title: Importance of b value in diffusion weighted imaging for the diagnosis of pancreatic cancer.
abstract: OBJECTIVE
  To investigate the use of multi-b-value diffusion-weighted imaging in diagnosing pancreatic cancer.
  
  
  METHODS
  We retrospectively analyzed 33 cases of pancreatic cancer and 12 cases of benign pancreatic tumors at the Second Affiliated Hospital of Kunming Medical University from December 2008 to January 2011. The demographic characteristics, clinical presentation, routine magnetic resonance imaging and diffusion weighted imaging (DWI) features with different b values were reviewed. Continuous data were expressed as mean ± SD. Comparisons between pancreatic cancer and benign pancreatic tumors were performed using the Student's t test. A probability of P < 0.05 was considered statistically significant.
  
  
  RESULTS
  Thirty-three patients with pancreatic cancer were identified. The mean age at diagnosis was 60 ± 5.6 years. The male: female ratio was 21:12. Twenty cases were confirmed by surgical resection and 13 by biopsy of metastases. T1 weighted images demonstrated a pancreatic head mass in 16 patients, a pancreatic body mass in 10 cases, and a pancreatic tail mass with pancreatic atrophy in 7 cases. Eight patients had hepatic metastases, 13 had invasion or envelopment of mesenteric vessels, 4 had bone metastases, and 8 had lymph node metastases. DWI demonstrated an irregular intense mass with unclear margins. Necrotic tissue demonstrated an uneven low signal. A b of 1100 s/mm² was associated with a high intensity signal with poor anatomical delineation. A b of 700 s/mm² was associated with apparent diffusion coefficients (ADCs) that were useful in distinguishing benign and malignant pancreatic tumors (P < 0.05). b values of 50, 350, 400, 450 and 1100 s/mm² were associated with ADCs that did not differentiate the two tumors.
  
  
  CONCLUSIONS
  Low b value images demonstrated superior anatomical details when compared to high b value images. Tumor tissue definition was high and contrast with the surrounding tissues was good. DWI was useful in diagnosing pancreatic cancer.
authors.affiliation: Jin-Gang Hao, Jia-Ping Wang, Ya-Lv Gu, Department of Radiology, the Second Affiliated Hospital of Kunming Medical University, Kunming 650101, Yunnan Province, China.
authors.forename: Jin-Gang
authors.initials: JG
authors.lastname: Hao
authors.forename: Jia-Ping
authors.initials: JP
authors.lastname: Wang
authors.forename: Ya-Lv
authors.initials: YL
authors.lastname: Gu
authors.forename: Ming-Liang
authors.initials: ML
authors.lastname: Lu
mesh_terms: D000368:Aged; D002681:China; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010190:Pancreatic Neoplasms / Q000473:pathology* / Q000556:secondary / Q000601:surgery; D011237:Predictive Value of Tests; D012189:Retrospective Studies
keywords: Apparent diffusion coefficient; Diffusion weighted imaging; Magnetic resonance imaging; Pancreatic cancer; b value