title: Challenges for the functional diffusion map in pediatric brain tumors.
abstract: BACKGROUND
  The functional diffusion map (fDM) has been suggested as a tool for early detection of tumor treatment efficacy. We aim to study 3 factors that could act as potential confounders in the fDM: areas of necrosis, tumor grade, and change in tumor size.
  
  
  METHODS
  Thirty-four pediatric patients with brain tumors were enrolled in a retrospective study, approved by the local ethics committee, to examine the fDM. Tumors were selected to encompass a range of types and grades. A qualitative analysis was carried out to compare how fDM findings may be affected by each of the 3 confounders by comparing fDM findings to clinical image reports.
  
  
  RESULTS
  Results show that the fDM in areas of necrosis do not discriminate between treatment response and tumor progression. Furthermore, tumor grade alters the behavior of the fDM: a decrease in apparent diffusion coefficient (ADC) is a sign of tumor progression in high-grade tumors and treatment response in low-grade tumors. Our results also suggest using only tumor area overlap between the 2 time points analyzed for the fDM in tumors of varying size.
  
  
  CONCLUSIONS
  Interpretation of fDM results needs to take into account the underlying biology of both tumor and healthy tissue. Careful interpretation of the results is required with due consideration to areas of necrosis, tumor grade, and change in tumor size.
authors.affiliation: Imaging and Biophysics Unit, UCL Institute of Child Health, University College London, London, UK (M.G-S., J.D.C., C.A.C.); Department of Radiology, Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK (D.E.S.); Department of Neuro-oncology, Great Ormond Street Hospital for Children NHS Foundation Trust, London UK (K.P.P.); Neural Development Unit, Birth Defects Research Centre, UCL Institute of Child Health, University College London, London, UK (S.M.L.P., T.S.J.); Department of Histopathology, Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK (S.M.L.P., T.S.J.).
authors.forename: Matthew
authors.initials: M
authors.lastname: Grech-Sollars
authors.forename: Dawn E
authors.initials: DE
authors.lastname: Saunders
authors.forename: Kim P
authors.initials: KP
authors.lastname: Phipps
authors.forename: Ramneek
authors.initials: R
authors.lastname: Kaur
authors.forename: Simon M L
authors.initials: SM
authors.lastname: Paine
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Jacques
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Clayden
authors.forename: Chris A
authors.initials: CA
authors.lastname: Clark
mesh_terms: D000293:Adolescent; D001254:Astrocytoma / Q000473:pathology*; D001932:Brain Neoplasms / Q000473:pathology*; D002648:Child; D002675:Child, Preschool; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D005909:Glioblastoma / Q000473:pathology*; D006801:Humans; D007223:Infant; D008297:Male
keywords: apparent diffusion coefficient; childhood tumors; diffusion-weighted magnetic resonance imaging; functional diffusion map; parametric response map