Blood flow: insights from ultrasound

Ultrasonic pulse-echo systems can provide range-finding, time-position and real-time two-dimensional images of soft-tissue structures within the body. The Doppler effect can be used to study motion and blood flow. Continuous wave Doppler instruments provide information about velocity and direction of flow; depth discrimination can be obtained by pulsing the ultrasound. Two-dimensional Doppler flow imaging can be achieved by manual scanning of a probe over the skin surface. The combination of real-time pulse-echo imaging with pulsed Doppler blood flow detection in the duplex scanner makes it possible to localize the anatomical position of the Doppler sample volume. Real-time Doppler colour flow imaging combines traditional ultrasonic scanning with a two-dimensional flow map. Using appropriate ultrasonic instruments, blood flow volume rates, blood flow velocity profiles, pressure gradients, orifice areas, flow disturbances, jets, characteristics of blood vessels and the circulatory system, and tissue perfusion can all be investigated. These investigations have clinical applications in the study of cardiac, cerebral and peripheral blood flow, blood flow in the female pelvis, the fetus, the abdomen, the neonate, and in malignant tumours. Contemporary ultrasonic diagnosis employs exposure levels that are apparently free from biological risk, but other factors need to be taken into account in considering the prudent use of ultrasonic methods. Promising research is being carried out into the mechanism of ultrasonic scattering by blood, Doppler speckle, time-domain processing for blood flow imaging, methods for increasing the scanning speed, Doppler flow microscopy and contrast agents. The new technology that will result from this research should lead to further substantial progress in ultrasonic blood flow studies.     

A review of the measurement of blood velocity and related quantities using Doppler ultrasound

Ultrasound systems can be used to investigate blood flow by use of the Doppler effect. The flow information may be displayed as either a real-time sonogram or a two-dimensional colour image. Estimates of maximum velocity using commercial systems are in error by typically 10-100 per cent; this is associated with the inability of the single-beam Doppler method to measure the true direction of flow, and with geometric spectral broadening. Vector Doppler systems acquire Doppler information along two beam directions and are able to measure accurately the velocity and direction of motion within the scan plane. The small beam width of modern Doppler systems means that the condition of uniform insonation, required for estimation of mean velocity from mean frequency shift, is not valid except for the very smallest vessels. Other quantities related to the velocity may also be estimated, such as the volumetric flow and wall shear stress. Flow visualization using colour flow imaging suffers from dependence of the displayed colour on the direction of blood motion. The vector Doppler technique may be extended to colour flow to give improved visualization of flow, in which there is no angle dependence within the scan plane.     

基于叠加态涡旋光多普勒效应的物体速度探测

涡旋光携带轨道角动量,具有螺旋相位,其坡印廷矢量与光轴存在夹角。涡旋光坡印廷矢量的角向分量会引起旋转多普勒效应,可对旋转速度进行直接测量。利用涡旋光的线性多普勒效应与旋转多普勒效应可以对物体的线速度以及转动速进行探测,对物体的复合运动状态进行描述。在此基础上,利用叠加了不同轨道角动量模式的涡旋光对目标进行探测,不同的轨道角动量模式会造成不同的频移,结合线性多普勒效应造成的频移可以测量复合运动具体速度成分。由此提出了一种叠加态涡旋光对于复合运动的测量模型,并分析了不同运动状态对探测结果的影响。     

Motion compensation for in vivo subcellular optical microscopy

In this review, we focus on the impact of tissue motion on attempting to conduct subcellular resolution optical microscopy, in vivo. Our position is that tissue motion is one of the major barriers in conducting these studies along with light induced damage, optical probe loading as well as absorbing and scattering effects on the excitation point spread function and collection of emitted light. Recent developments in the speed of image acquisition have reached the limit, in most cases, where the signal from a subcellular voxel limits the speed and not the scanning rate of the microscope. Different schemes for compensating for tissue displacements due to rigid body and deformation are presented from tissue restriction, gating, adaptive gating and active tissue tracking. We argue that methods that minimally impact the natural physiological motion of the tissue are desirable because the major reason to perform in vivo studies is to evaluate normal physiological functions. Towards this goal, active tracking using the optical imaging data itself to monitor tissue displacement and either prospectively or retrospectively correct for the motion without affecting physiological processes is desirable. Critical for this development was the implementation of near real time image processing in conjunction with the control of the microscope imaging parameters. Clearly, the continuing development of methods of motion compensation as well as significant technological solutions to the other barriers to tissue subcellular optical imaging in vivo, including optical aberrations and overall signal‐to‐noise ratio, will make major contributions to the understanding of cell biology within the body.     

Ultrasonic investigation of blood flow.

Ultrasound and the Doppler effect are used to measure blood velocity non-invasively in order to diagnose blood vessel disease. Intrusive lesions on arterial walls give rise to an alteration of the time-varying blood velocity waveform and local blood flow disturbance which are detected and measured using the envelope and width of the Doppler signal spectrogram respectively. Flow may also be imaged in colour superimposed on a grey-scale anatomical image allowing vessel narrowing and the accompanying flow disturbance to be visualized. Developments in three-dimensional imaging, angle tolerant velocity measurements and increased sensitivity using second harmonic backscatter from encapsulated-bubble contrast media ensure increasing use of this modality.     

大视场空间相机的像移速度场模型及卫星三轴姿态稳定度分析

针对大视场空间相机的像移补偿,建立了基于坐标变换和姿态动力学的离轴三反大视场空间相机通用像移速度场模型。建模过程中考虑了离轴三反光学系统的离轴角对像移模型的影响,推导了离轴三反大视场空间相机的像速场解析式。以某大视场空间相机为例,分析了3种典型成像姿态下焦面像移速度和偏流角的分布特点,研究了卫星姿态稳定度对相机成像质量的影响。分析表明,卫星三轴姿态稳定度的降低会导致相机焦面动态传递函数(MTF)下降,其中俯仰姿态稳定度对焦面动态MTF的影响最大;并且随着积分级数增加,下降会愈发明显。相机侧摆姿态成像时,对卫星姿态稳定度的要求更高。以传递函数下降5%为限,积分级数为96级的大视场空间相机,要求卫星姿态稳定度控制在0.001(°)/s以内。实验结果验证了文中对卫星姿态稳定度的分析,证明了像移速度场模型的准确性,为大视场空间相机像移补偿提供了可靠依据。     

Motion Target Imaging by Non-Linear Stepped-Frequency Chirp Pulse Train

Traditional stepped-frequency chirp pulse train methods suffer from high sidelobes and difficulty in compensating for the Doppler effect caused by target motion. This paper investigates a class of non-linear stepped-frequency chirp pulse train which has low sidelobes and the capability to cancel clutter and to compensate for target motion. A new Doppler matched filter has been developed for estimation of the target’s radial velocity, which avoids the multiple bursts required by other methods. The high signal-to-noise ratio resulting from the application of sub-pulse compression improves the accuracy of estimation. The Cramer–Rao bound for the lower limit on the velocity estimation is derived to demonstrate the performance of the proposed method.     

深空光通信中光束瞄准技术研究

研究了深空光通信中的光束精确瞄准技术。从航天器和天体的运动规律出发,建立了一种基于航天器和地球星历表的深空光通信的瞄准理论,导出了瞄准矢量在航天器星上坐标系中角度,角速度,角加速度的变化规律,对两终端的相对运动进行分析,导出提前瞄准角和接收光波长多普勒频移的变化规律,进行了计算机仿真。结果表明,瞄准角度、角速度、角加速度、提前瞄准角呈现出周期性变化,在当前的技术水平下,在深空距离下能实现光束的精确对准。接收光波长的多普勒频移也呈现周期性变化,其大小在0.07 nm以内,决定了深空光通信中窄带滤光片的带宽应在0.7 nm以上,也表明在深空光通信中,采用相干探测方法将面临严重挑战。     

Stroboscopic two-dimensional ultrasonic velocity profiling for measuring flow transition in Taylor Couette systems

Flow characterization in a Taylor Couette system was made by investigating the radial velocity component with Ultrasonic Doppler Velocimetry based flow mapping. With the technique presented in this work, it is possible to measure the radial velocity components for variable axial position in a Couette cell within Taylor vortex flow (TVF), wavy vortex flow (WVF), modulated vortex flow (MVF) as well as spiral vortex domains in a conical shaped gap. The resulting maps for the different flow states show the location of vortices in the annular gap between the inner and outer cylinder. Cylindrical and conical concentrically rotating inner bodies were applied and respective flow patterns were analyzed. The method uses a stroboscopic triggering to synchronize flow measurements and rotational motion. The oscillation frequency f of unsteady motion in WVF, MVF, and spirals can be obtained from the power spectrum of velocity. The UVP transducer was preferably positioned in radial direction, perpendicular to the surface of the inner rotating body for measuring the radial velocity component. At the same time, the transducer was moved with constant velocity vertically along the outer cylinder height.     

基于锁相放大器的全光纤式激光多普勒测速系统

为了提高激光多普勒测速系统的测量精度及其实用性,基于锁相放大器和光纤设计搭建了一套激光多普勒测速系统。该系统的优点在于,锁相放大器的引入能够放大信号并可避免杂散光影响,从而大大提高系统的信噪比;此外,利用光纤取代传统的传输与接收光路,有效避免振动、灰尘、杂散光等环境因素影响,使实验条件大大简化。利用该系统测量移动平面镜和漫射面镜的结果表明,该系统能够准确测量移动物体的速率,误差在1%以内。该系统将来可应用于在线监测活体组织的血液流速测量中。     

航空摆扫相机转弯成像像移分析及补偿

为保证航空摆扫相机转弯成像过程中的成像质量,对其像移计算及补偿方法进行了研究。根据航空摆扫相机的成像原理,利用几何建模及速度矢量分解建立了转弯成像像移计算模型,给出了基于均值补偿的转弯前向像移补偿方法。转弯前向像移补偿分析表明:相机焦距为500 mm,曝光时间为0.01 s,速高比为0.02 rad/s,纵向视场角为10°,转弯角速度为0.5(°)/s时,最大前向像移补偿残差量为2.22μm;转弯角速度为1.5(°)/s时,最大前向像移补偿残差量为3.36μm。另外,转弯横向像移补偿分析表明:横向像移量随纵向视场角幅值的增加而增大,曝光时间为0.005 s,横向视场角为30(°),转弯角速度为1(°)/s时,横向像移量在纵向视场角为4.5°时达到3μm。转弯成像试飞实验结果表明:得到的图像像质优良,无几何形变,前向像移补偿良好,验证了本文提出的转弯成像像移补偿方法的正确性。     

随掘连续超前探测异常体辨识成像研究

本文提出了一种新型随掘连续超前探测异常体辨识成像方法,有效解决了固定场源超前探测单次成像准确度差的问题,为巷道掘进与超前探测并行作业提供有力支撑。首先,构建了随掘连续超前探测异常体辨识成像理论模型;然后,对异常体辨识成像效果及成像准确度提高方法进行研究,在可有效辨识前方异常几何体形态的基础上,通过扩大随掘里程、加快电位采集频率和增加电位测点数量,将电导率均方误差分别从0.273降至0.156、0.173降至0.153、0.183降至0.167,成像准确度逐渐增高;最后,分析了随掘场源前方不同类型、形状异常体成像效果,构建泥槽实验系统并进行了成像效果对比实验,验证了本方法的有效性。     

Ultrasound measurement of large bubbles rising in angled slug pipe flows

This study details the problem of the ultrasonic detection of large bubbles rising rapidly in an upward gas–liquid two-phase pipe flow and proposes a new method to solve the problem. The proposed method uses two types of information, namely the echo intensity reflected by large bubbles and the Doppler frequency, which have different features in interface detection. The method using the Doppler frequency performs well in the detection of large bubbles regardless of the interface condition, whereas the method using the echo intensity has trouble in detecting an uneven interface. In contrast, the information of the echo intensity guarantees high accuracy of the interface detection even if that of the Doppler frequency has low accuracy for the detection owing to many small bubbles existing in the liquid film. Here, the two methods are combined to overcome their problems, and a validation test confirms that the results of the combined method agree well with the results of image processing. As demonstrations of the proposed method, the slug frequency, velocity, and airflow rate of large bubbles in an air-lift pump are obtained. The results confirm that the proposed method can be adopted for the high velocity of slug flow in various applications.     

用于超声散斑跟踪血流测速的多角度平面波局部运动补偿

血流速度剖面用于计算壁面剪切率等血流动力学指标,与动脉粥样硬化病程发展密切相关。 超快超声散斑跟踪广泛用 于血流速度剖面估计,然而多角度平面波复合成像存在血流散射体的运动伪影,不利于流速估计。 提出了一种多角度平面波复 合成像的局部运动补偿法,对射频信号时间序列的相邻帧进行局部运动补偿来消除不同径向位置的运动伪影,从而提高流速测 量准确性。 相比直接相干复合,B-MoCo 法将仿真、仿体实验中流速测量结果的归一化均方根误差平均减小了 10. 37% 、 37. 82% ,说明了 B-MoCo 法的有效性。 基于兔骼动脉的实测实验进一步证明了 B-MoCo 法的临床可行性。 综上,B-MoCo 法能够 有效提高血流速度剖面的测量精度,有助于相关心血管疾病的早期诊断与病程监测。     

四足机器人Trot步态的偏航运动控制

为解决四足机器人Trot步态的偏航运动控制问题,借鉴两轮差速驱动的原理将机身的运动分解为两着地腿的运动,再基于弹簧倒立摆模型对单个着地腿的前进速度和侧移速度进行控制,最后通过控制两着地腿的运动来控制机器人整体的运动,从而实现对机器人偏航角的控制.基于这种思想,可以对偏航角、前进速度和侧移速度的控制进行统一设计,简化了基于三维模型的四足机器人运动控制的难度.在虚拟样机中进行仿真实验,发现控制方法在前进速度为零和非零时都能对偏航角进行很好的控制.     

Motion of a solid body supported on a narrow rectangular area on a horizontal plane with orthotropic friction. Part 1. Inertia motion

The problem of motion of a solid body which rests on a narrow rectangular area carried on a horizontal plane is discussed, assuming that the force of friction is orthotropic. A relationship is formulated between the velocity of the point of intersection of the diagonals of this area and the angular velocity of the body at the moment of stopping. The findings can be applied to simulation of the motion of a system of bodies and to solution of contact problems.     

Dual-Measurement-Method and its extension for accurately resolving the secondary flows in LDA (Laser Doppler Anemometry) applications

In LDA (Laser Doppler Anemometry) applications in flow measurements, it is always inevitable that small deviations between the LDA and the flow coordinate systems occur. This will lead to a velocity shift in each measured velocity component. In the cases where the secondary flows are of many orders smaller than the main flow, the velocity shift embedded in the measurements can be as large as the actual secondary flow itself. The secondary flow structure could then be totally distorted through the measurements.In order to accurately resolve the secondary flow structures across the main flow, a method known as the Dual-Measurement-Method (DMM) has been developed and shown to be very efficient. The method is based on the “reflection design” of the LDA layout and aims to find out the velocity shift existing in the measurement results. For situations where the “reflection design” of the LDA layout is restricted, the Dual-Measurement-Method has been extended in a way that three arbitrary measurements have to be carried out. The calculation processes in finding out the velocity shift from three such measurements have been outlined and validated. An example of use indicates that just in that case the secondary flows have to be resolved as accurately as possible.     

A DETAILED DESIGN OF A LAB-BUILT MODULATOR DRIVER FOR A MÖSSBAUER SPECTROMETER

The Doppler modulation system is a principal part of a Mössbauer spectrometer. It includes the Doppler modulator (velocity transducer) and a control system (the modulator driver) which consists of a function generator that produces a reference signal by which the vibrator can be controlled and the error correction circuit that corrects the motion of the vibrator according to the reference signal. The motion of the driver must be identical to the preferred wave shape for the operation of the spectrometer. The aim of the present article is to design and test a low cost lab-built modulator velocity driver for a Mössbauer spectrometer to be used in the constant acceleration (triangular) mode of operation, although it can be used in the other operational modes. A triangular wave is stored in RAM. The axis of the vibrator carries two coils, one for the driving signal and the other for the pickup signal which gives the shape of the motion of the driver (i.e., the actual motion of the source). The stored reference triangular wave is compared with the one from the pickup coil and the difference between them gives an error signal. The error signal will be zero if the motion of the vibrator is identical to that of the stored wave. This error signal is added to the driving pulse in a suitable phase and amplitude in order to obtain a source motion with minimized deviation from its correct value.     

基于YOLO v3的室内场景中人体检测方法的研究

针对传统人体检测算法,存在着鲁棒性差和对光照条件要求较为苛刻的问题,借鉴目标检测的最新研究成果,以YOLO v3网络为基础,对室内场景制做了相应的室内场景人体识别数据集;同时,结合人体成像具有宽高不一致的特点,聚类选取初始框的数量和规格,改进候选框在X轴和Y轴的分布密度,将红外夜视图片和常规图片混合训练,并利用运动检测...     

Doppler ultrasound-based measurement of tendon velocity and displacement for application toward detecting user-intended motion

The motivation of this research is to non-invasively monitor the wrist tendon's displacement and velocity, for purposes of controlling a prosthetic device. This feasibility study aims to determine if the proposed technique using Doppler ultrasound is able to accurately estimate the tendon's instantaneous velocity and displacement. This study is conducted with a tendon mimicking experiment consisting of two different materials: a commercial ultrasound scanner, and a reference linear motion stage set-up. Audio-based output signals are acquired from the ultrasound scanner, and are processed with our proposed Fourier technique to obtain the tendon's velocity and displacement estimates. We then compare our estimates to an external reference system, and also to the ultrasound scanner's own estimates based on its proprietary software. The proposed tendon motion estimation method has been shown to be repeatable, effective and accurate in comparison to the external reference system, and is generally more accurate than the scanner's own estimates. After establishing this feasibility study, future testing will include cadaver-based studies to test the technique on the human arm tendon anatomy, and later on live human test subjects in order to further refine the proposed method for the novel purpose of detecting user-intended tendon motion for controlling wearable prosthetic devices.