感器的成像系统设计

为了解决目前国内自主研发的激光位移传感器基准工作距离短和测量范围小的问题,设计了一种适用于远距离测量的大量程激光位移传感器成像光学系统。基于激光三角测量原理,结合具体使用要求计算了大量程激光位移传感器的性能指标和成像光学系统的设计参数。选择5片式透镜结构作为系统的初始结构,利用光学设计软件对大量程激光位移传感器成像光学系统进行了仿真,完成了系统优化和性能分析,实现了基准工作距离为1 000 mm、量程为±500 mm、分辨率为0.4 mm的大量程激光位移传感器成像系统设计。结果表明,在测量范围±500 mm内,系统均可以满足成像质量要求。该激光位移传感器成像系统具有工作距离远、测量量程大、结构简单的特点,可满足1 000 mm远距离处大量程范围的测量使用要求。     

PET用新型深度编码探测器设计

平行性问题或作用深度问题影响着正电子放射层析系统(PET)的成象分辨率。本文提出和评价了一种二阶深度编码探测器,这个探测器是由两层LSO晶体和位置灵敏型光电倍增管(PS-PMT)组成,上层的晶体相对于下层的晶体的位置在X和Y方向上都有半个晶体阵列单元的错位,因为每个晶体的输出光的重心位置分布在PS-PMT上不同的位置,所以通过计算其重心位置就可在象平面上区别开每个晶体。根据PET系统的应用要求,我们验证了探测器的性能。伽马射线垂直入射时,上层晶体阵列的固有空间分辨率为1.15mmFWHM,下层晶体列阵为1.34mm FWHM.钠伽马辐射源的511keV能量峰处的平均能量分辨率对于下层晶体为19.7%,上层为23.6%.通过类似的技术亦可实现3阶、4阶深度编码探测器。     

Quantitative x-ray phase-contrast imaging using a single grating of comparable pitch to sample feature size

The ability to quantitatively retrieve transverse phase maps during imaging by using coherent x rays often requires a precise grating or analyzer-crystal-based setup. Imaging of live animals presents further challenges when these methods require multiple exposures for image reconstruction. We present a simple method of single-exposure, single-grating quantitative phase contrast for a regime in which the grating period is much greater than the effective pixel size. A grating is used to create a high-visibility reference pattern incident on the sample, which is distorted according to the complex refractive index and thickness of the sample. The resolution, along a line parallel to the grating, is not restricted by the grating spacing, and the detector resolution becomes the primary determinant of the spatial resolution. We present a method of analysis that maps the displacement of interrogation windows in order to retrieve a quantitative phase map. Application of this analysis to the imaging of known phantoms shows excellent correspondence.     

Modeling the encoding structure and spatial resolution of photon counting imagers with Vernier anode readout

We present the spatial resolution estimation methods for a photon counting system with a Vernier anode.A limiting resolution model is provided according to discussions of surface encoding structure and quantized noise. The limiting resolution of a Vernier anode is revealed to be significantly higher than that of a microchannel plate. The relationship between the actual spatial resolution and equivalent noise charge of a detector is established by noise analysis and photon position reconstruction. The theoretical results are demonstrated to be in good agreement with the experimental results for a 1.2 mm pitch Vernier anode.     

The 10 MHz ultrasonic near-field: calculations, hydrophone and optical diffraction tomography measurements

The near-field from a 10 MHz ultrasound transducer has been studied using three different techniques; theoretical calculations, miniature hydrophone measurements and optical diffraction tomography (ODT). The motive was twofold; to evaluate the measurement possibilities of ODT for high-frequency ultrasound and to verify the calculated complexity of near-fields from real ultrasound transducers designed for use in blood perfusion measurements. Calculations of the field from an ideal piston transducer were done with surface integrals of the Kirchhoff function and the measured transducer was designed to approximate this ideal. Contour maps, from the three methods, of pressure amplitude from 1 to 30 mm along the beam are presented with beam profiles at 5 and 45 mm. The results imply that ODT has an increased spatial resolution compared with the 0.5 and 1.0 mm hydrophones. However, even better spatial resolution is needed to draw definite conclusions regarding the complexity of the near-field of the 10 MHz transducer.     

Design and experiments on a wide range fiber Bragg grating sensor for health monitoring of coal mines

The tunnel collapse problem of coal mine is very common and its damage is very serious. It also seriously endangers people's lives and property safety. At present, a variety of instruments are used for tunnel roof structure health monitoring in most of the coal mines at home and abroad. In this paper, a displacement sensor using optical fiber grating technology was designed, which could be used to prevent the problem of coal mine tunnel collapse by monitoring the coal mine tunnel roof displacement. Firstly, finite element analysis was demonstrated to simulate the stress and displacement of coal mine tunnel roof to determine where to install the sensor. Then the characteristics of the fiber Bragg grating sensor were analyzed in detail and the sensor structure was designed according to the actual requirements in the coal mine. At last, the feasibility of the whole system was experimentally verified. The cross-sensitivity of the temperature and displacement issue with FBG sensors could be eliminated by using matched pairs of FBG. The measuring range of 50 mm and the measurement resolution up to 0.06 mm could be obtained with the proposed sensor.     

Parallel-plate RF resonator imaging of chemical shift resolved capillary flow

Magnetic resonance imaging has been introduced to study flow in microchannels using pure phase spatial encoding with a microfabricated parallel-plate nuclear magnetic resonance (NMR) probe. The NMR probe and pure phase spatial encoding enhance the sensitivity and resolution of the measurement. In this paper, ¹H NMR spectra and images were acquired at 100 MHz. The B₁ magnetic field is homogeneous and the signal-to-noise ratio of 30 μl doped water for a single scan is 8×10⁴. The high sensitivity of the probe enables velocity mapping of the fluids in the micro-channel with a spatial resolution of 13×13 μm. The parallel-plate probe with pure phase encoding permits the acquisition of NMR spectra; therefore, chemical shift resolved velocity mapping was also undertaken. Results are presented which show separate velocity maps for water and methanol flowing through a straight circular micro-channel. Finally, future performance of these techniques for the study of microfluidics is extrapolated and discussed.     

Two-photon confocal microscopy as a tool for nonequilibrium charge-carrier lifetime tomography in semiconductor materials

By the example of ZnSe crystals, the capabilities of two-photon confocal microscopy as a tool for obtaining “planar” maps of nonequilibrium charge-carrier lifetimes in semiconductor materials and for investigating other direct-gap semiconductors and semiconductor heterostructures are considered. It is shown that such maps with a depth step and an in-plane resolution of several microns can be obtained for distances from the surface up to 1 mm. This technique is used to visualize inhomogeneities in the crystals under study and to examine their structure and luminescence characteristics.     

NMR velocimetry of falling liquid films

First results on NMR velocimetry of falling liquid films are presented. A film of average thickness 1 mm and width 40 mm is sustained by a continuous flow of silicon oil over a vertical plate made from PMMA. The spatial distribution of velocities is measured using a double spin--echo imaging pulse sequence supplemented by a bipolar velocity encoding gradient. Spin density and velocity images as well as two-dimensional velocity maps of different situations, i.e., undisturbed and disturbed falling film flow, are discussed. Experimental and theoretical velocity data for undisturbed film flow are compared.