Magnetic resonance elastography (MRE) outperforms acoustic force radiation impulse (ARFI) in predicting oesophageal varices in obese NAFLD cirrhosis

PURPOSE

Liver stiffness measurement (LSM) by transient elastography has been shown to underperform in high-risk varices (HRVs) prediction in obese non-alcoholic fatty liver disease (NAFLD) compensated cirrhosis (CC). LSM by magnetic resonance elastography (MRE) and acoustic force radiation impulse (ARFI) has been shown to be useful in prediction of oesophageal varices (EVs), but has limited evidence in obese NAFLD-CC.

METHODS

Obese patients with NAFLD-CC who underwent MRE and ARFI for LSM and endoscopy for screening of varices were enrolled. Performance of MRE and ARFI for predicting EVs or HRVs was evaluated using area under receiver operating characteristics (AUROC) curves and regression analyses were performed for predictor variables.

RESULTS

One hundred eight patients [mean age 54.7 ± 9.6 years, median BMI, 28.5 (26.4-30.0) kg/m2. 72.2% diabetics, 45.4% hypertensive] were enrolled. Fifty-two (48.1%) had no varices, while 29 (26.8%) and 27 (25%) had low-risk varices (LRVs) and HRVs, respectively. MRE-LSM was higher in patients with LRVs (p = 0.01) or HRVs (p = 0.001) against those without varices. ARFI-LSM did not differ significantly between those without and with LRVs or HRVs (p > 0.05 for all). There was a low correlation between ARFI-LSM and MRE-LSM in the overall cohort (r = 0.19). Only platelet count (PC) [0.98 (0.97-0.99)] and MRE-LSM [1.8 (1.26-2.79)] were predictors of HRVs. At a cut-off of 4.75, MRE showed a sensitivity of 96.3%. Model combining MRE-LSM with PC had a diagnostic AUROC of 0.77 and 0.76 for EVs and HRVs.

CONCLUSION

In obese NAFLD-CC, MRE-LSM is significantly higher in patients with varices. MRE combined with PC predicts EVs and HRVs with better accuracy than ARFI.

Acoustic Radiation Forced Impulse of the Liver and the Spleen, Combined with Spleen Dimension and Platelet Count in New Ratio Scores, Identifies High-Risk Esophageal Varices in Well-Compensated Cirrhotic Patients

Acoustic radiation forced impulse (ARFI) is an integrated ultrasound method, measuring stiffness by point shear wave elastography. To evaluate the diagnostic performance of the ARFI of the liver and the spleen, combined with spleen dimension and platelet count, in predicting high-risk esophageal varices (HRVs) in cirrhotic patients, a prospective and cross-sectional study was conducted between February 2017 and February 2021. The following ratio scores were calculated based on ARFI measurements: ALSDP (ARFI Liver-Spleen Diameter-to-Platelet Ratio Score), ASSDP (ARFI Spleen-Spleen Diameter-to-Platelet Ratio Score), ASSAP (ARFI Spleen-Spleen Area-to-Platelet Ratio Score), and ALSAP (ARFI Liver-Spleen Area-to-Platelet Ratio Score). In 100 enrolled subjects, spleen ARFI, ASSDP, and ASSAP were significantly associated with HRVs in the prospective short- and long-term follow-ups and in the cross-sectional study (p < 0.05), while ALSDP and ALSAP were associated with HRVs only in the prospective long-term follow-up and cross-sectional study (p< 0.05). ASSAP was the best ARFI ratio score for HRVs at the long-term follow-up [value of area under curve (AUC) = 0.88], although all the ARFI ratio scores performed better than individual liver and spleen ARFI (AUC > 0.7). In our study, ARFI ratio scores can predict, in well-compensated cirrhotic patients, the risk of developing HVRs in short- and long-term periods.

Longitudinal assessment of liver stiffness using ARFI technique does not support increased risk of fibrosis in rheumatoid arthritis patients on methotrexate

AIMS

To assess the liver stiffness in patients with rheumatoid arthritis treated with methotrexate monotherapy using non-invasive, ultrasound-based elastography (acoustic radiation force impulse (ARFI) imaging) in a longitudinal approach.

METHODS

In total, 23 MTX-naive patients were longitudinally assessed using acoustic radiation force impulse (ARFI) imaging. Baseline assessments were carried out between July 2018 and April 2019, and the follow-up evaluations took place after an average of 2.6 years. The main outcome variable was the mean shear wave velocity as measured by the ARFI method. It was calculated from 10 valid ARFI measurements for each patient. Inferential statistical analyses (within-group comparisons) were performed using t-tests for dependent samples or suitable nonparametric procedures.

RESULTS

The main finding was that observed ARFI shear wave velocities did not increase during the observation period. In fact, this parameter decreased over time from 1.07 m/s (SD = 0.23) at baseline without MTX exposure to 0.97 m/s (SD = 0.16) at follow-up after a mean of 2.6 years (P = 0.013). Moreover, the magnitude of the change in shear wave velocity could not be predicted by indicators of inflammation or disease activity, BMI, age, sex or NSAR intake (corresponding regression analysis: corrected R2 = 0.344; P = 0.296).

CONCLUSIONS

No increased risk of liver fibrosis was found in RA patients treated with MTX monotherapy during observation period.

Correlation of Acoustic Radiation Force Impulse Imaging with Chronicity Markers in Native Renal Biopsy

Introduction. Acoustic Radiation Force Impulse (ARFI) is an ultrasound parameter which has shown promise in assessing liver stiffness, but there are limited data on the correlation of ARFI with chronicity markers in renal biopsies. Objectives. Determine ARFI values in ultrasound and correlate with chronicity markers in renal biopsy. Determine whether ARFI can be used as a non-invasive chronicity predictor compared to renal length, Resistive Index (RI), and cortical thickness. Patients and Methods. Two hundred and fifty patients were enrolled in the study. The ultrasound variables ARFI, renal length, RI, and cortical thickness values were assessed by the radiologist prior to renal biopsy. The biopsy slides were graded as per the Mayo Clinic consensus report scoring system by an experienced pathologist. Results. Among 250 study participants, 167 were males and 83 were females. IgA nephropathy was the most common pathology (n=47;19%), followed by diabetic nephropathy (n=42;17%), membranous nephropathy (n=35;14%), FSGS (n=27;11%), and MCD (n=19; 8%). The mean eGFR was 55.9 ± 42.12 ml/min/1.73 m2. The average renal length was 10.086 ± 1.01 cm. The average cortical thickness was 0.707 ± 0.134 cm. Resistive index was 0.68 ± 0.09. Acoustic radiation force impulse had weak negative correlation (r=-0.286; p=0.0001) with total pathological score and weak positive correlation with eGFR (r=0.279; p=0.0001). RI was a better indicator for histologically evaluated chronicity with positive correlation coefficient (r=0.416; p=0.0005) compared to renal length, cortical thickness, and ARFI. Conclusion. ARFI didn't corelate with the pathological score in renal biopsies. RI had better predictive value for chronicity in native renal biopsies.

The impact of amplitude modulation frequency in harmonic motion imaging on inclusion characterization

OBJECTIVE

Ultrasound elasticity imaging techniques aim to provide a non-invasive characterization of tissue mechanical properties to detect pathological changes and monitor disease progression. Harmonic motion imaging (HMI) is an ultrasound-based elasticity imaging technique that utilizes an oscillatory acoustic radiation force to induce localized displacements and estimate relative tissue stiffness. Previous studies have applied a low amplitude modulation (AM) frequency of 25 or 50 Hz in HMI to assess the mechanical properties of different tissue types. In this study, we investigate the dependence of AM frequency in HMI and whether the frequency can be adjusted based on the size and mechanical properties of the underlying medium for enhanced image contrast and inclusion detection.

METHODS

A tissue-mimicking phantom with embedded inclusions at different sizes and stiffnesses was imaged within a range of AM frequencies from 25 to 250 Hz at 25-Hz step size.

DISCUSSION

The AM frequency at which the maximum contrast and CNR are achieved depends on the size and stiffness of the inclusions. A general trend shows that contrast and CNR peak at higher frequencies for smaller inclusions. In addition, for some inclusions with the same size but different stiffnesses, the optimized AM frequency increases with the stiffness of the inclusion. Nevertheless, there is a shift between the frequencies at which the contrast peaks and those with maximum CNR. Finally, in agreement with the phantom findings, imaging an ex-vivo human specimen with a 2.7-cm breast tumor at a range of AM frequencies showed that the highest contrast and CNR are achieved at the AM frequency of 50 Hz.

CONCLUSION

These findings indicate that the AM frequency can be optimized in different applications of HMI, especially in the clinic, for improved detection and characterization of tumors with different geometries and mechanical properties.

Increase of liver stiffness and altered bile acid metabolism after triple CFTR modulator initiation in children and young adults with cystic fibrosis

BACKGROUND

Novel cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapies (elexacaftor/tezacaftor/ivacaftor-ETI) promise clinically significant and sustained improvements for patients with cystic fibrosis (CF). In this study, we investigated the impact of ETI therapy on liver stiffness and bile acid metabolism in a cohort of children and young adults with CF.

METHODS

A prospective observational study (NCT05576324) was conducted from September 2020 to November 2021 enrolling CF patients naive to ETI. Standard laboratory chemistry, sweat test, lung function, share wave velocity (SWV) derived by acoustic radiation force impulse imaging (ARFI) and serum bile acid profiles were assessed before and 6 months after induction of ETI therapy.

RESULTS

A total of 20 patients (10 aged <20 years) completed the study. While lung function and BMI improved after ETI therapy, ARFI SWV increased in CF patients <20 years of age (from 1.27 to 1.43 m/s, p = 0.023). Bile acid (BA) profiles revealed a decrease in unconjugated (5.75 vs 1.46, p = 0.007) and increase in glycine-conjugated derivatives (GCDCA) (4.79 vs 6.64 p = 0.016). There was a positive correlation between ARFI SWV values and GCDCA (r = 0.80, p < 0.0001). Glycine-conjugated BA provided high diagnostic accuracy to predict increased ARFI measurements (AUC 0.90) and clinical (Colombo) CFLD grading (AUC 0.97).

CONCLUSIONS

ARFI SWV and bile acid profiles provide evidence for early increase in liver stiffness and altered bile acid metabolism in young CF patients after initiation of ETI and may serve as synergistic measures for detection of hepatic complications during ETI therapy.

The synergized diagnostic value of VTQ with chemokine CXCL13 in lung tumors

Virtual Touch Tissue Quantification (VTQ) offers several advantages in the diagnosis of various lung diseases. Chemokine expression levels, such as CXCL13, play a vital role in the occurrence and development of tumors and aid in the diagnosis process. The purpose of this study was to evaluate the combined value of VTQ and changes in CXCL13 expression levels for the diagnosis of lung tumors. A total of 60 patients with thoracic nodules and pleural effusion were included, with 30 of them having malignant pleural effusion (based on pathology) and the remaining 30 having benign thoracic nodules and pleural effusion. The relative expression level of CXCL13 was measured in the collected pleural effusions using Enzyme-Linked Immunosorbent Assay (ELISA). The relationship between CXCL13 expression levels and various clinical features was analyzed. A Receiver Operating Characteristic (ROC) curve analysis was conducted on the VTQ results and relative expression levels of CXCL13, and the areas under the curve, critical values, sensitivity, and specificity were calculated. Multivariate analysis incorporating multiple indicators was performed to determine the accuracy of lung tumor diagnosis. The results showed that the expression levels of CXCL13 and VTQ were significantly higher in the lung cancer group compared to the control group (P < 0.05). In the Non-Small Cell Lung Cancer (NSCLC) group, CXCL13 expression levels increased with later TNM staging and poorer tumor differentiation. The expression level of CXCL13 in adenocarcinoma was higher than that in squamous cell carcinoma. The ROC curve analysis revealed that CXCL13 had an area under the curve (AUC) of 0.74 (0.61, 0.86) with an optimal cut-off value of 777.82 pg/ml for diagnosing lung tumors. The ROC curve analysis of VTQ showed an AUC of 0.67 (0.53, 0.82) with a sensitivity of 60.0% and a specificity of 83.3%, and an optimal diagnostic cut-off of 3.33 m/s. The combination of CXCL13 and VTQ for diagnosing thoracic tumors had an AUC of 0.842 (0.74, 0.94), which was significantly higher than either factor alone. The results of the study demonstrate the strong potential of combining VTQ results with chemokine CXCL13 expression levels for lung tumor diagnosis. Additionally, the findings suggest that elevated relative expression of CXCL13 in cases of malignant pleural effusion caused by non-small cell lung cancer may indicate a poor prognosis. This provides promising potential for using CXCL13 as a screening tool and prognostic indicator for patients with advanced lung cancer complicated by malignant pleural effusion.

Acoustic Radiation Force Impulse Elastography Assessment of Lymphoedema Tissue: An Insight into Tissue Stiffness

Palpation remains essential for evaluating lymphoedema to detect subtle changes that may indicate progression. As palpation sense is not quantifiable, this study investigates the utility of ultrasound elastography to quantify stiffness of lymphoedema tissue and explore the influence of the pitting test on tissue stiffness. Fifteen women with unilateral arm lymphoedema were scanned using a Siemens S3000 Acuson ultrasound (Siemens, Germany) with 18 MHz and 9 MHz linear transducers to assess tissue structure and tissue stiffness with Acoustic Radiation Force Impulse elastography. Ninety sites were assessed, three on each of the lymphoedema-affected and contralateral unaffected arms. A subgroup of seven lymphoedema-affected sites included additional elastography imaging after a 60-s pitting test. Dermal tissue stiffness was greater than subcutaneous tissue stiffness regardless of the presence of pathology (p < 0.001). Lymphoedematous tissue exhibited a higher dermal to subcutaneous tissue stiffness ratio than contralateral sites (p = 0.005). Subgroup analysis indicated that the pitting test reduces dermal tissue stiffness (p = 0.018) and may alter the stiffness of the subcutaneous tissue layer. Elastography demonstrates potential as a complement to lymphoedema palpation assessment. The novel pre-test and post-pitting elastography imaging protocol yielded information representative of lymphoedema tissue characteristics that could not be ascertained from pre-test elastography images alone.

[Quantitative imaging in nephrology: limits and potentials of elastosonography]

Chronic kidney disease is characterized by increasingly amplified fibrotic processes regardless of etiology. The severity of renal fibrosis seems to correlate with an increased risk of end-stage renal disease; therefore, monitoring of renal fibrosis over time may play an important role in the follow-up of both focal and diffuse renal diseases and in evaluating the response to treatments. Renal biopsy is the only method capable of providing objective and comparable information on the extent of fibrosis, but it is not suitable for outpatient monitoring of chronic kidney disease due to its invasiveness. Elastosonography is an innovative and non-invasive ultrasound method that allows the measurement of tissue elasticity through the transmission of mechanical waves and the measurement of their propagation speed. Although some authors have demonstrated the usefulness of elastosonographic techniques for the quantification of liver fibrosis, few studies have investigated the applications of elastosonography in renal pathology. Furthermore, the depth of native kidneys, the high anisotropy of the renal tissue, and the possibility of examining only a small region of interest currently limit its spread in clinical practice. The aim of this review is to examine the physical principles of elastosonography and to review the latest evidence about the possible applications of the ARFI (acoustic radiation force impulse) technique in the study of kidney diseases.

Cirrhosis of Wilson's disease: High and low cutoff using acoustic radiation force impulse (ARFI) -Comparison and combination with serum fibrosis index

BACKGROUND

Acoustic Radiation Force Impulse (ARFI), Fibrosis-4(FIB-4) and Aspartate transaminase to platelet ratio index (APRI) are valuable non-invasive methods to evaluate fibrosis in hepatitis virus. Yet, they are rarely used in Wilson's disease.

OBJECTIVE

Evaluate the diagnostic efficacy of ARFI, FIB-4, APRI, combined detection in cirrhosis with WD, and speculate the optimal high, low cutoff.

METHODS

This retrospective study was authorized by hospital ethics Committee (number:2021MCZQ02). 102 patients with WD completed ARFI and laboratory examination on the same day. The intraclass correlation coeffcient (ICC) of ARFI among three sonographers was 0.896 (95%CI:0.859-0.925, p = 0.000). The stage of liver involvement was classified into 5 categories according to clinical manifestations, laboratory examination, and liver morphologic characteristics: I, normal; II, biochemical abnormal only; III, abnormal liver morphologic features without sighs of cirrhosis; IV, clinical and imaging sighs of compensateded cirrhosis (Child-Pugh A); V, decompensated cirrhosis (Child-Pugh B and C). This stage system served as the reference standard. The diagnostic efficacy was analyzed by Logistic regression, ROC curve. The optimal low cut-off with high sensitivity (SE) and low negative likelihood ratio (NLR) and high cut-off with high specificity (SP) and positive likelihood ratio (PLR) were derived.

RESULTS

The diagnostic value of ARFI (0.85, 95%CI:0.77-0.92, p = 0.000) in distiguishing cirrhosis with WD was higher than FIB-4 (0.59, 95%CI: 0.47-0.70, p = 0.127), APRI (0.70, 95%CI: 0.59-0.81, p = 0.000). The low, high cut-off of ARFI for excluding, diagnosing cirrhosis with WD was 1.47 m/s(SE: 98%, NLR:0.09), 2.11 m/s(SP:98%, PLR:27.4), 37 (36%) patients could be spared a liver biopsy. When ARFI was 1.47∼2.11 m/s, liver biopsy was recommended. After combined with ARFI, the AUROC of FIB-4, APRI were increased respectively (p <  0.001), there were not different between ARFI and combined detection(p >  0.05).

CONCLUSION

ARFI could replace some unnecessary liver biopsy according to high diagnostic efficacy for identifying cirrhosis of WD. The combined detection can also be used as an important model to predict cirrhosis in WD.

Ultrasound elastography for the detection of capsular fibrosis in breast implants: First results

BACKGROUND

Capsular contractures around breast implants usually develop leading to pain and aesthetically inadequate results and ultimately often requires the replacement of the implants. Textured silicone implants are the most commonly placed implant, but polyurethane-coated implants are increasingly being used in an attempt to ameliorate the long-term complications associated with implant insertion.

AIM

Capsular contracture is traditionally classified using the Baker scale, a subjective classification system based upon clinical findings. Aim of this study was to evaluate the association between pain due capsular contraction, Baker score and different techniques of US elastography.

MATERIAL AND METHODS

Patients were contacted who had undergone an implant replacement due to capsular contracture. Inclusion criterion was the re-implantation of a PU-coated implant. In the third year after changing the implant a follow-up examination was performed in 16 patients with 23 implants. A conventional examination with anamnesis, tactile and visual findings to obtain a Baker score, and ultrasound examinations including shear wave elastography, ARFI and compound elastography were performed. In addition, pain was evaluated using a visual analogue scale (VAS).

RESULTS

The pain data showed a significant improvement (before implant exchange: 4.1±2.8 score points) with significance in favor of the current state (1.7±1.0 pain score points; p = 0.002). All patients suffered from less or no pain three years after exchange of the implant. Pain values and elastography (ARFI values) correlated well (r = 0,873), with increasing Baker score the ARFI values increased. US elastography evaluations can locally determine tissue density but correlate only to a limited extent with the test findings according to Baker. US elastography values of mammary gland tissue without implant did not differ from mammary gland tissue around implants.

CONCLUSION

Preoperative Baker scores prior to exchange and the current Baker scores at the follow-up showed significantly lower score points three years after exchange of the implants. Ultrasound elastography seems to be an objective classification of capsular fibrosis. These first results motivate to initiate a prospective multicenter investigation.

Methotrexate does not increase the risk of liver fibrosis in patients with rheumatoid arthritis: assessment by ultrasound elastography (ARFI-MetRA study)

OBJECTIVES

Only limited data are available on the risk of liver fibrosis in patients with rheumatoid arthritis on long-term methotrexate treatment. To assess the risk of liver fibrosis in patients with rheumatoid arthritis treated with methotrexate, non-invasive, ultrasound-based elastography [acoustic radiation force impulse (ARFI) imaging] was applied.

METHODS

In total, 119 patients were assessed using acoustic radiation force impulse (ARFI) imaging between July 2018 and April 2019. In a cross-sectional, single-centre study design, ARFI scores were compared between patient subgroups with (n = 65) and without (n = 54) methotrexate exposure. The main outcome variable was the mean fibrosis score as measured by the ARFI method. The mean shear wave velocity was calculated from 10 valid ARFI measurements for each patient. Inferential statistical analyses (between group) were performed using ANOVA for independent samples in the case of continuous outcome variables.

RESULTS

Sixty-five patients with and fifty-four patients without MTX exposure were assessed using the ARFI elastography method. Participating patients on MTX medication (1.113 m/s) showed ARFI scores that were comparable to those of participants without MTX exposure (1.062 m/s); P = 0.228. The mean cumulative dose in the group of MTX-exposed patients was 3602 mg.

CONCLUSION

The mean value of the repeated determination of liver density using ARFI imaging did not differ significantly between the MTX-exposed and MTX-naive patients with RA. No increased rate of liver fibrosis was found among RA patients treated with MTX.

The value of acoustic radiation force impulse imaging in preoperative prediction for efficacy of high-Intensity focused ultrasound uterine fibroids ablation

Objective: To investigate the application value of acoustic radiation force impulse imaging in preoperative prediction for efficacy of High-Intensity Focused Ultrasound uterine fibroids ablationMethods: A prospective study was conducted on 32 women (41 fibroids) undergoing HIFU uterine fibroids ablation between January 2019 and September 2019. The virtual touch tissue quantification (VTQ) technique was used for the preoperative determination of uterine fibroids shear wave velocity (SWV). The stiffness of the preoperative uterine fibroids was graded on a virtual touch tissue image (VTI). All uterine fibroids were ablated with a single point ablation acoustic power of 400 W. All patients underwent pelvic cavity MRI examination for the measurement of the size, volume and non-perfused volume (NPV) of fibroids within the first month after HIFU ablation. The ablation rate of uterine fibroids was calculated according to the formula: ablation rate = NPV × 100/target fibroid volume. The patients were divided into two groups based on the postoperative ablation rate: ≥70% ablation rate group, and＜70% ablation rate group. The preoperative SWV and VTI grade of uterine fibroids were compared between the two groups. The correlation of preoperative uterine fibroids' SWV and VTI grade with HIFU ablation rate were analyzed using the Spearman's correlation coefficient. The optimal cutoff points in preoperative uterine fibroids SWV of 70% ablation rate were determined by receiver operating curve (ROC) analysis.Results: A total of 30 patients (73.17%, 30/41) showed ablation rate ≥70%, with preoperative uterine fibroids' SWV values of (3.42 ± 0.71) m/s. Of these, 24 patients (80%, 24/30) had VTI grades II-III. On the other hand, 26.83% (11/41) showed ablation rate <70%, with preoperative uterine fibroids' SWV values of (4.02 ± 0.69) m/s; of these, 63.6% (7/11) had VTI grade IV. The SWV values and VTI grades of preoperative uterine fibroids were significantly different in the two groups (p < 0.05). Interestingly, postoperative ablation rate was negatively correlated with preoperative uterine fibroids' SWV values (r= -0.536, p = 0.0003) and VTI grades (r= -0.511, p = 0.001). The area under the ROC curve of preoperative uterine fibroids' SWV values with ablation rate <70% was 0.75 at a cutoff value of 3.915 m/s (p < 0.05). Specificity was 72.7% and sensitivity was 80.1%; the positive predictive value was 72.7%, and the negative predictive value was 80%.Conclusion: ARFI technique is an effective and feasible noninvasive ultrasound technique for the preoperative prediction of the efficacy of HIFU uterine fibroids ablation.

Usability and Pitfalls of Shear-Wave Elastography for Evaluation of Muscle Quality and Its Potential in Assessing Sarcopenia: A Review

Sarcopenia is age-related progressive and generalized loss of skeletal muscle mass and strength. Its prevalence is rising, which poses a burden for society because it increases disability and dependency and therefore raises health care costs. Muscle mass quality, however-an essential part of sarcopenia-is not easily diagnosable yet. Recent interest has risen for ultrasonographic evaluation of muscle. This review introduces muscle elastography as a possible, easy and cheap tool to evaluate qualitative muscle parameters. Basic principles of muscle elastography are described, as well as different elastography techniques and some technical considerations. Furthermore, a proposal for practical guidelines is offered and factors influencing muscle stiffness are highlighted.

Elasticity standard values of the thoracolumbar fascia assessed with acoustic radiation force impulse elastography on healthy volunteers: A cross section study

INTRODUCTION

Determining the normal values for acoustic radiation force impulse (ARFI) shear wave elastography of the thoracolumbar fascia (TLF) and define possible factors of influence.

METHODS

We measured the shear wave velocity (SWV) in m/s and the diameter (anterior-posterior) in mm of the TLF bilateral in 267 healthy participants with the Acuson S3000™ (Siemens) using the virtual touch image quantification mode (VTIQ). The parameters were tested for correlations with the anthropometric data of the participants, between different age groups and the genders, as well as information obtained from the history, such as smoking and sporting activities.

RESULTS

We determined a mean SWV of 3.28 ± 0.55 m/s for the left thoracolumbar fascia and 3.44 ± 0.55 m/s for the right. The diameter on the right was 2.7 ± 0.8 mm. On the left, it was 2.7 ± 0.9 mm. Neither body mass index (BMI) nor gender had a significant effect on either of the measured parameters (p > 0.05). The same goes for regular medication, sporting activity or the consumption of alcohol (p > 0.05). The results concerning the effect of smoking and age were inconclusive as they only had a significant influence to either the right or the left side of the TLF but not on the other side.

CONCLUSIONS

We collected the normal value for ARFI shear wave elastography of the TLF in 267 healthy participants. Furthermore, neither gender, BMI, sports activity nor the consumption of alcohol affected the elasticity or the diameter of the thoracolumbar fascia.

Acoustic radiation force impulse point shear wave elastography of the liver and spleen in patients with Gaucher disease type 1: Correlations with clinical data and markers of disease severity

PURPOSE

To evaluate the feasibility of acoustic radiation force impulse point shear wave elastography (ARFI-pSWE) of the liver and spleen in patients with Gaucher disease type 1 (GD1), and to assess correlations between organ stiffness and clinico-radiologic data, particularly the GD1 Severity Scoring System (GD-DS3).

MATERIALS AND METHODS

We retrospectively evaluated the results of ARFI-pSWE as measures of liver and spleen stiffness in 57 patients with GD1. The feasibility of the method was assessed. Correlations between elastography data and clinical data related to the metabolic syndrome, laboratory tests, and GD1-related clinico-radiologic data (bone marrow burden score, GD-DS3) were assessed.

RESULTS

ARFI-pSWE provided reliable results (i.e. standard deviation <30% of the mean value between the measurements) in 50/57 patients. Significant liver fibrosis was present in 35/50 patients (70%). Liver stiffness significantly correlated with GD-DS3 score (p = .03), and number of fulfilled criteria of metabolic syndrome (p = .03). Spleen stiffness significantly correlated with age (p = .021), body mass index (p = .002), number of fulfilled criteria of metabolic syndrome (p = .02), and several laboratory parameters (alanine aminotransferase, gamma glutamyltranspeptidase, triglycerides, cholesterol), and nearly significantly with GD-DS3 score (p = .059).

CONCLUSION

ARFI-pSWE is a useful tool for a more detailed assessment of disease severity in patients with GD1, which adds relevant information to the standard clinical scores. Thus, elastography might allow for extended therapy monitoring, especially in patients with significant liver fibrosis. Spleen elastography showed promising results; thus, its role should be further investigated.

Different Effects of Foam Rolling on Passive Tissue Stiffness in Experienced and Nonexperienced Athletes

CONTEXT

Foam rolling (FR) has been developed into a popular intervention and has been established in various sports disciplines. However, its effects on target tissue, including changes in stiffness properties, are still poorly understood.

OBJECTIVE

To investigate muscle-specific and connective tissue-specific responses after FR in recreational athletes with different FR experience.

DESIGN

Case series.

SETTING

Laboratory environment.

PARTICIPANTS

The study was conducted with 40 participants, consisting of 20 experienced (EA) and 20 nonexperienced athletes (NEA).

INTERVENTION

The FR intervention included 5 trials per 45 seconds of FR of the lateral thigh in the sagittal plane with 20 seconds of rest between each trial.

MAIN OUTCOME MEASURES

Acoustic radiation force impulse elastosonography values, represented as shear wave velocity, were obtained under resting conditions (t0) and several times after FR exercise (0 min [t1], 30 min [t2], 6 h [t3], and 24 h [t4]). Data were assessed in superficial and deep muscle (vastus lateralis muscle; vastus intermedius muscle) and in connective tissue (iliotibial band).

RESULTS

In EA, tissue stiffness of the iliotibial band revealed a significant decrease of 13.2% at t1 (P ≤ .01) and 12.1% at t3 (P = .02). In NEA, a 6.2% increase of stiffness was found at t1, which was not significantly different to baseline (P = .16). For both groups, no significant iliotibial band stiffness changes were found at further time points. Also, regarding muscle stiffness, no significant changes were detected at any time for EA and NEA (P > .05).

CONCLUSIONS

This study demonstrates a significant short-term decrease of connective tissue stiffness in EA, which may have an impact on the biomechanical output of the connective tissue. Thus, FR effects on tissue stiffness depend on the athletes' experience in FR, and existing studies have to be interpreted cautiously in the context of the enrolled participants.

Efficient shear wave elastography using transient acoustic radiation force excitations and MR displacement encoding

PURPOSE

To present a novel MR shear wave elastography (MR-SWE) method that efficiently measures the speed of propagating wave packets generated using acoustic radiation force (ARF) impulses.

METHODS

ARF impulses from a focused ultrasound (FUS) transducer were applied sequentially to a preselected set of positions and motion encoded MRI was used to acquire volumetric images of the propagating shear wavefront emanating from each point. The wavefront position at multiple propagation times was encoded in the MR phase image using a train of motion encoding gradient lobes. Generating a transient propagating wavefront at multiple spatial positions and sampling each at multiple time-points allowed for shear wave speed maps to be efficiently created. MR-SWE was evaluated in tissue mimicking phantoms and ex vivo bovine liver tissue before and after ablation.

RESULTS

MR-SWE maps, covering an in-plane area of ~5 × 5 cm, were acquired in 12 s for a single slice and 144 s for a volumetric scan. MR-SWE detected inclusions of differing stiffness in a phantom experiment. In bovine liver, mean shear wave speed significantly increased from 1.65 ± 0.18 m/s in normal to 2.52 ± 0.18 m/s in ablated region (n = 581 pixels; P-value < 0.001).

CONCLUSION

MR-SWE is an elastography technique that enables precise targeting and excitation of the desired tissue of interest. MR-SWE may be particularly well suited for treatment planning and endpoint assessment of MR-guided FUS procedures because the same device used for therapy can be used as an excitation source for tissue stiffness quantification.

Acoustic radiation force impulse (ARFI) shear wave elastography of the bowel wall in healthy volunteers and in ulcerative colitis

Background

Acoustic radiation force impulse (ARFI) elastography is a non-invasive, ultrasound-based approach of evaluation of tissue elasticity. It has not yet been systematically applied to the bowel wall.

Purpose

To perform ARFI elastography of the bowel wall in healthy volunteers and patients with ulcerative colitis (UC).

Material and Methods

A high-frequency ultrasound (with bowel wall thickness and vascularization score) and an ARFI elastography of the bowel wall were performed in 20 patients with UC and 13 healthy volunteers. At least 10 ARFI measurements were obtained within the terminal ileum and the ascending, transverse, descending, and sigmoid colon and correlated with results of high-frequency ultrasound.

Results

The UC group had mostly moderate disease activity. All patients had signs of inflammation upon B-mode ultrasound. Eight patients showed an ulcerative (ileo)pancolitis. Overall, ARFI elastography values and wall thickness were higher in the UC group than in the group of healthy volunteers (P = 0.021 and P < 0.001, respectively). ARFI velocities of the separate segments were significantly higher in the transverse (P = 0.045) and sigmoid colon (P = 0.032) in case of UC.

Conclusion

ARFI elastography of the bowel wall of the colonic frame and the terminal ileum is feasible but shows high standard deviation. ARFI shear wave velocities appear to be slightly higher in patients with UC than in healthy volunteers, particularly in the sigmoid and transverse colon. Further studies are needed.

Noninvasive Assessment of Liver Disease in Patients With Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is estimated to afflict approximately 1 billion individuals worldwide. In a subset of NAFLD patients, who have the progressive form of NAFLD termed nonalcoholic steatohepatitis (NASH), it can progress to advanced fibrosis, cirrhosis, hepatocellular carcinoma, and liver-related morbidity and mortality. NASH is typically characterized by a specific pattern on liver histology, including steatosis, lobular inflammation, and ballooning with or without peri-sinusoidal fibrosis. Thus, key issues in NAFLD patients are the differentiation of NASH from simple steatosis and identification of advanced hepatic fibrosis. Until now, liver biopsy has been the gold standard for identifying these 2 critical end points, but has well-known limitations, including invasiveness; rare but potentially life-threatening complications; poor acceptability; sampling variability; and cost. Furthermore, due to the epidemic proportion of individuals with NAFLD worldwide, liver biopsy evaluation is impractical, and noninvasive assessment for the diagnosis of NASH and fibrosis is needed. Although much of the work remains to be done in establishing cost-effective strategies for screening for NASH, advanced fibrosis, and cirrhosis, in this review, we summarize the current state of the noninvasive assessment of liver disease in NAFLD, and we provide an expert synthesis of how these noninvasive tools could be utilized in clinical practice. Finally, we also list the key areas of research priorities in this area to move forward clinical practice.

Shear wave elastography prior to transjugular intrahepatic portosystemic shunt may predict the decrease in hepatic vein pressure gradient

BACKGROUND

Transjugular intrahepatic portosystemic shunt (TIPS) is a procedure used to treat portal hypertension complications. Our aim was to evaluate liver and spleen stiffness measurement (LSM and SSM, respectively) changes using acoustic radiation force impulse imaging (ARFI) in comparison to Child-Pugh scores for predicting hepatic venous pressure gradient (HVPG) decreases after TIPS implantation.

METHODS

This prospective study included 31 consecutive clinically significant portal hypertension patients with TIPS indication. All patients received LSM and SSM before TIPS, at baseline, 2 days (follow-up 1) and 6 weeks (follow-up 2) post-implantation. HVPG was performed during the TIPS procedure.

RESULTS

The mean decrease in HVPG after TIPS was 63%. LSM and SSM decreased significantly between baseline and follow-up 2 (p < 0.001 and p < 0.001, respectively). At baseline, follow-up 1 and follow-up 2, significant correlations were detected between mean SSM and mean HVPG (p = 0.026; p = 0.018; p = 0.002, respectively). HVPG decreased to ≤ 10 mmHg in 61% of patients for which LSM, SSM, and Child-Pugh score were predictors (p = 0.033, p = 0.002 and p = 0.030, respectively). The area under the curve (AUC) for LSM, SSM, and Child-Pugh was 0.88, 0.90, and 0.84, respectively, with close sensitivity and specificity. SSM had the highest diagnostic accuracy for predicting an HVPG decrease to ≤ 10 mmHg in comparison to LSM and Child-Pugh score.

CONCLUSION

Spleen stiffness is superior to liver stiffness and Child-Pugh score as a non-invasive surveillance tool for evaluating patients with clinically significant portal hypertension (HVPG ≥ 10 mmHg) prior to TIPS.

Is Acoustic Radiation Force Impulse (ARFI) Ultrasound Elastography Valuable in the Assessment of Cervical Lymphadenopathy?

Cervical lymphadenopathy frequently poses a diagnostic challenge as neither clinical nor imaging assessment can reliably differentiate between benign and malignant lymphadenopathy. Non-invasive differentiation between the two may help to reduce the number of FNAC or biopsy. The purpose of this study was to evaluate whether the new ARFI technique (Virtual Touch Quantification), in conjunction with gray scale sonography and Doppler, can help in the characterization and differentiation of benign from malignant cervical lymphadenopathy. Fifty adult patients with cervical lymphadenopathy were included in the study and sonoelastography was done. Sonoelastographic findings were compared to the gold standard histopathology or cytopathology. ARFI measurements in benign and malignant enlarged lymph nodes were compared using the Student t test and ROC curve was used to arrive at the Youden index, sensitivity, specificity, PPV, NPV and diagnostic accuracy. Sonographic patterns indicative of malignancy includes heterogenous echopattern, short axis/long axis ratio > 0.5, absent echogenic fatty hilum and mixed vascular pattern. Sensitivity, specificity, PPV, NPV and accuracy in differentiation between the benign and malignant lymph nodes using ARFI elastography was 79.17, 100, 100, 83.9 and 89.9% respectively. ROC curve analysis of SWVs for differentiation between the malignant and benign lymph nodes gave a cut-off value of 2.8 m/s with an area under curve of 0.892. ARFI imaging technique quantifies the tissue stiffness of the cervical lymph nodes non-invasively and aids in characterisation and differentiation of benign from malignant cervical lymphadenopathy in conjunction with conventional sonography.

Multiple-point magnetic resonance acoustic radiation force imaging

PURPOSE

To implement and evaluate an efficient multiple-point MR acoustic radiation force imaging pulse sequence that can volumetrically measure tissue displacement and evaluate tissue stiffness using focused ultrasound (FUS) radiation force.

METHODS

Bipolar motion-encoding gradients were added to a gradient-recalled echo segmented EPI pulse sequence with both 2D and 3D acquisition modes. Multiple FUS-ON images (FUS power > 0 W) were interleaved with a single FUS-OFF image (FUS power = 0 W) on the TR level, enabling simultaneous measurements of volumetric tissue displacement (by complex subtraction of the FUS-OFF image from the FUS-ON images) and proton resonance frequency shift MR thermometry (from the OFF image). Efficiency improvements included partial Fourier acquisition, parallel imaging, and encoding up to 4 different displacement positions into a single image. Experiments were performed in homogenous and dual-stiffness phantoms, and in ex vivo porcine brain.

RESULTS

In phantoms, 16-point multiple-point magnetic resonance acoustic radiation force imaging maps could be acquired in 5 s to 10 s for a 2D slice, and 60 s for a 3D volume, using parallel imaging and encoding 2 displacement positions/image. In ex vivo porcine brain, 16-point multiple-point magnetic resonance acoustic radiation force imaging maps could be acquired in 20 s for a 3D volume, using partial Fourier and parallel imaging and encoding 4 displacement positions/image. In 1 experiment it was observed that tissue displacement in ex vivo brain decreased by approximately 22% following FUS ablation.

CONCLUSION

With the described efficiency improvements it is possible to acquire volumetric multiple-point magnetic resonance acoustic radiation force imaging maps, with simultaneous proton resonance frequency shift MR thermometry maps, in clinically acceptable times.

Clinical efficacy of novel elastography using acoustic radiation force impulse (ARFI) for diagnosis of malignant thyroid nodules

Objective

Acoustic radiation force impulse (ARFI) imaging is a recent ultrasound elastography technique; consequently, its efficacy is not fully known. In this study, we compared ARFI imaging with conventional strain elastography (SE) and shear wave velocities (SWVs) to evaluate the utility of ARFI imaging for diagnosing thyroid nodules.

Subjects and Methods

In this study we examined 233 thyroid nodules (183 benign nodules and 50 malignant nodules) isolated from human patients. The nodules were evaluated with SE and ARFI imaging, and SWVs of the nodules were simultaneously measured. ARFI images were classified using a four‐point score based on grayscale intensity of the images. The sensitivity, specificity, and diagnostic accuracy were compared between SE and ARFI imaging. Finally, SWVs for each score of SE and ARFI imaging were compared.

Results

The new scoring system for ARFI imaging can be divided into four virtual touch imaging (VTI) scores. Nodules with a VTI score of 3 or 4 as determined by ARFI imaging were determined to be malignant. The sensitivity, specificity, and diagnostic accuracy, respectively, were 63.2%, 66.3%, and 65.6% for SE, compared with 80.0%, 86.3%, and 85.0% for ARFI imaging. The median SWVs of the nodules were 1.57 m/s, 1.73 m/s, 1.88 m/s, and 2.09 m/s for VTI scores of 1, 2, 3, and 4, respectively. The SWVs of VTI scores 3 and 4 were significantly higher than those of VTI scores 1 and 2.

Conclusions

The diagnostic accuracy of ARFI imaging for differentiating malignant thyroid nodules was higher than that of SE. The VTI scores of the nodules accurately reflected their SWVs.

Level of Evidence

4

Point shear wave elastography of the pancreas in patients with cystic fibrosis: a comparison with healthy controls

PURPOSE

Manifestations of cystic fibrosis in the pancreas are gaining in clinical importance as patients live longer. Conventional ultrasonography and point shear wave elastography (pSWE) imaging are non-invasive and readily available diagnostic methods that are easy to perform. The aim of this study was to perform conventional ultrasonography and obtain pSWE values in the pancreases of patients with cystic fibrosis and to compare the findings with those of healthy controls.

METHODS

27 patients with cystic fibrosis (13 women/14 men; mean age 27.7 ± 13.7 years; range 9-58 years) and 60 healthy control subjects (30 women/30 men; mean age 30.3 ± 10.0 years; range 22-55 years) underwent examinations of the pancreas with conventional ultrasound and pSWE imaging.

RESULTS

Patients with cystic fibrosis have an echogenic pancreatic parenchyma. We found cystic lesions of the pancreas in six patients. pSWE imaging of the pancreatic parenchyma gave significantly lower shear wave velocities in patients with cystic fibrosis than in the control group (1.01 m/s vs 1.30 m/s; p < 0.001).

CONCLUSIONS

Using pSWE imaging in vivo, we have shown that the pancreas is considerably softer in patients with cystic fibrosis than in a healthy control population.

Elasticity standard values of the Achilles tendon assessed with acoustic radiation force impulse elastography on healthy volunteers: a cross section study

Background

To determine normal values for acoustic radiation force impulse (ARFI) shear wave elastography of the Achilles tendon.

Methods

Using the VTIQ mode with the Acuson S3000™ (Siemens Healthcare, Erlangen, Germany), we measured the shear wave velocity (SWV) in m/s and the diameter in mm of both Achilles tendons in 182 healthy volunteers. The tendon was displayed in a sagittal view with a relaxed tendon. The parameters were tested for correlations with the anthropometric data of the subjects, between the genders and different age groups, as well as information obtained from the history, such as smoking and sporting activities.

Results

Using a sagittal acoustic window, we determined a mean SWV of 9.09 ± 0.71 m/s for the left Achilles tendon and 9.17 ± 0.61 m/s for the right. There was a significant difference between the results for the right and left side (p < 0.05). The diameter on the left was 4.7 ± 0.9 mm. On the right, it was 4.8 ± 0.9 mm. Likewise there was a significant difference between the results for the diameter of the left and right side (p < 0.05). Neither gender, body mass index (BMI) nor age had a significant effect on either of the measured parameters (p > 0.05). The same goes for the consumption of tobacco and alcohol (p > 0.05).

Conclusions

Age, gender, BMI, smoking or the consumption of alcohol did not affect either the elasticity or the diameter of the Achilles tendon.

Elastography methods for the non-invasive assessment of portal hypertension

The gold standard to assess the presence and severity of portal hypertension remains the hepatic vein pressure gradient, however the recent development of non-invasive assessment using elastography techniques offers valuable alternatives. In this review, we discuss the diagnostic accuracy and utility of such techniques in patients with portal hypertension due to cirrhosis. Areas covered: A literature search focused on liver and spleen stiffness measurement with different elastographic techniques for the assessment of the presence and severity of portal hypertension and oesophageal varices in people with chronic liver disease. The combination of elastography with parameters such as platelet count and spleen size is also discussed. Expert commentary: Non-invasive assessment of liver fibrosis and portal hypertension is a validated tool for the diagnosis and follow-up of patients. Baveno VI recommended the combination of transient elastography and platelet count for ruling out varices needing treatment in patients with compensated advanced chronic liver disease. Assessment of aetiology specific cut-offs for ruling in and ruling out clinically significant portal hypertension is an unmet clinical need. The incorporation of spleen stiffness measurements in non-invasive algorithms using validated software and improved measuring scales might enhance the non-invasive diagnosis of portal hypertension in the next 5 years.

Can ARFI elastography be used to differentiate parathyroid from thyroid lesions?

OBJECTIVES

To assess if elasticity score (ES) and shear wave velocity (SWV) measurement obtained using ARFI elastography can differentiate between parathyroid lesions and thyroid nodules.

MATERIALS AND METHODS

ARFI elastography was performed on patients with primary hyperparathyroidism or solid thyroid nodules who were being considered for surgery using virtual touch quantification and virtual touch imaging (VTI) software. Only patients with surgical histopathology (47 parathyroid lesions, 38 benign thyroid nodules and 55 malignant thyroid nodules) were included for final analysis. SWV and ES of the parathyroid and thyroid nodules were compared and their ability to differentiate between parathyroid and thyroid was analyzed using receiver operating characteristic curve analysis.

RESULTS

There were 39 solitary adenomas, 2 double adenomas and 4 parathyroid hyperplasias with mean size of 19.6 ± 9.7 mm in 44 patients (21 male, 23 females) with primary hyperparathyroidism. The mean SWV of the parathyroid lesion (1.6 ± 0.78 m/s) was significantly different from benign (2.11 ± 0.8 m/s) and malignant (4.3 ± 2.71 m/s) thyroid nodules, p < 0.05; so was the ES, Chi square = 51.6, p < 0.001. The majority of parathyroid lesions (n = 37, 78.7%) had ES of 2 with speckled (n = 42, 89.3%) appearance, and none showed ES of 4. The diagnostic performance of speckled appearance on VTI, elasticity score and SWV measurements was 0.901, 0.724 and 0.797, respectively, to differentiate between parathyroid and thyroid lesions.

CONCLUSIONS

Parathyroid lesions are softer than thyroid nodules. A shear wave velocity of 1.72 m/s can differentiate between parathyroid lesions and thyroid nodules.

Measurement of Spleen Stiffness With Acoustic Radiation Force Impulse Imaging Predicts Mortality and Hepatic Decompensation in Patients With Liver Cirrhosis

BACKGROUND & AIMS

Hepatic venous pressure gradient can predict mortality and hepatic decompensation in patients with cirrhosis. Measurement of hepatic venous pressure gradient requires an invasive procedure; therefore, prognostic markers are needed that do not require invasive procedures. We investigated whether measurements of spleen stiffness, made by acoustic radiation force impulse (ARFI) imaging, associated with mortality and decompensation in patients with cirrhosis, compared with liver stiffness and other markers.

METHODS

We measured spleen stiffness in 393 patients diagnosed with cirrhosis (based on histologic or physical, laboratory, and radiologic findings) at a hospital in Japan from September 2010 through August 2013 (280 patients with compensated and 113 patients with decompensated cirrhosis). Patients underwent biochemical, ARFI, ultrasonography, and endoscopy evaluations every 3 or 6 months to screen for liver-related complications until their death, liver transplantation, or the end of the study period (October 2015). The primary outcome was the accuracy of spleen stiffness in predicting mortality and decompensation, measured by Cox proportional hazards model analysis. We compared spleen stiffness with other noninvasive parameters using the Harrell's C-index analysis.

RESULTS

During a median follow-up period of 44.6 months, 67 patients died and 35 patients developed hepatic decompensation. In the multivariate analysis, spleen stiffness was an independent parameter associated with mortality, after adjustment for levels of alanine aminotransferase and serum sodium, and the model for end-stage liver disease score (P < .001). Spleen stiffness was associated independently with decompensation after adjustment for Child-Pugh score and model for end-stage liver disease score (P < .001). Spleen stiffness predicted mortality and decompensation with greater accuracy than other parameters (C-indexes for predicting mortality and decompensation were 0.824 and 0.843, respectively). A spleen stiffness cut-off value of 3.43 m/s identified the death of patients with a 95.3% negative predictive value and 75.8% accuracy. A spleen stiffness cut-off value of 3.25 m/s identified patients with decompensation with a 98.8% negative predictive value and 68.9% accuracy.

CONCLUSIONS

Spleen stiffness, measured by ARFI imaging, can predict death of patients with cirrhosis with almost 76% accuracy and hepatic decompensation with almost 70% accuracy. It might be a useful noninvasive test to predict patient outcome. UMIN Clinical Trials Registry no. UMIN000004363.

Point shear-wave elastography in chronic pancreatitis: A promising tool for staging disease severity

BACKGROUND

Objectives: ElastPQ^®-pSWE is an ultrasound technique developed to stage disease severity in patients with chronic liver diseases. Little data is available about its application to the pancreas. We aimed to assess the feasibility and reproducibility of pancreatic stiffness (PS) measurements in patients with chronic pancreatitis and their relationship with clinical and laboratory data.

MATERIAL AND METHODS

52 consecutive patients with chronic pancreatitis (CP) (40 males; median age 60 years) underwent hepatic and pancreatic pSWE. Liver stiffness was measured by transient elastography, 42 healthy subjects being controls (25 males; median age 54 years). Pancreatic pSWE inter-observer agreement was analyzed by intraclass correlation coefficient (ICC). The effects of clinical, laboratory and US data on PS measurements were evaluated by linear regression.

RESULTS

pSWE was feasible in all the CP patients, but one. Pancreatic stiffness was significantly higher in CP patients than healthy controls (4.3 ± SD 2.4 vs. 2.8 ± SD 1.1 kPa, respectively, p = 0.001). Significantly higher values in the CP group were observed in patients with longer disease duration (>10 vs. ≤10 years) (5.8 ± SD 4 vs. 3.9 ± SD 1.5 kPa, respectively, p = 0.01), on chronic analgesic drugs (6.0 vs. 3.5 kPa, p < 0.05) and with lower body weight (p < 0.05, r = -0.38). At multivariate analysis all the three variables resulted independently associated to the pancreatic stiffness value. The ICC for PS was 0.77.

CONCLUSIONS

ElastPQ^®-pSWE is promising and reproducible in assessing pancreatic stiffness, which mainly reflects disease length and severity. Accordingly, its use is of potential value in stratifying CP patients by identifying those with a more serious degree of disease.

Simultaneous MR thermometry and acoustic radiation force imaging using interleaved acquisition

PURPOSE

A novel and practical method for simultaneously performing MR acoustic radiation force imaging (ARFI) and proton resonance frequency (PRF)-shift thermometry has been developed and tested. This could be an important tool for evaluating the success of MR-guided focused ultrasound procedures for which MR-thermometry measures temperature and thermal dose and MR-ARFI detects changes in tissue mechanical properties.

METHODS

MR imaging was performed using a gradient recalled echo segmented echo-planar imaging pulse sequence with bipolar motion encoding gradients (MEG). Images with ultrasound pulses (ON) and without ultrasound pulses (OFF) during the MEG were interleaved at the repetition time (TR) level. ARFI displacements were calculated by complex subtraction of ON-OFF images, and PRF temperature maps were calculated by baseline subtraction. Evaluations in tissue-mimicking phantoms and ex vivo porcine brain tissue were performed. Constrained reconstruction improved the temporal resolution of dynamic measurements.

RESULTS

Simultaneous maps of displacement and temperature were acquired in 2D and 3D while keeping tissue heating < 1°C. Accuracy of the temperature maps was comparable to the standard PRF sequence. Using constrained reconstruction and subsampled k-space (R = 4.33), 3D simultaneous temperature and displacement maps can be acquired every 4.7 s.

CONCLUSION

This new sequence acquires simultaneous temperature and displacement maps with minimal tissue heating, and can be applied dynamically for monitoring tissue mechanical properties during ablation procedures. Magn Reson Med 79:1515-1524, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Reproducibility of 2-Dimensional Shear Wave Elastography Assessment of the Liver: A Direct Comparison With Point Shear Wave Elastography in Healthy Volunteers

OBJECTIVES

Two-dimensional shear wave elastography (2D-SWE) imaging for the noninvasive assessment of tissue stiffness was assessed for reproducibility in healthy volunteers in quantifying liver elasticity, compared with an established point shear wave elastography (p-SWE) technique also known as virtual touch quantification (VTQ) (SIEMENS).

METHODS

Eleven healthy volunteers were examined by four experienced operators on two occasions, separated by two weeks (sessions A and B). Ten 2D-SWE using LOGIQ E9 and p-SWE measurements using VTQ (in meters per second) were consecutively taken from deep portions of liver segments 5 or 6 away from vascular structures, using standard techniques. Inter- and intra-observer agreement was assessed by intraclass coefficient (ICC).

RESULTS

A total of 880 2D-SWE and p-SWE velocities were recorded. Mean values from the four operators ranged between 1.188 and 1.196 m/s for 2D-SWE and 1.170 to 1.207 m/s for p-SWE. Interobserver reproducibility was good for both sessions with ICCs of 0.88 and 0.93 (2D-SWE) and 0.87 and 0.93 (p-SWE). The overall intra-operator reproducibility between sessions A and B was good for both p-SWE and 2D-SWE with ICC of 0.87 and 0.83, respectively. For inter- and intra-observer variability, the ICC was more than or equal to 0.71, indicating that the results were reliable. There was a strong and significant correlation between the 2D-SWE and p-SWE measurements (r = 0.87, P = .0006), but their velocities did not agree equally across different velocities.

CONCLUSIONS

Two-dimensional SWE using LOGIQ E9 is a reliable and reproducible method for measuring elasticity in healthy volunteers and has a similar degree of reliability as p-SWE using VTQ, but absolute measurements from the two techniques should not be used interchangeably.

Ultrasound Evaluation of Liver Fibrosis

Early diagnosis of liver fibrosis is an important factor affecting the efficacy of chronic hepatitis treatment. In the past, the diagnosis of liver fibrosis was dependent on a liver biopsy which has several shortcomings as sampling error, intra- or inter-observation variations and possible procedure-related complications. Ultrasound-based elastography, tissue elastography (TE) and acoustic radiation force impulse (ARFI) have been developed to assess liver fibrosis. Current clinical evidence indicates that TE and ARFI had high sensitivities and specificities to diagnosis from significant fibrosis to liver cirrhosis. TE and ARFI can not only assess liver fibrosis but can also be used to predict prognosis. In practical, ARFI can also be used on a regular basis to evaluate the degree of liver fibrosis for chronic hepatitis B and C, nonalcoholic fatty liver disease, and alcoholic liver disease.

Acoustic radiation force impulse imaging of kidneys - a phantom study

Aim of the study

Since there have been only few works reporting the diagnosis of kidneys using Acoustic Radiation Force Impulse technique and those works do not provide consistent results of shear wave velocity measurements in renal tissue, we have decided to use kidney phantoms with known properties to examine the reliability of the method itself in a controlled setup similar to kidneys examination.

Materials and methods

Four gelatin-based phantoms imitating different clinical situations were manufactured – two with thick and two with thin renal cortex, each type at a depth similar to a normal-weight or overweight patient. For each phantom, a series of interest points was chosen and for each point 20 Shear Wave Velocity measurements were taken using the build-in Virtual Touch Tissue Quantification^™ tool in a Siemens Acuson S2000 ultrasound scanner equipped with a 6C1 HD Transducer (Siemens Mountainview, USA).

Results

Mean Shear Wave Velocity values obtained for all the examined points ranged from 2.445 to 3.941 m/s, with standard deviation exceeding 0.1 in only one case out of 29 points, but differing significantly between all points.

Conclusions

The obtained results indicate that the method is highly reliable as long as the measurement volume contains a uniform tissue region. If the measurement window covers a region with different properties even partially, the obtained results are affected. The variance of measured values on the other hand is not affected by the said non-uniformity of material under examination. Furthermore, the variance of measured values does not show a clear dependency on the depth at which the shear wave velocities are measured.

Evaluation of Renal Parenchyma Elasticity With Acoustic Radiation Force Impulse Quantification in Nutcracker Syndrome and Comparisons With Grayscale Doppler Sonography and Laboratory Findings

OBJECTIVES

We sought to evaluate renal parenchymal elasticity with Virtual Touch quantification of acoustic radiation force impulse imaging in nutcracker syndrome and to compare shear-wave velocity (SWV) values with grayscale Doppler sonography and laboratory findings.

METHODS

Thirty-eight healthy volunteers and forty-three nutcracker syndrome patients were enrolled in this prospective study. SWV values for both kidneys in nutcracker syndrome patients and healthy volunteers were evaluated. Grayscale Doppler ultrasound and laboratory findings were obtained and compared with SWV values in both nutcracker syndrome patients and healthy volunteers.

RESULTS

In nutcracker syndrome patients, SWV values for the left kidney were significantly lower than those for the right kidney (n = 43; 1.93 ± 0.43 m/s vs 2.53 ± 0.45 m/s [P < .001]). Healthy volunteers' SWV values for both kidneys had no statistically significant differences. There was a statistically significant difference between nutcracker syndrome patients and healthy volunteers for the SWV values and body mass index values. There was no statistically significant correlation between SWV values of nutcracker syndrome patients and age, gender, glomerular filtration rate, body mass index, vein diameter ratio, peak velocity ratio, or resistive indices.

CONCLUSIONS

Acoustic radiation force impulse imaging offers new, additional information on the affected left kidney parenchymal changes in nutcracker syndrome patients.

Dynamic contrast-enhanced ultrasound and elastography assess deltoid muscle integrity after reverse shoulder arthroplasty

BACKGROUND

The outcome after reverse shoulder arthroplasty (RSA) depends on the condition of the deltoid muscle, which we assessed with new ultrasound modalities and electromyography (EMG). Contrast-enhanced ultrasound (CEUS) and acoustic radiation force impulse (ARFI) were applied to assess perfusion and elasticity of the deltoid muscle compared with the clinical and functional outcome.

METHODS

The study recruited 64 patients (mean age, 72.9 years) treated with RSA between 2004 and 2013. The deltoid muscle was examined with EMG and ultrasound imaging. Functional scores such as Constant score and American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form score were assessed. Among other CEUS parameters, the wash-in perfusion index, time to peak, and rise time were compared between the operated-on and contralateral shoulders as well as between patients with above-average and below-average outcome. The stiffness of the deltoid muscle was analyzed with ARFI.

RESULTS

After RSA, deltoid perfusion (wash-in perfusion index, Δ = -12% ± 22%, P = .0001) and shoulder function (Constant score, Δ = -14 ± 24, P < .0001) were both inferior compared with the contralateral side. This perfusion deficit was associated with a limited range of motion (time to peak and anteversion: r = -0.290, P = .022). Deltoid perfusion was higher in patients with above-average outcome (rise time, Δ = 33% ± 13%, P = .038). The operated-on deltoid muscles showed higher stiffness than the contralateral muscles (ARFI, Δ = 0.2 ± 0.9 m/s, P = .0545). EMG excluded functionally relevant axillary nerve injuries in the study population.

CONCLUSIONS

CEUS revealed reduced mean perfusion of the deltoid muscle after RSA. Reduced perfusion was associated with limited range of motion and below-average outcome. Functional shoulder impairment after RSA might be predicted by noninvasive CEUS as a surrogate parameter for the integrity of the deltoid muscle.

Acoustic radiation force impulse shear wave elastography (ARFI) of acute and chronic pancreatitis and pancreatic tumor

INTRODUCTION

Acoustic Radiation Force Impulse (ARFI) elastography evaluates tissue stiffness non-invasively and has rarely been applied to pancreas examinations so far. In a prospective and retrospective analysis, ARFI shear wave velocities of healthy parenchyma, pancreatic lipomatosis, acute and chronic pancreatitis, adenocarcinoma and neuroendocrine tumor (NET) of the pancreas were evaluated and compared.

MATERIAL AND METHODS

In 95 patients ARFI elastography of the pancreatic head, and also of the tail for a specific group, was analysed retrospectively. Additionally, prospectively in 100 patients ARFI was performed in the head and tail of the pancreas.

RESULTS

A total of 195 patients were included in the study. Healthy parenchyma (n=21) and lipomatosis (n=30) showed similar shear wave velocities of about 1.3m/s. Acute pancreatitis (n=35), chronic pancreatitis (n=53) and adenocarcinoma (n=52) showed consecutively increasing ARFI values, respectively. NET (n=4) revealed the highest shear wave velocities amounting to 3.62m/s. ARFI elastography showed relevant differences between acute pancreatitis and chronic pancreatitis or adenocarcinoma. With a cut-off value of 1.74m/s for the diagnosis of a malignant disease the sensitivity was 91.1% whereas the specificity amounted to 60.4%.

CONCLUSION

ARFI shear wave velocities present differences in various pathologies of the pancreas. Acute and chronic pancreatitis as well as neoplastic lesions show high ARFI values. Very high elasticity values may indicate malignant disease of the pancreas. However, there is a considerable overlap between the entities.

Diagnostic Accuracy of Acoustic Radiation Force Impulse (ARFI) in Diagnosis of Liver Fibrosis among Egyptian Patients with Chronic HCV Infection

BACKGROUND:

Acoustic radiation force impulse (ARFI) evaluates liver stiffness non-invasively and was invented recently. This technique can easily and accurately assess the degree of liver fibrosis in clinical practice.

AIM:

The aim of this study was to detect the diagnostic performance of ARFI elastography in the staging of fibrosis in some Egyptian patients with chronic HCV infection.

PATIENTS AND METHODS:

One hundred ninety patients with chronic HCV infection; 142 men and 48 women were enrolled in the study. They underwent liver biopsy examination for liver fibrosis detection. All demographic; clinical and biochemical data were recoded. ARFI examination was done for all subjects to detect liver stiffness measurement in relation to liver fibrosis detected by pathological examination of liver biopsies.

RESULTS:

Medians of liver stiffness measurement by shear wave velocity showed a significant increase as a grade of liver fibrosis increases (p ≤ 0.0001, highly significant). Liver stiffness was directly correlated to age, AST; ALT; INR and liver steatosis (p values were: 0.009; 0.0001; 0.013; 0.006 and 0.04 respectively, significant). On the other hand, liver stiffness was inversely correlated to albumin; prothrombin concentration and platelets (p values were: 0.0001; 0.001, and 0.0001, respectively, significant). We found that shear wave velocity can predict F1; F2; F3 and F4 at cut-off values: 1.22; 1.32; 1.44 and 1.8 respectively.

CONCLUSION:

ARFI is a diagnostic noninvasive promising technique for liver fibrosis diagnosis among Egyptian patients with chronic HCV infection.

Experimental Validation of ARFI Surveillance of Subcutaneous Hemorrhage (ASSH) Using Calibrated Infusions in a Tissue-Mimicking Model and Dogs

Acoustic radiation force impulse (ARFI) Surveillance of Subcutaneous Hemorrhage (ASSH) has been previously demonstrated to differentiate bleeding phenotype and responses to therapy in dogs and humans, but to date, the method has lacked experimental validation. This work explores experimental validation of ASSH in a poroelastic tissue-mimic and in vivo in dogs. The experimental design exploits calibrated flow rates and infusion durations of evaporated milk in tofu or heparinized autologous blood in dogs. The validation approach enables controlled comparisons of ASSH-derived bleeding rate (BR) and time to hemostasis (TTH) metrics. In tissue-mimicking experiments, halving the calibrated flow rate yielded ASSH-derived BRs that decreased by 44% to 48%. Furthermore, for calibrated flow durations of 5.0 minutes and 7.0 minutes, average ASSH-derived TTH was 5.2 minutes and 7.0 minutes, respectively, with ASSH predicting the correct TTH in 78% of trials. In dogs undergoing calibrated autologous blood infusion, ASSH measured a 3-minute increase in TTH, corresponding to the same increase in the calibrated flow duration. For a measured 5% decrease in autologous infusion flow rate, ASSH detected a 7% decrease in BR. These tissue-mimicking and in vivo preclinical experimental validation studies suggest the ASSH BR and TTH measures reflect bleeding dynamics.

Ultrasound Elastography Used for Preventive Non-Invasive Screening in Early Detection of Liver Fibrosis

Background

Early discovery of liver fibrosis is becoming more popular because of enhanced incidence of hepatocellular carcinoma. Ultrasound-based liver elastography is a method used to approve suspected liver fibrosis or cirrhosis. We assessed the clinical usefulness of acoustic radiation force impulse shear wave elasticity imaging (ARFI-SWEI) as a preventive screening method to uncover fibrosis.

Methods

We screened 382 patients by native routine sonography for abnormal liver results and divided them into six groups: group 1: normal liver, groups 2-4: fatty liver grade I-III, group 5: liver cirrhosis, and group 6: inhomogenic liver tissue. Then ARFI-SWEI was performed and the results were compared with published shear wave velocity cut-off values that were predictive of each fibrosis stage (F0-4). A control group consisted of 20 healthy volunteers.

Results

The part of liver fibrosis ≥ F2 was in groups 1-4: 20-32%, group 5: 100%, and group 6: 91%. Main causes for fibrosis stage ≥ F2 were (non)-alcoholic steatohepatitis, chronic viral or autoimmune hepatitis and chronic heart failure.

Conclusions

Screening of the liver tissue in b-mode ultrasound can underestimate possible liver fibrosis; by using ARFI-SWEI, liver fibrosis can be uncovered early. It is a suitable preventive method comparable to colonoscopy for colon cancer.

Influence of age, sex, body mass index, alcohol, and smoking on shear wave velocity (p-SWE) of the pancreas

Purpose

A variety of elastographic techniques have been developed to facilitate the non-invasive assessment of tissue properties. The goal of the study was to examine the influence of gender, age, BMI, alcohol consumption, and smoking in healthy volunteers.

Methods

Of the 263 participants who met all the study inclusion criteria, 234 had successful measurements. The examination was performed with the Siemens Acuson S3000 (Siemens Healthcare, Erlangen, Germany), using the 6C1 curved array transducer with the virtual touch tissue quantification (VTQ) method.

Results

The values determined with the curved array in the head of the pancreas were 1.44 ± 0.39 m/s for women and 1.19 ± 0.29 m/s for men; in the body, the results were 1.49 ± 0.37 m/s for women and 1.26 ± 0.30  m/s for men; in the tail, the corresponding values were 1.29 ± 0.36 m/s for women and 1.05 ± 0.30 m/s for men. Comparison of gender showed that men have significantly lower mean values than women. There were significantly higher values in all parts of the organ with the increasing age of the participants (p < 0.0001). For BMI, there was a significant correlation with the values only when considering the BMI in continuous form. Alcohol consumption and smoking did not have any significant effects.

Conclusions

ARFI-VTQ is qualified for use on pancreatic tissue. Further studies are required to examine the influence of other factors in larger populations.

Acoustic radiation force impulse accuracy and the impact of hepatic steatosis on liver fibrosis staging

INTRODUCTION

The accuracy of Acoustic Radiation Force Impulse (ARFI) imaging has been validated in the setting of hepatitis C, however, the accuracy in the setting of fatty liver disease (FLD) has been less well-established. The aim of this study was to assess the accuracy of ARFI in the setting of hepatic steatosis.

METHODS

Patients with biopsy proven or sonographically diagnosed liver steatosis were assessed for ARFI trends including: inter-operator concordance, interquartile range, ARFI failure rate, relationship between ARFI velocity and steatosis severity, and concordance between biopsy and ARFI fibrosis scores.

RESULTS

Three hundred and forty-nine patients were assessed (53 'biopsy' cohort and 296 'ultrasound' cohort), with 28 patients having biopsy on the same day as ARFI. Low stages of fibrosis (F0/1) were over-estimated by ARFI in 62% of cases with biopsy correlation (n = 16, P < 0.001), with ARFI offering increased accuracy in regard to higher-stage fibrosis (14/15 cases, 93%). In both the biopsy and ultrasound cohorts the failure rate and median inter-quartile range increased with increasing steatosis, and the inter-operator concordance remained good across all liver steatosis severities.

CONCLUSION

In the setting of steatosis, ARFI is very sensitive in detecting, and accurate in diagnosing, higher stages of fibrosis regardless of steatosis severity. It tends to overestimate the fibrosis category in lower stages of fibrosis. The present study does not show conclusively if the presence of steatosis or its severity independently alters ARFI measurements.

The effect of applied transducer force on acoustic radiation force impulse quantification within the left lobe of the liver

Introduction: Acoustic Radiation Force Impulse (ARFI) Quantification measures shear wave velocities (SWVs) within the liver. It is a reliable method for predicting the severity of liver fibrosis and has the potential to assess fibrosis in any part of the liver, but previous research has found ARFI quantification in the right lobe more accurate than in the left lobe. A lack of standardised applied transducer force when performing ARFI quantification in the left lobe of the liver may account for some of this inaccuracy. The research hypothesis of this present study predicted that an increase in applied transducer force would result in an increase in SWVs measured.

Methods: ARFI quantification within the left lobe of the liver was performed within a group of healthy volunteers (n = 28). During each examination, each participant was subjected to ARFI quantification at six different levels of transducer force applied to the epigastric abdominal wall.

Results: A repeated measures ANOVA test showed that ARFI quantification was significantly affected by applied transducer force (p = 0.002). Significant pairwise comparisons using Bonferroni correction for multiple comparisons showed that with an increase in applied transducer force, there was a decrease in SWVs.

Conclusion: Applied transducer force has a significant effect on SWVs within the left lobe of the liver and it may explain some of the less accurate and less reliable results in previous studies where transducer force was not taken into consideration. Future studies in the left lobe of the liver should take this into account and control for applied transducer force.

Incorporation of Noninvasive Measures of Liver Fibrosis Into Clinical Practice: Diagnosis and Prognosis

Noninvasive methods are increasingly used for the assessment of liver fibrosis. Two categories of markers include serum-based markers (biologic properties) or ultrasound and magnetic resonance imaging-based techniques that use the principles of elastography (physical properties) to indirectly assess liver fibrosis. Serum markers can be either direct or indirect markers of the fibrosis process. Common elastography-based studies include vibration-controlled transient elastography, point shear wave elastography, and 2-dimensional shear wave elastography and magnetic resonance elastography. A common theme among all techniques is the inability to accurately differentiate between minimal or moderate stages of fibrosis but superior performance in identifying subjects with cirrhosis or normal liver parenchyma. Noninvasive markers may also serve as prognostic tools to course the natural history of chronic liver disease as well as identify cirrhotic patients at highest risk of future decompensation. Further research is needed to identify the role of noninvasive markers in following asymptomatic individuals, especially in patients with nonalcoholic fatty liver disease.

Evaluation of a three-dimensional MR acoustic radiation force imaging pulse sequence using a novel unbalanced bipolar motion encoding gradient

PURPOSE

MR guided focused ultrasound procedures require accurate focal spot localization in three dimensions. This study presents a three-dimensional (3D) pulse sequence for acoustic radiation force imaging (ARFI) that efficiently localizes the focal spot by means of ultrasound induced tissue displacement over a large field-of-view.

METHODS

A novel unbalanced bipolar motion encoding gradient was implemented to maximize time available for motion encoding, reduce echo times, and allow for longer echo train lengths. Two advanced features, kz reduction factor (KZRF) and kz -level interleaving, were implemented to reduce tissue heating. Studies in gelatin phantoms compared the location of peak displacement and temperature measured by 3D MR thermometry. MR-ARFI induced tissue heating was evaluated through a parametric study of sequence parameters and MR thermometry measurements during repeated application of ARFI sonication patterns. Sequence performance was characterized in the presence of respiration and tissue inhomogeneity.

RESULTS

The location of peak displacement and temperature rise agreed within 0.2 ± 0.1 mm and 0.5 ± 0.3 mm in the transverse and longitudinal direction, respectively. The 3D displacement maps were acquired safely, and the KZRF and kz -level interleaving features reduced tissue heating by 51%. High quality displacement maps were obtained despite respiration and tissue inhomogeneities.

CONCLUSION

This sequence provides a safe, accurate, and simple approach to localizing the focal spot in three dimensions with a single scan. Magn Reson Med 76:803-813, 2016. © 2015 Wiley Periodicals, Inc.

Deep bleeder acoustic coagulation (DBAC)-Part I: development and in vitro testing of a research prototype cuff system

Background

Bleeding from limb injuries is a leading cause of death on the battlefield, with deep wounds being least accessible. High-intensity focused ultrasound (HIFU) has been shown capable of coagulation of bleeding (cautery). This paper describes the development and refereed in vitro evaluation of an ultrasound (US) research prototype deep bleeder acoustic coagulation (DBAC) cuff system for evaluating the potential of DBAC in the battlefield. The device had to meet quantitative performance metrics on automated operation, therapeutic heating, bleeder detection, targeting accuracy, operational time limits, and cuff weight over a range of limb sizes and bleeder depths. These metrics drove innovative approaches in image segmentation, bleeder detection, therapy transducers, beam targeting, and dose monitoring. A companion (Part II) paper discusses the in vivo performance testing of an animal-specific DBAC system.

Materials and methods

The cuff system employed 3D US imaging probes (“Ix”) for detection and localization (D&L) and targeting, with the bleeders being identified by automated spectral Doppler analysis of flow waveforms. Unique high-element-count therapeutic arrays (“Tx”) were developed, with the final cuff prototype having 21 Tx’s and 6 Ix’s. Spatial registration of Ix’s and Tx’s was done with a combination of image-registration, acoustic time-of-flight measurement, and tracking of the cuff shape via a fiber optic sensor. Acoustic radiation force impulse (ARFI) imaging or thermal strain imaging (TSI) at low-power doses were used to track the HIFU foci in closed-loop targeting. Recurrent neural network (RNN) acoustic thermometry guided closed-loop dosing. The cuff was tested on three phantom “limb” sizes: diameters = 25, 15, and 7.5 cm, with bleeder depths from 3.75 to 12.5 cm. “Integrated Phantoms” (IntP) were used for assessing D&L, closed-loop targeting, and closed-loop dosing. IntPs had surrogate arteries and bleeders, with blood-mimicking fluids moved by a pulsatile pump, and thermocouples (TCs) on the bleeders. Acoustic dosing was developed and tested using “HIFU Phantoms” having precisely located TCs, with end-of-dose target ∆T = 33–58 °C, and skin temperature ∆T ≤ 20 °C, being required.

Results

Most DBAC cuff performance requirements were met, including cuff weight, power delivery, targeting accuracy, skin temperature limit, and autonomous operation. The automated D&L completed in 9 of 15 tests (65 %), detecting the smallest (0.6 mm) bleeders, but it had difficulty with the lowest flow (3 cm/sec) bleeders, and in localizing bleeders in the smallest (7.5 cm) phantoms. D&L did not complete within the 9-min limit (results ranged 10–21 min). Closed-loop targeting converged in 20 of 31 tests (71 %), and closed-loop dosing power shut-off at preset ∆Ts was operational.

Summary and conclusion

The main performance objectives of the prototype DBAC cuff were met, however the designs required a number of challenging new technology developments. The novel Tx arrays exhibited high power with significant beam steering and focusing flexibility, while their integrated electronics enabled the required compact, lightweight configurability and simplified driving controls and cable/connector architecture. The compounded 3D imaging, combined with sophisticated software algorithms, enabled automated D&L and initial targeting and closed-loop targeting feedback via TSI. The development of RNN acoustic thermometry made possible feedback-controlled dosing. The lightweight architecture required significant design and fabrication effort to meet mechanical functionalities. Although not all target specifications were met, future engineering solutions addressing these performance deficiencies are proposed. Lastly, the program required very complex limb test phantoms and, while very challenging to develop, they performed well.

Liver stiffness measurements and short-term survival after left ventricular assist device implantation: A pilot study

BACKGROUND

Hepatic dysfunction can contribute to the clinical outcome of patients with end-stage chronic heart failure (HF). This pilot study evaluated the importance of liver stiffness (LS) measurements by acoustic radiation force impulse (ARFI) imaging elastography in patients with end-stage chronic HF who underwent left ventricular assist device (LVAD) implantation.

METHODS

The study enrolled 28 patients (23 men), mean age of 54 ± 11 years, with end-stage chronic HF selected for LVAD implantation. At baseline, all patients received LS measurements using ARFI elastography. Hepatic venous pressure gradient measurements and transjugular liver biopsies were performed in 16 patients. Liver stiffness was measured 21 days (Follow-up 1, n = 23) and 485 ± 136 days (Follow-up 2, n = 13) after LVAD implantation. Patients were classified according to their baseline LS into Group I (low baseline LS [no significant fibrosis = Metavir F < 2]) or Group II (high baseline LS [significant fibrosis = Metavir F ≥ 2]).

RESULTS

LS at baseline was higher in Group II than in Group I (p < 0.001) and decreased significantly after LVAD implantation (Follow-up 1, p = 0.002; Follow-up 2, p = 0.002). Baseline LS correlated with liver fibrosis (p = 0.049) and central venous pressure (p = 0.001). Non-survivors showed higher LS (p = 0.019), bilirubin (p = 0.018), Model for End-Stage Liver Disease score (p = 0.001), and liver fibrosis (p = 0.004) compared with the survivors. In the univariate analysis, LS was a significant factor (p = 0.017) in predicting survival after LVAD implantation.

CONCLUSIONS

ARFI elastography shows that LS is influenced by central venous congestion and histologic changes of the liver in patients with end-stage chronic HF. LS may predict the outcome in patients after LVAD implantation.

The role of viscosity estimation for oil-in-gelatin phantom in shear wave based ultrasound elastography

Shear wave based ultrasound elastography utilizes mechanical excitation or acoustic radiation force to induce shear waves in deep tissue. The tissue response is monitored to obtain elasticity information about the tissue. During the past two decades, tissue elasticity has been extensively studied and has been used in clinical disease diagnosis. However, biological soft tissues are viscoelastic in nature. Therefore, they should be simultaneously characterized in terms of elasticity and viscosity. In this study, two shear wave-based elasticity imaging methods, shear wave dispersion ultrasound vibrometry (SDUV) and acoustic radiation force impulsive (ARFI) imaging, were compared. The discrepancy between the measurements obtained by the two methods was analyzed, and the role of viscosity was investigated. To this end, four types of gelatin phantoms containing 0%, 20%, 30% and 40% castor oil were fabricated to mimic different viscosities of soft tissue. For the SDUV method, the shear elasticity μ1 was 3.90 ± 0.27 kPa, 4.49 ± 0.16 kPa, 2.41 ± 0.33 kPa and 1.31 ± 0.09 kPa; and the shear viscosity μ2 was 1.82 ± 0.31 Pa•s, 2.41 ± 0.35 Pa•s, 2.65 ± 0.13 Pa•s and 2.89 ± 0.14 Pa•s for 0%, 20%, 30% and 40% oil, respectively in both cases. For the ARFI measurements, the shear elasticity μ was 7.30 ± 0.20 kPa, 8.20 ± 0.31 kPa, 7.42 ± 0.21 kPa and 5.90 ± 0.36 kPa for 0%, 20%, 30% and 40% oil, respectively. The SDUV results demonstrated that the elasticity first increased from 0% to 20% oil and then decreased for the 30% and 40% oil. The viscosity decreased consistently as the concentration of castor oil increased from 0% to 40%. The elasticity measured by ARFI showed the same trend as that of the SDUV but exceeded the results measured by SDUV. To clearly validate the impact of viscosity on the elasticity estimation, an independent measurement of the elasticity and viscosity by dynamic mechanical analysis (DMA) was conducted on these four types of gelatin phantoms and then compared with SDUV and ARFI results. The shear elasticities obtained by DMA (3.44 ± 0.31 kPa, 4.29 ± 0.13 kPa, 2.05 ± 0.29 kPa and 1.06 ± 0.18 kPa for 0%, 20%, 30% and 40% oil, respectively) were lower than those by SDUV, whereas the shear viscosities obtained by DMA (2.52 ± 0.32 Pa·s, 3.18 ± 0.12 Pa·s, 3.98 ± 0.19 Pa·s and 4.90 ± 0.20 Pa·s for 0%, 20%, 30% and 40% oil, respectively) were greater than those obtained by SDUV. However, the DMA results showed that the trend in the elasticity and viscosity data was the same as that obtained from the SDUV and ARFI. The SDUV results demonstrated that adding castor oil changed the viscoelastic properties of the phantoms and resulted in increased dispersion of the shear waves. Viscosity can provide important and independent information about the inner state of the phantoms, in addition to the elasticity. Because the ARFI method ignores the dispersion of the shear waves, namely viscosity, it may bias the estimation of the true elasticity. This study sheds further light on the significance of the viscosity measurements in shear wave based elasticity imaging methods.

A theoretical study of inertial cavitation from acoustic radiation force impulse imaging and implications for the mechanical index

The mechanical index (MI) attempts to quantify the likelihood that exposure to diagnostic ultrasound will produce an adverse biological effect by a non-thermal mechanism. The current formulation of the MI implicitly assumes that the acoustic field is generated using the short pulse durations appropriate to B-mode imaging. However, acoustic radiation force impulse (ARFI) imaging employs high-intensity pulses up to several hundred acoustic periods long. The effect of increased pulse durations on the thresholds for inertial cavitation was studied computationally in water, urine, blood, cardiac and skeletal muscle, brain, kidney, liver and skin. The results indicate that, although the effect of pulse duration on cavitation thresholds in the three liquids can be considerable, reducing them by, for example, 6%-24% at 1 MHz, the effect on tissue is minor. More importantly, the frequency dependence of the MI appears to be unnecessarily conservative; that is, the magnitude of the exponent on frequency could be increased to 0.75. Comparison of these theoretical results with experimental measurements suggests that some tissues do not contain the pre-existing, optimally sized bubbles assumed for the MI. This means that in these tissues, the MI is not necessarily a strong predictor of the probability of an adverse biological effect.

Changes in liver stiffness using acoustic radiation force impulse imaging in patients with obstructive cholestasis and cholangitis

BACKGROUND

Acoustic radiation force impulse imaging is used to assess stages of liver fibrosis. The aim of our study was to evaluate liver stiffness changes in patients with biliary obstruction with or without sclerosing cholangitis after biliary drainage.

METHODS

A total of 71 patients were enrolled in this prospective study (cohort N=51, control group N=20); 51 patients with obstructive cholestasis, indicated for endoscopic retrograde cholangiography, received stiffness measurement by acoustic radiation force impulse imaging before and 1-2 days after endoscopic retrograde cholangiography. Seventeen patients with obstructive cholestasis had primary or secondary sclerosing cholangitis. Forty one patients had a follow-up acoustic radiation force impulse imaging measurement after 3.0 ± 9.31 weeks.

RESULTS

In all patients with obstructive cholestasis, stiffness decreased significantly after biliary drainage (p<0.001). The main decrease was observed within 2 days after endoscopic retrograde cholangiography (1.92-1.57 m/s, p<0.001) and correlated with the decrease of bilirubin and alkaline phosphatase (p=0.04 and p=0.002, respectively). In patients with sclerosing cholangitis, the initial decrease of stiffness after biliary drainage was weaker than in those without (2.1-1.85 m/s vs. 1.81-1.43 m/s, p=0.016).

CONCLUSION

Acoustic radiation force impulse imaging elastography shows that liver stiffness is increased by biliary obstruction, and decreases after endoscopic retrograde cholangiography irrespective of the aetiology. In patients with sclerosing cholangitis the reduction in stiffness after biliary drainage is impaired.