眼内肿瘤超声弹性成像的鉴别诊断价值

目的:探讨眼内肿瘤超声弹性成像的鉴别诊断价值。方法:回顾性分析50例(55眼)眼内肿瘤患者的临床资料,对患者病变眼实施二维超声,彩色多普勒超声以及超声弹性成像检查,对肿瘤和周围正常组织之间的应变率比值进行测算,并参考临床诊断结果,对不同类型肿瘤所具备的应变率比值进行计算。结果:脉络膜黑色素瘤、脉络膜转移癌与视网膜母细胞瘤的应变率比值分别为(42.16±17.77)、(49.58±5.11)、(48.17±11.68),差异无统计学意义(P0.05),但均高于脉络膜血管瘤的应变率比值(14.35±5.11),差异有统计学意义(P0.05)。结论:眼内良性与恶性肿瘤间存在明显硬度差,因此超声弹性成像可有效鉴别眼内肿瘤的良恶性。     

不同扩散敏感系数颈髓白质纤维束磁共振扩散张量成像分析

目的:对不同扩散敏感系数b值对正常人颈髓白质纤维束磁共振扩散张量成像进行实际分析,为此方法的合理应用提供依据,并对各向异性进行探讨。方法:将27例经过检查正常的健康志愿者,将其分为2组,颈髓白质纤维束扩散张量成像用单次激发自旋回波(SE-EPI)序列进行检测。并利用DTI对白质纤维束成像。颈髓的各个节段的各向异性分数值用不同的扩散敏感系数即b值测得,用统计学方法分析所得颈髓各节段的FA值。结果:当采用b=300s/mm2时,测得颈髓矢状位成像FA均值为0.6582±0.0704,横轴位成像所得FA均值为0.7685±0.0586;当采用b=600s/mm2时,测得颈髓矢状位成像FA均值为0.6585±0.0736,横轴位成像FA均值为0.7784±0.0651。同组矢状位颈髓FA的均值要小于横轴位颈髓FA的均值,要偏大,其差异是具有统计学意义的(p<0.05)。结论:当b值为300s/mm2时的FA优于当b值为600s/mm2,其能够反映出各个节段白质纤维的各项异性,白质纤维束的三维成像能够反映出其分布和走向,为临床推广和使用提供依据。     

壳聚糖即型水凝胶的理化性质、止血功能和生物相容性研究

报道了壳聚糖即型水凝胶,通过红外光谱和扫描电镜对该水凝胶进行了结构分析与表征,测定了其基本理化性质,并探讨了其止血功能和生物安全性。该水凝胶的红外光谱证实了西弗碱反应的发生,证明该水凝胶是由羟丙基壳聚糖和改性海藻酸钠交联而成;SEM照片显示该水凝胶的骨架是连续均一的蜂窝状网络结构;该水凝胶成胶迅速,最短成胶时间为10s,凝胶强度约为50g/cm2,溶胀率约为14.7%,pH值为7.5。在大鼠肝脏损伤出血模型的止血实验中,壳聚糖水凝胶具有优异的止血功能,止血时间和出血量均优于空白对照组(P0.01),与纤维蛋白胶组无显著性差异(P0.05)。壳聚糖水凝胶对细胞生长无明显抑制作用,其在体内降解伴随着组织炎症反应,炎症反应程度随材料的降解而减轻。     

基于有效耗能的改进Park-Ang双参数损伤模型及其计算研究

Park-Ang双参数地震损伤模型考虑了地震作用的首次超越破坏与累积损伤破坏两方面因素,较好的定义了结构的破坏,被后续研究广泛应用,但无法区分不同幅值作用下结构破坏的差异。分析了不同位移幅值下钢筋混凝土柱的破坏特点,研究了结构损伤与结构耗能之间的关系。试验表明弹性阶段(位移幅值小于一倍屈服位移)的试件几乎不发生破坏,造成钢筋混凝土柱破坏的能量集中在相持阶段和破坏阶段,定义非弹性阶段引起结构破坏的滞回耗能为导致结构破坏的有效耗能。基于有效耗能假设引入有效耗能因子e,提出了改进的Park-Ang双参数地震损伤模型。对建议模型进行了21组钢筋混凝土柱的试验数据验证,计算结果表明:有效耗能因子可以反映相同耗能下不同位移幅值引起的结构破坏差异,有效耗能因子e物理意义明确,改进后的双参数地震损伤模型计算精度高,离散性小,能够区分不同位移幅值下钢筋混凝土柱的破坏差异,较好地评估了RC结构的损伤性能。     

腹主动脉CT血管成像的低剂量对比剂应用分析

目的:探讨腹主动脉CT血管成像的低剂量对比剂的应用价值。方法:选取行腹主动脉CT血管成像检查的患者63例,依据对比剂量及注射流速的不同,分为3组,均应用碘海醇,A组对比剂用量为90ml,生理盐水20ml,注射流率4ml/s,B组和C组对比剂剂量和流率按照公式获得。比较各组腹主动脉及其分支的CT值、肾动脉及其分支的评分。结果:三组患者腹主动脉内CT值、腹腔干内CT比较差异显著(P0.05);A组患者对比剂用量为90ml,B组与C组对比剂用量分别为(51±8)ml、(40±8)ml,差异显著(P0.05)。结论:腹主动脉CT血管呈现低剂量对比剂的临床应用效果显著,应用个体化注射方式可在满足临床诊断的前提下,最大程度上减少对比剂的使用剂量。     

医学超声成像中近场相位屏模型的研究

0引言医学超声成像中存在着相位畸变问题,主要原因是由于人体组织中声速分布的不均匀性,如脂肪中的声速大约为1470m/s,而胶原组织中的声速约为1665m/s,颅骨中的声速介于2060 m/s到3360 m/s之间[1]。而我们在设计超声成像系统时,大都假定声速在人体组织中的传播速度均为固定不变的数值(通常取1540 m/s)。当超声波在人体内传播时,由于波前经过的路径不同而产生了相位畸变,使得     

肝脏三维重建技术应用于精准肝脏外科中的价值分析

目的:探讨肝脏三维重建技术应用于精准肝脏外科中的价值。方法:将我院2019年2月至2020年4月期间80例肝癌患者分组,按照随机数字表法分为对照组40例,采用CT检查;观察组40例,采用肝脏三维重建技术成像,观察两组临床效果、围术期状况、炎症水平及免疫功能。结果:观察组总有效率(95.00%)高于对照组(75.00%)(P0.05);观察组手术时间及肝门阻断时间与对照组对比无统计学差异(P0.05),住院时间及下床活动时间短于对照组,术中出血量少于对照组(P0.05);观察组IgG、IgM、IgA水平均高于对照组(P0.05);观察组CD8~+水平低于对照组,CD4~+及CD3~+水平均高于对照组(P0.05)。结论:肝脏三维重建技术应用于精准肝脏外科中可显著改善患者围术期状况,降低炎症水平,提高免疫功能,从而提高临床效果。     

基于脑微结构信息检测的扩散峭度成像多b值组合优化

扩散峭度成像(DKI)引入高阶峭度张量来量化水分子扩散的非高斯程度,并可采用多种扩散敏感因子b值参与模型拟合,能反映组织复杂结构更微小变化,因而在脑神经科学研究与临床诊断中具有独特优势.但目前尚缺乏不同b值组合DKI数据采集对不同脑微结构特征的比较分析和针对不同临床需求制定DKI数据采集的最优b值组合方案的思路.本文从脑脊液、灰质和白质的DKI图像对比度角度,结合基于体素统计分析方法比较了5个不同b值组合与高、低2个b值组合采集方案对DKI成像指标的影响及在胼胝体局部组织微结构特征表达的差异.结果表明,低b值(1 000 s/mm~2)和高b值(2 000 s/mm~2)采集成像皆有较强的组织分辨能力,而过多增加b值组合个数会增大拟合误差并增加采集时间;使用高、低2个b值(2 000 s/mm~2与1 000 s/mm~2)的组合采集方案较适合于一般DKI临床诊断.     

不同体重正常SD大鼠肝脏血流动力学的超声观察

目的:该研究旨在用高频超声观察SD大鼠体重对门静脉内径、门静脉及肝固有动脉血流动力学的影响。方法:按体重将100只SD大鼠分为两组,A组:200~300 g;B组:300~400 g。采用5.0~12.0 MHz超声探头测定大鼠门静脉内径,门静脉最大血流速度及肝固有动脉收缩期血流峰值速度、舒张期末血流速度及阻力指数。结果:A组SD大鼠门静脉内径(0.172±0.030)cm;B组SD大鼠门静脉内径(0.189±0.030)cm。门静脉内径在不同体重间存在显著差异(P0.01)。门静脉流速、肝固有动脉收缩期最大峰值流速、舒张期末流速及阻力差异无统计学意义。结论:在大鼠肝脏疾病模型的观测和评估实验中,动物体重应尽可能一致。     

孔隙对碳/环氧层压板层间剪切强度影响的神经网络预测(英文)

采用一种新的方法研究了孔隙(孔隙率、孔隙形状和尺寸)对复合材料层压板[(±45)4/(0,90)/(±45)2]S,[(±45)/(0,90)2/(±45)]S和[(±45)/04/(0,90)/02]S的层间剪切强度影响的非线性关系。建立了了一个四层前馈型BP网络神经网络。采用真空袋和热压罐技术制备了含不同孔隙率的复合材料层压板。神经网络的算法为Levenberg-Marquardt算法。研究结果表明:Levenberg-Marquardt算法的预测能力较高,即,92%的B(决定系数)值大于0.9。而且,神经网络的结构会影响不同孔隙率的环氧树脂基复合材料的层间剪切强度的预测结果。     

On the thermal effects associated with radiation force imaging of soft tissue

Several laboratories are investigating the use of acoustic radiation force to image the mechanical properties of tissue. Acoustic Radiation Force Impulse (ARFI) imaging is one approach that uses brief, high-intensity, focused ultrasound pulses to generate radiation force in tissue. This radiation force generates tissue displacements that are tracked using conventional correlation-based ultrasound methods. The tissue response provides a mechanism to discern mechanical properties of the tissue. The acoustic energy that is absorbed by tissue generates radiation force and tissue heating. A finite element methods model of acoustic heating has been developed that models the thermal response of different tissues during short duration radiation force application. The beam sequences and focal configurations used during ARFI imaging are modeled herein; the results of these thermal models can be extended to the heating due to absorption associated with other radiation force-based imaging modalities. ARFI-induced thermal diffusivity patterns are functions of the transducer f-number, the tissue absorption, and the temporal and spatial spacing of adjacent ARFI interrogations. Cooling time constants are on the order of several seconds. Tissue displacement due to thermal expansion is negligible for ARFI imaging. Changes in sound speed due to temperature changes can be appreciable. These thermal models demonstrate that ARFI imaging of soft tissue is safe, although thermal response must be monitored when ARFI beam sequences are being developed.     

Rapid tracking of small displacements with ultrasound

Time-delay estimators, such as normalized cross correlation and phase-shift estimation, form the computational basis for elastography, blood flow measurements, and acoustic radiation force impulse (ARFI) imaging. This paper examines the performance of these algorithms for small displacements (less than half the ultrasound pulse wavelength). The effects of noise, bandwidth, stationary echoes, kernel size, downsampling, interpolation, and quadrature demodulation on the accuracy of the time delay estimates are measured in terms of bias and jitter. Particular attention is given to the accuracy and resolution of the displacement measurements and to the computational efficiency of the algorithms. In most cases, Loupas' two-dimensional (2-D) autocorrelator performs as well as the gold standard, normalized cross correlation. However, Loupas' algorithm's calculation time is significantly faster, and it is particularly suited to operate on the signal data format most commonly used in ultrasound scanners. These results are used to implement a real-time ARFI imaging system using a commercial ultrasound scanner and a computer cluster. Images processed with the algorithms are examined in an ex vivo liver ablation study.     

A finite-element method model of soft tissue response to impulsive acoustic radiation force

Several groups are studying acoustic radiation force and its ability to image the mechanical properties of tissue. Acoustic radiation force impulse (ARFI) imaging is one modality using standard diagnostic ultrasound scanners to generate localized, impulsive, acoustic radiation forces in tissue. The dynamic response of tissue is measured via conventional ultrasonic speckle-tracking methods and provides information about the mechanical properties of tissue. A finite-element method (FEM) model has been developed that simulates the dynamic response of tissues, with and without spherical inclusions, to an impulsive acoustic radiation force excitation from a linear array transducer. These FEM models were validated with calibrated phantoms. Shear wave speed, and therefore elasticity, dictates tissue relaxation following ARFI excitation, but Poisson's ratio and density do not significantly alter tissue relaxation rates. Increased acoustic attenuation in tissue increases the relative amount of tissue displacement in the near field compared with the focal depth, but relaxation rates are not altered. Applications of this model include improving image quality, and distilling material and structural information from tissue's dynamic response to ARFI excitation. Future work on these models includes incorporation of viscous material properties and modeling the ultrasonic tracking of displaced scatterers.     

On the effects of reflected waves in transient shear wave elastography

In recent years, novel quantitative techniques have been developed to provide noninvasive and quantitative stiffness images based on shear wave propagation. Using radiation force and ultrafast ultrasound imaging, the supersonic shear imaging technique allows one to remotely generate and follow a transient plane shear wave propagating in vivo in real time. The tissue shear modulus, i.e., its stiffness, can then be estimated from the shear wave local velocity. However, because the local shear wave velocity is estimated using a time-of- flight approach, reflected shear waves can cause artifacts in the estimated shear velocity because the incident and reflected waves propagate in opposite directions. Such effects have been reported in the literature as a potential drawback of elastography techniques based on shear wave speed, particularly in the case of high stiffness contrasts, such as in atherosclerotic plaque or stiff lesions. In this letter, we present our implementation of a simple directional filter, previously used for magnetic resonance elastography, which separates the forward- and backward-propagating waves to solve this problem. Such a directional filter could be applied to many elastography techniques based on the local estimation of shear wave speed propagation, such as acoustic radiation force imaging (ARFI), shearwave dispersion ultrasound vibrometry (SDUV), needle-based elastography, harmonic motion imaging, or crawling waves when the local propagation direction is known and high-resolution spatial and temporal data are acquired.     

Assessing and improving acoustic radiation force image quality using a 1.5-D transducer design

A 1.5-D transducer array was proposed to improve acoustic radiation force impulse (ARFI) imaging signal-to-noise ratio (SNRARFI) and image contrast relative to a conventional 1-D array. To predict performance gains from the proposed 1.5-D transducer array, an analytical model for SNRARFI upper bound was derived. The analytical model and 1.5-D ARFI array were validated using a finite element modelbased numerical simulation framework. The analytical model demonstrated good agreement with numerical results (correlation coefficient = 0.995), and simulated lesion images yielded a significant (2.92 dB; p < 0.001) improvement in contrast-tonoise ratio when rendered using the 1.5-D ARFI array.     

Image quality, tissue heating, and frame rate trade-offs in acoustic radiation force impulse imaging

The real-time application of acoustic radiation force impulse (ARFI) imaging requires both short acquisition times for a single ARFI image and repeated acquisition of these frames. Due to the high energy of pulses required to generate appreciable radiation force, however, repeated acquisitions could result in substantial transducer face and tissue heating. We describe and evaluate several novel beam sequencing schemes which, along with parallel-receive acquisition, are designed to reduce acquisition time and heating. These techniques reduce the total number of radiation force impulses needed to generate an image and minimize the time between successive impulses. We present qualitative and quantitative analyses of the trade-offs in image quality resulting from the acquisition schemes. Results indicate that these techniques yield a significant improvement in frame rate with only moderate decreases in image quality. Tissue and transducer face heating resulting from these schemes is assessed through finite element method modeling and thermocouple measurements. Results indicate that heating issues can be mitigated by employing ARFI acquisition sequences that utilize the highest track-to-excitation ratio possible.     

A parallel tracking method for acoustic radiation force impulse imaging

Radiation force-based techniques have been developed by several groups for imaging the mechanical properties of tissue. Acoustic Radiation Force Impulse (ARFI) imaging is one such method that uses commercially available scanners to generate localized radiation forces in tissue. The response of the tissue to the radiation force is determined using conventional B-mode imaging pulses to track micron-scale displacements in tissue. Current research in ARFI imaging is focused on producing real-time images of tissue displacements and related mechanical properties. Obstacles to producing a real-time ARFI imaging modality include data acquisition, processing power, data transfer rates, heating of the transducer, and patient safety concerns. We propose a parallel receive beamforming technique to reduce transducer heating and patient acoustic exposure, and to facilitate data acquisition for real-time ARFI imaging. Custom beam sequencing was used with a commercially available scanner to track tissue displacements with parallel-receive beamforming in tissue-mimicking phantoms. Using simulations, the effects of material properties on parallel tracking are observed. Transducer and tissue heating for parallel tracking are compared to standard ARFI beam sequencing. The effects of tracking beam position and size of the tracked region are also discussed in relation to the size and temporal response of the region of applied force, and the impact on ARFI image contrast and signal-to-noise ratio are quantified.     

Acoustic radiation force impulse imaging of myocardial radiofrequency ablation: initial in vivo results

Acoustic radiation force impulse (ARFI) imaging techniques were used to monitor radiofrequency (RF) ablation of ovine cardiac tissue in vivo. Additionally, ARFI M-mode imaging methods were used to interrogate both healthy and ablated regions of myocardial tissue. Although induced cardiac lesions were not visualized well in conventional B-mode images, ARFI images of ablation procedures allowed determination of lesion location, shape, and relative size through time. The ARFI M-mode images were capable of distinguishing differences in behavior through the cardiac cycle between healthy and damaged tissue regions. As conventional sonography is often used to guide ablation catheters, ARFI imaging, which requires no additional equipment, may be a convenient modality for monitoring lesion formation in vivo.     

GPU-based real-time small displacement estimation with ultrasound

General purpose computing on graphics processing units (GPUs) has been previously shown to speed up computationally intensive data processing and image reconstruction algorithms for computed tomography (CT), magnetic resonance (MR), and ultrasound images. Although some algorithms in ultrasound have been converted to GPU processing, many investigative ultrasound research systems still use serial processing on a single CPU. One such ultrasound modality is acoustic radiation force impulse (ARFI) imaging, which investigates the mechanical properties of soft tissue. Traditionally, the raw data are processed offline to estimate the displacement of the tissue after the application of radiation force. It is highly advantageous to process the data in real-time to assess their quality and make modifications during a study. In this paper, we present algorithms for efficient GPU parallel processing of two widely used tools in ultrasound: cubic spline interpolation and Loupas' two-dimensional autocorrelator for displacement estimation. It is shown that a commercially available graphics card can be used for these computations, achieving speed increases up to 40x compared with single CPU processing. Thus, we conclude that the GPU-based data processing approach facilitates real-time (i.e., <1 second) display of ARFI data and is a promising approach for ultrasonic research systems.     

Lower-limb vascular imaging with acoustic radiation force elastography: Demonstration of in vivo feasibility

Acoustic radiation force impulse (ARFI) imaging characterizes the mechanical properties of tissue by measuring displacement resulting from applied ultrasonic radiation force. In this paper, we describe the current status of ARFI imaging for lower-limb vascular applications and present results from both tissue-mimicking phantoms and in vivo experiments. Initial experiments were performed on vascular phantoms constructed with polyvinyl alcohol for basic evaluation of the modality. Multilayer vessels and vessels with compliant occlusions of varying plaque load were evaluated with ARFI imaging techniques. Phantom layers and plaque are well resolved in the ARFI images, with higher contrast than B-mode, demonstrating the ability of ARFI imaging to identify regions of different mechanical properties. Healthy human subjects and those with diagnosed lower-limb peripheral arterial disease were imaged. Proximal and distal vascular walls are well visualized in ARFI images, with higher mean contrast than corresponding B-mode images. ARFI images reveal information not observed by conventional ultrasound and lend confidence to the feasibility of using ARFI imaging during lower-limb vascular workup.