Anna Gallotti

Acoustic Radiation Force Impulse (ARFI) technique in ultrasound with Virtual Touch tissue quantification of the upper abdomen

Purpose. Virtual Touch tissue quantification is an implementation of ultrasound (US) Acoustic Radiation Force Impulse (ARFI) imaging that provides numerical measurements (wave-velocity values) of tissue stiffness. The aim of this study was to define the normal values of shear-wave speed for the healthy liver, gallbladder, pancreas, spleen and kidneys. Materials and methods. Thirty-five young healthy volunteers underwent Virtual Touch tissue quantification after having signed an informed consent form. All upper abdominal organs were examined by two independent operators. A phantom fluid model was also evaluated. All mean wave-velocity values were analysed and compared. Results. One hundred and forty measurements of liver, pancreas, spleen and kidneys, and 70 measurements of the gallbladder lumen were performed. Twenty measurements on the phantom were also performed. Comparing all measurements separately made by each operator in different parts of the organs, no statistically significant differences were observed. A “XXXX/0” value was always obtained from all measurements performed on the gallbladder lumen and on the phantom fluid model. Liver, pancreas, spleen and kidney mean values were 1.59 m/s, 1.40 m/s, 2.44 m/s and 2.24 m/s, respectively. Conclusions. Virtual Touch tissue quantification is a new, promising implementation of the US ARFI technique, which provides numerical measurements of tissue stiffness. The mean shear-wave speed is lower in the pancreatic parenchyma than in the liver and kidney, whereas the spleen is characterised by the highest mean value. In Riassunto Obiettivo. Il Virtual Touch tissue quantification è una applicazione quantitativa della tecnica ecografica Acoustic Radiation Force Impulse (ARFI) che fornisce valori numerici dell’elasticità dei tessuti. Lo scopo dello studio è definire i valori di normalità di fegato, colecisti, pancreas, milza e reni. Materiali e metodi. Sono stati studiati 35 giovani volontari sani. Un consenso informato è stato ottenuto prima dell’esame. Gli organi addominali superiori sono stati studiati da due operatori indipendenti. È stato inoltre studiato un phantom contenente acqua. Tutti i valori medi di velocità di propagazione dell’onda sono stati analizzati e confrontati. Risultati. Sono state effettuate 140 misurazioni su fegato, pancreas, milza e reni, 70 nel lume della colecisti e 20 nel phantom. Confrontando tutte le misurazioni eseguite da ciascun operatore in differenti parti dei vari organi addominali, non sono risultate differenze statisticamente significative. Tutte le misurazioni effettuate su colecisti e phantom hanno fornito un valore definito “XXXX/0”. Fegato, pancreas, milza e reni avevano valori medi rispettivamente di 1,59 m/s, 1,40 m/s, 2,44 m/s e 2,24 m/s. Conclusioni. Il Virtual Touch tissue quantification è una promettente applicazione della tecnica ecografica ARFI, che consente una valutazione espressa in numeri della durezza dei tessuti. Il valore medio della velocità di propagazione dell’onda nel parenchima pancreatico è inferiore rispetto a quella misurata nel fegato e nei reni, mentre la milza è caratterizzata da valore medio più alto. Nei fluidi semplici, come l’acqua, viene sempre riscontrato ABDOMINAL RADIOLOGY RADIOLOGIA ADDOMINALE Radiol med (2010) 115:889–897 DOI 10.1007/s11547-010-0504-5 Acoustic Radiation Force Impulse (ARFI) technique in ultrasound with Virtual Touch tissue quantification of the upper abdomen Tecnica Acoustic Radiation Force Impulse (ARFI) nello studio ecografico con Virtual Touch tissue quantification dell’addome superiore A. Gallotti • M. D’Onofrio • R. Pozzi Mucelli Istituto di Radiologia, Policlinico G. B. Rossi, Università di Verona, Piazzale L. A. Scuro 10, 37134 Verona, Italy Correspondence to: M. D’Onofrio, Tel.: +39-045-8124301, Fax: +39-045-8027490, e-mail: mirko.donofrio@univr.it Received: 19 May 2009 / Accepted: 28 July 2009 / Published online: 15 January 2010

Tissue Quantification With Acoustic Radiation Force Impulse Imaging: Measurement Repeatability and Normal Values in the Healthy Liver

OBJECTIVE The purpose of this study was to describe the most reliable measurement procedure for acoustic radiation force impulse technology and to define the normal wave velocity values in a healthy liver. SUBJECTS AND METHODS Twenty healthy volunteers underwent acoustic radiation force impulse imaging tissue quantification and were enrolled in this prospective study. All patients were examined by two independent operators at the same time. Twenty-four measurements per subject were obtained. Intraoperator and interoperator evaluations were performed. Statistical comparison of all mean data was performed with Students t test. A value of p < 0.05 was considered significant. A comparative analysis was performed, and interclass correlation coefficients were calculated. RESULTS The operators obtained 960 measurements. A statistically significant difference was found between the mean shear wave velocity values obtained by one operator deep in the right lobe of the liver and the values obtained on the surface of the right lobe (1.56 vs 1.90 m/s) and between the mean values obtained deep in the right lobe and those obtained deep in the left lobe (1.56 vs 1.84 m/s). The other operator had similar results. The distribution of all mean values obtained by both operators deep in the right hepatic lobe exhibited less dispersion (95% CI, 1.391-1.725) than those obtained on the surface (95% CI, 1.664-2.136). In 77.5% of cases, the shear wave speeds were between 1 and 2 m/s. No statistically significant difference was found in the comparisons performed on the right hepatic lobe by the two operators. The interclass correlation coefficient calculated for measurements deep in the right lobe was 0.87 (p < 0.0001). CONCLUSION Acoustic radiation force impulse imaging quantification of hepatic tissue is more reproducible when applied to the deeper portion of the right lobe of the liver.

Acoustic Radiation Force Impulse Elastography for fibrosis evaluation in patients with chronic hepatitis C: An international multicenter study

AIM The aim of this international multicenter study was to evaluate the reliability of Acoustic Radiation Force Impulse (ARFI) elastography for predicting fibrosis severity, in patients with chronic hepatitis C. PATIENTS AND METHODS We compared ARFI to liver biopsy (LB) in 914 patients (10 centers, 5 countries) with chronic hepatitis C. In each patient LB (evaluated according to the METAVIR score) and ARFI measurements were performed (median of 5-10 valid measurements, expressed in meters/second - m/s). In 400 from the 914 patients, transient elastography (TE) was also performed (median of 6-10 valid measurements, expressed in kiloPascals - kPa). RESULTS Valid ARFI measurements were obtained in 911 (99.6%) of 914 cases. On LB 61 cases (6.7%) had F0, 241 (26.4%) had F1, 202 (22.1%) had F2, 187 (20.4%) had F3, and 223 (24.4%) had F4 fibrosis. A highly significant correlation (r=0.654) was found between ARFI measurements and fibrosis (p<0.0001). The predictive values of ARFI for various stages of fibrosis were: F ≥ 1 - cut-off>1.19 m/s (AUROC=0.779), F ≥ 2 - cut-off>1.33 m/s (AUROC=0.792), F ≥ 3 - cut-off>1.43 m/s (AUROC=0.829), F=4 - cut-off>1.55 m/s (AUROC=0.842). The correlation with histological fibrosis was not significantly different for TE in comparison with ARFI elastography: r=0.728 vs. 0.689, p=0.28. TE was better than ARFI for predicting the presence of liver cirrhosis (p=0.01) and fibrosis (F ≥ 1, METAVIR) (p=0.01). CONCLUSION ARFI elastography is a reliable method for predicting fibrosis severity in chronic hepatitis C patients.

Acoustic Radiation Force Impulse (ARFI) ultrasound imaging of solid focal liver lesions

OBJECTIVE The aim of this paper was to evaluate the application of ARFI ultrasound imaging and its potential value for characterizing focal solid liver lesions. MATERIALS AND METHODS In this multicentric prospective study, over a total non-consecutive period of four months, all patients underwent ARFI US examination. Two independent operators performed 5 measurements per each lesion and 2 measurements in the surrounding liver. According to the definitive diagnosis, a mean velocity value and standard deviations were obtained in each type of focal solid lesion, compared by using t-test, and the inter-operator evaluation was performed by using the Students t-test. A comparison between the total mean values of each type of lesion and the mean value of the parenchyma was performed. RESULTS 40 lesions were evaluated and a total of 400 measurements were obtained. The lesions were: 6/40(15%) hepatocellular carcinomas, 7/40(17.5%) hemangiomas, 5/40(12.5%) adenomas, 9/40(22.5%) metastases and 13/40(32.5%) focal nodular hyperplasias. The total mean values obtained were: 2.17 m/s in HCCs, 2.30 m/s in hemangiomas, 1.25 m/s in adenomas, 2.87 m/s in metastases and 2.75 m/s in FNHs. The inter-operator evaluation resulted non-statistically different (p>0.05). A significant difference (p<0.05) was always found by comparing adenomas to the other lesions. 160 measurements were obtained in the surrounding parenchyma, with a no significant difference between values measured in adenomas and in the surrounding liver. CONCLUSIONS ARFI technology with Virtual Touch tissue quantification could non-invasively provide significant complementary information regarding the tissue stiffness, useful for the differential diagnosis of focal solid liver lesions.

Pancreatic multicenter ultrasound study (PAMUS)

AIM To describe the typical CEUS pattern of pancreatic lesions and to evaluate the diagnostic accuracy of Contrast-enhanced ultrasound (CEUS) in their characterization. MATERIALS AND METHODS All US and CEUS examinations of focal pancreatic masses performed in six centers during a period of five years were reviewed. Inclusion criteria were: focal pancreatic mass pathologically proved, visible at ultrasound (US) and studied with CEUS. All lesions were then evaluated for size, aspect and enhancement pattern. Sensitivity, specificity, positive and negative predictive values with 95% CIs were calculated to define diagnostic accuracy of CEUS in respect to pathology. Diagnostic confidence of US and CEUS, discerning between benign and malignant lesions, were represented by using ROC (receiver operating characteristics) curves. Agreement was evaluated by means of k statistics. RESULTS 1439 pancreatic lesions were included. At CEUS the lesions were divided into solid (89%) and cystic (12%) masses and classified into six and eight categories, respectively. Among the solid lesions, adenocarcinomas were characterized with an accuracy of 87.8%. Among the cystic lesions, cystic tumors were diagnosed with an accuracy of 97.1%. ROC curve area increased from 0.637 for US to 0.877 for CEUS (p<0.0001). Inter-observer agreement was slightly higher for solid (k=0.78) than cystic (k=0.62) lesions. In none of the centers side effects were reported. CONCLUSION CEUS is accurate in the characterization of pancreatic lesions. CEUS should be considered as a complementary imaging method for pancreatic lesions characterization.

The influence of aminotransferase levels on liver stiffness assessed by Acoustic Radiation Force Impulse Elastography: A retrospective multicentre study

BACKGROUND Acoustic Radiation Force Impulse Elastography is a new method for non-invasive evaluation of liver fibrosis. AIM To evaluate the impact of elevated alanine aminotransferase levels on liver stiffness assessment by Acoustic Radiation Force Impulse Elastography. METHODS A multicentre retrospective study including 1242 patients with chronic liver disease, who underwent liver biopsy and Acoustic Radiation Force Impulse. Transient Elastography was also performed in 512 patients. RESULTS The best Acoustic Radiation Force Impulse cut-off for predicting significant fibrosis was 1.29 m/s in cases with normal alanine aminotransferase levels and 1.44 m/s in patients with alanine aminotransferase levels>5 × the upper limit of normal. The best cut-off for predicting liver cirrhosis were 1.59 and 1.75 m/s, respectively. Acoustic Radiation Force Impulse cut-off for predicting significant fibrosis and cirrhosis were relatively similar in patients with normal alanine aminotransferase and in those with alanine aminotransferase levels between 1.1 and 5 × the upper limit of normal: 1.29 m/s vs. 1.36 m/s and 1.59 m/s vs. 1.57 m/s, respectively. For predicting cirrhosis, the Transient Elastography cut-offs were significantly higher in patients with alanine aminotransferase levels between 1.1 and 5 × the upper limit of normal compared to those with normal alanine aminotransferase: 12.3 kPa vs. 9.1 kPa. CONCLUSION Liver stiffness values assessed by Acoustic Radiation Force Impulse and Transient Elastography are influenced by high aminotransferase levels. Transient Elastography was also influenced by moderately elevated aminotransferase levels.

Acoustic radiation force impulse (ARFI) ultrasound imaging of pancreatic cystic lesions

PURPOSE To evaluate the ARFI ultrasound imaging with Virtual Touch tissue quantification in studying pancreatic cystic lesions, compared with phantom fluid models. MATERIALS AND METHODS Different phantom fluids at different viscosity or density (water, iodinate contrast agent, and oil) were evaluated by two independent operators. From September to December 2008, 23 pancreatic cystic lesions were prospectively studied. All lesions were pathologically confirmed. RESULTS Non-numerical values on water and numerical values on other phantoms were obtained. Inter-observer evaluation revealed a perfect correlation (rs=1.00; p<0.0001) between all measurements achieved by both operators per each balloon and fluid. Among the pancreatic cystic lesions, 14 mucinous cystadenomas, 4 pseudocysts, 3 intraductal papillary-mucinous neoplasms and 2 serous cystadenomas were studied. The values obtained ranged from XXXX/0-4,85 m/s in mucinous cystadenomas, from XXXX/0-3,11 m/s in pseudocysts, from XXXX/0-4,57 m/s in intraductal papillary-mucinous neoplasms. In serous cystadenomas all values measured were XXXX/0m/s. Diagnostic accuracy in benign and non-benign differentiation of pancreatic cystic lesions was 78%. CONCLUSIONS Virtual Touch tissue quantification can be applied in the analysis of fluids and is potentially able to differentiate more complex (mucinous) from simple (serous) content in studying pancreatic cystic lesions.

Imaging techniques in pancreatic tumors

Conventional ultrasonography represents the first diagnostic imaging modality for the study of pancreatic tumors. Contrast-enhanced ultrasound has significantly improved the accuracy of first-line examination and may influence the choice of second-line investigations: multidetector computed tomography is considered the gold standard for studying pancreatic solid lesions and tumor staging, while MRI with magnetic resonance cholangiopancreatography allows better study of pancreatic cystic lesions and the ductal system. To definitely diagnose a pancreatic lesion, image-guided fine-needle-aspiration or biopsy are very often required. PET with 18-fluorodeoxyglucose, endoscopic ultrasound and intraoperative ultrasonography remain techniques often employed in the third line. This article reviews the imaging techniques generally used for diagnosing the main pancreatic tumors, and a work-up algorithm is finally proposed.

Acoustic radiation force impulse of the liver

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

Resectable Pancreatic Adenocarcinoma: Is the Enhancement Pattern at Contrast-Enhanced Ultrasonography a Pre-Operative Prognostic Factor?

The aim of our study was to determine whether the enhancement pattern of pancreatic adenocarcinoma at contrast-enhanced ultrasonography (CEUS) is related to patient prognosis after resection. CEUS of 42 resected adenocarcinomas were retrospectively reviewed. Tumors were divided into two groups: group A=poorly vascularized (presence of avascular areas) or group B=well vascularized (absence of avascular areas). All lesions were resected and underwent pathological examination assessing tumor differentiation as: undifferentiated (poorly differentiated) or differentiated (moderately and well differentiated). Mean vascular density (MVD) was also evaluated. CEUS enhancement and pathology were correlated (Spearmans test). Survival was analyzed with the Kaplan-Meier method. Multivariate analysis was performed with the Cox regression model. There were 30 differentiated and 12 undifferentiated adenocarcinomas at pathology. At CEUS, 10 lesions were poorly vascularized, whereas 32 lesions were well vascularized. Positive correlation was observed between CEUS groups and tumoral differentiation (rs=0.51; p=0.001) and between CEUS and MVD (rs=0.74; p<0.0001). Median survival in patients with group A vascularization at CEUS was significantly lower than in group B (p=0.015). Cox proportional hazard model revealed the presence of poorly vascularized tumor at CEUS (p=0.0001) as a predictor of higher mortality. In conclusion, CEUS enables accurate depiction of the vascularization of adenocarcinoma, with positive correlation to histology grade and MVD.