基于多尺度传递熵的脑肌电信号耦合分析

神经运动控制中脑肌电同步特征可以反映皮层与肌肉之间的功能联系. 为定量研究脑电和肌电信号在不同时间尺度上的同步耦合特征, 提出多尺度传递熵方法实现静态握力输出下的脑肌电耦合分析: 对同步采集的头皮脑电信号(EEG) 和表面肌电信号(EMG)进行多尺度化, 计算不同尺度因子下EEG与EMG间的传递熵值, 获取不同耦合方向(EEG→EMG及EMG→EEG)上的非线性脑肌电耦合特征; 进一步计算功能频段下的显著性面积指标, 定量分析不同尺度下皮层肌肉功能耦合强度的差异. 分析结果显示, 静态握力输出时beta频段(15–35 Hz)皮层肌肉功能耦合特征显著, 且beta2频段(25–35 Hz)在不同尺度上EEG→EMG方向的耦合强度大于EMG→EEG方向, 耦合强度最大值和方向间耦合强度差异显著值均出现于较高时间尺度. 研究结果揭示: 皮层肌肉功能耦合具有双向性, 且耦合强度在不同时间尺度和不同功能频段上有所差异, 可利用多尺度传递熵定量刻画大脑皮层与肌肉之间的非线性同步特征及功能联系.     

低强度脉冲超声的骨骼肌修复效应及生物学机制研究*

骨骼肌是保持人体姿态和运动机能的重要组织器官。大量研究采用低强度脉冲超声治疗骨折、骨不连、肌腱和韧带损伤等并取得了较好的效果。然而应用低强度脉冲超声进行肌肉相关疾病治疗的研究相对较少,详细的机制仍不确定。该文综合相关研究报道,介绍了应用低强度脉冲超声进行肌肉修复的生物效应和细胞、肌细胞因子和细胞内信号转导通路的超声作用机制的研究现状。对现有研究存在的问题做了分析,并对肌肉组织损伤的超声治疗和对抗的研究方向进行了展望。     

基于变分模态分解-传递熵的脑肌电信号耦合分析

皮层肌肉功能耦合是大脑皮层和肌肉组织间的相互作用, 脑肌电信号的多尺度耦合特征可以体现皮层-肌肉间多时空的功能联系. 本文引入变分模态分解并与传递熵结合, 构建变分模态分解-传递熵模型应用于脑肌间耦合研究. 首先基于变分模态分解将同步采集的脑电(EEG) 和肌电(EMG) 信号分别进行时频尺度化, 然后计算不同时频尺度间的传递熵值, 获取不同耦合方向(EEG→EMG 及EMG→EEG) 上不同尺度间的非线性耦合特征. 结果表明, 在静态握力输出条件下, 皮层与肌肉beta (15—35 Hz) 频段间的耦合强度最为显著; EEG→EMG 方向上脑电与肌电高gamma (50—72 Hz) 频段的耦合强度总体上高于EMG→EEG 方向.研究结果揭示皮层-肌肉功能耦合具有双向性, 且脑肌间不同耦合方向上、不同频段间的耦合强度有所差异.因此可利用变分模态分解-传递熵方法定量刻画大脑皮层与肌肉各时频段之间的非线性同步特征及功能联系.     

基于LABVIEW的脑电信号虚拟采集系统设计

在神经科学研究领域,对大脑的观察主要来源于对脑电信号的收集与分析。当前对脑电信号收集的方法是通过专业脑电设备将信号收集保存,再由专业软件处理。由于这类仪器非常昂贵,系统体积也比较大,软件更新快,现在只能用在科学研究上,根本无法用于有规模的实验教学,更不可能一人一机。为此,提出了一种基于LABVIEW的脑电信号虚拟采集系统设计方法,使脑电收集与分析可以广泛地应用于教学。该方法首先对脑电信号虚拟采集系统的硬件进行构造,然后以硬件构造为依据,利用AR模型功率谱估计对脑电信号进行特征提取,在特征提取过程中,对模型类型与模型系数算法以及模型最佳阶数进行分析,最后通过将二阶低通滤波器与二阶高通滤波器进行串联,形成4阶Bessel带通滤波器,实现脑电信号的滤波,并以脑电信号传输电路的设计完成脑电信号虚拟采集系统的设计。实验结果证明,所提方法可以快速地对脑电信号虚拟采集系统进行设计,并为该领域的研究发展提供支撑。#$NL关键词：LABVIEW;脑电信号;虚拟采集系统;     

基于变分模态分解-相干分析的肌间耦合特性

肌间耦合是肢体运动过程中不同肌肉间的相互关联与相互协调作用.通过研究肌电信号(s EMG)间特征频段的耦合特性可以获得肌肉间的功能联系及中枢神经系统支配肢体运动的执行与协调方式机理.本文将变分模态分解与相干分析相结合,构建变分模态分解-相干分析模型,定量描述肢体运动中相关肌肉sEMG在特征频段的耦合特性.在20%最大自主收缩力静态负荷强度下,采集20名健康被试的sEMG,基于变分模态分解方法将sEMG时频尺度化,进而分析不同sEMG在特征频段的相干性,并计算显著相干面积指标,定量分析肌间特征频段的功能耦合特性.结果表明:低负荷静态握力维持过程中,指浅屈肌与尺侧腕曲肌、指浅屈肌与指伸肌的beta与gamma频段耦合强度随时间推进而增强;相较于指浅屈肌与指伸肌,疲劳状态下指浅屈肌与尺侧腕曲肌beta与gamma频段耦合强度变化更显著,且瞬时频率特征变化相似,揭示运动致疲劳过程中协同肌受中枢神经系统控制以更加同步的方式活动.     

可将超声波转换成光信号的新型超材料

传统超声技术主要依靠将超声波转换成电信号来产生图像。几十年来，这种技术已经取得了很大的进步，但带宽和灵敏度的限制一直是超声技术产生高质量诊断图像的主要障碍。     

植物微弱电信号在线采集系统的设计

植物电信号是细胞在生命活动中发出的电磁信号,由于其信号幅值为微伏级,在采集过程中,其有效信号很容易被噪声所淹没;依据植物电位信号的高阻抗源特性以及植物电位信号采集技术的特点,选择贴片电极作为测量植物表面电位信号的传感电极,有效降低了引导电极对植物的伤害和对植物电信号的干扰;采用AD8221芯片,设计了采集放大器电路用于采集植物电位信号,并搭建了植物电信号的采集系统,整个采集系统由放大电路、A/D转换电路、MCU、MAX232和计算机组成;以芦荟为实验对象,测得12 ℃时芦荟叶片电信号幅值的最大值是0.51 mV,最小值是-0.22 mV;结果表明该采集系统能够很好地采集植物电信号,为下一步的信号分析打下了坚实的基础。     

基于MYO和Android的肌电假肢手控制系统设计与实现*

针对目前假肢手控制系统成本高、操作不灵活、实用性差等问题,设计了一种基于MYO和Android的肌电假肢手控制系统。在Android平台上,开发了一款智能终端应用,实现了对MYO臂环采集的表面肌电信号进行数据处理和模式识别,并实时控制假肢手完成五种模式。实验结果表明,系统的在线识别率可达98.2%,并可在300ms左右完成一次识别过程,满足了假肢手控制的精度和实时性要求。该系统设计成本低廉、方便携带且易于扩展,很好地满足了截肢患者对假肢手控制的需求。     

超声技术的基石——超声换能器的原理及设计

超声换能器是在超声频率范围内将交变的电信号转换成声信号或者将外界声场中的声信号转换为电信号的能量转换器件,它是超声技术中的关键器件,其性能好坏直接关系到超声应用技术的效果和使用范围.由于超声技术的应用范围很广,且超声新技术层出不穷,因而与此对应的超声换能器的种类也很多.文章对不同应用背景下多种类型超声换能器的原理及设计进行了阐述,分析了不同类型超声换能器的性能参数及设计要求,简要总结了超声换能器的性能参数测试方法,并对超声换能器的发展趋势进行了一定的分析.     

基于sEMG的特征包络线提取与动作识别研究

针对表面肌电信号模式识别在康复器械以及智能假肢中的应用问题,通过平方调解法来提取多通道sEMG特征包络线,以提高手指动作识别速率与正确率;首先将手指动作采集实验获取的表面肌电信号进行平方处理,再经低通滤波形成包络线;利用幅值乘方法对不同的动作类型的包络线进行处理并形成学习用的教师样本标签,最后通过BP神经网络完成动作的识别分类;实验结果显示,屈拇指、屈食指、屈中指、屈无名指、屈小指和屈五指这6种动作的平均识别正确率为94.93%,每次动作识别的平均延时为50.7 ms。     

Quantitative assessment of skeletal muscle activation using muscle functional MRI

The purpose of the present study is to determine whether muscle functional MRI (mfMRI) can be used to obtain three-dimensional (3-D) images useful for evaluating muscle activity, and if so, to measure the distribution of muscle activity within a medial gastrocnemius (MG) muscle. Seven men performed 5 sets of 10 repetitions of a calf-raise exercise with additional 15% of body-weight load. Magnetic resonance images were obtained before and immediately after the exercise. To threshold images, only those pixels showing transverse relaxation time (T2) greater than the mean+1 S.D. of the entire regions of interest (ROIs) in the preexercise image and T2 lower than the mean+1 S.D. of the entire ROIs in the postexercise image were identified. The survived pixels showing T2 are defined as active muscle. Those thresholded images were 3-D reconstructed, and this was used to determine area of active muscle along transverse, longitudinal and vertical axes. At the exercise level used in the present study, the percentage volume of activated muscle in the MG was 62.8+/-4.5%. There was a significant correlation between percentage volume of activated muscle and integrated electromyography (r=.78, P<.05). Percentage areas of activated muscle were significantly larger in the medial than in the lateral region, in the anterior than in the posterior region and in the distal than in the proximal region (P<.05). These results suggest that mfMRI can be used to evaluate the muscle activity and to determine intramuscular variations of activity within skeletal muscle.     

Shadow effects in simulated ultrasound images derived from computed tomography images using a focused beam tracing model

Simulation of ultrasound images based on computed tomography (CT) data has previously been performed with different approaches. Shadow effects are normally pronounced in ultrasound images, so they should be included in the simulation. In this study, a method to capture the shadow effects has been developed, which makes the simulated ultrasound images appear more realistic. The method using a focused beam tracing model gives diffuse shadows that are similar to the ones observed in measurements on real objects. Ultrasound images of a cod (Gadus morhua) were obtained with a BK Medical 2202 ProFocus ultrasound scanner (BK Medical, Herlev, Denmark) equipped with a dedicated research interface giving access to beamformed radio frequency data. CT images were obtained with an Aquilion ONE Toshiba CT scanner (Toshiba Medical Systems Corp., Tochigi, Japan). CT data were mapped from Hounsfield units to backscatter strength, attenuation coefficients, and characteristic acoustic impedance. The focused beam tracing model was used to create maps of the transmission coefficient and scattering strength maps. Field II was then used to simulate an ultrasound image of 38.9 × 55.3 × 4.5 mm, using 10(6) point scatterers. As there is no quantitative method to assess quality of a simulated ultrasound image compared to a measured one, visual inspection was used for evaluation.     

A method to obtain reference images for evaluation of ultrasonic tissue characterization techniques

A general problem when evaluating ultrasonic methods for tissue characterization is that "a golden standard" is seldom known. This paper describes a manual method to obtain a reference image, with the same geometry as the ultrasound image, indicating spatial location of the different tissue types present in the biological tissue scanned in vitro. A 30 x 10 x 2 mm3 piece of formalin fixed porcine tissue was molded into an agar block, which on the top surface, contained a set of fiducial markers, spaced 2.5 mm. The block was submerged into 20 degrees C water and a set of parallel 7.5 MHz spatial compound ultrasound images of tissue and fiducial markers were recorded each 0.5 mm. Guided by the fiducial markers, the agar block was subsequently cut into slices 2.5 mm thick, photographed and finally analyzed histologically identifying these tissues: collagen rich, collagen poor, micro vessels and muscle fibres. Due to: (1) the cutting procedure, (2) the finite size of the ultrasound beam and (3) the spatial variation in propagation velocity, the macroscopic photographs did not align completely with the ultrasound images. Likewise, the histological image is a geometrically distorted version of the macroscopic photograph, due to the histological preparation process. The histological information was "mapped back" into the format of the ultrasound images the following way: On the macroscopic images, outlines were drawn manually which defined the border of the tissue. These outlines were superimposed on the corresponding ultrasound images (identified via the fiducial markers) and modified to encompass what appeared to be tissue regions on the ultrasound images and subsequently re-applied to the macroscopic image. This modified macroscopic outline was used as guideline when drawing outlines identifying regions of the various tissue types. Specifically, the macroscopic image revealed the borders between the different tissues, while the histological image identified the four tissue types. A set of 12 reference images based on modified macroscopic outlines was created. The overlap between the ultrasound images and the macroscopic images--which are the geometrical basis for the final reference images--was between 77% and 93%. A set of 12 reference images spaced 2.5 mm, identifying spatial location of four different tissue types in porcine muscle has been created. With the reference images, it is possible to quantitatively compare different ultrasound based tissue classification techniques.     

Experimental evaluation of an ultrasound technique for the biometric recognition of human hand anatomic elements

In this work the moving ultrasound linear array technique has been used to perform 3D echographic images of different human hands, in order to evaluate this technique to biometric recognition purposes. An automated set up, based on a commercial echographic machine provided with a high frequency (12 MHz) linear array, has been built up. The probe is moved in the direction orthogonal to the array and at each step a B-scan is performed and stored to form a 3D matrix representing the under skin hand volume.B-scan and C-scan images of the hand of different users were analysed and compared. The results have shown that, in the analysed region (about 10 mm under the palm skin), there are several anatomic elements (including hand bones, bending tendons, muscle tissue, blood vessels) that can be exploited for measurements of biometric parameters.The characteristics of the proposed technique are compared with those of the 2D optical hand geometry, which is a well established biometric technique, and its possible advantages are underlined and discussed.     

Stiffness change of the supraspinatus muscle can be detected by magnetic resonance elastography

Magnetic resonance elastography (MRE) and ultrasound shear wave elastography (SWE) are imaging techniques to measure stiffness of the soft tissue using magnetic resonance imaging (MRI) and ultrasound images, respectively. The purpose of this study was to explore the feasibility of the MRE measurement to evaluate the change in supraspinatus (SSP) muscle stiffness before and after rotator cuff tear, and to compare the result with those of SWE. Six swine shoulders were used. The skin and subcutaneous fat were removed, and the stiffness value of the SSP muscle was measured by MRE and SWE. The MRE measurement was performed with 0.3 T open MRI and the vibration from a pneumatic driver system with active driver to a passive driver to create the shear wave in the tissue. The passive driver was placed on the center of the SSP muscle. The stiffness was estimated from the wave images using local frequency estimation methods. In the SWE measurement, the probe of the ultrasound was placed on the center of the SSP muscle. The shear wave propagation speed was measured at a depth of 1 cm from the surface, and the stiffness was calculated. After those measurements, the rotator cuff tendon was detached from the greater tuberosity, and MRE and SWE measurements were then performed in the same manner again. The differences in the stiffness values were compared between before and after the rotator cuff tendon tear on both the MRE and SWE measurements. The results indicated that stiffness values on MRE and SWE were 9.3 ± 1.8 and 10.0 ± 1.2 kPa respectively before the rotator cuff tear, and 7.3 ± 1.3 and 8.0 ± 0.8 kPa respectively after the tendon detachment. Stiffness values were significantly lower after the tendon detachment on both the MRE and SWE measurements (p < 0.05). Our results demonstrated that stiffness values of the SSP muscle on MRE and SWE were lower after rotator cuff detachment. From this result, MRE may be a feasible method for quantification of the change in rotator cuff muscle stiffness.     

Differential ultrasonic imaging for the characterization of lesions induced by high intensity focused ultrasound

High intensity focused ultrasound (HIFU) is an effective technique for noninvasive local creating coagulative necrotic lesions in deep target volumes without damage to the overlaying or surrounding tissues. It is very important to detect and evaluate lesions generated by HIFU during treatment procedures. This study describes the development of several differential ultrasonic imaging techniques to characterize lesions based on estimation of relative changes in tissue properties derived from backscattered RF data. A single, spherical HIFU transducer was used to produce lesions in soft tissues. The RF signals were recorded as outputs from a modified diagnostic ultrasound system. After some preprocessing, the integrated backscatter values, which can be used as an indicator of the microstructure and backscattering property of tissues, were calculated before and after HIFU treatment. The differential integrated backscatter values were subsequently used to form images revealing the lesion areas. The differential attenuation imaging with the same RF data was also performed, which has been proposed by a few researchers. The results of the differential integrated backscatter imaging were compared with that of the differential attenuation imaging and the former method offers some advantages over the latter method. The two methods above are both based on spectrum analysis and would spend much computational time. Therefore, some simple digital differential imaging methods, including absolute difference (AD), sum absolute differences (SAD), and sum squared differences (SSD) algorithms, were also proposed to detect HIFU-induced lesions. However, these methods cannot provide the information of the degree of tissue damage. Experiments in vitro bovine muscle and liver validated the method of differential integrated backscatter imaging for the characterization of HIFU-induced lesions. And the AD, SAD, and SSD algorithms can be implemented in real-time during HIFU therapy to visualize the lesions.     

Estimation and visualization of longitudinal muscle motion using ultrasonography: A feasibility study

Ultrasonography is a convenient and widely used technique to look into the longitudinal muscle motion as it is radiation-free and real-time. The motion of localized parts of the muscle, disclosed by ultrasonography, spatially reflects contraction activities of the corresponding muscles. However, little attention was paid to the estimation of longitudinal muscle motion, especially towards estimation of dense deformation field at different depths under the skin. Yet fewer studies on the visualization of such muscle motion or further clinical applications were reported in the literature. A primal–dual algorithm was used to estimate the motion of gastrocnemius muscle (GM) in longitudinal direction in this study. To provide insights into the rules of longitudinal muscle motion, we proposed a novel framework including motion estimation, visualization and quantitative analysis to interpret synchronous activities of collaborating muscles with spatial details. The proposed methods were evaluated on ultrasound image sequences, captured at a rate of 25 frames per second from eight healthy subjects. In order to estimate and visualize the GM motion in longitudinal direction, each subject was asked to perform isometric plantar flexion twice. Preliminary results show that the proposed visualization methods provide both spatial and temporal details and they are helpful to study muscle contractions. One of the proposed quantitative measures was also tested on a patient with unilateral limb dysfunction caused by cerebral infarction. The measure revealed distinct patterns between the normal and the dysfunctional lower limb. The proposed framework and its associated quantitative measures could potentially be used to complement electromyography (EMG) and torque signals in functional assessment of skeletal muscles.     

Improvement of ultrasound speckle image velocimetry using image enhancement techniques

Ultrasound-based techniques have been developed and widely used in noninvasive measurement of blood velocity. Speckle image velocimetry (SIV), which applies a cross-correlation algorithm to consecutive B-mode images of blood flow has often been employed owing to its better spatial resolution compared with conventional Doppler-based measurement techniques. The SIV technique utilizes speckles backscattered from red blood cell (RBC) aggregates as flow tracers. Hence, the intensity and size of such speckles are highly dependent on hemodynamic conditions. The grayscale intensity of speckle images varies along the radial direction of blood vessels because of the shear rate dependence of RBC aggregation. This inhomogeneous distribution of echo speckles decreases the signal-to-noise ratio (SNR) of a cross-correlation analysis and produces spurious results. In the present study, image-enhancement techniques such as contrast-limited adaptive histogram equalization (CLAHE), min/max technique, and subtraction of background image (SB) method were applied to speckle images to achieve a more accurate SIV measurement. A mechanical sector ultrasound scanner was used to obtain ultrasound speckle images from rat blood under steady and pulsatile flows. The effects of the image-enhancement techniques on SIV analysis were evaluated by comparing image intensities, velocities, and cross-correlation maps. The velocity profiles and wall shear rate (WSR) obtained from RBC suspension images were compared with the analytical solution for validation. In addition, the image-enhancement techniques were applied to in vivo measurement of blood flow in human vein. The experimental results of both in vitro and in vivo SIV measurements show that the intensity gradient in heterogeneous speckles has substantial influence on the cross-correlation analysis. The image-enhancement techniques used in this study can minimize errors encountered in ultrasound SIV measurement in which RBCs are used as flow tracers instead of exogenous contrast agents.     

Development of a 64 channel ultrasonic high frequency linear array imaging system

In order to improve the lateral resolution and extend the field of view of a previously reported 48 element 30 MHz ultrasound linear array and 16-channel digital imaging system, the development of a 256 element 30 MHz linear array and an ultrasound imaging system with increased channel count has been undertaken. This paper reports the design and testing of a 64 channel digital imaging system which consists of an analog front-end pulser/receiver, 64 channels of Time-Gain Compensation (TGC), 64 channels of high-speed digitizer as well as a beamformer. A Personal Computer (PC) is used as the user interface to display real-time images. This system is designed as a platform for the purpose of testing the performance of high frequency linear arrays that have been developed in house. Therefore conventional approaches were taken it its implementation. Flexibility and ease of use are of primary concern whereas consideration of cost-effectiveness and novelty in design are only secondary. Even so, there are many issues at higher frequencies but do not exist at lower frequencies need to be solved. The system provides 64 channels of excitation pulsers while receiving simultaneously at a 20–120 MHz sampling rate to 12-bits. The digitized data from all channels are first fed through Field Programmable Gate Arrays (FPGAs), and then stored in memories. These raw data are accessed by the beamforming processor to re-build the image or to be downloaded to the PC for further processing. The beamformer that applies delays to the echoes of each channel is implemented with the strategy that combines coarse (8.3 ns) and fine delays (2 ns). The coarse delays are integer multiples of the sampling clock rate and are achieved by controlling the write enable pin of the First-In-First-Out (FIFO) memory to obtain valid beamforming data. The fine delays are accomplished with interpolation filters. This system is capable of achieving a maximum frame rate of 50 frames per second. Wire phantom images acquired with this system show a spatial resolution of 146 μm (lateral) and 54 μm (axial). Images with excised rabbit and pig eyeball as well as mouse embryo were also acquired to demonstrate its imaging capability.     

A comparison of HIFU-induced lesion size measurement based on gross histological examination and image of bovine thigh in vitro

The aim of this study was to investigate the agreement in HIFU-induced lesion sizes between measurements based on gross histological examination and those from images. Experiments were conducted in an experimental arrangement with a three-way multiscan ultrasonic inspection system and imaging was done by B-mode ultrasound (US). Bovine thigh muscle with and without fascia lata was treated with an in situ spatially averaged focal intensity ranging between 750 W cm(-2) and 1565 W cm(-2) and sonication-time was variable from 8 to 20s. Assessment of the two measurement methods showed a rather weak correlation in the samples without fascia lata. For clarity and convenience in the discussion, sample muscles with and without fascia lata were labeled F and M, respectively. It was difficult to measure the lesion size from ultrasonographic images of F samples, so there was disagreement in the samples with fascia lata. This investigation showed that the presence of fascia lata in bovine thigh muscle has the likely effect of affecting the ultrasound image and makes it difficult to distinguish coagulated tissue from surrounding healthy tissue. There was no significant correlation between ultrasonography and the gross histological findings in M samples. Data supported that at for an in situ spatially averaged focal intensity ranging between 750 W cm(-2) and 1565 W cm(-2) and relatively shorter exposures (sonication-time variable from 1 to 8s) higher correlation between image and gross histology measurement was found in excised bovine muscle specimens.