Elastographic imaging of thermal lesions in the liver in vivo following radiofrequency ablation: preliminary results

Radiofrequency (RF) ablation is an interstitial focal ablative therapy that can be used in a percutaneous fashion. This modality provides in situ destruction of hepatic tumors. However, local recurrence rates after RF ablative therapy are as high as 34% to 55%, believed to be due in part to the inability to visualize accurately the zone of necrosis (thermal lesion). This can lead to the incomplete ablation of the tumor, generally in areas near the tumor edges. In this paper, we show that ultrasound (US)-based in vivo elastography can accurately depict thermal lesions after thermal therapy. However, elastography of the liver and other abdominal organs is challenging due to the difficulty in providing controlled and reproducible compression. The use of the RF ablation probe as the compressor/displacement device reduces lateral slippage or nonaxial motion that may occur with externally applied compressions or imaging during the respiratory cycle. This technique also provides controlled and reproducible compressions of the liver for in vivo elastographic imaging. Comparison of elastograms with histology of ablated tissue demonstrates a close relationship between elastographic image features and histopathology. (E-mail: tvarghese@facstaff.wisc.edu)     

微波消融灶组织病理变化与超声弹性成像图对照的实验研究

目的研究微波消融灶大体标本不同区域与弹性成像图相应区域问的关系,探讨超声弹性成像评价微波消融组织病理改变的可行性。方法单导水冷2450MHz微波,作用功率50w,作用时间200s,消融离体猪臀部肌组织,消融前、消融后即刻行静态超声弹性检查,分别测量弹性图的蓝色区及蓝色区＋绿色区大小。消融后测量大体标本灰白色＋灰粉色区及灰白色区大小。大体标本常规甲醛固定,石蜡切片,HE染色,光镜下观察各消融区域组织细胞变化,并采用配对t检验比较大体标本测值及镜下检查结果同弹性图相应测值。结果共进行了30次微波消融,形成30个消融灶。所有消融灶最终均能获得满意的弹性成像图。消融后消融灶剖面大体观呈以天线为长轴的椭圆形,由中心向外依次分为：棕黄色区,光镜下肌细胞完全破坏、崩解;灰白色区,硬而致密;光镜下肌细胞凝固性坏死;灰粉色区,光镜下肌细胞形态大致正常,细胞问水肿。消融后,弹性图像显示消融灶呈椭圆形,中心为较均匀蓝色,周边呈宽度较均匀一致绿色,与周围混杂颜色的正常组织分界清楚。弹性图蓝色区＋绿色区（灰白色区＋灰粉色区）长、宽、高测值分别为（3．750±0．289）、（2．773±0．264）、（2．223±0．229）cm,大体标本总消融区长、宽、高测值分别为（3．768±0．277）、（2．668±0．337）、（2．291±0．378）cm。2种方法长、宽、高测值的差异均无统计学意义（t=-0．568、1．994、1．078,P均〉0．05）,且有相关性（r=-0．86、0．69、0．62,P均〈0．01）。弹性图蓝色区长、宽、高测值分别为（3．307±0．231）、（2．260±0．269）、（1．827±0．271）cm,大体标本灰白色区长、宽、高测值分别为（3．280±0．273）、（1．980±0．373）、（1．840±0．297）cm。2种方法长、高测值的差异亦无统计学意义（t=0．576、0．238,P均〉0．05）,且有相关性（F0．76、0．71,P均〈0．01）。结论微波消融后超声弹性图像的蓝色区＋绿色区与消融灶标本灰白色区＋灰粉色区（凝固性坏死区＋水肿区）相对应,蓝色区与灰白色区（凝固性坏死区）相对应,超声弹性成像可以初步反映组织的热损伤程度。     

Comparison of Displacement Tracking Algorithms for in Vivo Electrode Displacement Elastography

Hepatocellular carcinoma and liver metastases are common hepatic malignancies presenting with high mortality rates. Minimally invasive microwave ablation (MWA) yields high success rates similar to surgical resection. However, MWA procedures require accurate image guidance during the procedure and for post-procedure assessments. Ultrasound electrode displacement elastography (EDE) has demonstrated utility for non-ionizing imaging of regions of thermal necrosis created with MWA in the ablation suite. Three strategies for displacement vector tracking and strain tensor estimation, namely coupled subsample displacement estimation (CSDE), a multilevel 2-D normalized cross-correlation method, and quality-guided displacement tracking (QGDT) have previously shown accurate estimations for EDE. This paper reports on a qualitative and quantitative comparison of these three algorithms over 79 patients after an MWA procedure. Qualitatively, CSDE presents sharply delineated, clean ablated regions with low noise except for the distal boundary of the ablated region. Multilevel and QGDT contain more visible noise artifacts, but delineation is seen over the entire ablated region. Quantitative comparison indicates CSDE with more consistent mean and standard deviations of region of interest within the mass of strain tensor magnitudes and higher contrast, while Multilevel and QGDT provide higher CNR. This fact along with highest success rates of 89% and 79% on axial and lateral strain tensor images for visualization of thermal necrosis using the Multilevel approach leads to it being the best choice in a clinical setting. All methods, however, provide consistent and reproducible delineation for EDE in the ablation suite.     

Magnetic resonance elastography: Non-invasive mapping of tissue elasticity

Magnetic resonance elastography (MRE) is a phase-contrast-based MRI imaging technique that can directly visualize and quantitatively measure propagating acoustic strain waves in tissue-like materials subjected to harmonic mechanical excitation. The data acquired allows the calculation of local quantitative values of shear modulus and the generation of images that depict tissue elasticity or stiffness. This is significant because palpation, a physical examination that assesses the stiffness of tissue, can be an effective method of detecting tumors, but is restricted to parts of the body that are accessible to the physician's hand. MRE shows promise as a potential technique for 'palpation by imaging', with possible applications in tumor detection (particularly in breast, liver, kidney and prostate), characterization of disease, and assessment of rehabilitation (particularly in muscle). We describe MRE in the context of other recent techniques for imaging elasticity, discuss the processing algorithms for elasticity reconstruction and the issues and assumptions they involve, and present recent ex vivo and in vivo results.     

Ultrasound elastography using multiple images

Displacement estimation is an essential step for ultrasound elastography and numerous techniques have been proposed to improve its quality using two frames of ultrasound RF data. This paper introduces a technique for calculating a displacement field from three (or multiple) frames of ultrasound RF data. To calculate a displacement field using three images, we first derive constraints on variations of the displacement field with time using mechanics of materials. These constraints are then used to generate a regularized cost function that incorporates amplitude similarity of three ultrasound images and displacement continuity. We optimize the cost function in an expectation maximization (EM) framework. Iteratively reweighted least squares (IRLS) is used to minimize the effect of outliers. An alternative approach for utilizing multiple images is to only consider two frames at any time and sequentially calculate the strains, which are then accumulated. We formally show that, compared to using two images or accumulating strains, the new algorithm reduces the noise and eliminates ambiguities in displacement estimation. The displacement field is used to generate strain images for quasi-static elastography. Simulation, phantom experiments and in vivo patient trials of imaging liver tumors and monitoring ablation therapy of liver cancer are presented for validation. We show that even with the challenging patient data, where it is likely to have one frame among the three that is not optimal for strain estimation, the introduction of physics-based prior as well as the simultaneous consideration of three images significantly improves the quality of strain images. Average values for strain images of two frames versus ElastMI are: 43 versus 73 for SNR (signal to noise ratio) in simulation data, 11 versus 15 for CNR (contrast to noise ratio) in phantom data, and 5.7 versus 7.3 for CNR in patient data. In addition, the improvement of ElastMI over both utilizing two images and accumulating strains is statistically significant in the patient data, with p-values of respectively 0.006 and 0.012.     

Volumetric Elasticity Imaging with a 2-D CMUT Array

This article reports the use of a two-dimensional (2-D) capacitive micro-machined ultrasound transducer (CMUT) to acquire radio-frequency (RF) echo data from relatively large volumes of a simple ultrasound phantom to compare three-dimensional (3-D) elasticity imaging methods. Typical 2-D motion tracking for elasticity image formation was compared with three different methods of 3-D motion tracking, with sum-squared difference (SSD) used as the similarity measure. Differences among the algorithms were the degree to which they tracked elevational motion: not at all (2-D search), planar search, combination of multiple planes and plane independent guided search. The cross-correlation between the predeformation and motion-compensated postdeformation RF echo fields was used to quantify motion tracking accuracy. The lesion contrast-to-noise ratio was used to quantify image quality. Tracking accuracy and strain image quality generally improved with increased tracking sophistication. When used as input for a 3-D modulus reconstruction, high quality 3-D displacement estimates yielded accurate and low noise modulus reconstruction. (E-mail: tgfisher@wisc.edu)     

Axial-Shear Strain Imaging for Differentiating Benign and Malignant Breast Masses

Axial strain imaging has been utilized for the characterization of breast masses for over a decade; however, another important feature namely the shear strain distribution around breast masses has only recently been used. In this article, we examine the feasibility of utilizing in vivo axial-shear strain imaging for differentiating benign from malignant breast masses. Radio-frequency data was acquired using a VFX 13-5 linear array transducer on 41 patients using a Siemens SONOLINE Antares real-time clinical scanner at the University of Wisconsin Breast Cancer Center. Free-hand palpation using deformations of up to 10% was utilized to generate axial strain and axial-shear strain images using a two-dimensional cross-correlation algorithm from the radio-frequency data loops. Axial-shear strain areas normalized to the lesion size, applied strain and lesion strain contrast was utilized as a feature for differentiating benign from malignant masses. The normalized axial-shear strain area feature estimated on eight patients with malignant tumors and 33 patients with fibroadenomas was utilized to demonstrate its potential for lesion differentiation. Biopsy results were considered the diagnostic standard for comparison. Our results indicate that the normalized axial-shear strain area is significantly larger for malignant tumors compared with benign masses such as fibroadenomas. Axial-shear strain pixel values greater than a specified threshold, including only those with correlation coefficient values greater than 0.75, were overlaid on the corresponding B-mode image to aid in diagnosis. A scatter plot of the normalized area feature demonstrates the feasibility of developing a linear classifier to differentiate benign from malignant masses. The area under the receiver operator characteristic curve utilizing the normalized axial-shear strain area feature was 0.996, demonstrating the potential of this feature to noninvasively differentiate between benign and malignant breast masses. (E-mail: tvarghese@wisc.edu)     

Normal and shear strain estimation using beam steering on linear-array transducers

In current ultrasound elastography, only the axial component of the displacement vector is estimated and used to produce strain images. A method was recently proposed by our group to estimate both the axial and lateral components of a displacement vector following a uniaxial compression. Previous work evaluated the technique using both simulations and a mechanically translated phased array transducer. In this paper, we present initial results using beam steering on a linear array transducer attached to a commercial scanner to acquire echo signals for estimating 2-D displacement vectors. Single-inclusion and anthropomorphic breast phantoms with different boundary properties between the inclusion and background material are imaged by acquiring echo data along beam lines ranging from -15 degrees to 15 degrees relative to the compression direction. 1-D cross-correlation is used to calculate "angular displacements" in each acquisition direction, yielding axial and lateral components of the displacement vector. Strain tensor components are estimated from these displacements. Features on shear strain images generated for the inclusion phantom agree with those predicted using FEA analysis. Experimental results demonstrate the utility of this technique on clinical scanners. Shear strain tensors obtained using this method may provide useful information for the differentiation of benign from malignant tumors. For the linear array transducer used in this study, the optimum angular increment is around 3 degrees. However, more work is required for the selection of an appropriate value for the maximum beam angle for optimal performance of this technique.     

Ex Vivo and In Vivo Assessment of the Non-linearity of Elasticity Properties of Breast Tissues for Quantitative Strain Elastography

The aim of this study was to reveal the background to the image variations in strain elastography (strain imaging [SI]) depending on the manner of manipulation (compression magnitude) during elasticity image (EI) acquisition. Thirty patients with 33 breast lesions who had undergone surgery followed by SI assessment in vivo were analyzed. An analytical approach to tissue elasticity based on the stress-elastic modulus (Young's modulus) relationship was adopted. Young's moduli were directly measured ex vivo in surgical specimens ranging from 2.60 kPa (fat) to 16.08 kPa (invasive carcinoma) under the weak-stress condition (<0.2–0.4 kPa, which corresponds to the appropriate “light touch” technique in SI investigation. The contrast (ratio) of lesion to fat in elasticity ex vivo gradually decreased as the stress applied increased (around 1.0 kPa) on the background of significant non-linearity of the breast tissue. Our results indicate that the differences in non-linearity in elasticity between the different tissues within the breast under minimal stress conditions are closely related to the variation in EI quality. The significance of the “pre-load compression” concept in tissue elasticity evaluation is recognized. Non-linearity of elasticity is an essential attribute of living subjects and could provide useful information having a considerable impact on clinical diagnosis in quantitative ultrasound elastography.     

In vivo assessment of myocardial stiffness with acoustic radiation force impulse imaging

Acoustic radiation force impulse (ARFI) imaging has been demonstrated to be capable of visualizing variations in local stiffness within soft tissue. Recent advances in ARFI beam sequencing and parallel imaging have shortened acquisition times and lessened transducer heating to a point where ARFI acquisitions can be executed at high frame rates on commercially available diagnostic scanners. In vivo ARFI images were acquired with a linear array placed on an exposed canine heart. The electrocardiogram (ECG) was also recorded. When coregistered with the ECG, ARFI displacement images of the heart reflect the expected myocardial stiffness changes during the cardiac cycle. A radio-frequency ablation was performed on the epicardial surface of the left ventricular free wall, creating a small lesion that did not vary in stiffness during a heartbeat, though continued to move with the rest of the heart. ARFI images showed a hemispherical, stiffer region at the ablation site whose displacement magnitude and temporal variation through the cardiac cycle were less than the surrounding untreated myocardium. Sequences with radiation force pulse amplitudes set to zero were acquired to measure potential cardiac motion artifacts within the ARFI images. The results show promise for real-time cardiac ARFI imaging.     

Performances and Limitations of Several Ultrasound-Based Elastography Techniques: A Phantom Study

The objective of this study is to assess strain and shear wave (SW) elastography performance in terms of accuracy by performing in vitro measurements on a calibrated elastography phantom. Acquisitions were done on a phantom containing 4 inclusions (12–74 kPa) embedded in a homogeneous background material (30 kPa). We performed qualitative assessment on elastograms, semiquantitative assessment with strain or elasticity ratios between each inclusion and the background and quantitative evaluation with SW acquisitions. Ratio and elasticity estimations were compared with expected values. Biases, relative errors and 95% confidence intervals (95% CI) were calculated. All techniques adequately classified inclusions as harder or softer than the background. For stiffness ratio estimation, SW methods were more precise than strain methods and had significantly higher percentages of correctly classified measurements (p = 0.008). Quantitative stiffness measurements were reproducible despite constant biases. SW elastography methods provide more reproducible estimations of tissue stiffness ratio than strain methods, as well as reproducible quantitative tissue stiffness despite constant biases.     

实时组织弹性成像压力反馈控制的实验研究

目的探讨在实时组织弹性成像（RTE）检查过程中,通过定量反馈控制探头施加的压力范围与压放频率对应变比值（SR）测量重复性的影响。 方法在HITACHI preirus型超声诊断仪,L74M线阵超声探头上加装压力传感器,使探头施加在组织上的压力范围及压放频率实时反馈在笔记本电脑上便于观察。15位不同熟练程度的超声医师分别在压力反馈信息引导下对硬度为80 kPa、直径为10.4 mm、深度为3.0 cm的超声仿体进行3组不同条件的弹性成像检查：组1为不加压力反馈的常规方法;组2施加0~80 g的压力范围、1.5次/s的压放频率的压力;组3施加40~120 g的压力范围、1.5次/s的压放频率的压力,3组条件下均获得满意的弹性成像图并测量SR值,每位操作医师每组条件下均获得15幅弹性成像图及相应的SR值。计算3组实验条件下不同医师SR测量值的CV值,采用单因素陪分析比较组与组之间CV值有无差异,两两比较采用SNK-q检验。 结果3组实验条件下15名医师的CV值比较,差异有统计学意义（F=15.853,P<0.01）,组2与组3的CV值均低于组1的CV值,差异均有统计学意义（q=4.732、5.038,P均<0.01）,组2与组3的CV值比较,差异无统计学意义（q=0.625,P>0.05）。 结论通过对RTE检查中的压力范围与压放频率进行定量控制来指导按压,较使用压放综合指标可提高其SR值测量的重复性,而当压力前负荷较小时对测量结果影响不大。     

Impact of gas bubbles generated during interstitial ablation on elastographic depiction of in vitro thermal lesions.

OBJECTIVE: Artifacts from gas bubble formation during radio frequency ablation along with the poor intrinsic contrast between normal and treated regions (zone of necrosis) are considerable problems for the visualization of the necrotic region on conventional sonography. Sonographic elastography is very effective for visualizing the zone of necrosis, but it uses the same echo signals to estimate strain as those used to form gray scale images. Thus, the impact of gas bubbles on strain images or elastograms must be investigated. METHODS: Radio frequency ablation was performed in vitro on liver tissue samples, approximately 40 x 40 x 20 mm, encased in 80-mm cubed gelatin phantoms. Elastograms generated at different instants during the ablation procedures were obtained on a real-time scanner with a 5-MHz linear array. Sequences of elastograms illustrate the growth of the thermal lesion. RESULTS: Degradation of the distal boundary of the thermal lesion was observed. The degradation was confined to the lower-fifth quadrant of the thermal lesion. However, accurate estimates of lesion areas could still be obtained by extrapolation of the thermal lesion boundary. CONCLUSIONS: Elastograms of thermal lesions in vitro can be obtained during radio frequency ablation. Some loss of thermal lesion boundary information on strain images was observed in regions where attenuation due to gas bubbles reduced the signal-noise ratio of the echo signals.     

剪切波弹性成像评价肝脏微波消融灶边界的实验研究

目的探讨超高速剪切波弹性成像（SWE）在定量评估肝脏微波消融边界中的可行性与准确性。 方法取健康雄性5月龄五指山猪15只，行开腹直视下肝脏微波消融术，消融功率选定40 W，根据消融时间分设为15 s、30 s、60 s三组。消融后即刻采用SWE测量消融灶的弹性模量值。术后利用HE染色、烟酰胺腺嘌呤二核苷酸（NADH）黄递酶组织化学染色评估肝组织的损伤程度。 结果本实验共进行有效消融156次，有效SWE测量740次，得到有效病理结果131个。消融灶弹性模量值呈阶梯式同心圆分布，从中心向外周可分为3个区域。同一消融时间下弹性模量值在周边正常组织区域、消融边界区域、消融中心区域阶梯式增高（P均<0.01）。消融功率40 W，消融时间15 s、30 s、60 s在周边正常组织区域和消融边界区域的弹性模量值差异无统计学意义（P均>0.05），但在消融中心区域，其弹性模量值随消融时间的缩短而呈阶梯式降低，［60 s：（97.16±14.58）kPa>30 s：（77.84±9.64）kPa>15 s：（38.92±3.12）kPa］，差异有统计学意义（F=2 131.832，P<0.01）。不同消融时间的消融边界区域弹性模量值保持在22.68~23.56 kPa。 结论微波消融灶消融边界区域弹性模量值范围相对固定，SWE有助于定量评估肝脏微波消融边界，其在超声消融的监测与评估方面具有较强的实用价值。     

Ultrasound-based elastography: a novel approach to assess radio frequency ablation of liver masses performed with expandable ablation probes: a feasibility study

OBJECTIVE: The purpose of this study was to evaluate the technical feasibility of ultrasound-based elastography as a tool for assessing the size and shape of the coagulation necrosis caused by radio frequency ablation (RFA) probes using expandable electrodes ex vivo as well as in a patient with a liver metastasis. METHODS: A commercially available expandable RFA probe was used to create a 3-cm ablation in a piece of bovine liver. The ablation probe was used in situ to induce tissue deformation for elastography before and after ablation. Ultrasonic radio frequency data were processed to generate elasticity strain images. The appearance of the ablation zone was compared with magnetic resonance imaging and a gross section specimen. One patient with malignant metastatic disease to the liver and a clinical indication for RFA was investigated for the feasibility of percutaneous elastography of RFA using the same technique. Sonographic strain images were compared with the appearance of the nonenhancing ablation zone on contrast-enhanced computed tomography. RESULTS: Ex vivo, the ablation zone on ultrasound-based elastography was represented by an area of increased stiffness and was well demarcated from the nonablated surrounding tissue. The size and shape of the ablated zone on the strain image correlated well with the gross specimen and the magnetic resonance imaging appearance. Strain images obtained from the patient showed results similar to those of the ex vivo experiment and correlated well with the nonenhancing area of ablation on contrast-enhanced computed tomography. CONCLUSIONS: Ultrasound-based elastography may be a promising tool for displaying the ablation zone created by expandable RFA probes.     

Elastographic imaging of thermal lesions in the liver in vivo following radiofrequency ablation: preliminary results

Radiofrequency (RF) ablation is an interstitial focal ablative therapy that can be used in a percutaneous fashion. This modality provides in situ destruction of hepatic tumors. However, local recurrence rates after RF ablative therapy are as high as 34% to 55%, believed to be due in part to the inability to visualize accurately the zone of necrosis (thermal lesion). This can lead to the incomplete ablation of the tumor, generally in areas near the tumor edges. In this paper, we show that ultrasound (US)-based in vivo elastography can accurately depict thermal lesions after thermal therapy. However, elastography of the liver and other abdominal organs is challenging due to the difficulty in providing controlled and reproducible compression. The use of the RF ablation probe as the compressor/displacement device reduces lateral slippage or nonaxial motion that may occur with externally applied compressions or imaging during the respiratory cycle. This technique also provides controlled and reproducible compressions of the liver for in vivo elastographic imaging. Comparison of elastograms with histology of ablated tissue demonstrates a close relationship between elastographic image features and histopathology.     

Performance assessment of HIFU lesion detection by harmonic motion imaging for focused ultrasound (HMIFU): a 3-D finite-element-based framework with experimental validation

Harmonic motion imaging for focused ultrasound (HMIFU) is a novel high-intensity focused ultrasound (HIFU) therapy monitoring method with feasibilities demonstrated in vitro, ex vivo and in vivo. Its principle is based on amplitude-modulated (AM) - harmonic motion imaging (HMI), an oscillatory radiation force used for imaging the tissue mechanical response during thermal ablation. In this study, a theoretical framework of HMIFU is presented, comprising a customized nonlinear wave propagation model, a finite-element (FE) analysis module and an image-formation model. The objective of this study is to develop such a framework to (1) assess the fundamental performance of HMIFU in detecting HIFU lesions based on the change in tissue apparent elasticity, i.e., the increasing Young’s modulus, and the HIFU lesion size with respect to the HIFU exposure time and (2) validate the simulation findings ex vivo. The same HMI and HMIFU parameters as in the experimental studies were used, i.e., 4.5-MHz HIFU frequency and 25 Hz AM frequency. For a lesion-to-background Young’s modulus ratio of 3, 6 and 9, the FE and estimated HMI displacement ratios were equal to 1.83, 3.69 and 5.39 and 1.65, 3.19 and 4.59, respectively. In experiments, the HMI displacement followed a similar increasing trend of 1.19, 1.28 and 1.78 at 10-s, 20-s and 30-s HIFU exposure, respectively. In addition, moderate agreement in lesion size growth was found in both simulations (16.2, 73.1 and 334.7 mm²) and experiments (26.2, 94.2 and 206.2 mm²). Therefore, the feasibility of HMIFU for HIFU lesion detection based on the underlying tissue elasticity changes was verified through the developed theoretical framework, i.e., validation of the fundamental performance of the HMIFU system for lesion detection, localization and quantification, was demonstrated both theoretically and ex vivo.     

A Freehand Ultrasound Elastography System with Tracking for In Vivo Applications

Ultrasound transducers are commonly tracked in modern ultrasound navigation/guidance systems. In this article, we demonstrate the advantages of incorporating tracking information into ultrasound elastography for clinical applications. First, we address a common limitation of freehand palpation: speckle decorrelation due to out-of-plane probe motion. We show that by automatically selecting pairs of radio frequency frames with minimal lateral and out-of-plane motions, combined with a fast and robust displacement estimation technique, greatly improves in vivo elastography results. We also use tracking information and image-quality measures to fuse multiple images with similar strains that are taken from roughly the same location so as to obtain a high-quality elastography image. Finally, we show that tracking information can be used to give the user partial control over the rate of compression. Our methods are tested on a tissue-mimicking phantom, and experiments have been conducted on intraoperative data acquired during animal and human experiments involving liver ablation. Our results suggest that in challenging clinical conditions, our proposed method produces reliable strain images and eliminates the need for a manual search through the ultrasound data in order to find radio frequency pairs suitable for elastography.     

准静态弹性成像技术检测聚焦超声致离体组织损伤

目的 用准静态弹性成像检测聚焦超声(FUS)在离体组织中形成的损伤。方法 在仿体实验中采取多种方法提高运动估计的精度。通过分段线性拟合等算法对位移数据进行后处理,优化位移估计结果,采用基于小波变换的数字低通差分算法抑制应变估计中高频噪声的干扰。在此基础上用准静态弹性成像检测FUS在离体猪肌肉组织中形成的损伤。结果 采用分段线性拟合算法和基于小波变换的数字低通差分算法可显著改善运动估计的准确性。弹性成像可检测小剂量FUS辐照后在组织内形成的损伤,主要表现为损伤区域的力学特性与周围组织具有明显差异。结论 弹性成像可用于评价FUS形成的组织损伤。