声脉冲辐射力成像技术无创检测慢性肝纤维化的初步研究

目的探讨声脉冲辐射力成像技术（ARFI）检测慢性肝纤维化的价值。方法使用西门子超声的声脉冲辐射力成像技术检测320例受检者肝脏右叶,包括无肝病或脂肪肝的志愿者173例、乙肝病毒阳性而病理显示无肝硬化的患者84例和乙肝后病理证实肝硬化的患者63例,比较三组受检者的肝右叶感兴趣区的横向弹性参数值。结果 三组受检者的肝右叶感兴趣区弹性参数有显著差异（p〈0．001）,随着慢性肝病程度的加重,弹性参数值增加,两者有一定相关性。结论声脉冲辐射力成像技术可无创反映肝组织的弹性硬度,间接评估肝纤维化,具有潜在的临床应用价值.     

声辐射力弹性成像在腹部占位性病变中的应用进展

声辐射力成像技术是超声弹性成像新技术,能对深部脏器组织的弹性特征进行定性、定量分析,具有一定的临床应用价值.本文就声辐射力弹性成像技术在腹部占位性病变中的应用进展作一综述.     

声辐射力弹性成像:弹性成像的新发展

弹性成像作为一种重要的组织定征手段在过去20年里成为研究热点。传统的静态/准静态弹性成像难以从体外对体内通过机械方法进行有效施压,近年来研究者专注于新的远程"触诊"手段,即声辐射力弹性成像。本文对三种主要声辐射力弹性成像方法,即谐波运动成像、脉冲声辐射力成像和剪切波弹性成像的研究进行综述。     

声辐射力脉冲弹性成像技术在肝脏疾病中的应用进展

声辐射力脉冲弹性成像（acoustic radiation force impulse,ARFI）技术是近几年来推出的新型弹性成像技术,能够对组织弹性分布特征进行定性、定量评价,具有无创、快速、价廉等优势,成为目前临床研究热点之一。2013年欧洲超声医学与生物学联合会（European Federation of Societies of Ultrasound in Medicine and Biology,EFSUMB）根据成像原理不同将弹性成像技术大致分为三大类.     

声辐射力脉冲成像技术在子宫肌瘤变性与否鉴别诊断中的应用

目的 探讨声辐射力脉冲成像技术在子宫肌瘤变性与否鉴别诊断中的应用价值。 方法 回顾性分析经手术病理结果证实子宫肌瘤患者98例共115个病灶，采用声辐射力脉冲成像技术（ARFI）术前对所有子宫肌瘤进行检测，记录检测区域的常规超声声像图、应力式弹性图像、声触诊组织成像（VTI）及剪切波速（VTQ），根据手术病理结果按是否变性分变性组和未变性组，并对数据进行统计分析。 结果 变性组和未变性组子宫肌瘤内部回声无明显差异，直径大者更容易变性。变性组应力式弹性评分、面积比及VTQ值均低于未变性组，差异有统计学意义（P＜0.05）。ARFI技术判断子宫肌瘤变性与否的ROC曲线下面积为0.72，VTQ截断值为2.52m/s ，此时判断子宫肌瘤变性的敏感度、特异度和准确率分别为65.52% 、79.10%和88.69% 。ARFI技术联合应力式弹性成像评估子宫肌瘤变性与否的敏感度、特异度、阳性预测值、阴性预测值及准确率分别为86.36%、96.59%、70.37%、91.40%和90.43%。 结论 ARFI技术可以提供组织硬度的量化指标，与应力式弹性成像联合应用可显著提高诊断准确性，有助于子宫肌瘤变性与否的鉴别诊断。     

声脉冲辐射力成像技术评估慢性乙肝病毒携带者肝脏硬度的初步探讨

目的:探讨声脉冲辐射力成像技术(ARFI)检测乙肝病毒携带者肝脏硬度的价值。方法:使用西门子S2000彩色多普勒超声显像仪的声脉冲辐射力成像技术对乙肝病毒携带者106例及健康对照组62例的肝右后叶进行肝剪切波速度测定,比较两组间的肝剪切波速度值。结果:乙肝病毒携带者肝剪切波速度值明显高于对照组,差异具有统计学意义(P<0.01)。结论:声脉冲辐射力成像技术可无创反映肝组织的弹性硬度,具有潜在的临床应用价值。     

多模态超声特征结合机器学习可预测乳腺浸润导管癌中Ki-67的表达水平

目的 探讨多模态超声特征结合机器学习预测乳腺浸润导管癌中Ki-67高表达的可行性。方法 回顾性分析155例乳腺浸润导管癌患者,155个病灶经病理证实。术前行常规超声和声辐射力脉冲成像,免疫组化染色记录Ki-67的表达,将患者分为Ki-67高表达组（n=105）和低表达组（n=50）。采用Logistic回归分析得出独立危险因素,采用随机森林及Logistic回归模型预测。结果 单因素分析显示Ki-67表达与肿块最大径、边界、腋窝淋巴结状态、阻力指数、声触诊组织成像及声触诊组织定量的差异有统计学意义（P<0.05）。多因素分析结果显示,最大直径、边界、声触诊组织定量及阻力指数对Ki-67为独立危险因素。随机森林模型结果显示,Ki-67表达影响因素的重要性排序依次是最大直径、声触诊组织定量、阻力指数及边界。随机森林及Logistic回归模型预测乳腺浸润导管癌中Ki-67高表达曲线下面积分别为0.871、0.866,Ki-67值与肿块直径呈正相关关系（r=0.319,P<0.001）。结论 多模态超声特征结合机器学习可用于预测乳腺浸润导管癌Ki-67的表达水平。     

声辐射力脉冲成像技术在肝脏的应用研究进展

声辐射力脉冲成像(acoustic radiation force impulse,ARFI)技术是一种组织弹性成像的新技术,利用标准探头发射的固定频率(2.67MHz)短时程(约262ms)聚焦声脉冲,机械激发感兴趣区(ROI,最大为1cm×0.6cm)内的组织,使组织产生局灶性纵向位移。ARFI技术包括声触诊组织成     

声触诊组织量化技术在甲状腺超声诊断中的应用进展

声脉冲辐射力弹性成像(acoustic radiation force impulse imaging,ARFI)是近年来推出的超声成像新技术,声触诊组织量化技术(virtual touch tissue quantification,VTQ)是其中之一。声脉冲辐射力使组织产生纵向压缩及横向振动,间接反映组织弹性,实现了无创检测特定解剖部位的组织弹性,具有无创、准确、客观等特性。本文对ARFI在甲状腺超声诊断中的临床应用进行综述。VTQ技术可对正常甲状腺、甲状腺弥漫性病变(桥本甲状腺炎和弥漫性毒性甲状腺肿)、甲状腺良恶性结节鉴别进行定量诊断,与实时弹性成像(real time elastography,RTE)、超声造影、细针穿刺等联合应用,可进一步提高诊断准确率。     

超声弹性成像技术及其应用进展

超声弹性成像技术是近年来新兴的检查方法,通过获取有关组织弹性信息进行成像。弹性成像技术能提供占位病变的良恶性、肝脏纤维化程度、慢性疼痛性肌肉神经损伤程度等组织硬度信息。目前应用于临床的弹性成像检查方法主要有：实时组织弹性成像技术、瞬时弹性成像技术、实时剪切波弹性成像技术（剪切波弹性成像技术）、超高速剪切波成像技术及声辐射力弹性成像技术。随着越来越多的弹性成像技术被大家认识,超声诊断的准确性会更高,超声检查对病变组织硬度的测量已经进入定量诊断的新阶段。     

Magnetic Resonance Imaging for the Exploitation of Bubble-Enhanced Heating by High-Intensity Focused Ultrasound: A Feasibility Study in ex Vivo Liver

Bubble-enhanced heating (BEH) may be exploited to improve the heating efficiency of high-intensity focused ultrasound in liver and to protect tissues located beyond the focal point. The objectives of this study, performed in ex vivo pig liver, were (i) to develop a method to determine the acoustic power threshold for induction of BEH from displacement images measured by magnetic resonance acoustic radiation force imaging (MR-ARFI), and (ii) to compare temperature distribution with MR thermometry for HIFU protocols with and without BEH. The acoustic threshold for generation of BEH was determined in ex vivo pig liver from MR-ARFI calibration curves of local tissue displacement resulting from sonication at different powers. Temperature distributions (MR thermometry) resulting from “conventional” sonications (20 W, 30 s) were compared with those from “composite” sonications performed at identical parameters, but after a HIFU burst pulse (0.5 s, acoustic power over the threshold for induction of BEH). Displacement images (MR-ARFI) were acquired between sonications to measure potential modifications of local tissue displacement associated with modifications of tissue acoustic characteristics induced by the burst HIFU pulse. The acoustic threshold for induction of BEH corresponded to a displacement amplitude of approximately 50 μm in ex vivo liver. The displacement and temperature images of the composite group exhibited a nearly spherical pattern, shifted approximately 4 mm toward the transducer, in contrast to elliptical shapes centered on the natural focal position for the conventional group. The gains in maximum temperature and displacement values were 1.5 and 2, and the full widths at half-maximum of the displacement data were 1.7 and 2.2 times larger than in the conventional group in directions perpendicular to ultrasound propagation axes. Combination of MR-ARFI and MR thermometry for calibration and exploitation of BEH appears to increase the efficiency and safety of HIFU treatment.     

声脉冲辐射力成像技术在肝脏疾病中的应用

声脉冲辐射力成像(ARFI)技术是近年来新兴的超声弹性成像技术,具备定性和定量分析组织弹性的能力。本文就ARFI技术在肝脏疾病的应用现状及进展进行综述。     

Biomedical Applications of Radiation Force of Ultrasound: Historical Roots and Physical Basis

Radiation force is a universal phenomenon in any wave motion, electromagnetic or acoustic. Although acoustic and electromagnetic waves are both characterized by time variation of basic quantities, they are also both capable of exerting a steady force called radiation force. In 1902, Lord Rayleigh published his classic work on the radiation force of sound, introducing the concept of acoustic radiation pressure, and some years later, further fundamental contributions to the radiation force phenomenon were made by L. Brillouin and P. Langevin. Many of the studies discussing radiation force published before 1990 were related to techniques for measuring acoustic power of therapeutic devices; also, radiation force was one of the factors considered in the search for noncavitational, nonthermal mechanisms of ultrasonic bioeffects. A major surge in various biomedical applications of acoustic radiation force started in the 1990s and continues today. Numerous new applications emerged including manipulation of cells in suspension, increasing the sensitivity of biosensors and immunochemical tests, assessing viscoelastic properties of fluids and biological tissues, elasticity imaging, monitoring ablation of lesions during ablation therapy, targeted drug and gene delivery, molecular imaging and acoustical tweezers. We briefly present in this review the major milestones in the history of radiation force and its biomedical applications. In discussing the physical basis of radiation force and its applications, we present basic equations describing the relationship of radiation stress with parameters of acoustical fields and with the induced motion in the biological media. Momentum and force associated with a plane-traveling wave, equations for nonlinear and nonsteady-state acoustic streams, radiation stress tensor for solids and biological tissues and radiation force acting on particles and microbubbles are considered. (E-mail: armen@artannlabs.com)     

Experimental studies of the thermal effects associated with radiation force imaging of soft tissue

Many groups are studying acoustic radiation force-based imaging modalities to determine the mechanical properties of tissue. Acoustic Radiation Force Impulse (ARFI) imaging is one of these modalities that uses standard diagnostic ultrasound scanners to generate localized, impulsive, acoustic radiation force in tissue. This radiation force generates tissue displacements that are tracked using conventional correlation-based ultrasound methods. The dynamic response of tissue to this impulsive radiation force provides information about the mechanical properties of the tissue. The generation of micron-scale displacements using acoustic radiation force in tissue requires the use of high-intensity acoustic beams, and the soft tissue heating associated with these high-intensity beams must be evaluated to ensure safety when performing ARFI imaging in vivo. Experimental studies using thermocouples have validated Finite Element Method (FEM) models that simulate the heating of soft tissue during ARFI imaging. Spatial maps of heating measured with the thermocouples are in good agreement with FEM model predictions, with cooling time constants measured and modeled to be on the order of several seconds. Transducer heating during ARFI imaging has been measured to be less than 1 degrees C for current clinical implementations. These validated FEM models can now be used to simulate soft tissue heating associated with different transducers, beam spacing, focal configurations and thermal material properties. These experiments confirm that ARFI imaging of soft tissue is safe, although thermal response must be monitored when developing ARFI beam sequences for specific tissue types and organsystems.     

A finite element model of remote palpation of breast lesions using radiation force: factors affecting tissue displacement

The early detection of breast cancer reduces patient mortality. The most common method of breast cancer detection is palpation. However, lesions that lie deep within the breast are difficult to palpate when they are small. Thus, a method of remote palpation, which may allow the detection of small lesions lying deep within the breast, is currently under investigation. In this method, acoustic radiation force is used to apply localized forces within tissue (to tissue volumes on the order of 2 mm3) and the resulting tissue displacements are mapped using ultrasonic correlation based methods. A volume of tissue that is stiffer than the surrounding medium (i.e., a lesion) distributes the force throughout the tissue beneath it, resulting in larger regions of displacement, and smaller maximum displacements. The resulting displacement maps may be used to image tissue stiffness. A finite-element-model (FEM) of acoustic remote palpation is presented in this paper. Using this model, a parametric analysis of the affect of varying tissue and acoustic beam characteristics on radiation force induced tissue displacements is performed. The results are used to evaluate the potential of acoustic remote palpation to provide useful diagnostic information in a clinical setting. The potential for using a single diagnostic transducer to both generate radiation force and track the resulting displacements is investigated.     

Elastic Deformation of Soft Tissue-Mimicking Materials Using a Single Microbubble and Acoustic Radiation Force

Mechanical effects of microbubbles on tissues are central to many emerging ultrasound applications. Here, we investigated the acoustic radiation force a microbubble exerts on tissue at clinically relevant therapeutic ultrasound parameters. Individual microbubbles administered into a wall-less hydrogel channel (diameter: 25–100 µm, Young's modulus: 2–8.7 kPa) were exposed to an acoustic pulse (centre frequency: 1 MHz, pulse length: 10 ms, peak-rarefactional pressures: 0.6–1.0 MPa). Using high-speed microscopy, each microbubble was tracked as it pushed against the hydrogel wall. We found that a single microbubble can transiently deform a soft tissue-mimicking material by several micrometres, producing tissue loading–unloading curves that were similar to those produced using other indentation-based methods. Indentation depths were linked to gel stiffness. Using a mathematical model fitted to the deformation curves, we estimated the radiation force on each bubble (typically tens of nanonewtons) and the viscosity of the gels. These results provide insight into the forces exerted on tissues during ultrasound therapy and indicate a potential source of bio-effects.     

BSS-based filtering of physiological and ARFI-induced tissue and blood motion

Blind source separation (BSS) for adaptive filtering is presented in application to imaging both physiological and acoustic radiation force impulse (ARFI)-induced tissue and blood motion in the common carotid artery. The collected raw radiofrequency (RF) data includes vessel wall motion, blood flow and ARFI-induced motion. In the context of these complex motion patterns, the same BSS adaptive filtering method was employed for three diverse applications: 1. clutter filtering ensembles prior to blood velocity estimation, 2. extracting small axial velocity components from noisy velocity measurements given large flow angles and 3. reducing noise in measured ARFI-induced tissue displacement profiles to enhance differentiation of local tissue structures. The filter separated physiological vessel wall motion from axial blood flow and ARFI-induced motion; successful filter performance is demonstrated in velocity estimates, color flow images and ARFI displacement profiles. The results demonstrate the breadth of applications for BSS adaptive filtering in the clinical imaging environment.     

Acoustic radiation force on a spherical contrast agent shell near a vessel porous wall--theory

Contrast agent microshells (CAMSs) are under intensive investigation for their wide applications in biomedical imaging and drug delivery. In drug delivery applications, CAMSs are guided to the targeted site before fragmentation by high-intensity ultrasound waves leading to the drug release. Prediction of the acoustic radiation force used to nondestructively guide a CAMS to the suspected site is becoming increasingly important and gaining attention particularly because it increases the system efficiency. The goal of this work is to present a theoretical model for the time-averaged (static) acoustic radiation force experienced by a CAMS near a blood vessel wall. An exact solution for the scattering of normal incident plane acoustic waves on an air-filled elastic spherical shell immersed in a nonviscous fluid near a porous and nonrigid boundary is employed to evaluate the radiation force function (which is the radiation force per unit energy density per unit cross-sectional surface). A particular example is chosen to illustrate the behavior of the time-averaged (static) radiation force on an elastic polyethylene spherical shell near a porous wall, with particular emphasis on the relative thickness of the shell and the distance from its center to the wall. This proposed model allows obtaining a priori information on the static radiation force that may be used to advantage in related as drug delivery and contrast agent imaging. This study should assist in the development of improved models for the evaluation of the time-averaged acoustic radiation force on a cluster of CAMSs in viscous and heat-conducting fluids. (E-mail: mitri@lanl.gov)     

Acoustic radiation force impulse imaging: in vivo demonstration of clinical feasibility

The clinical viability of a method of acoustic remote palpation, capable of imaging local variations in the mechanical properties of soft tissue using acoustic radiation force impulse (ARFI) imaging, is investigated in vivo. In this method, focused ultrasound (US) is used to apply localized radiation force to small volumes of tissue (2 mm(3)) for short durations (less than 1 ms) and the resulting tissue displacements are mapped using ultrasonic correlation-based methods. The tissue displacements are inversely proportional to the stiffness of the tissue and, thus, a stiffer region of tissue exhibits smaller displacements than a more compliant region. Due to the short duration of the force application, this method provides information about the mechanical impulse response of the tissue, which reflects variations in tissue viscoelastic characteristics. In this paper, experimental results are presented demonstrating that displacements on the order of 10 microm can be generated and detected in soft tissues in vivo using a single transducer on a modified diagnostic US scanner. Differences in the magnitude of displacement and the transient response of tissue are correlated with tissue structures in matched B-mode images. The results comprise the first in vivo ARFI images, and support the clinical feasibility of a radiation force-based remote palpation imaging system.     

Analysis of contrast in images generated with transient acoustic radiation force

Several mechanical imaging methods are under investigation that use focused ultrasound (US) as a source of mechanical excitation. Images are then generated of the tissue response to this localized excitation. One such method, acoustic radiation force impulse (ARFI) imaging, utilizes a single US transducer on a commercial US system to transmit brief, high-energy, focused acoustic pulses to generate radiation force in tissue and correlation-based US methods to detect the resulting tissue displacements. Local displacements reflect relative mechanical properties of tissue. The resolution of these images is comparable with that of conventional B-mode imaging. The response of tissue to focused radiation force excitation is complex and depends upon tissue geometry, forcing function geometry (i.e., region of excitation, or ROE) and tissue mechanical and acoustic properties. Finite element method (FEM) simulations using an experimentally validated model and phantom experiments have been performed using varying systems, system configurations and tissue-mimicking phantoms to determine their impact on image quality. Image quality is assessed by lesion contrast. Due to the dynamic nature of ARFI excitation, lesion contrast is temporally-dependent. Contrast of spherical inclusions is highest immediately after force cessation, decreases with time postforce and then reverses, due to shear wave interaction with internal boundaries, differences in shear modulus between lesions and background and inertial effects. In images generated immediately after force cessation, contrast does not vary with applied force, increases with lesion stiffness and increases as the ROE size decreases relative to the size of the structure being imaged. These studies indicate that improved contrast in radiation force-generated images will be achieved as ROE size decreases; however, frame rate and thermal considerations present trade-offs with small ROE size.