title: Influence of different frequencies and insertion depths on the diagnostic accuracy of liver elastography by acoustic radiation force impulse imaging (ARFI).
abstract: BACKGROUND
  Acoustic Radiation Force Impulse Imaging (ARFI) is an innovative elastography for staging of liver fibrosis. We evaluated the diagnostic accuracy of different probes to perform ARFI at different insertion depths.
  
  
  METHODS
  In a prospective study, 89 chronic HCV infected patients underwent ARFI elastography using both available probes (c-ARFI: C4-1-MHz; l-ARFI: L9-4 MHz) in comparison to Fibroscan(®). Variability of ARFI elastography at different insertion depths was systematically evaluated in 39 patients (44%). According to Fibroscan(®) elastography, 32 patients (36%) presented with liver cirrhosis, 23 patients (26%) had significant fibrosis and 34 patients (38%) had no significant fibrosis.
  
  
  RESULTS
  Mean propagation velocity with c-ARFI was 1.70±0.67m/s and 1.91±0.87m/s with l-ARFI. Results of both probes were correlated to each other (p<0.001; r=0.70) and to Fibroscan(®) (p<0.001, r=0.82 and 0.84, respectively). In patients with significant fibrosis or with cirrhosis, mean values by l-ARFI were significantly higher than by c-ARFI (p<0.001). For detection of liver cirrhosis, AUROC was 0.97 for c-ARFI (cut-off level 1.72m/s) and 0.90 for l-ARFI (cut-off 2.04m/s). Correlation coefficients of c-ARFI with Fibroscan(®) were highest at an insertion depth of 5-6cm (r=0.882 and 0.864, respectively, p<0.001) and at 3-4cm for l-ARFI (r=0.850 and 0.838, respectively, p<0.001).
  
  
  CONCLUSIONS
  ARFI elastography with the linear and with the convex probes showed comparable validity and accuracy in the estimation of liver stiffness. The linear probe gave higher ARFI values. The most accurate insertion depth was 5-6cm for c-ARFI and 3-4cm for l-ARFI indicating that measurements should not be performed close to the liver capsule.
authors.affiliation: Department of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany. potthoff.andrej@mh-hannover.de
authors.forename: Andrej
authors.initials: A
authors.lastname: Potthoff
authors.forename: Dina
authors.initials: D
authors.lastname: Attia
authors.forename: Sven
authors.initials: S
authors.lastname: Pischke
authors.forename: Janina
authors.initials: J
authors.lastname: Kirschner
authors.forename: Ingmar
authors.initials: I
authors.lastname: Mederacke
authors.forename: Heiner
authors.initials: H
authors.lastname: Wedemeyer
authors.forename: Michael P
authors.initials: MP
authors.lastname: Manns
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Gebel
authors.forename: Kinan
authors.initials: K
authors.lastname: Rifai
mesh_terms: D000465:Algorithms; D055119:Elastic Modulus; D054459:Elasticity Imaging Techniques / Q000379:methods*; D005260:Female; D006526:Hepatitis C / Q000150:complications* / Q000000981:diagnostic imaging* / Q000503:physiopathology; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008103:Liver Cirrhosis / Q000000981:diagnostic imaging* / Q000209:etiology* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity