This copy is for personal use only. To order printed copies, contact Purpose: Materials and Methods: Results: Conclusion:

This copy is for personal use only. To order printed copies, contact reprints@rsna.org Original Research n Pediatric Imaging Feasibility and Diagnostic Accuracy of Supersonic Shear- Wave Elastography for the Assessment of Liver Stiffness and Liver Fibrosis in Children: A Pilot Study of 96 Patients 1 Stéphanie Franchi-Abella, MD Lucie Corno, MD Emmanuel Gonzales, MD, PhD Guillemette Antoni, MD Monique Fabre, MD Béatrice Ducot, PhD Danièle Pariente, MD Jean-Luc Geisson, PhD Mickael Tanter, PhD Jean-Michel Corréas, MD, PhD 1 From the Departments of Pediatric Radiology (S.F.A., L.C., D.P.), Pediatric Hepatology (E.G.), and Epidemiology (G.A., B.D.), Hôpital Bicêtre, Hôpitaux Universitaires Paris Sud, Assistance Publique Hôpitaux de Paris, Université Paris Sud, 78 rue du Général Leclerc, 94275 Le Kremlin Bicêtre, France; Departments of Pathology (M.F.) and Adult Radiology (J.M.C.), Hôpital Necker, Assistance Publique Hôpitaux de Paris, Université Paris V, Assistance Publique Hôpitaux de Paris, Paris, France; and Institut Langevin, ESPCI ParisTech, CNRS UMR7587, INSERM U979, Paris, France (J.L.G., M.T.). Received December 12, 2014; revision requested January 12, 2015; revision received April 21; accepted April 30; final version accepted May 21. Address correspondence to S.F.A. (e-mail: stephanie. franchi@bct.aphp.fr). q RSNA, 2015 Purpose: Materials and Methods: Results: Conclusion: To evaluate the feasibility of using supersonic shear-wave elastography (SSWE) in children and normal values of liver stiffness with the use of control patients of different ages (from neonates to teenagers) and the diagnostic accuracy of supersonic shear wave elastography for assessing liver fibrosis by using the histologic scoring system as the reference method in patients with liver disease, with a special concern for early stages of fibrosis. The institutional review board approved this prospective study. Informed consent was obtained from parents and children older than 7 years. First, 51 healthy children (from neonate to 15 years) were analyzed as the control group, and univariate and multivariate comparisons were performed to study the effect of age, transducer, breathing condition, probe, and position on elasticity values. Next, 45 children (from 1 month to 17.2 years old) who underwent liver biopsy were analyzed. SSWE measurements were obtained in the same region of the liver as the biopsy specimens. Biopsy specimens were reviewed in a blinded maer by a pathologist with the use of METAVIR criteria. The areas under the receiver operating characteristics curve (AUCs) were calculated for patients with fibrosis stage F0 versus those with stage F1 F2, F2 or higher, F3 or higher, and F4 or higher. A successful rate of SSWE measurement was 100% in 96 patients, including neonates. Liver stiffness values were significantly higher when an SC6-1 probe (Aixplorer; SuperSonic Imagine SA, Aix-enProvence, France) was used than when an SL15-4 probe (Aixplorer) was used (mean 6 standard deviation, 6.94 kpa 6 1.42 vs 5.96 kpa 6 1.31; P =.006). There was no influence of sex, the location of measurement, or respiratory status on liver elasticity values (P =.41.93), although the power to detect such a difference was low. According to the degree of liver fibrosis at liver biopsy, 88.5% 96.8% of patients were correctly classified, with AUCs of 0.90 0.98 (95% confidence interval [CI]: 0.8, 1.0). The AUC for patients with stage F0 versus stage F1 F2 was 0.93 (95% CI: 0.87, 0.99). SSWE allows accurate assessment of liver fibrosis, even in children with early stage (F1 F2) disease, and the choice of transducer influences liver stiffness values. q RSNA, 2015 Online supplemental material is available for this article. 554 radiology.rsna.org n Radiology: Volume 278: Number 2 February 2016

Although liver biopsy is still considered the reference standard for diagnosing and staging liver fibrosis in children, its limitations (eg, invasiveness and interobserver and sampling variability) are well known (1,2). The inapplicability of repeating biopsy in clinical practice prevents easy longitudinal evaluation. Among the noninvasive methods of measuring liver stiffness that is supposed to mainly result from fibrosis, quantitative elastography methods are based on the estimation of shear-wave velocity (measured in m/sec) in the liver because it is related to the stiffness of the tissue (Young modulus, measured in kpa). Several clinical ultrasonographic Advances in Knowledge Liver stiffness measurements obtained with supersonic shearwave elastography (SSWE) had a success rate of 100% in 96 children, including neonates; sex, the location of measurement, and respiratory status (eg, apnea versus free-breathing) do not seem to influence liver stiffness measurements (P =.41 to P =.93). Liver stiffness values were significantly higher when a curvilinear 6-1 MHz transducer was used compared with a linear 15-4 MHz transducer; for the SL15-4 probe (Aixplorer; SuperSonic Imagine SA, Aix-enProvence, France), liver stiffness values in healthy children were 5.96 kpa 6 1.31, and for the SC6-1 probe (Aixplorer), they were 6.94 kpa 6 1.42 for (P =.006). SSWE had high diagnostic accuracy for differentiating lower stages of fibrosis (F0 and F1) from higher stages (F2 F4), with an area under the receiver operating characteristics curve (AUC) of 0.98 (95% confidence interval [CI]: 0.95, 1.0), and liver with no fibrosis from mild and moderate fibrosis (stage F1 F2), with an AUC of 0.93 (95% CI: 0.87, 0.99). systems are currently available for quantitative elastography measurements in clinical practice, such as transient elastography, acoustic radiation force impulse (ARFI), point shear-wave elastography, and supersonic shear wave elastography (SSWE). Whereas a large number of studies consider the diagnostic accuracy of transient elastography and ARFI for detecting liver fibrosis with histologic correlations in adults, only six pediatric series that used transient elastography or ARFI and showed good diagnostic accuracy for the detection of mild and severe liver fibrosis are published (Table E1 [online]) (3 9). However, transient elastography has some limitations in young children, with some authors reporting technical failure in 17% of children younger than 2 years old and others reporting technical failure in 10% of children of any age, and the possibilities of obtaining intercostal measurements in pediatric liver recipients who underwent left lobe grafting are limited (6,10,11). There are few studies on SSWE, and only one concerns children (10 21). Most of them focus on the assessment of substantial fibrosis and cirrhosis, which are usually diagnosed at physical examination, and few are on the detection of early stage liver fibrosis, despite its role as a predictor of disease outcomes and its impact on therapy and follow-up (7,12). The purpose of the present study was to evaluate the feasibility of performing SSWE and determine normal values of liver stiffness in children by using control patients of different ages (from neonates to teenagers) and assess its diagnostic accuracy in assessing Implications for Patient Care SSWE can be used to noninvasively detect and stage liver fibrosis in children (including infants) with diffuse liver disease. Liver stiffness values should be interpreted taking into account the probe used to obtain measurements and underlying pathologic conditions. liver fibrosis by using the histologic scoring system as the reference method in patients with liver disease, with special concern paid to those with early stages of liver fibrosis. Materials and Methods The patent holder for real-time shear wave elastography is Institut Langevin Ondes et Images (Paris, France), where author M.T. is an employee. M.T. is a cofounder and shareholder of SuperSonic Imagine (Aix-en-Provence, France). J.L.G. is a consultant for SuperSonic Imagine (Aix-en-Provence, France). S.F.A. gave lectures about applications of ultrafast imaging in children for SuperSonic Imagine. SuperSonic Imagine did not provide any type of support for this study. Data and information submitted for publication were controlled by authors who do not have any financial interest in the Institut Langevin Ondes et Images or SuperSonic Imagine (S.F.A., L.C., G.A., E.G., B.D., M.F., D.P., J.M.C.). Study Population The study protocol was approved by the institutional review board. Informed consent was obtained from both parents and children older than 7 years. Two groups of patients were Published online before print 10.1148/radiol.2015142815 Content codes: Radiology 2016; 278:554 562 Abbreviations: ARFI = acoustic radiation force impulse AUC = area under the receiver operating characteristics curve SSWE = supersonic shear-wave elastography Author contributions: Guarantors of integrity of entire study, S.F.A., L.C., D.P., J.L.G.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; approval of final version of submitted manuscript, all authors; agrees to ensure any questions related to the work are appropriately resolved, all authors; literature research, S.F.A., E.G., M.F., J.L.G., J.M.C., M.T.; clinical studies, S.F.A., L.C., E.G., M.F., D.P.; statistical analysis, G.A., B.D., J.L.G.; and manuscript editing, S.F.A., E.G., M.F., D.P., J.L.G., M.T. Conflicts of interest are listed at the end of this article. Radiology: Volume 278: Number 2 February 2016 n radiology.rsna.org 555

prospectively included: a control group of children with no medical history suggestive of liver disorder who were referred for abdominal or renal ultrasonography (US) (group 1) and a second group of children with liver disease who underwent liver biopsy within 4 months from the time SSWE was performed (group 2). In group 1, 51 children (26 girls and 25 boys) were included and arbitrarily divided into the following five subgroups according to age: premature newborns, less than 1 year old, 1 5 years old, 5 10 years old, and more than 10 years old. The patients were referred for abdominal US because of the presence of urogenital disorders (n = 17); abdominal pain (n = 12); premature birth (n = 7); neurologic disorders (n = 5); genital disorders (n = 4); abdominal trauma with no liver injury (n = 3); sickle cell disease (n = 2); and bronchiolitis, joint pain, and fever (n = 1). Forty-seven children were included in group 2, and two were excluded because biopsy specimens did not allow reliable histologic evaluation of fibrosis. Thus, the data from 45 patients were analyzed. There were 26 girls and 19 boys, with a median age of 2 years (range, 1 month to 17 years). Indications for liver biopsy were liver transplantation in 18 patients (mean age, 7 years 6 4.9 [standard deviation]; range, 1 17 years), 10 of whom had an interval of less than 45 days after transplantation and eight of whom had an interval of more than 45 days after transplantation; biliary atresia in 11 patients (mean age, 0.5 year 6 0.4; range, 0.1 1.8 years); cholestasis of unknown origin in eight patients (mean age, 0.6 year 6 0.5; range, 0.1 2.1 years); and other causes (portal obstruction with cavernoma in three, progressive familial intrahepatic cholestasis type 2 in two, sclerosing cholangitis in two, and acute leukemia in one) in eight patients (mean age, 6.7 years 6 3.3; range, 0.3 14.2 years). The median time between SSWE and liver biopsy was 2 days (range, 0 111 days). Twenty-four children underwent SSWE and liver biopsy on the same day. Two patients underwent repeated Figure 1 Figure 1: SSWE measurements in a 2-year-old boy from the control group. US images obtained with a SC6-1 transducer show a stiffness color map (top), which is homogeneous, with blue areas that correspond with low values of liver stiffness on the color scale, and SSWE measurements in the regions of interest (bottom), which confirm that liver elasticity values are normal. liver biopsies (two and three, respectively); only the first biopsy was considered for this study. Liver Stiffness Measurements All patients were evaluated by one radiologist (S.F.A., with 12 years of experience, or L.C., with 2 years of experience) who was trained to perform SSWE. SSWE was performed in the US room or the incubator for premature newborns. A complete evaluation of the liver was performed by using B-mode and Doppler imaging before obtaining SSWE measurements. Children underwent imaging in the supine position with the right arm raised to widen the intercostal spaces. Liver stiffness measurements were obtained with SSWE (Aixplorer; SuperSonic Imagine SA, Aix-en-Provence, France). SSWE is based on the velocity estimation of a shear wave, which is generated by the radiation force of a focused beam (13). SSWE measurements were obtained by using two different transducers: a high frequency linear transducer SL15-4 (4 15 MHz) and a low frequency convex abdominal transducer SC6-1 (1 6 MHz). The transducer was positioned in the intercostal space and epigastric area to assess the right and left (or left graft) sides of the liver, respectively, and a large liver area was selected with B-mode imaging, avoiding rib attenuation and vessels. An SSWE sequence measurement was then launched by using a stiffness color map with a fixed size (2 3 1.5 cm with an SL15-4 transducer and 2 3 2.5 cm with an SC6-1 transducer) (Figs 1, 2). Care was taken to not include large 556 radiology.rsna.org n Radiology: Volume 278: Number 2 February 2016

Figure 2 Figure 2: SSWE measurements obtained with a SL15-4 transducer in a 4-month-old baby with biliary atresia and a METAVIR score of F4 at liver biopsy. US images show the stiffness color map (top), which is heterogeneous, with yellow and red areas that correspond with high elasticity values on the color scale, and SSWE measurements in the regions of interest (bottom), which are 43 50 kpa. blood vessels or biliary structures in the regions of interest. Measurements were classified as failed when no or weak signals were obtained in the SSWE box for all acquisitions. Group 1: feasibility study in healthy children. We evaluated the number of technical failures in obtaining liver stiffness measurements and studied the influence of the location of the probe (inside or outside the intercostal space), breathing condition (eg, free breathing and apnea), and transducer (ie, SL15-4 and SC6-1) on liver stiffness measurements by obtaining combinations of measurement conditions in each patient according to his or her ability to breathhold and age. Combinations of measurement conditions consisted of one transducer with one respiratory condition and one probe location. Because of technical limitations related to the size of the children, the SL15-4 transducer was used in all patients except those who were older than 10 years, and the SC6-1 transducer was used in all patients except neonates. For example, because neonates caot breath hold and are too small for the SC6-1 transducer, they only underwent two series of liver stiffness measurements: one with free breathing, an SL15-4 probe, and an intercostal transducer position and the other with free breathing, an SL15-4 probe, and an epigastric transducer position. The combinations of conditions of liver stiffness measurements according to age, the number of patients per age group, and the number of measurements per patient and per age group are summarized in Table E2 (online). For each combination of measurement conditions (type of transducer, breathing condition, and transducer position), at least three consecutive different stiffness color maps were obtained with two to three regions of interest selected, resulting in 10 liver stiffness measurements. A total of 1740 liver stiffness measurements were obtained, which corresponded to 174 combinations of measurement conditions (Table E2 [online]). All SSWE measurements were obtained in less than 10 minutes. Group 2: children who underwent liver biopsy. The choice of transducer was determined on the basis of the patient s age. When possible, 10 measurements were obtained in the intercostal position (right lobe). When an intercostal position was not possible, an epigastric position (left lobe graft liver) was used. If possible, SSWE was performed during a short breath hold (, 3 seconds). Otherwise, the acquisitions were made during normal, gentle breathing. Liver Biopsy and Histologic Studies (Group 2) Liver biopsy was performed percutaneously with a 16- or 18-gauge needle (Hepafix; Braun, Melsungen, Germany) in 30 patients, surgically in 11 patients, in an explanted liver after transplantation in four patients, and with transjugular access with a transjugular liver biopsy set (Laboratories 100; Cook Medical, Bloomington, Ind) in two patients. Biopsy specimens were fixed in 10% buffered formalin and embedded in paraffin. The following stains for Radiology: Volume 278: Number 2 February 2016 n radiology.rsna.org 557

coective tissues were routinely used: Masson trichrome, Picrosirius red, and reticulin (Gordon Sweet). The length of each specimen was recorded. At least 10 portal tracts were required for fibrosis staging. The mean length of biopsy specimens was 11.2 mm 6 4.75 (range, 6 24 mm). All needle biopsy specimens except two had at least 10 portal tracts (mean, 15.1 portal tracts per biopsy specimen). The two patients with fibrotic liver microbiopsy specimens were excluded from the study. Specimens were analyzed by a single pathologist (M.F., with 30 years of experience) who was blinded to SSWE results but not to patients clinical and biologic data. Liver fibrosis was evaluated semiquantitatively according to the METAVIR scoring system, in which F0 = absent, F1 = stellate enlargement of portal tract without septa formation, F2 = enlargement of portal tract with rare septa formation and intact architecture, F3 = numerous septa but no obvious cirrhosis, and F4 = cirrhosis. Statistical Analysis Liver elasticity in group 1. The mean of the 10 measurements obtained with one combination of conditions of measurements in each patient was calculated and used for statistical analysis. The mean values and standard deviation of elasticity according to age, sex, type of transducer, transducer location, and breathing pattern were calculated. A multivariate linear regression model that included patient age and sex, transducer type, and type of respiration was used to study the effect of age, sex, transducer type and type of respiration on elasticity. Comparisons between age classes, sex, transducer type, and respiration were made by Wald tests. Relationship between liver elasticity and degree of fibrosis. Children in group 1 (except premature babies) were added to patients with a score of F0. To compare values obtained with the same transducer in children who presented with liver disorders, the elasticity values used were chosen according to patients age. For infants younger than 1 year, the mean of the elasticity Table 1 Mean Elasticity Values and P Values For Differences between Sex, Location of the Probe, Respiratory Conditions, and Type of Probe in the Control Group (Group 1) Characteristic No. of Measurements* Mean Elasticity P Value Sex.41 Male 87 6.61 6 1.33 Female 87 6.54 6 1.58 Transducer position.81 Intercostal 89 6.53 6 1.38 Epigastric 85 6.62 6 1.54 Respiratory condition.93 Free breathing 123 6.42 6 1.52 Apnea 51 6.96 6 1.23 Type of transducer.006 SL15-4 65 5.96 6 1.31 SC6-1 109 6.94 6 1.42 Note. A total of 174 combinations (one patient with one probe plus one respiratory condition plus one approach), with 10 measurements obtained per combination, were performed, for a total 1740 measurements. The mean of the 10 measurements was calculated and used for statistical analysis. P values refer to the difference between consecutive characteristics and were determined with the Wald test. * Data are the number of groups of 10 measurements obtained. Data are the mean (in kpa) plus or minus standard deviation. values were obtained with an SL15-4 transducer, and for children over 1 year old, the mean of the values was obtained with an SC6-1 transducer. The receiver operating characteristics curve was used to determine the optimal cut-off value for the presence of any (F0), mild to moderate (F1 F2), substantial ( F2), and severe ( F3) fibrosis and cirrhosis (F4). The diagnostic performance of the method was expressed as sensitivity, specificity, and correctly classified patients. Cut-off values that gave the best proportion of correctly classified patients were selected. The standard error for the area under the receiver operating characteristics curve (AUC) and asymptotic normal confidence intervals were calculated by using an algorithm suggested by DeLong, DeLong, and Clarke-Pearson (14). Correlation between elasticity and the degree of fibrosis was also evaluated with the Spearman coefficient test. For all analyses, P,.05 was considered to indicate a significant difference. Statistical analysis was performed with SAS version 9.3 (StataCorp, College Station, Tex) and Stata version 12.1 (StataCorp) software. Results Control Group 1 Measurements were possible in all patients. In all cases, elastograms were homogeneous and dark blue by using a 50-kPa stiffness scale (Fig 1). Mean liver elasticity value was 6.58 kpa 6 1.46 in the whole group considering both transducers. A significant difference was found for mean elasticity between the two transducers: 5.96 kpa 6 1.31 for SL15-4 and 6.94 kpa 6 1.42 for SC6-1 (P =.006) (Table 1). There was no influence of sex, the location of the measurement, or respiratory status on mean liver elasticity values (Table 1). Considering all measurements, there was no significant difference between age groups (P =.11). The mean elasticity value exhibited a trend to increase with age when using the SL15-4 transducer (P =.05) (Fig 3, Table 2). Assessment of Liver Fibrosis (Group 2) The median values, range, and standard deviation of SSWE measurements obtained for each fibrosis stage (METAVIR score) are shown in Table 3. Sensitivity, specificity, AUC, positive and 558 radiology.rsna.org n Radiology: Volume 278: Number 2 February 2016

negative likelihood ratio, and the percentage of correctly classified patients are given according to the optimal cutoff values of SSWE for each METAVIR stage selected to favor the proportion of correctly classified patients (Table 4 ). AUCs were above 0.93 regardless of the transducer used and the degree of fibrosis, with 88.5% 96.8% of patients correctly classified. Cut-off values varied depending on the transducer used Figure 3 and were higher with the SC6-1 except in the case of severe fibrosis. In seven of the 45 evaluations, there was discordance between elasticity values and histologic type. Liver fibrosis was overestimated by SSWE measurement in five patients: a transplant recipient who presented with acute rejection, a patient with avascular liver related to hepatic vein obstruction, a patient with ischemic-necrotic lesions, a patient with biliary atresia, and a patient with acute leukemia and hepatic involvement. In two patients, liver fibrosis was underestimated by the measurement of SSWE, one of whom received a liver transplant and experienced acute rejection and the other presented with sclerosing cholangitis. When considering all transducers, the Spearman correlation coefficient between the SSWE values and liver fibrosis histologic score was high in the whole population (r = 0.83; P,.0001), but it varied depending on the type of pathologic condition present; it was low for biopsy performed less than 45 days after liver transplantation (r = 0.60; P =.05), moderate for biopsy performed more than 45 days after liver transplantation (r = 0.79; P =.006) and biliary atresia (r = 0.77; P =.005), and high for other type of cholestasis (r = 0.87; P =.005) and other diseases (r = 0.89; P =.003). Figure 3: Box plots show SSWE measurements for each age group. The bottom and top of the box are the first and third quartiles, and the band inside the box is the second quartile (the median). The top and bottom of the whiskers represent the highest and lowest data within 1.5 interquartile range of the upper and lower quartiles, respectively. Discussion In this study, we showed that SSWE was feasible in very young patients, including neonates, and that its diagnostic accuracy was good for assessing even early stages of fibrosis (F1 F2) that are usually missed at physical examination and with other noninvasive techniques. Another important finding is that the underlying pathologic condition and the transducer used to obtain measurements should be taken Table 2 Mean Elasticity Values according to Age in the Control Group (n = 51) Age Group, Mean, and P Value No. of Patients Age Mean Elasticity (kpa) Mean Range All Probes SL15-4 SC6-1 P Value Age group Preterm newborn* 7 34.0 weeks 6 2.7 30 35 weeks 5.69 6 0.92 5.69 6 0.92,1 year 15 2.7 months 6 2.6 0.2 8 months 5.73 6 1.40 5.65 6 1.42 6.00 6 1.38.54 1 5 years 7 3.3 years 6 0.9 1.5 4.5 years 6.68 6 1.12 6.35 6 0.82 6.85 6 1.24.27 5 10 years 10 8.1 years 6 1.1 6.5 10 years 7.00 6 1.32 6.64 6 1.39 7.14 6 1.29.05.10 years 12 13.9 years 6 2.8 10 18 years 6.97 6 1.55 6.97 6 1.55 Mean 6.58 6 1.46 5.96 6 1.31 6.94 6 1.42.006 P value.11.05.12 Note. Unless otherwise indicated, data are mean plus or minus standard deviation. P values refer to the difference between measurements obtained with the transducers according to age group and were determined with the Wald test. * Gestational age. Radiology: Volume 278: Number 2 February 2016 n radiology.rsna.org 559

into account when interpreting SSWE measurements. SSWE appears to be useful in infants and children, especially when compared with transient elastography, the use of which appears to be limited in children less than 5 years old and in pediatric liver recipients with left lateral grafting and no intercostal access, with as much as 17% of measurements reported to be invalid in previous studies (6,10,11). In the control group, liver elasticity values seemed to be influenced by the transducer (SL15-4 vs SC6-1). Mean elasticity values were 5.96 kpa 6 1.31 for the SL15-4 and 6.94 kpa 6 1.42 for the SC6-1 (P =.006). Similar results that showed a significant difference in healthy liver stiffness measurements depending on the probe used have been reported in adults and children by using transient elastography with small (S+), medium (M+), and extra-large (XL+) probes (11,15,16). However, two pediatric studies that used ARFI did not demonstrate differences between the measurements obtained with two transducers (4C1 and 9L4) except in neonates (1 month old) (17,18). This may be related to the use of a velocity scale rather than an elasticity scale. Therefore, tissue stiffness is displayed with a compressed dynamic because the speed of the shear wave is proportional to the square root of the elastic shear modulus, c s = (E/3r), which may hide tiny differences between measurements. The influence of the transducer on measurements is related to the relationship between the viscoelastic properties of the tissues and the frequency of the transducer, as well as the broadband characteristics of the mechanical excitation generated with the ultrasonic radiation force of the shear wave elastography mode. In a few other pediatric studies that reported on transient elastography or ARFI techniques and used different transducers, there is no analysis of the results according to the transducer used (9,10). These findings are important because they show that the stiffness value should be interpreted according to the transducer frequency and that same transducer should be Table 3 Median, Range, Standard Deviation, and No. of Patients for Each Fibrosis Stage Using METAVIR Score on Liver Biopsy in Group 2 Characteristic METAVIR Stage F0 F1 F2 F3 F4 Median (kpa) 6.3 9.1 13.5 21.0 35.1 Range (kpa) 4.3 9.1 5.7 16.8 9.6 19.1 9.5 59.6 17.6 87.3 Standard deviation 2.1 2.5 3.2 17.34 23.15 No. of patients 4 19 8 7 7 Table 4 Clinical Performance of SSWE by Using Optimal Measurement Cut-Off Values according to the Probe Used Probe All SL15-4 SC6-1 Characteristic METAVIR Score F0 vs F1 F2 No. biopsy specimens 48 vs 27 15 vs 9 33 vs 18 Cut-off value (kpa) 7.898 7.30 9.09 AUC 0.93 0.99 0.89 95% CI 0.86, 0.99 0.97, 1.0 0.78, 0.99 Sensitivity (%) 85.2 100 72.2 Specificity (%) 91.7 93.3 100 Correctly classified (%) 89.3 95.8 90.2 METAVIR Score F2 No. biopsy specimens 67 vs 22 20 vs 10 47 vs 12 Cut-off value (kpa) 12.143 9.491 12.143 AUC 0.98 0.99 0.97 95% CI 0.95, 1.0 0.97, 1.0 0.94, 1.0 Sensitivity (%) 86.0 100 91.7 Specificity (%) 97.1 95 95.7 Correctly classified (%) 94.4 96.7 94.9 METAVIR Score F3 No. biopsy specimens 78 vs 14 24 vs 6 51 vs 8 Cut-off value (kpa) 17.602 32.84 17,602 AUC 0.97 0.96 0.98 95% CI 0.94, 1.0 0.89, 1.0 0.95, 1.0 Sensitivity (%) 78.6 83.3 75.0 Specificity (%) 98.7 100 100 Correctly classified (%) 95.5 96.7 96.6 METAVIR Score F4 No. biopsy specimens 82 vs 7 26 vs 4 59 vs 3 Cut-off value (kpa) 23.48 AUC 0.98 95% CI 0.95, 1.0 Sensitivity (%) 85.7 Specificity (%) 97.7 Correctly classified (%) 96.6 Note. Patients in group 1 (excluding preterm babies) were considered to have a METAVIR score of F0 and were added to the subset of those with a score of F0 in group 2 to add statistical power to the study. CI = confidence interval. 560 radiology.rsna.org n Radiology: Volume 278: Number 2 February 2016

used for follow-up evaluation to allow comparison. SSWE allowed for noninvasive assessment of liver fibrosis, with 88.5% 96.8% of infants and children correctly classified according to their stage of fibrosis, even those who presented with mild or moderate fibrosis (stage F1 F2). Although a diagnosis of substantial fibrosis (stage F2 or greater) has been regarded as an important target in most studies of adults with viral hepatitis infection, the detection of early stages (F1 and F2) of fibrosis is important in children because minor liver fibrosis is often a predictor of disease outcomes and can affect therapy and follow-up (6,7,19,20). In our study, the detection of low stages of fibrosis (stage F1 F2) when compared with healthy or stage F0 livers was very good, with AUC of 0.90 for the SC6-1 transducer and 0.99 for the SL15-4 transducer and 88.9% of patients appropriately classified with the SC6-1 transducer and 95.8% of patients appropriately classified with the SL15-4 transducer. When comparing our results with those in the pediatric literature using different US elastographic techniques, only one study that evaluated the accuracy of transient elastography for identifying fibrosis in a homogeneous group of teenagers with nonalcoholic steatohepatitis had better results for diagnosing any, substantial, or severe fibrosis (Table E1 [online]) (3,5,6,8,9,21). Cut-off values for staging liver fibrosis vary among studies that used SSWE. Ferraioli et al (22) Tutar et al (21), and our study reported cut-off values of 7.1 kpa versus 10.4 kpa versus 12, 1 kpa for stage F2, respectively. These variations may be related to the type of liver disease. For example, steatosis significantly increased mean shear wave elastography values and was considered a confounding factor in assessing fibrosis in patients with nonalcoholic steatohepatitis (21,22). Other underlying disorders influence the diagnostic accuracy of liver stiffness measurements, such as inflammation, venous obstruction, and cholestasis. Thus, the choice of cut-off values should be assessed according to the type of pathologic condition present (6,23). Our study has several limitations. First, we did not perform any biologic liver tests in the control group to assess for liver disease. Second, the choice of the METAVIR scoring system can be questioned because it is mainly used in patients with chronic viral hepatitis C infection, but it is widely used in pediatric patients with liver disease. However, it is based on architectural modifications and is not perfectly adapted to the various types of pediatric liver conditions. The use of computer-assisted digital analysis of Sirius red stained histologic sections in future studies will help quantify liver fibrosis of any cause at histologic analysis (24). We did not assess interobserver reproducibility. In conclusion, our study showed the potential of SSWE techniques to detect liver fibrosis, especially early stages that are challenging for clinicians and with other elastographic techniques, in the pediatric population. Further studies in larger homogeneous groups of patients with pathologic conditions and with correlation to liver biopsy with quantitative morphometric evaluation of fibrosis are required to precisely establish the place of this technique in treating patients. Disclosures of Conflicts of Interest: S.F.A. Activities related to the present article: disclosed no relevant activities. Activities not related to the present article: payment for lectures from SuperSonic Imagine. Other activities: disclosed no relevant activities. L.C. disclosed no relevant activities. E.G. disclosed no relevant activities. G.A. disclosed no relevant activities. M.F. disclosed no relevant activities. B.D. disclosed no relevant activities. D.P. disclosed no relevant activities. J.L.G. Activities related to the present article: consultant for SuperSonic Imagine. Activities not related to the present article: consultant for SuperSonic Imagine. Other activities: disclosed no relevant activities. J.M.C. disclosed no relevant activities. M.T. Activities related to the present article: disclosed no relevant activities. Activities not related to the present article: co-founder, shareholder, and consultant for SuperSonic Imagine. Other activities: disclosed no relevant activities. References 1. Bedossa P, Dargère D, Paradis V. Sampling variability of liver fibrosis in chronic hepatitis C. Hepatology 2003;38(6):1449 1457. 2. Cohen MB, A-Kader HH, Lambers D, Heubi JE. Complications of percutaneous liver bi- opsy in children. Gastroenterology 1992; 102(2):629 632. 3. de Lédinghen V, Le Bail B, Rebouissoux L, et al. Liver stiffness measurement in children using FibroScan: feasibility study and comparison with Fibrotest, aspartate transaminase to platelets ratio index, and liver biopsy. J Pediatr Gastroenterol Nutr 2007;45(4): 443 450. 4. Eiler J, Kleinholderma U, Albers D, et al. Standard value of ultrasound elastography using acoustic radiation force impulse imaging (ARFI) in healthy liver tissue of children and adolescents. Ultraschall Med 2012;33(5): 474 479. 5. Noruegas MJ, Matos H, Gonçalves I, Cipriano MA, Sanches C. Acoustic radiation force impulse-imaging in the assessment of liver fibrosis in children. Pediatr Radiol 2012; 42(2):201 204. 6. Fitzpatrick E, Quaglia A, Vimalesvaran S, Basso MS, Dhawan A. Transient elastography is a useful noninvasive tool for the evaluation of fibrosis in paediatric chronic liver disease. J Pediatr Gastroenterol Nutr 2013;56(1):72 76. 7. Nobili V, Monti L, Alisi A, Lo Zupone C, Pietrobattista A, Tomà P. Transient elastography for assessment of fibrosis in paediatric liver disease. Pediatr Radiol 2011;41(10): 1232 1238. 8. Iacobellis A, Marcellini M, Andriulli A, et al. Non invasive evaluation of liver fibrosis in paediatric patients with nonalcoholic steatohepatitis. World J Gastroenterol 2006;12(48): 7821 7825. 9. Hanquinet S, Rougemont AL, Courvoisier D, et al. Acoustic radiation force impulse (ARFI) elastography for the noninvasive diagnosis of liver fibrosis in children. Pediatr Radiol 2013;43(5):545 551. 10. Engelma G, Gebhardt C, Weing D, et al. Feasibility study and control values of transient elastography in healthy children. Eur J Pediatr 2012;171(2):353 360. 11. Goldschmidt I, Streckenbach C, Dingema C, et al. Application and limitations of transient liver elastography in children. J Pediatr Gastroenterol Nutr 2013;57(1):109 113. 12. Martínez SM, Crespo G, Navasa M, Forns X. Noninvasive assessment of liver fibrosis. Hepatology 2011;53(1):325 335. 13. Bercoff J, Tanter M, Fink M. Supersonic shear imaging: a new technique for soft tissue elasticity mapping. IEEE Trans Ultrason Ferroelectr Freq Control 2004;51(4):396 409. 14. DeLong ER, DeLong DM, Clarke-Pearson DL. Comparing the areas under two or Radiology: Volume 278: Number 2 February 2016 n radiology.rsna.org 561

more correlated receiver operating characteristic curves: a nonparametric approach. Biometrics 1988;44(3):837 845. 15. Ferraioli G, Lissandrin R, Zicchetti M, Filice C. Assessment of liver stiffness with transient elastography by using S and M probes in healthy children. Eur J Pediatr 2012;171(9):1415; author reply 1417. 16. Myers RP, Pomier-Layrargues G, Kirsch R, et al. Feasibility and diagnostic performance of the FibroScan XL probe for liver stiffness measurement in overweight and obese patients. Hepatology 2012;55(1):199 208. 17. Hanquinet S, Courvoisier D, Kanavaki A, Dhouib A, Anooshiravani M. Acoustic radiation force impulse imaging-normal values of liver stiffness in healthy children. Pediatr Radiol 2013;43(5):539 544. 18. Fontanilla T, Cañas T, Macia A, et al. Normal values of liver shear wave velocity in healthy children assessed by acoustic radiation force impulse imaging using a convex probe and a linear probe. Ultrasound Med Biol 2014;40(3):470 477. 19. Pereira TN, Walsh MJ, Lewindon PJ, Ramm GA. Paediatric cholestatic liver disease: Diagnosis, assessment of disease progression and mechanisms of fibrogenesis. World J Gastrointest Pathophysiol 2010;1(2):69 84. 20. Castera L. Noninvasive methods to assess liver disease in patients with hepatitis B or C. Gastroenterology 2012;142(6):1293 1302, e4. 21. Tutar O, Beşer OF, Adaletli I, et al. Shear wave elastography in the evaluation of liver fibrosis in children. J Pediatr Gastroenterol Nutr 2014;58(6):750 755. 22. Ferraioli G, Tinelli C, Dal Bello B, et al. Accuracy of real-time shear wave elastography for assessing liver fibrosis in chronic hepatitis C: a pilot study. Hepatology 2012;56(6): 2125 2133. 23. Gae-Carrié N, Ziol M, de Ledinghen V, et al. Accuracy of liver stiffness measurement for the diagnosis of cirrhosis in patients with chronic liver diseases. Hepatology 2006; 44(6):1511 1517. 24. Germani G, Burroughs AK, Dhillon AP. The relationship between liver disease stage and liver fibrosis: a tangled web. Histopathology 2010;57(6):773 784. 562 radiology.rsna.org n Radiology: Volume 278: Number 2 February 2016