Acoustic Radiation Force Elastography Research Articles

A Preliminary Study on the Safety of Elastography during Pregnancy: Hypoacusia, Anthropometry, and Apgar Score in Newborns.

Transient or acoustic radiation force elastography (ARFE) is becoming the most extended technology to assess cervical effacement, additionally to the Bishop test and conventional ultrasound. However, a debate on the fetal safety has been opened due to the high intensity focused beam emitted to produce shear waves. This work is aimed at providing preliminary data to assess clinical effects of fetal exposure. A follow-up study in newborns of 42 women exposed to ARFE during pregnancy was carried out to explore neonatal hypoacusia, Apgar test, and anthropometry. No hypoacusia cases attributable to ARFE were observed. The Apgar test at five minutes scored normally in all the newborns. Comparisons between anthropometric measurements showed no significant statistically differences. The results preclude to state the harmfulness nor the safety of ARFE. However, given the concern on the high level of energy and the potential risk of harmful bioeffects, larger studies are recommended.

Does acoustic radiation force elastography improve the diagnostic capability of ultrasound in the preoperative characterization of masses of the parotid gland?

Ultrasound is the method of choice for preoperative evaluation of tumours of the parotid glands. However, existing methods do not allow for clear differentiation between the most common benign tumours and malignant tumours. The aim of our study was to evaluate if acoustic radiation force, Virtual Touch Quantification (VTQ) elastography helps to improve the preoperative evaluation of parotid masses. We investigated the parenchyma of 102 parotid glands, 14 lymph nodes of healthy volunteers and 51 tumours of the parotid gland via ultrasound, colour Doppler ultrasound and VTQ. The results were matched with histopathology and analyzed. The perfusion in pleomorphic adenoma, the most frequent benign tumour of the parotid gland, was significantly lower in comparison to malignant tumours. All tumours showed statistically significant higher perfusion in comparison to the parenchyma or the lymph nodes of the gland. Shear wave velocity of the user-defined region of interest was statistically significant more frequently an overflow value higher than 8.5 m/s in total tumours in comparison to parenchyma or lymph nodes. The different tumour types presented no significant difference in the shear wave velocity. VTQ in combination with classical ultrasound examination provides additional data useful in distinguishing between benign and malignant tumours and thus shows promise for integration into preexisting ultrasound protocols. However, despite the improvement, clear differentiation of tumours is still not possible and further investigation is recommended.

A Frequency-Shift Method to Measure Shear-Wave Attenuation in Soft Tissues.

In vivo quantification of shear-wave attenuation in soft tissues may help to better understand human tissue rheology and lead to new diagnostic strategies. Attenuation is difficult to measure in acoustic radiation force elastography because the shear-wave amplitude decreases due to a combination of diffraction and viscous attenuation. Diffraction correction requires assuming a cylindrical wavefront and an isotropic propagation medium, which may not be the case in some applications. In this paper, the frequency-shift method, used in ultrasound imaging and seismology, was adapted for shear-wave attenuation measurement in elastography. This method is not sensitive to diffraction effects. For a linear frequency dependence of the attenuation, a closed-form relation was obtained between the decrease in the peak frequency of the gamma-distributed wave amplitude spectrum and the attenuation coefficient of the propagation medium. The proposed method was tested against a plane-wave reference method in homogeneous agar-gelatin phantoms with 0%, 10%, and 20% oil concentrations, and hence different attenuations of 0.117, 0.202, and 0.292 [Formula: see text]/Hz, respectively. Applicability to biological tissues was demonstrated with two ex vivo porcine liver samples (0.79 and 1.35 [Formula: see text]/Hz) and an in vivo human muscle, measured along (0.43 [Formula: see text]/Hz) and across (1.77 [Formula: see text]/Hz) the tissue fibers. In all cases, the data supported the assumptions of a gamma-distributed spectrum for the source and linear frequency attenuation for the tissue. This method provides tissue attenuation, which is relevant diagnostic information to model viscosity, in addition to shear-wave velocity used to assess elasticity. Data processing is simple and could be performed automatically in real time for clinical applications.

The effect of ultrasound with acoustic radiation force on rabbit lung tissue: a preliminary study.

Acoustic radiation force (ARF) elastography has recently become available. The previous animal studies have revealed lung injuries induced by diagnostic ultrasound, but the effects on the lung resulting from exposure to ultrasound with ARF are unknown. This study aimed to assess the risk of lung injury associated with ultrasound with ARF. A focused 2.5-MHz transducer that emits ultrasound with ARF was used. A rabbit was anesthetized, and the transducer was placed in the right subcostal region. Exposure settings of mechanical index (MI) 0.80, pulse duration 10ms, pulse repetition time 5s, and exposure time 150s were applied. One red spot (7×6mm) was observed on the surface of the right lung corresponding to the area of exposure. Alveolar hemorrhage was observed microscopically. This lesion was visible across a range of 20-170μm in depth from the pleural surface. The first example of lung hemorrhage induced by ultrasound with ARF was observed in this study. This observation suggests the possibility of lung injury in humans when ARF elastography is applied with the transducer directed toward the lung. Further studies are needed to determine the safety of this modality.

Acoustic Radiation Force Imaging Elastography Correlation with Liver Biopsy in the Evaluation of Staging of Liver Fibrosis

Background and Aim: Acoustic radiation force elastography (ARFI) is a novel technique for non-invasive assessment of liver fibrosis. In comparison to transient elastography, ARFI can be done in obese patients and at multiple sites of liver. Aim of this study was to investigate the accuracy of ARFI imaging as a non-invasive method for the assessment of liver fibrosis compared to histologic liver fibrosis score. Methods: A prospective comparison study of ARFI elastography was performed in a consecutive series of patients who underwent liver biopsy for the assessment of fibrosis. Mean ARFI velocities (m/s) were compared with Modified Ishak score (F0 to F4) for fibrosis in liver biopsy. Results: One hundred and fourteen patients (mean age 44 ± 13, M/F = 78/36) with liver diseases (cryptogenic = 39, hepatitis B = 37, non-alcoholic fatty liver disease = 32, autoimmune = 3, hepatitis C = 1 and others = 2) underwent ARFI and liver biopsies at the same time period. The mean ARFI (10 measurements per patients) velocities of our study populations was 2.07 ± 0.87 m/s (mean ± SD). The Spearman correlation coefficient between the median values of the ARFI and the histologic fibrosis stage of the Modified Ishak score was highly significant (P < 0.001) with rho = 0.7. Area under the receiver operating characteristic curve for the accuracy of ARFI imaging was 0.81 for the diagnosis of advanced fibrosis (fibrosis stage, F ≥ 3). Conclusion: ARFI imaging has strong correlation with the histologic fibrosis stage along with good accuracy for prediction of severe fibrosis. The authors have none to declare.

Sa1876 Evaluation of Acoustic Radiation Force Elastography (ARFI) in the Diagnosis of Hepatic Fibrosis and Portal Hypertension

Sa1876 Evaluation of Acoustic Radiation Force Elastography (ARFI) in the Diagnosis of Hepatic Fibrosis and Portal Hypertension

A survey of ultrasound elastography approaches to percutaneous ablation monitoring.

Percutaneous thermal ablation has been widely used as a minimally invasive treatment for tumors. Treatment monitoring is essential for preventing complications while ensuring treatment efficacy. Mechanical testing measurements on tissue reveal that tissue stiffness increases with temperature and ablation duration. Different types of imaging methods can be used to monitor ablation procedures, including temperature or thermal strain imaging, strain imaging, modulus imaging, and shear modulus imaging. Ultrasound elastography demonstrates the potential to become the primary imaging modality for monitoring percutaneous ablation. This review briefly presented the state-of-the-art ultrasound elastography approaches for monitoring radiofrequency ablation and microwave ablation. These techniques were divided into four groups: quasi-static elastography, acoustic radiation force elastography, sonoelastography, and applicator motion elastography. Their advantages and limitations were compared and discussed. Future developments were proposed with respect to heat-induced bubbles, tissue inhomogeneities, respiratory motion, three-dimensional monitoring, multi-parametric monitoring, real-time monitoring, experimental data center for percutaneous ablation, and microwave ablation monitoring.

Nature of acoustic nonlinear radiation stress

When a fluid is insonified with ultrasound, a flow consequence of a net stress becomes observable, which has been described as acoustic streaming, quartz wind, acoustic radiation force, or acoustic fountain. Following Sir James Lighthill's formulation of the Reynold's streaming, these phenomena have been attributed to a cumulative viscous effect. Instead, a multiscale effect, whereby the constitutive elastic nonlinearity scales from the ultrasonic to the macroscopic time, is here proposed and formulated to explain its origin. This raises an additional term in the Navier-Stokes equation, which ultimately stems from the anharmonicity of the atomic potential. In our experimental validation, this theory is consistent in water and for a range of ultrasonic configurations, whereas the formerly established viscous theory fails by an order of magnitude. This ultrasonic-fluid interaction, called nonlinear mechanical radiation since it is able to remotely exert a stress field, correctly explains a wide range of industrial and biomedical active ultrasonic uses including jet engines, acoustic tweezers, cyanobacteria propulsion mechanisms, nanofluidics, or acoustic radiation force elastography.

Acoustic Radiation Force Elastographyにおける音響放射力印加時の温度上昇に関する実験的検討

Acoustic Radiation Force Elastographyにおける音響放射力印加時の温度上昇に関する実験的検討

Application of shear wave imaging and shear wave dispersion ultrasound vibrometry in assessing viscoelastic properties of human thyroid: In vivo pilot study

Thyroid cancer is the fastest growing age and gender adjusted cancer in 2011 according the American Cancer Society. The majority of the clinically diagnosed thyroid nodules are benign while less than 5% represent intrathyroidal cancers. Currently, the clinical gold-standard procedure for assessing the thyroid nodules is needle biopsy, a procedure that is associated with significant financial burden as well as pain and risk for patients. Therefore, a noninvasive, affordable, and potentially widely available method to differentiate between benign and malignant thyroid nodules can play an important role in reducing the number of unnecessary biopsies. In this study, we investigate the feasibility of two acoustic radiation force elastography techniques, shear wave dispersion ultrasound vibrometry (SDUV) and comb-push ultrasound shear wave elastography (CUSE imaging), in identifying thyroid nodules (imaging) and differentiating between benign and malignant pathologies based on their elasticity and viscosity (SDUV measurements). Our preliminary results show that the measured shear elasticity and shear viscosity parameters depend on tissue type; hence, these measurements may be utilized to differentiate between healthy normal thyroid tissue, benign nodules, and malignant nodules. Further studies on a large population of patients is required to better evaluate the role of the combination of elasticity and viscosity properties of tissue in differentiating various thyroid nodules.

Experimental study on temperature rise of acoustic radiation force elastography.

Acoustic radiation force (ARF) elastography is potentially useful for imaging the elasticity of human tissue. Because a "push wave" that is used to generate ARF is a long burst wave comparable to that used in regular clinical imaging, detailed investigation of its safety is required. We focus on the transient temperature rise in the far field, where the beam paths are overlapped. Soft tissue mimicking a phantom and bone samples were exposed to a 2-MHz plane wave for 20s. The temperature rises in the far field were measured using a thermocouple. The temperature rises at 1ms, the time required for the displacement measurement, were estimated by fitting the experimental results. The results showed that the thermosensitivity of the bone was 36 times higher than that of the phantom, and the use of a repeated push wave may have exceeded the allowable maximum temperature rise, 1°C, on the bone surface. In conclusion, the imaging area, including the path of the push wave, should be carefully checked and the time interval for consecutive use should be adjusted to prevent thermal risk on the surface of the bone.

Impact of Nonlinear Distortion on Acoustic Radiation Force Elastography

High-intensity focused ultrasound (HIFU) produces an acoustic radiation force that induces tissue displacement, which can be measured by monitoring time shifts in the backscattered signals from interrogation pulses. If the pulse occurs simultaneously with the HIFU, the arrival time of the backscatter will be biased because nonlinearity associated with the HIFU changes the local sound speed. Measurements of the pressure field using 1.1 MHz HIFU and a 7.5 MHz pulse in water exhibited a nonlinearly induced apparent displacement (NIAD) that varied with the HIFU pressure, propagation distance and the timing of the pulse relative to the HIFU. Nonlinear simulations employing the KZK equation predicted NIADs that agreed with measurements. Experiments with chicken breast demonstrated a NIAD with magnitude similar to that expected from the radiation force. Finally it was shown that if two pulses were fired with different phases relative to the HIFU, then upon averaging, the NIAD could be mitigated.

Acoustic Radiation Force Elastography and Transient Elastography in Cystic Fibrosis: Liver Stiffness Is not increased in CF-Related Liver Disease in Adults

Patients with cystic fibrosis (CF) can develop cholestatic liver disease (CFLD). We evaluated ARFI, transient elastography (TE), and APRI-score in adult CF-patients for detection of CFLD. CFLD was defined by ≥2 of the criteria: hepatomegaly, abnormal findings in conventional sonography and elevated liver enzymes. 50 healthy controls and 40 patients with liver cirrhosis of different etiologies served as ARFI controls. ARFI and TE were performed in the right liver lobe. 55 CF patients were recruited (30 males, 25 females, age 30.3 years; n = 41 without CFLD, n = 14 with CLFD). CFLD-individuals (mean 1.16 m/s; 95% CI [0.93; 1.39]) showed an ARFI shear-wave velocity similar to CF-patients without liver involvement (mean 1.13 m/s; 95% CI [1.08; 1.17]). Both subgroups did not differ from healthy controls (mean 1.15 m/s; 95%CI [1.10; 1.20]). CF cases with liver cirrhosis (n = 6; mean 1.49 m/s) differed significantly from cirrhosis of other etiologies (mean 3.07 m/s; p<0.001). TE revealed a liver stiffness of 5.34 kPa (95% CI [3.34; 7.35]) in CFLD versus 3.98 kPa (95% CI [3.63; 4.33]) in non-CLFD cases (p = 0.002). Diagnostic performance for CFLD detection was comparable between ARFI (AUROC 0.885±0.09), TE (AUROC 0.895±0.09) and APRI-score (AUROC 0.93±0.07). Liver stiffness is not increased in CFLD. Diagnostic accuracy of ARFI and TE in CF is limited. Tissue stiffness depends on the etiology of liver disease.

Acoustic Radiation Force Elastography and Transient Elastography in Autoimmune Hepatitis: Left Liver Lobe Measurement Shows Better Accuracy for Early Detection of Fibrosis

Autoimmune hepatitis (AIH) can cause liver fibrosis and cirrhosis. We evaluated the performance of ARFI and transient elastography (TE) for staging in AIH patients. AIH was defined according to the International Autoimmune Hepatitis Group criteria. ARFI was performed in both liver lobes (l_ARFI and r_ARFI) and TE in the right lobe. Elastography results were compared with three different clinical patterns based on histology, laboratory values, and sonomorphology: (i) cirrhosis, (ii) pathological sonomorphology, (iii) AIH in remission with normal sonomorphology. 47 AIH patients were recruited (10 males, 37 females, age 54.2 years). Patients with normal liver morphology (n = 14) had a shear-wave velocity of 1.26±0.17 m/s (l_ARFI) and 1.18 ± 0.15 m/s (r_ARFI). TE revealed a liver stiffness of 4.75 ± 2.24 kPa. Individuals with liver cirrhosis (n = 17) had a significant increase of liver stiffness: 1.91±0.5 2m/s (l_ARFI), 1.91±0.65m/s (r_ARFI) and TE 19.59±17.43 kPa (p<0.05, respectively). Diagnostic performance for cirrhosis detection was comparable: AUROC was 0.778 (l_ARFI), 0.862 (r_ARFI) and 0.884 (TE). Group II (n = 16) had an increase in l_ARFI (1.66±0.37m/s, p<0.001) while r_ARFI (1.22±1.28 m/s) and TE (6.07±2.24 kPa) showed no increase: AUROC was 0.887 (l_ARFI), 0.685 (r_ARFI) and 0.815 (TE). ARFI and TE can reliably detect liver cirrhosis in autoimmune hepatitis with comparable accuracy. l_ARFI has a better accuracy for early detection of fibrosis than r_ARFI or TE.

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.

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. (E-mail: bfahey04@gmail.com)

A novel motion compensation algorithm for acoustic radiation force elastography

A novel method of physiological motion compensation for use with radiation force elasticity imaging has been developed. The method utilizes a priori information from finite element method models of the response of soft tissue to impulsive radiation force to isolate physiological motion artifacts from radiation force-induced displacement fields. The new algorithmis evaluated in a series of clinically realistic imaging scenarios, and its performance is compared to that achieved with previously described motion compensation algorithms. Though not without limitations, the new model-based motion compensation algorithm performs favorably in many circumstances and may be a logical choice for use with in vivo abdominal imaging.

In vivo visualization of abdominal malignancies with acoustic radiation force elastography

The utility of acoustic radiation force impulse (ARFI) imaging for real-time visualization of abdominal malignancies was investigated. Nine patients presenting with suspicious masses in the liver (n = 7) or kidney (n = 2) underwent combined sonography/ARFI imaging. Images were acquired of a total of 12 tumors in the nine patients. In all cases, boundary definition in ARFI images was improved or equivalent to boundary definition in B-mode images. Displacement contrast in ARFI images was superior to echo contrast in B-mode images for each tumor. The mean contrast for suspected hepatocellular carcinomas (HCCs) in B-mode images was 2.9 dB (range: 1.5–4.2) versus 7.5 dB (range: 3.1–11.9) in ARFI images, with all HCCs appearing more compliant than regional cirrhotic liver parenchyma. The mean contrast for metastases in B-mode images was 3.1 dB (range: 1.2–5.2) versus 9.3 dB (range: 5.7–13.9) in ARFI images, with all masses appearing less compliant than regional non-cirrhotic liver parenchyma. ARFI image contrast (10.4 dB) was superior to B-mode contrast (0.9 dB) for a renal mass. To our knowledge, we present the first in vivo images of abdominal malignancies in humans acquired with the ARFI method or any other technique of imaging tissue elasticity.