title: Diffusion-weighted MRI for monitoring tumor response to photodynamic therapy.
abstract: OBJECTIVE
  To examine diffusion-weighted MRI (DW-MRI) for assessing the early tumor response to photodynamic therapy (PDT).
  
  
  METHODS
  Subcutaneous tumor xenografts of human prostate cancer cells (CWR22) were initiated in athymic nude mice. A second-generation photosensitizer, Pc 4, was delivered to each animal by a tail vein injection 48 h before laser illumination. A dedicated high-field (9.4 Tesla) small animal MR scanner was used to acquire diffusion-weighted MR images pre-PDT and 24 h after the treatment. DW-MRI and apparent diffusion coefficients (ADC) were analyzed for 24 treated and 5 control mice with photosensitizer only or laser light only. Tumor size, prostate specific antigen (PSA) level, and tumor histology were obtained at different time points to examine the treatment effect.
  
  
  RESULTS
  Treated mice showed significant tumor size shrinkage and decrease of PSA level within 7 days after the treatment. The average ADC of the 24 treated tumors increased 24 h after PDT (P < 0.001) comparing with pre-PDT. The average ADC was 0.511 +/- 0.119 x 10(-3) mm(2)/s pre-PDT and 0.754 +/- 0.181 x 10(-3) mm(2)/s 24 h after the PDT. There is no significant difference in ADC values pre-PDT and 24 h after PDT in the control tumors (P = 0.20).
  
  
  CONCLUSIONS
  The change of tumor ADC values measured by DW-MRI may provide a noninvasive imaging marker for monitoring tumor response to Pc 4-PDT as early as 24 h.
authors.affiliation: Emory Center for Systems Imaging, Department of Radiology, Emory University, Atlanta, Georgia 30329, USA.
authors.forename: Hesheng
authors.initials: H
authors.lastname: Wang
authors.forename: Baowei
authors.initials: B
authors.lastname: Fei
mesh_terms: D000818:Animals; D014408:Biomarkers, Tumor; D045744:Cell Line, Tumor; D004058:Diffusion; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000494:pharmacology; D011471:Prostatic Neoplasms / Q000473:pathology* / Q000628:therapy*; D016896:Treatment Outcome
chemical_list: D014408:Biomarkers, Tumor; D017319:Photosensitizing Agents