title: Region of interest demarcation for quantification of the apparent diffusion coefficient in breast lesions and its interobserver variability.
abstract: OBJECTIVE
  We aimed to compare two different methods of region of interest (ROI) demarcation and determine interobserver variability on apparent diffusion coefficient (ADC) in breast lesions.
  
  
  METHODS
  Thirty-two patients with 39 lesions were evaluated with a 3.0 Tesla scanner using a diffusion-weighted sequence with several b-values. Two observers independently performed the ADC measurements using: 1) a small fixed area of 10 mm2 ROI within the area with highest restriction; 2) a large ROI so as to include the whole lesion. Differences were assessed using the Wilcoxon-rank test. Bland-Altman method and Spearman coefficient were applied for interobserver variability and correlation analysis.
  
  
  RESULTS
  ADC values measured using the two ROI demarcation methods were significantly different for both observers (P = 0.026; P = 0.033). There was no interobserver variability in ADC values using either method (large ROI, P = 0.21; small ROI, P = 0.64). ADC values of malignant lesions were significantly different between the two methods (P < 0.001). Variability in ADC was ≤0.008×10-3 mm2/s for both methods. When using the same method, ADC values were significantly correlated between the observers (small ROI: r=0.990, P < 0.001; large ROI: r=0.985, P < 0.001).
  
  
  CONCLUSIONS
  The choice of ROI demarcation method influences ADC measurements. Small ROIs show less overlap in ADC values and higher ADC reproducibility, suggesting that this method may improve lesion discrimination. Interobserver variability was low for both methods.
authors.affiliation: Department of Radiology, Hospital São João, Porto University School of Medicine, Porto, Portugal; School of Allied Health Sciences, Oporto Polytechnic Institute, Porto, Portugal. mlpnogueira@med.up.pt.
authors.forename: Luísa
authors.initials: L
authors.lastname: Nogueira
authors.forename: Sofia
authors.initials: S
authors.lastname: Brandão
authors.forename: Eduarda
authors.initials: E
authors.lastname: Matos
authors.forename: Rita Gouveia
authors.initials: RG
authors.lastname: Nunes
authors.forename: Hugo Alexandre
authors.initials: HA
authors.lastname: Ferreira
authors.forename: Joana
authors.initials: J
authors.lastname: Loureiro
authors.forename: Isabel
authors.initials: I
authors.lastname: Ramos
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology*; D003937:Diagnosis, Differential; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008875:Middle Aged; D015588:Observer Variation; D015203:Reproducibility of Results