基于同时多层激发和并行成像的心脏磁共振电影成像

磁共振成像（MRI）无创无害、对比度多、可以任意剖面成像的特点特别适合用于心脏成像,却因扫描时间长限制了其在临床上的应用.为了解决心脏磁共振电影成像屏气扫描时间过长的问题,该文提出了一种基于同时多层激发的多倍加速心脏磁共振电影成像及其影像重建的方法,该方法将相位调制多层激发（CAIPIRINHA）技术与并行加速（PPA）技术相结合,运用到分段采集心脏电影成像序列中,实现了在相位编码方向和选层方向的四倍加速,并使用改进的SENSE/GRAPPA算法对图像进行重建.分别在水模以及人体上进行了实验,将加速序列图像与不加速序列图像进行对比,结果验证了重建算法的有效性,表明该方法可以在保障图像质量以及准确测量心脏功能的前提下成倍节省扫描时间.     

Cardiac magnetic resonance imaging using radial k-space sampling and self-calibrated partial parallel reconstruction

Radial sampling has been demonstrated to be potentially useful in cardiac magnetic resonance imaging because it is less susceptible to motion than Cartesian sampling. Nevertheless, its capability of imaging acceleration remains limited by undersampling-induced streaking artifacts. In this study, a self-calibrated reconstruction method was developed to suppress streaking artifacts for highly accelerated parallel radial acquisitions in cardiac magnetic resonance imaging. Two- (2D) and three-dimensional (3D) radial k-space data were collected from a phantom and healthy volunteers. Images reconstructed using the proposed method and the conventional regridding method were compared based on statistical analysis on a four-point scale imaging scoring. It was demonstrated that the proposed method can effectively remove undersampling streaking artifacts and significantly improve image quality (P<.05). With the use of the proposed method, image score (1–4, 1=poor, 2=good, 3=very good, 4=excellent) was improved from 2.14 to 3.34 with the use of an undersampling factor of 4 and from 1.09 to 2.5 with the use of an undersampling factor of 8. Our study demonstrates that the proposed reconstruction method is effective for highly accelerated cardiac imaging applications using parallel radial acquisitions without calibration data.     

一种新型投影曝光调焦方法

为研究大面积激光投影光刻的调焦,利用Zemax光学设计软件模拟离焦对光程差（OPD）和调制传递函数（MTF）的影响,分析二者对投影曝光图形质量的影响,给出系统最大的离焦量值。提出一种利用显微镜的调焦方法,分析此方法的调焦误差主要来自于显微镜景深,根据景深表达式和系统最大离焦量值,选择一款景深不大于系统最大离焦量的显微镜来构建调焦系统,并基于该调焦系统进行光刻实验。实验结果表明:利用该方法对投影成像光刻进行调焦,无论是否离焦,边缘视场与中心视场的MTF均有差异,分辨率也有差异,但这种差异不影响光刻图形的质量。     

多路CCD成像非一致性动态校正新方法

在多路CCD成像结构中,由于影响各路成像参量不一致的因素较多,常规校正方法变得复杂和困难。在分析多路CCD成像机理的基础上,提出了一种利用小波变换的多路CCD成像非一致性动态校正新方法,即在分析同一目标成像中异路图像像元特性差异的基础上,利用小波变换构筑校正因子对后续的CCD捕获图像进行校正。为满足实时校正的需要,研究了动态条件下成像校正的时效性,分析了不同小波的动态校正效率。实验结果表明,校正后同一目标异路图像相关值为0．9975,Symlet3小波在两路及多路成像校正中均具有较高效率;在多路成像中,Symlet系列小波相对于其它类型小波校正效率相对突出。此方法为多路CCD成像非一致性在线校正提供了有效的途径。     

High-contrast imaging based on wavefront shaping to improve low signal-to-noise ratio photoacoustic signals using superpixel method

Photoacoustic(PA) imaging has drawn tremendous research interest for various applications in biomedicine and experienced exponential growth over the past decade. Since the scattering effect of biological tissue on ultrasound is two-to three-orders magnitude weaker than that of light, photoacoustic imaging can effectively improve the imaging depth.However, as the depth of imaging further increases, the incident light is seriously affected by scattering that the generated photoacoustic signal is very weak and the signal-to-noise ratio(SNR) is quite low. Low SNR signals can reduce imaging quality and even cause imaging failure. In this paper, we proposed a new wavefront shaping and imaging method of low SNR photoacoustic signal using digital micromirror device(DMD) based superpixel method. We combined the superpixel method with DMD to modulate the phase and amplitude of the incident light, and the genetic algorithm(GA) was used as the wavefront shaping algorithm. The enhancement of the photoacoustic signal reached 10.46. Then we performed scanning imaging by moving the absorber with the translation stage. A clear image with contrast of 8.57 was obtained while imaging with original photoacoustic signals could not be achieved. The proposed method opens new perspectives for imaging with weak photoacoustic signals.     

0.14 THz高分辨力成像雷达信号处理

为适应0.14 THz超高分辨雷达实时成像的需求,开发了基于CPU+GPU+FPGA的硬件架构和成像处理算法,算法以距离-多普勒为原型,引入L类维格纳分布变换提高横向分辨力,用Keystone变换方法对越距离单元徙动进行校正,并开发了系统非线性补偿算法。在载频0.14 THz、带宽5 GHz雷达样机上进行了逆合成孔径雷达成像试验,获得了3 cm3 cm的成像分辨力和实时成像能力,验证了信号处理方法的有效性。     

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).     

On the measurement of multi-component T2 relaxation in cartilage by MR spectroscopy and imaging

The multicomponent T₂ relaxation in bovine nasal cartilage (BNC) was investigated by nuclear magnetic resonance spectroscopy using the Carr-Purcell-Meiboom-Gill (CPMG) sequence and microscopic magnetic resonance imaging (μMRI) method using a CPMG-SE imaging sequence. All experimental data were analyzed by the non-negative least square (NNLS) procedure. Only one T₂ component was found in BNC by both experimental methods (about 113 and 170 ms before and after being enzymatically digested by trypsin). Several experimental and specimen-related factors were investigated in this study, and it was found that some of them could produce artificial multi-component T₂, including the use of the standard MSME imaging sequence at certain imaging gradients.     

Pixel super-resolution lensless in-line holographic microscope with hologram segmentation

We propose a resolution enhancement method for a lensless in-line holographic microscope(LIHM) by combining the hologram segmentation and pixel super-resolution(PSR) techniques. Our method is suitable for imaging specific target objects in samples, where the in-line hologram is disturbed by other objects in the samples. The resolution-enhancement capability of our method was proved by numerical simulations and imaging experiments while using a standard resolution target in a two-layer setup. We also applied our LIHM system to image the sample of living algae Euglena gracilis in water solution for further demonstration.     

皮棉杂质透射检测及成像目标增强方法

由于皮棉中白色或无色的杂质与皮棉反射特性相似，现有的光谱反射成像检测方法具有一定 的局限性.对皮棉杂质的光透射成像检测方法进行深入研究.在分析杂质及棉纤维透射特性基 础上，建立了光透射成像机理模型.研究了光透射成像系统中光源种类、光源能量、棉层厚 度及皮棉运动速度对成像目标的影响.根据棉层中透射光子的传播特性，提出利用高速CCD俘 获非漫射光子及统计滤波处理方法以增强成像目标，并分析了高速CCD曝光时间与成像目标 清晰度的量化关系.结果表明，所提出的光透射检测及成像目标增强方法，可获得清晰的目 标图像特征，检测结果与实际相符，此方法不仅为检测皮棉中各种白色或无色杂质提供一种 有效途径， 而且还可推广到红外及其他波段的成像系统中，对于微弱目标的透射成像检测 提供一种新的思路. 关键词： 皮棉杂质 透射成像 准直线光子 目标增强 统计滤波     

Extract echo signal in HFR imaging system

Ultrasonic high frame rate (HFR) method was developed by Jianyu Lu in 1997. This method constructs images in frequency domain; the spectrum of space domain objects is calculated based on the spectrum of echo signals, and the image is obtained by using IFFT (inverse fast Fourier transform). Because of this imaging process, the echo signal from each individual scatterer cannot be obtained directly. In this paper, we present a method, which can pick up the echo signal of every scatterer in HFR imaging method. Computer simulation has been performed to verify our method. With the new method we have developed, many other imaging methods, such as Doppler blood flow and elastic imaging, can be easily combined with HFR method to give more information of the imaged objects.     

High resolution inverse synthetic aperture radar imaging of three-axis-stabilized space target by exploiting orbital and sparse priors

The development of inverse synthetic aperture radar(ISAR) imaging techniques is of notable significance for monitoring, tracking and identifying space targets in orbit. Usually, a well-focused ISAR image of a space target can be obtained in a deliberately selected imaging segment in which the target moves with only uniform planar rotation. However, in some imaging segments, the nonlinear range migration through resolution cells(MTRCs) and time-varying Doppler caused by the three-dimensional rotation of the target would degrade the ISAR imaging performance, and it is troublesome to realize accurate motion compensation with conventional methods. Especially in the case of low signal-to-noise ratio(SNR),the estimation of motion parameters is more difficult. In this paper, a novel algorithm for high-resolution ISAR imaging of a space target by using its precise ephemeris and orbital motion model is proposed. The innovative contributions are as follows. 1) The change of a scatterer projection position is described with the spatial-variant angles of imaging plane calculated based on the orbital motion model of the three-axis-stabilized space target. 2) A correction method of MTRC in slant-and cross-range dimensions for arbitrarily imaging segment is proposed. 3) Coarse compensation for translational motion using the precise ephemeris and the fine compensation for residual phase errors by using sparsity-driven autofocus method are introduced to achieve a high-resolution ISAR image. Simulation results confirm the effectiveness of the proposed method.     

Real-time dynamic vocal tract imaging using an accelerated spiral GRE sequence and low rank plus sparse reconstruction

PurposeTo develop a real-time dynamic vocal tract imaging method using an accelerated spiral GRE sequence and low rank plus sparse reconstruction.MethodsSpiral k-space sampling has high data acquisition efficiency and thus is suited for real-time dynamic imaging; further acceleration can be achieved by undersampling k-space and using a model-based reconstruction. Low rank plus sparse reconstruction is a promising method with fast computation and increased robustness to global signal changes and bulk motion, as the images are decomposed into low rank and sparse terms representing different dynamic components. However, the combination with spiral scanning has not been well studied. In this study an accelerated spiral GRE sequence was developed with an optimized low rank plus sparse reconstruction and compared with L1-SPIRiT and XD-GRASP methods. The off-resonance was also corrected using a Chebyshev approximation method to reduce blurring on a frame-by-frame basis.ResultsThe low rank plus sparse reconstruction method is sensitive to the weights of the low rank and sparse terms. The optimized reconstruction showed advantages over other methods with reduced aliasing and improved SNR. With the proposed method, spatial resolution of 1.3*1.3 mm² with 150 mm field-of-view (FOV) and temporal resolution of 30 frames-per-second (fps) was achieved with good image quality. Blurring was reduced using the Chebyshev approximation method.ConclusionThis work studies low rank plus sparse reconstruction using the spiral trajectory and demonstrates a new method for dynamic vocal tract imaging which can benefit studies of speech disorders.     

Optical Imaging and Tissue Characterization with Polarization Discrimination of Time-Gated Signals

In this paper we demonstrated the effectiveness of imaging in a tissue phantom with isotropic scattering using polarization discrimination combined with the time gating method. This simple polarization discrimination technique was shown ineffective when it was applied to filamentous tissues. In this situation, we utilized the time-gated degree of polarization (DOP) imaging technique to show that the DOP measurement was quite effective for high-quality imaging of objects in filamentous tissues. We also applied this technique to the characterization of myocardial tissues and showed the difference between normal and abnormal tissues. In addition, we demonstrated a novel method for target depth determination in a turbid medium based on co-polarized light measurements. This method relied on the strong dependence of transmitted co-polarized intensity on target depth.     

Chemically selective NMR imaging of a 3-component (solid-solid-liquid) sedimenting system

A novel magnetic resonance imaging (MRI) technique which resolves the separate components of the evolving vertical concentration profiles of 3-component non-colloidal suspensions is described. This method exploits the sensitivity of MRI to chemical differences between the three phases to directly image the fluid phase and one of the solid phases, with the third phase obtained by subtraction. 19F spin-echo imaging of a polytetrafluoroethylene (PTFE) oil was interlaced with 1H SPRITE imaging of low-density polyethylene (LDPE) particles. The third phase was comprised of borosilicate glass spheres, which were not visible while imaging the PTFE or LDPE phases. The method is demonstrated by performing measurements on 2-phase materials containing only the floating (LDPE) particles, with the results contrasted to the experimental behaviour of the individual phases in the full 3-phase system. All experiments were performed using nearly monodisperse particles, with initial suspension volume fractions, phi(i), of 0.1.     

超声平面波同相正交信号频域波束形成算法

针对频域平面波波束形成算法尚不能直接应用于采用正交解调的超声成像系统中的实际问题,提出一种平面波同相正交信号频域波束形成方法.以平面波射频信号频域波束形成算法为基础,根据射频信号与同相正交信号波数空间变量之间的关系,推导了平面波同相正交信号与对应图像的频谱映射表达式,从而实现对正交解调后信号的频域超声图像重建.采用20...     

衍射增强成像方法在计算机断层成像中的应用

衍射增强成像是X射线相位衬度成像方法之一，这种方法具有较高的衬度和空间分辨率. 利用它对由轻元素组成的生物、医学样品成像可以观察到常规吸收成像无法观察到的内部微细结构. 这种方法在生物、医学、材料科学等无损检测领域中的应用研究，已成为当前国际上X射线成像领域中的研究热点. 讨论衍射增强成像方法和该方法在计算机断层成像中的应用. 实验结果表明，使用衍射增强成像方法获得的数据源能够重建出微米级的生物组织结构，这些组织结构信息在常规X射线断层成像中是难以得到的. 关键词： 衍射增强成像 CT重建 同步辐射 微细结构     

基于AFI的快速发射场B1+成像方法

该文提出了一种基于实际翻转角成像(Actual Flip-angle Imaging,AFI)的快速发射场测量方法(Fast AFI,FAFI),将多次激发平面回波成像(Multi-shot Echo Planar Imaging,Multi-shot EPI)的采集方式运用于AFI发射场(B_1~+)测量中,充分利用AFI序列中采集的等待时间,高倍数加速了水模和人体头部、腹部及盆腔的发射场测量.该文在水模和人体(n=16)实验中,验证了采用FAFI序列得到的B_1~+测量结果与AFI结果的一致性.FAFI序列大幅加速了发射场测量,为实现动态B_1~+匀场(B_1~+shimming)和快速局部激发提供了高效的发射场测量方法.     

An improved 3-D Look--Locker imaging method for T(1) parameter estimation

The 3-D Look-Locker (LL) imaging method has been shown to be a highly efficient and accurate method for the volumetric mapping of the spin lattice relaxation time T(1). However, conventional 3-D LL imaging schemes are typically limited to small tip angle RF pulses (5 degrees ), thereby improving the SNR and the accuracy of the method. In phantom studies, a mean T(1) measurement accuracy of less than 2% (0.2-3.1%) using a tip angle of 10 degrees was obtained for a range of T(1) from approximately 300 to 1,700 ms with a measurement time increase of only 15%. This accuracy compares favorably with the conventional 3-D LL method that provided an accuracy between 2.2% and 7.3% using a 5 degrees flip angle.     

Fat-water selective excitation in balanced steady-state free precession using short spatial-spectral RF pulses

Fat suppression is important but challenging in balanced steady-state free precession (bSSFP) acquisitions, for a number of clinical applications. In the present work, the practicality of performing fat-water selective excitations using spatial-spectral (SPSP) RF pulses in bSSFP sequence is examined. With careful pulse design, the overall duration of these SPSP pulses was kept short to minimize detrimental effects on TR, scan time and banding artifact content. Fat-water selective excitation using SPSP pulses was demonstrated in both phantom and human bSSFP imaging at 3T, and compared to results obtained using a two-point Dixon method. The sequence with SPSP pulses performed better than the two-point Dixon method, in terms of scan time and suppression performance. Overall, it is concluded here that SPSP RF pulses do represent a viable option for fat-suppressed bSSFP imaging.