Acoustic radiation force impulse imaging of thermally- and chemically-induced lesions in soft tissues: preliminary ex vivo results

The ability of acoustic radiation force impulse (ARFI) imaging to visualize thermally- and chemically-induced lesions in soft tissues was investigated. Lesions were induced in freshly excised bovine liver samples. Chemical lesions were induced via the injection of formaldehyde and thermal lesions were created using a radiofrequency (RF) ablation system. Although conventional sonography was unable to visualize induced lesions, ARFI imaging was capable of monitoring lesion size and boundaries. Agreement was observed between lesion size in ARFI images and in results from pathology. The fact that ARFI imaging requires no additional equipment aside from that needed for conventional ultrasonic imaging makes it a promising modality for monitoring lesion development in situations where sonography is already involved as a guiding mechanism, such as in procedures requiring precise catheter placement.     

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.     

In vivo guidance and assessment of liver radio-frequency ablation with acoustic radiation force elastography

The initial results from clinical trials investigating the utility of acoustic radiation force impulse (ARFI) imaging for use with radio-frequency ablation (RFA) procedures in the liver are presented. To date, data have been collected from 6 RFA procedures in 5 unique patients. Large displacement contrast was observed in ARFI images of both pre-ablation malignancies (mean 7.5 dB, range 5.7-11.9 dB) and post-ablation thermal lesions (mean 6.2 dB, range 5.1-7.5 dB). In general, ARFI images provided superior boundary definition of structures relative to the use of conventional sonography alone. Although further investigations are required, initial results are encouraging and demonstrate the clinical promise of the ARFI method for use in many stages of RFA procedures.     

Intracardiac echocardiography and acoustic radiation force impulse imaging of a dynamic ex vivo ovine heart model

Intracardiac echocardiography (ICE) has demonstrated utility in providing high-resolution cardiac ultrasound images for guidance of numerous catheter-based interventions, including radiofrequency ablations (RFA). However, the training of interventionalists and refinement of procedures involving intracardiac catheters is costly and time consuming due to necessary clinical and animal studies. As a result, research and development of ICE for other purposes is gradual and deliberate. Intracardiac acoustic radiation force impulse (ARFI) imaging has been demonstrated to be a suitable modality to monitor the progress of RFA procedures; however, a clinical protocol has been slow to develop due to the expense and demands of clinical experiments. We report on the development and use of an ex vivo heart model to evaluate ICE and intracardiac ARFI imaging. The ability of this model to provide clinically-relevant intracardiac imaging angles was investigated by inserting an intracardiac probe into the heart and imaging it from various positions and orientations. ARFI images of all four chambers also were formed. RFAs were also performed to create stiffer lesions within the right and left ventricles. Upon completion of the ablation, ARFI imaging was used to visualize the lesion and compared with images taken from pathology.The results show the ovine heart model to be a suitable apparatus for recreating several clinically-relevant intracardiac viewing angles of the heart. Also, the results indicate the potential of the heart model to be a valuable tool in the future development and refinement of a clinical protocol for intracardiac ARFI imaging based guidance and assessment of cardiac radiofrequency ablations.     

Delineation of Post-Procedure Ablation Regions with Electrode Displacement Elastography with a Comparison to Acoustic Radiation Force Impulse Imaging

We compared a quasi-static ultrasound elastography technique, referred to as electrode displacement elastography (EDE), with acoustic radiation force impulse imaging (ARFI) for monitoring microwave ablation (MWA) procedures on patients diagnosed with liver neoplasms. Forty-nine patients recruited to this study underwent EDE and ARFI with a Siemens Acuson S2000 system after an MWA procedure. On the basis of visualization results from two observers, the ablated region in ARFI images was recognizable on 20 patients on average in conjunction with B-mode imaging, whereas delineable ablation boundaries could be generated on 4 patients on average. With EDE, the ablated region was delineable on 40 patients on average, with less imaging depth dependence. Study of tissue-mimicking phantoms revealed that the ablation region dimensions measured on EDE and ARFI images were within 8%, whereas the image contrast and contrast-to-noise ratio with EDE was two to three times higher than that obtained with ARFI. This study indicated that EDE provided improved monitoring results for minimally invasive MWA in clinical procedures for liver cancer and metastases.     

声脉冲辐射力成像技术鉴别诊断肝脏良恶性局灶性病变

目的探讨声脉冲辐射力成像技术(ARFI)对肝脏良恶性局灶性病变的鉴别诊断价值。方法对64例患者76个肝脏局灶性病变进行ARFI检查并分析,包括声触诊组织成像技术(VTI)和声触诊组织量化技术(VTQ)。所有患者均经手术或穿刺病理证实或两种增强影像学检查(CEUS、CT、MRI)确诊。采用ROC曲线评价剪切波速(SWV)对肝脏局灶性病变良恶性的鉴别诊断价值,并确定临界点。结果 VTI声像图中,31个(31/40,77.50%)恶性病灶和13个(13/36,36.11%)良性病灶呈灰黑色(P<0.05);良性病灶SWV明显低于恶性病灶[(1.67±0.61)m/s vs(2.80±1.07)m/s,P<0.01)。以SWV=2.04m/s为临界点鉴别肝脏局灶性病变的良恶性,其敏感度、特异度和准确率分别是82.50%、80.60%和81.58%。结论 ARFI有助于鉴别诊断肝脏良恶性局灶性病变,具有良好的临床应用前景。     

声辐射力冲击成像对乳腺结节性质的鉴别诊断价值

目的探讨应用声辐射力冲击成像(ARFI)技术对乳腺良性与恶性结节病灶的鉴别诊断价值。方法以33例<10 mm恶性乳腺结节患者及同期20例良性乳腺结节患者为研究对象,利用ARFI的声触诊组织成像(VTI)定性结节范围和声触诊组织定量(VTQ)量化结节的剪切波速度,与临床病理结果比较,分析良恶性病灶的ARFI-VTI和ARFI-VTQ参数差异。结果 ARFI-VTI能定性病灶结节范围,病灶结节在VTI图中与二维图中的面积比参数在良恶性组间差异有显著统计学意义,恶性组>1,良性组≤1(P<0.01);ARFI-VTQ测值在良恶性结节间差异有显著统计学意义,良性结节组VTQ剪切波速度为(2.67±1.63)m/s,恶性结节组VTQ剪切波速度为(5.24±2.72)m/s(P<0.01);对小结节型乳腺癌的诊断与病理诊断符合率为97.0%,特异度为80.0%。结论 ARFI检查对结节<10 mm的乳腺良恶性肿瘤具有鉴别诊断价值,值得临床应用推广。     

Acoustic radiation force impulse (ARFI) imaging of the gastrointestinal tract

The evaluation of lesions in the gastrointestinal (GI) tract using ultrasound can suffer from poor contrast between healthy and diseased tissue. Acoustic Radiation Force Impulse (ARFI) imaging provides information about the mechanical properties of tissue using brief, high-intensity, focused ultrasound to generate radiation force and ultrasonic correlation-based methods to track the resulting tissue displacement. Using conventional linear arrays, ARFI imaging has shown improved contrast over B-mode images when applied to solid masses in the breast and liver. The purpose of this work is to (1) investigate the potential for ARFI imaging to provide improvements over conventional B-mode imaging of GI lesions and (2) demonstrate that ARFI imaging can be performed with an endocavity probe. ARFI images of an adenocarcinoma of the gastroesophageal (GE) junction, status-post chemotherapy and radiation treatment, demonstrate better contrast between healthy and fibrotic/malignant tissue than standard B-mode images. ARFI images of healthy gastric, esophageal, and colonic tissue specimens differentiate normal anatomic tissue layers (i.e., mucosal, muscularis and adventitial layers), as confirmed by histologic evaluation. ARFI imaging of ex vivo colon and small bowel tumors portray interesting contrast and structure that are not as well defined in B-mode images. An endocavity probe created ARFI images to a depth of over 2 cm in tissue-mimicking phantoms, with maximum displacements of 4 microm. These findings support the clinical feasibility of endocavity ARFI imaging to guide diagnosis and staging of disease processes in the GI tract.     

Percutaneous ablation of liver malignancies: imaging evaluation of treatment response.

Interventional procedures for percutaneous tumor ablation have gained an increasingly important role in the treatment of liver malignancies. After interventional therapies, diagnostic imaging has the key role to determine if the treated lesion is completely ablated or contains areas of residual viable neoplastic tissue. This is particularly important since in cases of incomplete necrosis of the lesions, treatment can be repeated, and tumor ablation can be further pursued. The evaluation of the therapeutic effect of the procedure arises different problems according to the histotype of the malignancy. In the case of hepatocellular carcinoma (HCC), detection of residual viable tumor is facilitated by the typical hypervascular pattern of this neoplasm. Contrast-enhanced US can be used to monitor tumor response, and, in cases of partial necrosis, to target the areas of residual viable tumor. With spiral CT or dynamic MR imaging, residual viable HCC is reliably depicted as it stands out in the arterial phase images against the unenhanced areas of coagulation necrosis. In the case of hypovascular metastases, a confident diagnosis of successfull ablation can be made when an area of thermal necrosis exceeding that of the original lesion is depicted. Peripheral inflammatory reaction following ablation procedures, that shows itself as an enhancing halo along the necrotic area boundary on spiral CT or dynamic MR images, should not be misinterpreted as tumor progression.     

声脉冲辐射力弹性成像检测乳腺良恶性肿块硬度的初步研究

目的应用声脉冲辐射力弹性成像(ARFI)技术评价乳腺肿块硬度,探讨其在鉴别诊断乳腺良、恶性肿块中的价值。方法分析90例共102个经病理证实的乳腺肿块常规超声及ARFI成像特征,记录声触诊组织成像与二维超声图像病灶面积比值(AR)、声触诊组织量化成像检测深度及剪切波速值(SWV)、病灶与周边相同深度正常乳腺组织剪切波速比值(R-SWV),分析乳腺癌与各良性病灶之间的差异。结果获取剪切波速的成功率>94%。乳腺癌较其他各良性病灶的声触诊组织成像显示图像更黑,其次为乳腺炎和乳腺纤维腺瘤。乳腺癌AR、SWV及R-SWV较各良性病灶均明显增高(P<0.01),AR、SWV、R-SWV诊断乳腺癌的cutoff值分别为1.66、6.71m/s、5.02,各良性病灶间比较差异均无统计学意义。结论应用AFRI弹性成像技术能定性、定量反映乳腺肿块的弹性特征,对乳腺癌的诊断具有一定的价值,尤其对于乳腺癌与乳腺炎的鉴别诊断有较大帮助。     

An integrated indenter-ARFI imaging system for tissue stiffness quantification

The goal of this work is to develop and characterize an integrated indenter-ARFI (acoustic radiation force impulse) imaging system. This system is capable of acquiring matched datasets of ARFI images and stiffness profiles from ex vivo tissue samples, which will facilitate correlation of ARFI images of tissue samples with independently-characterized material properties. For large and homogeneous samples, the indenter can be used to measure the Young's moduli by using Boussinesq's solution for a load on the surface ofa semi-infinite isotropic elastic medium. Experiments and finite element method (FEM) models were designed to determine the maximum indentation depth and minimum sample size for accurate modulus reconstruction using this solution. Applying these findings, indentation measurements were performed on three calibrated commercial tissue-mimicking phantoms and the results were in good agreement with the calibrated stiffness. For heterogeneous tissue samples, indentation can be used independently to characterize relative stiffness variation across the sample surface, which can then be used to validate the stiffness variation in registered ARFI images. Tests were performed on heterogeneous phantoms and freshly-excised colon cancer specimens to detect the relative stiffness and lesion sizes using the combined system. Normalized displacement curves across the lesion surface were calculated and compared. Good agreement ofthe lesion profiles was observed between indentation and ARFI imaging.     

低场MR动态增强对肝脏占位病变的诊断价值探讨

目的：探讨低场MR动态增强对肝脏占位病变的应用价值。方法：应用0．2T永磁型磁共振仪对24例肝脏占位性病变先行TIW1、T2WI平扫，再使用FMPSPGR(快速多层面扰相位梯度回波)序列，进一步对其中28个占位灶作同层块动态增强扫描。造影剂为磁显葡胺(Gd-DTPA)0．2mmol／kg。结果：在上下5～8cm范围内可显示肝脏占位病变的动态强化方式，有助于定性诊断。结论：低场MR动态增强可作为肝脏占位病变定性诊断的补充方法。     

Acoustic Radiation Force Impulse Imaging of Human Prostates Ex Vivo

It has been challenging for clinicians using current imaging modalities to visualize internal structures and detect lesions inside human prostates. Lack of contrast among prostatic tissues and high false positive or negative detection rates of prostate lesions have limited the use of current imaging modalities in the diagnosis of prostate cancer. In this study, acoustic radiation force impulse (ARFI) imaging is introduced to visualize the anatomical and abnormal structures in freshly excised human prostates. A modified Siemens Antares ultrasound scanner (Siemens Medical Solutions USA Inc., Malvern, PA) and a Siemens VF10-5 linear array were used to acquire ARFI images. The transducer was attached to a three-dimensional (3-D) translation stage, which was programmed to automate volumetric data acquisition. A depth dependent gain (DDG) method was developed and applied to 3-D ARFI datasets to compensate for the displacement gradients associated with spatially varying radiation force magnitudes as a function of depth. Nine human prostate specimens were collected and imaged immediately after surgical excision. Prostate anatomical structures such as seminal vesicles, ejaculatory ducts, peripheral zone, central zone, transition zone and verumontanum were visualized with high spatial resolution and in good agreement with McNeal's zonal anatomy. The characteristic appearance of prostate pathologies, such as prostate cancerous lesions, benign prostatic hyperplasia, calcified tissues and atrophy were identified in ARFI images based upon correlation with the corresponding histologic slides. This study demonstrates that ARFI imaging can be used to visualize internal structures and detecting suspicious lesions in the prostate and appears promising for image guidance of prostate biopsy. (E-mail:liang.zhai@duke.edu)     

Imaging of Thermal Effects during High-Intensity Ultrasound Treatment in Liver by Passive Elastography: A Preliminary Feasibility in Vitro Study

High-intensity focused ultrasound is a non-invasive modality for thermal ablation of tissues through locally increased temperature. Thermal lesions can be monitored by elastography, following the changes in the elastic properties of the tissue as reflected by the shear-wave velocity. Most studies on ultrasound elastography use shear waves created by acoustic radiation force. However, in the human body, the natural noise resulting from cardiac activity or arterial pulsatility can be used to characterize elasticity through noise-correlation techniques, in the method known as passive elastography. The objective of this study was to investigate the feasibility of monitoring high-intensity ultrasound treatments of liver tissue using passive elastography. Bovine livers were heated to 80°C using a high-intensity planar transducer and imaged with a high-frame-rate ultrasound imaging device. The dynamics of lesion formation are captured through tissue stiffening and lesion expansion.     

经皮微波消融良性肝局灶性病变的初步研究

目的 探讨运用经皮微波热消融治疗良性肝局灶性病变的原则和价值.方法 应用15G水冷式微波电极经皮消融14例15个良性肝局灶性病变,直径(26.2±13.6)mm(10～57 mm).结果 微波消融治疗次数为(1.4±0.5)次(1～2次),总治疗时间为(837±574)s(300～2057 s).随访1～35个月,中位随访期6个月.治疗后1个月增强影像检查显示,病灶均被微波消融所致凝固性坏死区完全覆盖.随访3个月以上者12例,随访影像检奁显示消融区范围逐渐缩小.围手术期和随访中无一例出现并发症.消融治疗副作用主要有局部疼痛不适(12/14例)、发热(8/14例)、肝酶学指标升高(14/14例)等,前两者持续时间1～9 d,肝酶学指标升高于治疗后1周左右恢复至治疗前水平.结论 经皮微波热消融具有安全、微创、消融彻底、毒副作用低等特点,在把握好适应证的前提下,可作为良性肝局灶性病变的一种可选择的治疗方法.     

MR True FISP序列在评价肝癌侵犯门脉诊断中的应用研究

目的：探讨磁共振真实稳态进动快速成像（MR True FISP序列）用于诊断肝癌侵犯门脉的准确性,建立无创影像学检查技术对肝癌侵犯门脉的评价体系,指导手术治疗。材料及方法：收集临床已确诊为肝癌,并高度怀疑门脉受侵的患者90例,并有完整的MRI检查资料,所有患者均明确手术或穿刺病理证实。将所有MRI图像进行汇总分析,最后将True FISP序列检查结果与增强门脉期检查结果及手术或穿刺病理结果对比并进行对比分析。结果：建立MR True FISP序列的最佳成像参数和扫描方法。True FISP图像与增强门脉期冠状位图像大部分为优,二者的可诊断率均为100%。与病理对照分析,True FISP序列对肝癌侵犯门脉的显示有高度的一致性。结论：规范MR True FISP序列显示门脉的最佳成像参数和扫描方法;MR True FISP序列可以很好的显示肝癌病灶对门脉的侵犯情况,对诊断肝癌侵犯门脉的准确性很高,建立无创影像学检查技术对肝癌侵犯门脉的评价体系,从而指导外科手术治疗。     

Feasibility of Using Ultrasonic Nakagami Imaging for Monitoring Microwave-Induced Thermal Lesion in Ex Vivo Porcine Liver

The feasibility of using ultrasonic Nakagami imaging to evaluate thermal lesions induced by microwave ablation (MWA) in ex vivo porcine liver was explored. Dynamic changes in echo amplitudes and Nakagami parameters in the region of the MWA-induced thermal lesion, as well as the contrast-to-noise ratio (CNR) between the MWA-induced thermal lesion and the surrounding normal tissue, were calculated simultaneously during the MWA procedure. After MWA exposure, a bright hyper-echoic region appeared in ultrasonic B-mode and Nakagami parameter images as an indicator of the thermal lesion. Mean values of the Nakagami parameter in the thermal lesion region increased to 0.58, 0.71 and 0.91 after 1, 3 and 5 min of MVA. There were no significant differences in envelope amplitudes in the thermal lesion region among ultrasonic B-mode images obtained after different durations of MWA. Unlike ultrasonic B-mode images, Nakagami images were less affected by the shadow effect in monitoring of MWA exposure, and a fairly complete hyper-echoic region was observed in the Nakagami image. The mean value of the Nakagami parameter increased from approximately 0.47 to 0.82 during MWA exposure. At the end of the postablation stage, the mean value of the Nakagami parameter decreased to 0.55 and was higher than that before MWA exposure. CNR values calculated for Nakagami parameter images increased from 0.13 to approximately 0.61 during MWA and then decreased to 0.26 at the end of the post-ablation stage. The corresponding CNR values calculated for ultrasonic B-mode images were 0.24, 0.42 and 0.17. This preliminary study on ex vivo porcine liver suggested that Nakagami imaging have potential use in evaluating the formation of MWA-induced thermal lesions. Further in vivo studies are needed to evaluate the potential application.     

The Feasibility of Myocardial Infarct Visualization Using Atrial Kick Induced Strain (AKIS) Contrast

The most common mechanical measure of the heart integrates ventricular strain between end-diastole and end-systole in order to provide a measure of contraction. Here an approach is described for estimating a correlate to local passive mechanical properties. Passive strain is measured by estimating ventricular strain during atrial systole. During atrial systole the atria contract causing passive stretching in the ventricles from increased volume. This modification to traditional cardiac strain is here termed atrial kick induced strain (AKIS) imaging. AKIS imaging was evaluated in a canine ablation model of chronic infarct and a canine true chronic infarct model. AKIS images of ablation lesions were compared against acoustic radiation force impulse (ARFI) images and tissue blanching, and true chronic infarct AKIS images were compared against delayed enhanced-contrast magnetic resonance. AKIS images were made with 2-D and 3-D ultrasound data. In both studies, AKIS images and the comparison images show good qualitative agreement and good contrast and contrast-to-noise ratio.     

Monitoring the formation of thermal lesions with heat-induced echo-strain imaging: a feasibility study

We investigated the feasibility of using echo-strain images to visualize the extent of high-intensity ultrasound (US)-induced thermal lesions during their formation. Echo-strain, defined as the relative deformation of the backscattered ultrasonic signal, is due to tissue expansion and to changes in the speed of sound during heating. First, a theoretical framework was developed to predict the influence of these effects on the echo signal. Then, a simulation tool was developed to create simulated echo-strain images in thermal lesions. Finally, experimental echo-strain images were acquired in 10 porcine liver samples in vitro for various exposure durations and ultrasonic intensities (resulting in lesions that extended 3 to 8 mm deep from the surface). For this purpose, radiofrequency (RF) frames were acquired at 8 frames per s while heating. For each consecutive pair of RF frames, an echo-strain image was calculated using standard elastographic processing. The echo-strain images were cumulated and displayed. The experimental echo-strain images were compared with gross pathology. The (isoechoic) lesions were visible both in simulated and in experimental cumulated echo-strain images as apparent expansion areas (tensile echo-strain), whereas surrounding tissues exhibited apparent compression. The tensile echo-strain area underestimated the lesion in simulations, but was representative of the lesion in experiments. High correspondence was found between the lesion depth measured from experimental cumulative echo-strain images (y) and from gross pathology (x) (Pearson's correlation = 0.90, linear regression y = x-0.1 mm, residual error = 0 +/- 0.9 mm). We hypothesized that significant tissue expansion made the thermal lesions highly visible in the experimental echo-strain images. In two cases, the ultrasonic intensity was too low to induce a lesion, and the corresponding experimental echo-strain images showed no visible lesion. We conclude that cumulative echo-strain images have the potential to monitor the formation of high-intensity US-induced thermal lesions.     

经直肠ARFI技术在前列腺病变中的研究

目的 探讨经直肠声辐射力脉冲成像技术(ARFI)对前列腺良恶性病变诊断的临床价值。方法 应用ARFI技术对72例前列腺占位性病变患者进行检查，测值与术后病理结果对照，鉴别其良恶性。结果 ARFI技术检测的前列腺恶性占位病变与前列腺良性占位病变组比较，剪切波速差异有显著性意义(P＜0.05)；前列腺良性占位与前列腺正常组剪切波速比较差异具有显著性（P＜0.05）。以剪切波速大于2.94m/s作为前列腺恶性占位的诊断标准，ARFI诊断前列腺良恶性占位的敏感性为86.7%，特异性为66.7%。结论 ARFI技术可以做为前列腺病变早期诊断的一种重要手段。