Acoustic radiation force on a cylindrical composite particle with an elastic thin shell and an internal eccentric liquid column in a plane ultrasonic wave field

A model with three-layer structure is introduced to explore the acoustic radiation force(ARF)on composite particles with an elastic thin shell.Combing acoustic scattering of cylinder and the thin-shell theorem,the ARF expression was derived,and the longitudinal and transverse components of the force and axial torque for an eccentric liquid-filled composite particle was obtained.It was found that many factors,such as medium properties,acoustic parameters,eccentricity,and radius ratio of the inner liquid column,affect the acoustic scattering field of the particle,which in turn changes the forces and torque.The acoustic response varies with the particle structures,so the resonance peaks of the force function and torque shift with the eccentricity and radii ratio of particle.The acoustic response of the particle is enhanced and exhibits higher force values due to the presence of the elastic thin shell and the coupling effect with the eccentricity of the internal liquid column.The decrease of the inner liquid density may suppress the high-order resonance peaks,and internal fluid column has less effects on the change in force on composite particle at ka>3,while limited differences exist at ka<3.The axial torque on particles due to geometric asymmetry is closely related to ka and the eccentricity.The distribution of positive and negative force and torque along the axis ka exhibits that composite particle can be manipulated or separated by ultrasound.Our theoretical analysis can provide support for the acoustic manipulation,sorting,and targeting of inhomogeneous particles.

Scheme of negative acoustic radiation force based on a multiple-layered spherical structure

Acoustic radiation force(ARF), as an important particle manipulation method, has been extensively studied in recent years. With the introduction of the concept of “acoustic tweezers”, negative acoustic radiation has become a research hotspot. In this paper, a scheme of realizing negative ARF based on the multiple-layered spherical structure design is proposed. The specific structure and design idea are presented. Detailed theoretical calculation analysis is carried out.Numerical simulations have been performed to verify the correctness of this prediction. The conjecture that the suppression of backscattering can achieve negative ARF is verified concretely, which greatly expands the application prospect and design ideas of the ARF. This work has laid a theoretical foundation for realizing precise control of the structure.

Acoustic radiation force impulse predicts long-term outcomes in a large-scale cohort:High liver cancer,low comorbidity in hepatitis B virus

BACKGROUND Acoustic radiation force impulse(ARFI)is used to measure liver fibrosis and predict outcomes.The performance of elastography in assessment of fibrosis is poorer in hepatitis B virus(HBV)than in other etiologies of chronic liver disease.AIM To evaluate the performance of ARFI in long-term outcome prediction among different etiologies of chronic liver disease.METHODS Consecutive patients who received an ARFI study between 2011 and 2018 were enrolled.After excluding dual infection,alcoholism,autoimmune hepatitis,and others with incomplete data,this retrospective cohort were divided into hepatitis B(HBV,n=1064),hepatitis C(HCV,n=507),and non-HBV,non-HCV(NBNC,n=391)groups.The indexed cases were linked to cancer registration(1987-2020)and national mortality databases.The differences in morbidity and mortality among the groups were analyzed.RESULTS At the enrollment,the HBV group showed more males(77.5%),a higher prevalence of prediagnosed hepatocellular carcinoma(HCC),and a lower prevalence of comorbidities than the other groups(P<0.001).The HCV group was older and had a lower platelet count and higher ARFI score than the other groups(P<0.001).The NBNC group showed a higher body mass index and platelet count,a higher prevalence of pre-diagnosed non-HCC cancers(P<0.001),especially breast cancer,and a lower prevalence of cirrhosis.Male gender,ARFI score,and HBV were independent predictors of HCC.The 5-year risk of HCC was 5.9%and 9.8%for those ARFI-graded with severe fibrosis and cirrhosis.ARFI alone had an area under the receiver operating characteristic curve(AUROC)of 0.742 for prediction of HCC in 5 years.AUROC increased to 0.828 after adding etiology,gender,age,and platelet score.No difference was found in mortality rate among the groups.CONCLUSION The HBV group showed a higher prevalence of HCC but lower comorbidity that made mortality similar among the groups.Those patients with ARFI-graded severe fibrosis or cirrhosis should receive regular surveillance.

Three-dimensional acoustic radiation force of a eukaryotic cell arbitrarily positioned in a Gaussian beam

Expressions are derived for calculating the three-dimensional acoustic radiation force(ARF)on a multilayer microsphere positioned arbitrarily in a Gaussian beam.A theoretical model of a three-layer microsphere with a cell membrane,cytoplasm,and nucleus is established to study how particle geometry and position affect the three-dimensional ARF,and its results agree well with finite-element numerical results.The microsphere can be moved relative to the beam axis by changing its structure and position in the beam,and the axial ARF increases with increasing outer-shell thickness and core size.This study offers a theoretical foundation for selecting suitable parameters for manipulating a three-layer microsphere in a Gaussian beam.

Characterization of focal liver masses using acoustic radiation force impulse elastography

AIM:To investigate the diagnostic performance of acoustic radiation force impulse(ARFI) elastography for characterizing focal liver mass by quantifying their stiffness.METHODS:This prospective study included 62 patients with a focal liver mass that was well visualized on conventional ultrasonography performed in our institution from February 2011 to November 2011.Among them,12 patients were excluded for ARFI measurement failure due to a lesion that was smaller than the region of the interest and at an inaccessible location(deeper than 8 cm)(n = 7) or poor compliance to hold their breath as required(n = 5).Finally,50 patients with valid ARFI measurements were enrolled.If a patient had multiple liver masses,only one mass of interest was chosen.The masses were diagnosed by histological examination or clinical diagnostic criteria.During ultrasonographic evaluation,stiffness,expressed as velocity,was checked 10 times per focal liver mass and the surrounding liver parenchyma.RESULTS:After further excluding three masses that were non-diagnostic on biopsy,a total of 47 focal mass lesions were tested,including 39(83.0%) malignant masses [24 hepatocellular carcinomas(HCC),seven cholangiocellular carcinomas(CCC),and eight liver metastases] and eight(17.0%) benign masses(five hemangiomas and three focal nodular hyperplasias,FNH).Thirty-seven(74.0%) masses were confirmed by histological examination.The mean velocity was 2.48 m/s in HCCs,1.65 m/s in CCCs,2.35 m/s in metastases,1.83 m/s in hemangiomas,and 0.97 m/s in FNHs.Although considerable overlap was still noted between malignant and benign masses,significant differences in ARFI values were observed between malignant and benign masses(mean 2.31 m/s vs 1.51 m/s,P = 0.047),as well as between HCCs and benign masses(mean 2.48 m/s vs 1.51 m/s,P = 0.006).The areas under the receiver operating characteristics curves(AUROC) for discriminating the malignant masses from benign masses was 0.724(95%CI,0.566-0.883,P = 0.048),and the AUROC for discriminating HCCs from benign masses was 0.813(95%CI,0.649-0.976,P = 0.008).To maximize the sum of sensitivity and specificity,an ARFI value of 1.82 m/s was selected as the cutoff value to differentiate malignant from benign liver masses.Furthermore,the cutoff value for distinguishing HCCs from benign masses was also determined to be 1.82 m/s.The diagnostic performance of the sum of the ARFI values for focal liver masses and the surrounding liver parenchyma to differentiate liver masses improved(AUROC = 0.853;95%CI,0.745-0.960;P = 0.002 in malignant liver masses vs benign ones and AUROC = 0.948;95%CI,0.896-0.992,P < 0.001 in HCCs vs benign masses).CONCLUSION:ARFI elastography provides additional information for the differential diagnosis of liver masses.However,our results should be interpreted in clinical context,because considerable overlap in ARFI values existed among liver masses.

Acoustic radiation force impulse of the liver

Acoustic radiation force impulse(ARFI)imaging is a new and promising ultrasound-based diagnostic technique that,evaluating the wave propagation speed,allows the assessment of the tissue stiffness.ARFI is implemented in the ultrasound scanner.By short-duration acoustic radiation forces(less than 1 ms),localized displacements are generated in a selected region of interest not requiring any external compression so reducing the operator dependency.The generated wave scan provides qualitative or quantitative(wave velocity values)responses.Several non-invasive methods for assessing the staging of fibrosis are used,in order to avoid liver biopsy.Liver function tests and transient elastography are non-invasive,sensitive and accurate tools for the assessment of liver fibrosis and for the discrimination between cirrhotic and non-cirrhotic liver.Many published studies analyse ARFI performance and feasibility in studying diffuse liver diseases and compare them to other diagnostic imaging modalities such as conventional ultrasonography and transient elastography.Solid focal liver lesions,both benign and malignant,are common findings during abdominal examinations.The accurate characterization and differential diagnosis are important aims of all the imaging modalities available today.Only few papers describe the application of ARFI technology in the study of solid focal liver lesions,with different results.In the present study,the existing literature,to the best of our knowledge,about ARFI application on diffuse and focal liver pathology has been evaluated and results and statistical analyses have been compared,bringing to the conclusion that ARFI can be used in the study of the liver with similar accuracy as transient elastography in diagnosing significant fibrosis or cirrhosis and has got some advantages in respect to transient elastography since it does not require separate equipment,better displays anatomical structures and measurements can be successfully carried out almost in every patient.

Evaluation of acoustic radiation force impulse imaging for determination of liver stiffness using transient elastography as a reference

AIM: To evaluate cut-off values and performance of acoustic radiation force impulse imaging (ARFI) using transient elastography [FibroScan■ (FS)] as a reference. METHODS: Six hundred and six patients were enrolled in this study.All patients underwent liver stiffness measurement with FS (FS-LS) and ARFI (with shear wave velocity quantification; ARFI-SWV) and the performance of ARFI in comparison to FS was determined. Sixtyeight patients underwent liver biopsy. RESULTS: Significantly higher success rates for the determination of liver stiffness were found using ARFI as compared to FS [604/606 (99.7%) vs 482/606 (79.5%); P < 0.001]. ARFI-SWV correlated significantly with FS-LS (r = 0.920, P < 0.001). ARFI-SWV increased significantly with the stage of fibrosis (1.09 ± 0.13 m/s for patients with no significant fibrosis (FS-LS < 7.6 kPa); 1.46 ± 0.27 m/s for patients with significant liver fibrosis (7.6 < FS-LS ≤ 13.0 kPa); and 2.55 ± 0.77 m/s for patients with liver cirrhosis (FS-LS > 13.0 kPa)). ARFI-SWV cut-off values were identified for no significant fibrosis (1.29 m/s; sensitivity 91.4% and specificity 92.6%) and for liver cirrhosis (1.60 m/s; sensitivity 92.3% and specificity 96.5%). The optimal cut-off value for predicting liver fibrosis (F ≥ 2) was 1.32 m/s (sensitivity 87.0% and specificity 80.0%) and for liver cirrhosis (F4) 1.62 m/s (sensitivity 100% and specificity 85.7%), for patients who underwent liver biopsy. An excellent inter-and intraobserver reproducibility was observed for ARFI-SWV determinations. CONCLUSION: An ARFI-SWV cut-off value of 1.29 m/s seems to be optimal for patients with no significant liver fibrosis and 1.60 m/s for patients with liver cirrhosis.

Acoustic radiation force impulse imaging for assessing liver fibrosis in alcoholic liver disease

AIM: To evaluate the performance of elastography by ultrasound with acoustic radiation force impulse(ARFI) in determining fibrosis stage in patients with alcoholic liver disease(ALD) undergoing alcoholic detoxification in relation to biopsy.METHODS: Eighty-three patients with ALD undergoing detoxification were prospectively enrolled. Each patient underwent ARFI imaging and a liver biopsy onthe same day. Fibrosis was staged according to the METAVIR scoring system. The median of 10 valid ARFI measurements was calculated for each patient.RESULTS: Sixty-nine males and thirteen females(one patient excluded due to insufficient biopsy size) were assessed with a mean alcohol consumption of 132.4 ± 128.8 standard drinks per week and mean cumulative year duration of 17.6 ± 9.5 years. Sensitivity and specificity were respectively 82.4%(0.70-0.95) and 83.3%(0.73-0.94)(AUROC = 0.87) for F ≥ 2 with a cut-off value of 1.63m/s; 82.4%(0.64-1.00) and 78.5%(0.69-0.89)(AUROC = 0.86) for F ≥ 3 with a cut-off value of 1.84m/s; and 92.3%(0.78-1.00] and 81.6%(0.72-0.90)(AUROC = 0.89) for F = 4 with a cut-off value of 1.94 m/s.CONCLUSION: ARFI is an accurate, non-invasive and easy method for assessing liver fibrosis in patients with ALD undergoing alcoholic detoxification.

Liver reserve function assessment by acoustic radiation force impulse imaging

AIM: To evaluate the utility of liver reserve function by acoustic radiation force impulse(ARFI) imaging in patients with liver tumors. METHODS: Seventy-six patients with liver tumors were enrolled in this study. Serum biochemical indexes, such as aminotransferase(ALT), aspartate aminotransferase(AST), serum albumin(ALB), total bilirubin(T-Bil), and other indicators were observed. Liver stiffness(LS) was measured by ARFI imaging, measurements were repeated 10 times, and the average value of the results was taken as the final LS value. Indocyanine green(ICG) retention was performed, and ICG-K and ICG-R15 were recorded. Child-Pugh(CP) scores were carried out based on patient's preoperative biochemical tests and physical condition. Correlations among CP scores,ICG-R15, ICG-K and LS values were observed and analyzed using either the Pearson correlation coefficient or the Spearman rank correlation coefficient. KruskalWallis test was used to compare LS values of CP scores, and the receiver-operator characteristic(ROC) curve was used to analyze liver reserve function assessment accuracy. RESULTS: LS in the ICG-R15 10%-20% group was significantly higher than in the ICG-R15 < 10% group; and the difference was statistically significant(2.19 ± 0.27 vs 1.59 ± 0.32, P < 0.01). LS in the ICG-R15 > 20% group was significantly higher than in the ICG-R15 < 10% group; and the difference was statistically significant(2.92 ± 0.29 vs 1.59 ± 0.32, P < 0.01). The LS value in patients with CP class A was lower than in patients with CP class B(1.57 ± 0.34 vs 1.86 ± 0.27, P < 0.05), while the LS value in patients with CP class B was lower than in patients with CP class C(1.86 ± 0.27 vs 2.47 ± 0.33, P < 0.01). LS was positively correlated with ICG-R15(r = 0.617, P < 0.01) and CP score(r = 0.772, P < 0.01). Meanwhile, LS was negatively correlated with ICG-K(r =-0.673, P < 0.01). AST, ALT and T-Bil were positively correlated with LS, while ALB was negatively correlated with LS(P < 0.05). The ROC curve revealed that the when the LS value was 2.34 m/s, the Youden index was at its highest point, sensitivity was 69.2% and specificity was 92.1%. CONCLUSION: For patients with liver tumors, ARFI imaging is a useful tool for assessing liver reserve function.

Factors correlating with acoustic radiation force impulse elastography in chronic hepatitis C

AIM: To investigate the factors other than fibrosis stage correlating with acoustic radiation force impulse (ARFI) elastograpy in chronic hepatitis C.

Application of acoustic radiation force impulse imaging for the evaluation of focal liver lesion elasticity

BACKGROUND: Acoustic radiation force impulse (ARFI) imaging is a new elastography method for the evaluation of tissue stiffness. This study aims to evaluate the performance of ARFI in noninvasive assessment of the tissue stiffness of focal liver lesion (FLL) and to explore its potential value in the differential diagnosis of FLL. METHODS: ARFI was performed in 140 patients with 154 FLLs, which included 28 hemangiomas (ANGIs), 14 focal nodular hyperplasias (FNHs), 61 hepatocellular carcinomas (HCCs), 39 metastases and 12 cholangiocellular carcinomas (CCCs). Virtual touch tissue quantification (VTTQ) values were obtained, analyzed and compared. The area under the receiver operating characteristic curve (AUROC) and optimal cut-off values were obtained using a receiver operating characteristic (ROC) curve analysis to assess diagnostic performance. All cases were definitively diagnosed using histopathology, CT, MRI or contrast-enhanced ultrasound. RESULTS: The VTTQ median values of ANGI, FNH, HCC metastasis and CCC were 1.30, 1.80, 2.52, 3.08 and 3.89 m/s respectively. A significant increase in the VTTQ values of different lesions was observed: ANGI【FNH【HCC【metastasis 【CCC (P【0.001). The AUROC (95% CI) of VTTQ values was 0.94 (0.90-0.98) for ANGI, 0.91 (0.87-0.96) for malignant lesions and 0.87 (0.79-0.94) for CCC. The sensitivity and specificity for ANGI (86.5%, 89.3%, respectively), malignancy (81.3% 92.9%, respectively), and CCC (91.7%, 72.5%, respectively) were associated with VTTQ cut-off values of 1.76, 2.22 and 3.00 m/s respectively.CONCLUSIONS: ARFI can accurately and objectively assess the elasticity of lesions by obtaining the shear wave elastic value of FLL with VTTQ. Therefore, ARFI is a novel, simple, noninvasive and useful diagnostic method for the characterization of FLL.

Primary biliary cirrhosis degree assessment by acoustic radiation force impulse imaging and hepatic fibrosis indicators

AIM: To evaluate the assessment of primary biliary cirrhosis degree by acoustic radiation force impulse imaging (ARFI) and hepatic fibrosis indicators. METHODS: One hundred and twenty patients who developed liver cirrhosis secondary to primary biliary cirrhosis were selected as the observation group, with the degree of patient liver cirrhosis graded by Child-Pugh (CP) score. Sixty healthy individuals were selected as the control group. The four indicators of hepatic fibrosis were detected in all research objects, including hyaluronic acid (HA), laminin (LN), type III collagen (PC III), and type IV collagen (IV-C). The liver parenchyma hardness value (LS) was then measured by ARFI technique. LS and the four indicators of liver fibrosis (HA, LN, PC III, and IV-C) were observed in different grade CP scores. The diagnostic value of LS and the four indicators of liver fibrosis in determining liver cirrhosis degree with PBC, whether used alone or in combination, were analyzed by receiver operating characteristic (ROC) curve. RESULTS: LS and the four indicators of liver fibrosis within the three classes (A, B, and C) of CP scores in the observation group were higher than in the control group, with C class > B class > A class; the differences were statistically significant (P < 0.01). Although AUC values of LS within the three classes of CP scores were higher than in the four indicators of liver fibrosis, sensitivity and specificity were unstable. The ROC curves of LS combined with the four indicators of liver fibrosis revealed that: AUC and sensitivity in all indicators combined in the A class of CP score were higher than in LS alone, albeit with slightly decreased specificity; AUC and specificity in all indicators combined in the B class of CP score were higher than in LS alone, with unchanged sensitivity; AUC values (0.967), sensitivity (97.4%), and specificity (90%) of all indicators combined in the C class of CP score were higher than in LS alone (0.936, 92.1%, 83.3%). CONCLUSION: The diagnostic value of PBC cirrhosis degree in liver cirrhosis degree assessment by ARFI combined with the four indicators of serum liver fibrosis is of satisfactory effectiveness and has important clinical application value.

Parameters affecting different acoustic radiation force impulse applications in the diagnosis of fibrotic liver changes

AIM: To analyze the virtual touch tissue quantification(VTTQ) and virtual touch imaging quantification(VTIQ) techniques, and identify possible factors that may influence VTTQ and VTIQ measurements.METHODS: One hundred and eighty-six(104 women/82 men) of 323 subjects met the inclusion criteria(age > 18 years, no history of chronic or gastrointestinal disease, body-mass index(BMI) < 30 kg/m2, a fasting period of at least three hours, no history of hepatotoxic pharmaceuticals, alcohol consumption < 24 g/d in men and < 12 g/d in women, and normal findings upon ultrasound examination of the abdomen). Measurements were taken at depths of 50 mm with VTTQ, 15 mm and 25 mm with VTIQ in the right hepatic lobe, and at 15 mm with only VTIQ in the left hepatic lobe. The examiner acquired six measurements per position, thereby giving 24 measurements in total.RESULTS: The 95% confidence intervals of mean were1.23-1.29 m/s for VTTQ and 1.29-1.37 m/s, 1.17-1.23 m/s, and 1.48-1.57 m/s for VTIQ in a depth of 15 mm and 25 mm in the right hepatic lobe and 15 mm in the left hepatic lobe. Only superficial measurements in the right hepatic lobe with the VTIQ method exhibited an effect of age on shear wave velocity. Measurements acquired using the 6C1 probe with the VTTQ method showed no dependence on BMI. By comparison, BMI influenced measurements taken with the VTIQ method using the 9L4 probe in the superficial and deep areas of the right hepatic lobe, as well as in the left hepatic lobe(P = 0.0160, P = 0.0019, P = 0.0173, respectively). Gender influenced measurements at depths of 50 mm with VTTQ and 25 mm with VTIQ in the right hepatic lobe(P = 0.0001, P = 0.0269). Significant differences were found between measurements with the 6C1(VTTQ) and 9L4 probes(VTIQ)(P = 0.0067), between superficial and deep measurements(P < 0.0001), and between the right and left lobes of the liver(P < 0.0001). CONCLUSION: Measurements in the right lobe and deep regions are preferable. Gender differences must be considered. BMI must be considered when assessing VTIQ technology.

Combined acoustic radiation force impulse, aminotransferase to platelet ratio index and Forns index assessment for hepatic fibrosis grading in hepatitis B

AIM: To investigate the combined diagnostic accuracy of acoustic radiation force impulse(ARFI), aspartate aminotransferase to platelet ratio index(APRI) and Forns index for a non-invasive assessment of liver fibrosis in patients with chronic hepatitis B(CHB). METHODS: In this prospective study, 206 patients had CHB with liver fibrosis stages F0-F4 classified by METAVIR and 40 were healthy volunteers were measured by ARFI, APRI and Forns index separately or combined as indicated. RESULTS: ARFI, APRI or Forns index demonstrated a significant correlation with the histological stage(all P < 0.001). According to the AUROC of ARFI and APRI for evaluating fibrotic stages more than F2, ARFI showed an enhanced diagnostic accuracy than APRI(P < 0.05). The combined measurement of ARFI and APRI exhibited better accuracy than ARFI alone when evaluating ≥ F2 fibrotic stage(Z = 2.77, P = 0.006). Combination of ARFI, APRI and Forns index did not obviously improve the diagnostic accuracy compared to the combination of ARFI and APRI(Z = 0.958, P = 0.338). CONCLUSION: ARFI + APRI showed enhanced diagnostic accuracy than ARFI or APRI alone for significant liver fibrosis and ARFI + APRI + Forns index shows the same effect with ARFI + APRI.

Axial acoustic radiation force on a fluid sphere between two impedance boundaries for Gaussian beam

The acoustic radiation force on a fluid sphere immersed in water between two boundaries given by a Gaussian beam is theoretically and numerically investigated in this work. Based on the finite series method, the Gaussian beam is expressed in terms of Bessel function and a weighting parameter. The effects of the two boundaries concerned in our study is worked out by the image theory. This work also provides a reference when considering the effects of certain factors such as the radius of the sphere and the distance between the sphere and two boundaries. The contrast with the acoustic radiation force on a fluid sphere near only one boundary is also made in this paper. Our study can offer a theoretical basis for acoustics manipulation, acoustic sensors in the field of biomedical ultrasound and material science.

Value of acoustic radiation force impulse elastography for the assessment of ascites syndrome

AIM:To assess the feasibility of performing acoustic radiation force impulse(ARFI) elastography in patients with ascites and its predictive value for the cirrhotic or non-cirrhotic etiology of ascites.METHODS:Our study included 153 patients with ascites,mean age 58.8 ± 13.1 years.One hundred and fifteen(75.2%) patients had ascites in the context of cirrhosis,29(18.9%) had non-cirrhotic ascites(diagnosed by clinical,ultrasound,endoscopic and/or laparoscopic criteria) and in 9(5.9%) cases we could not establish the etiology of ascites.We performed 10 ARFI measurements and the median value was calculated and expressed in meters/second(m/s).Among the 29 patients with non-cirrhotic ascites were included:20 laparoscopically demonstrated peritoneal carcinomatosis with histological confirmation,7 acute pancreatitis with ascites which later resolved,and one case each of lymphatic ascites and ascites in the context of a liver abscess.In 11 of the 20 patients with peritoneal carcinomatosis,the liver structure was homogenous in the ultrasound examination and in 9 patients the ultrasound exam revealed liver metastases.RESULTS:We could not obtain valid ARFI measurements in 5 patients(3.2%).The mean liver stiffness measurements by means of ARFI were statistically significantly higher in patients with cirrhotic ascites than in those with non-cirrhotic ascites:3.04 ± 0.70 vs 1.45 ± 0.59 m/s(P < 0.001).For a cut-off value of 1.8 m/s for predicting cirrhosis(and ascites in the context of cirrhosis),as obtained in a previous study,ARFI had 98.1% sensitivity,86.2% specificity,96.4% positive predictive value,92.5% negative predictive value and 95.6% accuracy for predicting cirrhotic ascites.For a cut-off value of 1.9 m/s the accuracy was 94.9% and for a 2 m/s cut-off value it was 92.8%.CONCLUSION:ARFI elastography is feasible in most patients with ascites and has a very good predictive value for the cirrhotic or non-cirrhotic etiology of ascites.

Axial acoustic radiation force on an elastic spherical shell near an impedance boundary for zero-order quasi-Bessel-Gauss beam

Shell structures have increasingly widespread applications in biomedical ultrasound fields such as contrast agents and drug delivery,which requires the precise prediction of the acoustic radiation force under various circumstances to improve the system efficiency.The acoustic radiation force exerted by a zero-order quasi-Bessel-Gauss beam on an elastic spherical shell near an impedance boundary is theoretically and numerically studied in this study.By means of the finite series method and the image theory,a zero-order quasi-Bessel-Gauss beam is expanded in terms of spherical harmonic functions,and the exact solution of the acoustic radiation force is derived based on the acoustic scattering theory.The acoustic radiation force function,which represents the radiation force per unit energy density and per unit cross-sectional surface,is especially investigated.Some simulated results for a polymethyl methacrylate shell and an aluminum shell are provided to illustrate the behavior of acoustic radiation force in this case.The simulated results show the oscillatory property and the negative radiation force caused by the impedance boundary.An appropriate relative thickness of the shell can generate sharp peaks for a polymethyl methacrylate shell.Strong radiation force can be obtained at small half-cone angles and the beam waist only affects the results at high frequencies.Considering that the quasi-Bessel-Gauss beam possesses both the energy focusing property and the non-diffracting advantage,this study is expected to be useful in the development of acoustic tweezers,contrast agent micro-shells,and drug delivery applications.

A Modified Monte Carlo Model of Speckle Tracking of Shear Wave Induced by Acoustic Radiation Force for Acousto-Optic Elasticity Imaging

A modified Monte Carlo model of speckle tracking of shear wave propagation in scattering media is proposed. The established Monte Carlo model mainly concerns the variations of optical electric field and speckle. The two- dimensional intensity distribution and the time evolution of speckles in different probe locations are obtained. The fluctuation of speckle intensity tracks the acoustic-radiation-force shear wave propagation, and especially the reduction of speckle intensity implies attenuation of shear wave. Then, the shear wave velocity is estimated quantitatively on the basis of the time-to-peak algorithm and linear regression processing. The results reveal that a smaller sampling interval yields higher estimation precision and the shear wave velocity is estimated more efficiently by using speckle intensity difference than by using speckle contrast difference according to the estimation error. Hence, the shear wave velocity is estimated to be 2.25 m/s with relatively high accuracy for the estimation error reaches the minimum （0.071）.

Normal values of shear wave velocity in liver tissue of healthy children measured using the latest acoustic radiation force impulse technology

BACKGROUND Several studies have demonstrated the feasibility and effectiveness of using ultrasound elastography to assess liver tissue stiffness.Virtual touch imaging quantification(VTIQ)based on acoustic radiation force impulse imaging has been developed as a latest and noninvasive method for assessing liver stiffness in children.AIM To determine the standard value in healthy children,and to identify possible factors that might influence the VTIQ measurement.METHODS With the ethical approval,202 children between 1 month and 15 years old were included in this study.None of them had any liver or systematic diseases.All children had a normal ultrasound scan and normal body mass index(BMI)range.The subjects were divided into four age and BMI groups.The effects of gender,age,liver lobe,measurement depth,and BMI on liver elasticity were investigated.RESULTS A significant correlation was found between age and shear wave velocity(SWV)value.At measurement depths of 1.5 cm and 2.0 cm in the left lobe,there were significant differences among the age groups.SWV values were significantly negatively correlated with the measurement depth.Gender,liver lobe,and BMI showed no significant effect on the SWV values.Age and BMI may influence the quality of the elastogram.CONCLUSION VTIQ is a noninvasive technique that is feasible to measure liver stiffness in children.The afore-mentioned velocity value obtained utilizing VTIQ method could be used as reference value for normal liver stiffness in children.

Acoustic radiation force on a multilayered sphere in a Gaussian standing field

We develop a model for calculating the radiation force on spherically symmetric multilayered particles based on the acoustic scattering approach.An expression is derived for the radiation force on a multilayered sphere centered on the axis of a Gaussian standing wave propagating in an ideal fluid,The effects of the sound absorption of the materials and sound wave on acoustic radiation force of a multilayered sphere immersed in water are analyzed,with particular emphasis on the shell thickness of every layer,and the width of the Gaussian beam.The results reveal that the existence of particle trapping behavior depends on the choice of the non-dimensional frequency ka,as well as the shell thickness of each layer.This study provides a theoretical basis for the development of acoustical tweezers in a Gaussian standing wave,which may benefit the improvement and development of acoustic control technology,such as trapping,sorting,and assembling a cell,and drug delivery applications.