title: Accuracy of visual scoring and semi-quantification of ultrasound strain elastography--a phantom study.
abstract: OBJECTIVE
  The aim of this study was to evaluate the performance of strain elastography in an elasticity phantom and to assess which factors influenced visual scoring, strain histograms and strain ratios. Furthermore this study aimed to evaluate the effect of observer experience on visual scorings.
  
  
  METHODS
  Two operators examined 20 targets of various stiffness and size (16.7 to 2.5 mm) in an elasticity phantom at a depth of 3.5 cm with a 5-18 MHz transducer. Two pre-settings were used yielding 80 scans. Eight evaluators, four experienced, four inexperienced, performed visual scorings. Cut-offs for semi-quantitative methods were established for prediction of target stiffness. Data was pooled in two categories allowing calculations of sensitivity and specificity. Statistical tests chi-square test and linear regression as relevant.
  
  
  RESULTS
  Strain ratios and strain histograms were superior to visual scorings of both experienced and inexperienced observers (p = 0.025, strain histograms vs. experienced observers, p<0.001, strain histograms vs. inexperienced observers, p = 0.044 strain ratios vs. experienced observers and p = 0.002 strain ratios vs. inexperienced observers). No significant difference in predicting target stiffness between strain ratios and strain histograms (p = 0.83) nor between experienced and inexperienced observers (p = 0.054) was shown when using four categories. When pooling data in two groups (80 kPa/45 kPa vs. 14/8 kPa) the difference between the observers became significant (p<0.001). Target size had a significant influence on strain ratios measurements (p = 0.017) and on visual scorings (p<0.001) but not on the strain histograms(p = 0.358). Observer experience had significant effect on visual scorings(p = 0.003).
  
  
  CONCLUSIONS
  Strain ratios and strain histograms are superior to visual scoring in assessing target stiffness in a phantom. Target size had a significant impact on strain ratios and visual scoring, but not on strain histograms. Experience influenced visual scorings but the difference between experienced and inexperienced observers was only significant when looking at two classes of target stiffness.
authors.affiliation: Department of Radiology, Rigshospitalet Copenhagen University Hospital, Copenhagen, Denmark.
authors.forename: Jonathan Frederik
authors.initials: JF
authors.lastname: Carlsen
authors.affiliation: Department of Radiology, Rigshospitalet Copenhagen University Hospital, Copenhagen, Denmark.
authors.forename: Caroline
authors.initials: C
authors.lastname: Ewertsen
authors.affiliation: Research Center of Gastroenterology and Hepatology, University of Medicine and Pharmacy, Craiova, Romania ; Department of Endoscopy, Gastrointestinal Unit, Copenhagen University Hospital Herlev, Herlev, Denmark.
authors.forename: Adrian
authors.initials: A
authors.lastname: Săftoiu
authors.affiliation: Department of Radiology, Rigshospitalet Copenhagen University Hospital, Copenhagen, Denmark ; Department of Vascular Surgery, Rigshospitalet Copenhagen University Hospital, Copenhagen, Denmark.
authors.forename: Lars
authors.initials: L
authors.lastname: Lönn
authors.affiliation: Department of Radiology, Rigshospitalet Copenhagen University Hospital, Copenhagen, Denmark.
authors.forename: Michael Bachmann
authors.initials: MB
authors.lastname: Nielsen
mesh_terms: D004548:Elasticity; D054459:Elasticity Imaging Techniques / Q000379:methods*; D006801:Humans; D016014:Linear Models; D015588:Observer Variation; D019047:Phantoms, Imaging; D011108:Polymers / Q000737:chemistry; D011312:Pressure; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014463:Ultrasonography / Q000379:methods*
chemical_list: D011108:Polymers