title: Diffusion-weighted MR imaging in pancreatic endocrine tumors correlated with histopathologic characteristics.
abstract: OBJECTIVE
  To retrospectively assess apparent diffusion coefficients (ADCs) of different subtypes of pancreatic endocrine tumors based on the World Health Organization (WHO) classification system and analyze the potentially responsible histopathologic characteristics.
  
  
  METHODS
  Following Institutional Review Board (IRB) approval, 18 patients with surgical pathology-proven pancreatic endocrine tumors were evaluated. Tumors were subcategorized based on the WHO grading classification into well-differentiated tumors with benign and uncertain behavior and endocrine carcinomas with well and poor differentiation. ADCs were measured on diffusion-weighted (DW) images and compared using Student's t-test and one-way analysis of variance. The correlation between ADCs, tumor cellularity, Ki-67 labeling index (an index of cell growth), and extracellular fibrosis were analyzed.
  
  
  RESULTS
  A difference was demonstrated in mean ADCs between well-differentiated endocrine tumors (1.75 ± 0.53) and endocrine carcinomas (1.00 ± 0.19 × 10(-3) mm(2) /sec) (P < 0.01). After excluding the three well-differentiated endocrine tumors with benign behavior and marked fibrosis, a significant inverse correlation between ADC values and cellularity of endocrine tumors was observed. An inverse correlation was seen between Ki-67 labeling index and ADC values (r = -0.70; P < 0.01).
  
  
  CONCLUSIONS
  Tumor cellularity and/or extracellular fibrosis may account for various ADCs in pancreatic endocrine tumors. ADC correlates well with the Ki-67 labeling index and may help predict growth of endocrine tumors.
authors.affiliation: Department of Radiology, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60611, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Wang
authors.forename: Zongming E
authors.initials: ZE
authors.lastname: Chen
authors.forename: Vahid
authors.initials: V
authors.lastname: Yaghmai
authors.forename: Paul
authors.initials: P
authors.lastname: Nikolaidis
authors.forename: Robert J
authors.initials: RJ
authors.lastname: McCarthy
authors.forename: Laura
authors.initials: L
authors.lastname: Merrick
authors.forename: Frank H
authors.initials: FH
authors.lastname: Miller
mesh_terms: D000328:Adult; D000368:Aged; D002277:Carcinoma / Q000175:diagnosis* / Q000473:pathology*; D002454:Cell Differentiation; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D019394:Ki-67 Antigen / Q000096:biosynthesis; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D018358:Neuroendocrine Tumors / Q000175:diagnosis* / Q000473:pathology*; D010190:Pancreatic Neoplasms / Q000175:diagnosis* / Q000473:pathology*; D019047:Phantoms, Imaging; D012189:Retrospective Studies
chemical_list: D019394:Ki-67 Antigen