MR与脑功能成像

MR功能成像(funcitionalm agnetic resonance,fMR)是一种新兴的、无创的和相对容易掌握的核磁共振检查技术。对于脑功能检查有较高的空间和时间精度及分辨率。其检查方法灵活多样,学术领域交叉性强,能适应多种实验,并且可以对同一检查目的进行多次重复检查。近年来MR脑功能成像的科学研究快速发展,其临床医学成果层出不穷。     

脑磁感应断层成像

脑磁感应断层成像技术具有功能成像和连续图像监护的优点。与其它电磁成像技术相比，可以克服颅骨的屏障影响，并可获得较高的空间分辨率。在脑成像方面具有潜在的应用前景。从实验系统、数值仿真、系统性能和关键问题等方面综述了脑磁感应断层成像技术的研究进展。     

一种基于微机的新型Morris水迷宫分析系统

我们设计了一种新型的能够在线和离线分析Morris水迷中过程的图像追踪系统。该系统以电荷耦合器件（CCD）和赛扬400微型计算机为基础，实验过程中不需要对实验动物作特殊标记，识别算法采用了轨迹预测、局部和全局相结合的搜索技术，从而使得追踪和记录实验动物（大鼠）的速度达到18帧／s，空间分辨率达到2cm。该系统提供了丰富的参数，并具有对任意点和任意时间段进行参数分析和轨迹显示的功能。实验结果可以保存为文本文件，方便地利用Excel等工具软件作进一步分析。     

脑磁感应断层成像

脑磁感应断层成像技术具有功能成像和连续图像监护的优点。与其它电磁成像技术相比,可以克服颅骨的屏障影响,并可获得较高的空间分辨率。在脑成像方面具有潜在的应用前景。从实验系统、数值仿真、系统性能和关键问题等方面综述了脑磁感应断层成像技术的研究进展。     

基于数字图像处理的人类视觉对比度分辨率限制测定

在人类视觉生理一物理学文献中，报道了人类视觉的空间分辨率限制（不能分辨视角小于1’的两点）、时间分辨率限制（不能分辨时间间隔小于0．1”出现的两幅不同图像）和频率（波长）分辨率（不能分辨波长差小于5m的两种颜色），但是没有对比度分辨率限制的数据报道，特别是基于现代数字技术的人类视觉对图像的对比度分辨率限制（阈值）的测定的报道。这里我们报告基于计算机数字图像处理技术的人类视觉对图像的对比度分辨率限制（阈值）的测定的现代测试方法、测试结果和数学模型。分别获得了在暗视觉和明视觉条件下的对比度分辨率限制随背景灰度而变化的函数关系。该研究结果将奠定隐身、隐形和反隐身、反隐形以及不依赖于红外技术的夜视系统的理论和技术以及相关产业的视觉生理学基础。     

右心室双出口合并多发肺血栓电子束CT诊断(1例报告)

电子束CT(EBCT)有高时间分辨率、密度分辨率和空间分辨率,横断面成像避免了影像重叠,有利于显示心脏大血管的解剖结构、空间位置及连接关系,对复杂心血管畸形的节段分析有重要价值.     

高分辨脑电图及其实现的技术途径

针对传统脑电图技术时间分辨率很高而空间分辨率太低的主要问题,近年来国外的一些实验室相继发展了一种称为“高分辨脑电图”的技术。通过结合一定的头模型,这种技术可由在头皮电极上测得的电位分布推算出颅内皮层上的电位分布,从而显著地提高了脑电图的的空间分辨率。这为脑科学,包括临床和认识领域又提供了一种新的有力的工具。本文着重介绍了目前几种有代表性的从头皮电位测量值重建皮层电位分布的方法：解析求解方法,数值求     

冠脉粥样硬化的断层影像检查方法及其临床应用

虽然选择性冠脉造影是诊断冠状动脉疾病的金标准,但该检查费用高,有一定的危险性。断层影像检查方法如电子束CT、多层螺旋CT、磁共振成像作为无创性的冠脉影像诊断技术,随着空间分辨率、时间分辨率的进一步提高以及各种扫描技术的进一步完善,必将成为一种有前途的诊断冠脉疾病以及其他心脏疾病的非侵袭性技术。     

高分辨脑电图及其实现的技术途径

针对传统脑电图技术时间分辨率很高而空间分辨率太低的主要问题,近年来国外的一些实验室相继发展了一种称为“高分辨脑电图”的技术。通过结合一定的头模型,这种技术可由在头皮电极上测得的电位分布推算出颅内皮层上的电位分布,从而显著地提高了脑电图的空间分辨率。这为脑科学,包括临床和认识领域又提供了一种新的有力的工具。本文着重介绍了目前几种有代表性的从头皮电位测量值重建皮层电位分布的方法：解析求解方法,数值求解方法（包括有限元法和边界元法）和皮层成像技术等。比较系统地分析了这些方法的技术特点,讨论了它们存在的主要优势与不足。     

医用全身正电子发射成像探测系统技术的研发热点和进展

医用全身正电子发射成像(PET)技术是最成功的分子影像技术之一,已经在肿瘤诊断、心血管疾病诊断和脑神经科学研究等领域得到了广泛的应用。然而,目前医用全身PET技术的系统灵敏度、空间分辨率和图像信噪比等方面还存在较大的不足和提升空间。系统灵敏度、空间分辨率和信噪比主要受晶体性能和晶体检测头设计的影响,而PET系统设计是在现有技术的基础上,通过对成像参数的平衡与优化,实现最佳的成像质量。随着闪烁晶体、光电传感器、高速电子系统等核心技术的发展,医用全身PET系统的性能有可能得到较大的提高。本文分析了相关技术的发展方向,并报告了最新进展。     

High Resolution Ultrasound Superharmonic Perfusion Imaging: <Emphasis Type="Italic">In Vivo</Emphasis> Feasibility and Quantification of Dynamic Contrast-Enhanced Acoustic Angiography

Mapping blood perfusion quantitatively allows localization of abnormal physiology and can improve understanding of disease progression. Dynamic contrast-enhanced ultrasound is a low-cost, real-time technique for imaging perfusion dynamics with microbubble contrast agents. Previously, we have demonstrated another contrast agent-specific ultrasound imaging technique, acoustic angiography, which forms static anatomical images of the superharmonic signal produced by microbubbles. In this work, we seek to determine whether acoustic angiography can be utilized for high resolution perfusion imaging in vivo by examining the effect of acquisition rate on superharmonic imaging at low flow rates and demonstrating the feasibility of dynamic contrast-enhanced superharmonic perfusion imaging for the first time. Results in the chorioallantoic membrane model indicate that frame rate and frame averaging do not affect the measured diameter of individual vessels observed, but that frame rate does influence the detection of vessels near and below the resolution limit. The highest number of resolvable vessels was observed at an intermediate frame rate of 3 Hz using a mechanically-steered prototype transducer. We also demonstrate the feasibility of quantitatively mapping perfusion rate in 2D in a mouse model with spatial resolution of ~100 μm. This type of imaging could provide non-invasive, high resolution quantification of microvascular function at penetration depths of several centimeters.     

吸收媒质中非线性X波的计算仿真

通过数值方法求解KZK方程,对吸收媒质中X波的非线性声场进行计算和仿真.结果表明:在非线性、衍射和吸收三种效应的综合作用下,X波的非线性声场同样具有类似于线性声场的显著的有限衍射特性,可以在整个成像区域获得一致的高分辨率,从而同时实现较高帧率和较高分辨率的超声成像.     

Laser speckle contrast imaging of cerebral blood flow in freely moving animals

We designed a miniature laser speckle imager that weighs ～20 g and is 3.1-cm high for full-field high-resolution imaging of cerebral blood flow (CBF) in freely moving animals. Coherent laser light illuminates the cortex through a multimode optical fiber bundle fixed onto the supporting frame of the imager. The reflected lights are then collected by a miniature macrolens system and imaged by a high-resolution CMOS camera at a high frame rate (50 fps). Using this miniature imager, we achieve high spatiotemporal resolution laser speckle contrast imaging of CBF in freely moving animals in real time.     

基于FPGA的数字X线图像的实时缩放模块

本文介绍了一个自行设计的数字化X射线影像实时处理系统中实现图像实时缩放的子系统.重点分析了缩放涉及的插值算法,设计并实现了基于FPGA的三次插值的模块,系统最终实现了对高显示分辨率和帧率下的X线图像的实时缩放.     

Imaging performance of an amorphous selenium digital mammography detector in a breast tomosynthesis system

In breast tomosynthesis a rapid sequence of N images is acquired when the x-ray tube sweeps through different angular views with respect to the breast. Since the total dose to the breast is kept the same as that in regular mammography, the exposure used for each image of tomosynthesis is 1/N. The low dose and high frame rate pose a tremendous challenge to the imaging performance of digital mammography detectors. The purpose of the present work is to investigate the detector performance in different operational modes designed for tomosynthesis acquisition, e.g., binning or full resolution readout, the range of view angles, and the number of views N. A prototype breast tomosynthesis system with a nominal angular range of +/-25 degrees was used in our investigation. The system was equipped with an amorphous selenium (a-Se) full field digital mammography detector with pixel size of 85 microm. The detector can be read out in full resolution or 2 x 1 binning (binning in the tube travel direction). The focal spot blur due to continuous tube travel was measured for different acquisition geometries, and it was found that pixel binning, instead of focal spot blur, dominates the detector modulation transfer function (MTF). The noise power spectrum (NPS) and detective quantum efficiency (DQE) of the detector were measured with the exposure range of 0.4-6 mR, which is relevant to the low dose used in tomosynthesis. It was found that DQE at 0.4 mR is only 20% less than that at highest exposure for both detector readout modes. The detector temporal performance was categorized as lag and ghosting, both of which were measured as a function of x-ray exposure. The first frame lags were 8% and 4%, respectively, for binning and full resolution mode. Ghosting is negligible and independent of the frame rate. The results showed that the detector performance is x-ray quantum noise limited at the low exposures used in each view of tomosynthesis, and the temporal performance at high frame rate (up to 2 frames per second) is adequate for tomosynthesis.     

Wide-field optical sectioning for live-tissue imaging by plane-projection multiphoton microscopy

Optical sectioning provides three-dimensional (3D) information in biological tissues. However, most imaging techniques implemented with optical sectioning are either slow or deleterious to live tissues. Here, we present a simple design for wide-field multiphoton microscopy, which provides optical sectioning at a reasonable frame rate and with a biocompatible laser dosage. The underlying mechanism of optical sectioning is diffuser-based temporal focusing. Axial resolution comparable to confocal microscopy is theoretically derived and experimentally demonstrated. To achieve a reasonable frame rate without increasing the laser power, a low-repetition-rate ultrafast laser amplifier was used in our setup. A frame rate comparable to that of epifluorescence microscopy was demonstrated in the 3D imaging of fluorescent protein expressed in live epithelial cell clusters. In this report, our design displays the potential to be widely used for video-rate live-tissue and embryo imaging with axial resolution comparable to laser scanning microscopy.     

Technical features of a CCD video camera system to record cardiac fluorescence data

A charge-coupled device (CCD) camera was used to acquie movies of transmembrane activity from thin slices of sheep ventricular epicardial muscle stained with a voltage-sensitive dye. Compared with photodiodes, CCDs have high spatial resolution, but low temporal resolution. Spatial resolution in our system ranged from 0.04 to 0.14 mm/pixel; the acquisition rate was 60, 120, or 240 frames/sec. Propagating waves were readily visualized after subtraction of a background image. The optical signal had an amplitude of 1 to 6 gray levels, with signal-to-noise ratios between 1.5 and 4.4. Because CCD cameras in-tegrate light over the frame interval, moving objects, including propagating waves, are blurred in the resulting movies. A computer model of such an integrating imaging system was developed to study the effects of blur, noise, filtering, and quantization on the ability to measure conduction velocity and action potential duration (APD). The model indicated that blurring, filtering, and quantization do not affect the ability to localize wave fronts in the optical data (i.e., no systematic error in determining spatial position), but noise does increase the uncertainty of the measurements. The model also showed that the low frame rates of the CCD camera introduced a systematic error in the calculation of APD: for cutoff levels >50%, the APD was erroneusly long. Both noise and quantization increased the uncertainty in the APD measurements. The optical measures of conduction velocity were not significantly different from those measured simultaneously with microelectrodes. Optical APDs, however, were longer than the electrically recorded APDs. This APD error could be reduced by using the 50% cutoff level and the fastest frame rate possible.     

Experimental comparison of high-density scintillators for EMCCD-based gamma ray imaging

Detection of x-rays and gamma rays with high spatial resolution can be achieved with scintillators that are optically coupled to electron-multiplying charge-coupled devices (EMCCDs). These can be operated at typical frame rates of 50 Hz with low noise. In such a set-up, scintillation light within each frame is integrated after which the frame is analyzed for the presence of scintillation events. This method allows for the use of scintillator materials with relatively long decay times of a few milliseconds, not previously considered for use in photon-counting gamma cameras, opening up an unexplored range of dense scintillators. In this paper, we test CdWO? and transparent polycrystalline ceramics of Lu?O?:Eu and (Gd,Lu)?O?:Eu as alternatives to currently used CsI:Tl in order to improve the performance of EMCCD-based gamma cameras. The tested scintillators were selected for their significantly larger cross-sections at 140 keV ((99m)Tc) compared to CsI:Tl combined with moderate to good light yield. A performance comparison based on gamma camera spatial and energy resolution was done with all tested scintillators having equal (66%) interaction probability at 140 keV. CdWO?, Lu?O?:Eu and (Gd,Lu)?O?:Eu all result in a significantly improved spatial resolution over CsI:Tl, albeit at the cost of reduced energy resolution. Lu?O?:Eu transparent ceramic gives the best spatial resolution: 65 μm full-width-at-half-maximum (FWHM) compared to 147 μm FWHM for CsI:Tl. In conclusion, these 'slow' dense scintillators open up new possibilities for improving the spatial resolution of EMCCD-based scintillation cameras.     

Characteristics of a charged-coupled-device-based optical mapping system for the study of cardiac arrhythmias

We develop an optical fluorescent mapping system that is able to record the action potential wavefront propagation within cardiac tissue samples with high spatial and temporal resolutions. The system's main component, the fluorescence acquisition device (customized CCD camera), offers a high spatial resolution of 128 x 128 pixels, with 12-bit digitization and a frame rate of 490 frames/s. The system is designed and implemented to image an area of approximately 20 x 20 mm at its minimum object distance of 140 mm, corresponding to a spatial resolution of approximately 3 line pairs/mm. Experiments using this system with di-4-ANEPPS-stained canine cardiac tissues with stimulated action potentials through external electrodes result in successful mappings of the distribution and propagation of the action potential wavefronts, showing the system's sensitivity to the change in fluorescence intensity in regions of action potentials. These data demonstrate this optical mapping system as a powerful device in the study of cardiac arrhythmia mechanisms.     

The performance of a CCD digital autoradiography imaging system

Autoradiography is a widely used technique for imaging trace quantities of radioactivity within biological samples, conventionally using photographic film. This method produces images with high spatial resolution, but it suffers from very low sensitivity and poor dynamic range. Digital autoradiography systems with greatly improved sensitivity and linearity are commercially available, but the spatial resolution is usually much less than that achieved using film. We report here the design, construction and characterization of a novel digital autoradiography system based on scientific-grade charged coupled devices (CCDs). Images of x-ray and beta emissions from radionuclides commonly used in autoradiography show that the system can perform high-speed quantitative imaging with a spatial resolution of approximately 30, microm. Using a frame by frame acquisition method the dynamic range is shown to be at least three orders of magnitude. The absolute detection efficiency is comparable to the best of the currently available digital systems. CCD images of 125I and 14C radioisotope distributions in tissue samples are superior to the equivalent film images and have been acquired in 1-10% of the time.