title: Intra- and interobserver variability of whole-tumour apparent diffusion coefficient measurements in nephroblastoma: a pilot study.
abstract: BACKGROUND
  The apparent diffusion coefficient (ADC) is potentially useful for assessing treatment response in nephroblastoma (Wilms tumour). However the precision of ADC measurements in these heterogeneous lesions is unknown.
  
  
  OBJECTIVE
  To assess intra- and interobserver variability of whole-tumour ADC measurements in viable parts of nephroblastomas at diagnosis and after preoperative chemotherapy.
  
  
  METHODS
  We included children with histopathologically proven nephroblastoma who had undergone MRI with diffusion-weighted imaging before and after preoperative chemotherapy. Three independent observers performed whole-tumour ADC measurements of all lesions, excluding non-enhancing areas. One observer evaluated all lesions on two occasions. We performed analyses using Bland-Altman plots and concordance correlation coefficient (CCC) calculations with 95% limits of agreement for median ADC, difference between pre- and post-chemotherapy median ADC (ADC shift) and percentage of pixels with ADC values <1.0 × 10(-3) mm(2)/s.
  
  
  RESULTS
  In 22 lesions (13 pretreatment and 9 post-treatment) in 10 children the interobserver variability in median ADC and ADC shift were within the interval of approximately ±0.1 × 10(-3) mm(2)/s (limits of agreement for median ADC ranged -0.08-0.11 × 10(-3) mm(2)/s and for ADC-shift -0.11-0.09 × 10(-3) mm(2)/s). The interobserver variability for percentage of low-ADC pixels was larger and also biased. The calculated CCC confirmed good intra- and interobserver agreement (ρ-c ranging from 0.968 to 0.996).
  
  
  CONCLUSIONS
  Measurements of whole-tumour ADC values excluding necrotic areas seem to be sufficiently precise for detection of chemotherapy-related change.
authors.affiliation: Department of Radiology, University Medical Centre Utrecht, Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands. alittooij@hotmail.com.
authors.forename: Annemieke S
authors.initials: AS
authors.lastname: Littooij
authors.affiliation: Department of Radiology, Great Ormond Street Hospital for Children, London, UK.|Department of Radiology, University College London Hospital, London, UK.
authors.forename: Paul D
authors.initials: PD
authors.lastname: Humphries
authors.affiliation: Department of Radiology, Great Ormond Street Hospital for Children, London, UK.
authors.forename: Øystein E
authors.initials: ØE
authors.lastname: Olsen
mesh_terms: D002675:Child, Preschool; D004058:Diffusion; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D007223:Infant; D007680:Kidney Neoplasms / Q000473:pathology* / Q000628:therapy*; D008297:Male; D015588:Observer Variation; D010865:Pilot Projects; D011379:Prognosis; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D016896:Treatment Outcome; D009396:Wilms Tumor / Q000473:pathology* / Q000628:therapy*
keywords: Apparent diffusion coefficient; Children; Diffusion-weighted imaging; Magnetic resonance imaging; Nephroblastoma; Observer variation; Wilms tumour