title: Noninvasive monitoring of radiation-induced treatment response using proton magnetic resonance spectroscopy and diffusion-weighted magnetic resonance imaging in a colorectal tumor model.
abstract: OBJECTIVE
  To examine whether in vivo proton magnetic resonance spectroscopy ((1)H MRS) and diffusion-weighted magnetic resonance imaging (DW-MRI) can monitor radiation-induced changes in HT29 xenografts in mice.
  
  
  METHODS
  HT29 xenografts in mice received a dose of 15Gy. In vivo(1)H MRS and DW-MRI were acquired pretreatment and 1, 3, 6 and 10 days post-irradiation. After imaging, tumors were excised for histological analysis. The amounts of necrosis, fibrosis and viable cells in the cross sections were scored and compared to changes in apparent diffusion coefficient (ADC) and choline/water ratio.
  
  
  RESULTS
  Radiation-induced necrosis in the xenografts was observed as increased tumor ADC. In-growth of fibrosis three days post-irradiation restricting water mobility was accompanied by decreased tumor ADC. Choline/water ratio correlated with metabolic activity and tumor growth.
  
  
  CONCLUSIONS
  ADC and choline/water ratio assessed by in vivo DW-MRI and (1)H MRS depicts radiation-induced changes in HT29 xenografts following irradiation.
authors.affiliation: Department of Medical Physics, Rikshospitalet-Radiumhospitalet Medical Center, Oslo, Norway. therese@radium.uio.no
authors.forename: Therese
authors.initials: T
authors.lastname: Seierstad
authors.forename: Kathrine
authors.initials: K
authors.lastname: Røe
authors.forename: Dag Rune
authors.initials: DR
authors.lastname: Olsen
mesh_terms: D000818:Animals; D002794:Choline / Q000032:analysis; D015179:Colorectal Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D038524:Diffusion Magnetic Resonance Imaging; D004195:Disease Models, Animal; D009682:Magnetic Resonance Spectroscopy; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D014183:Transplantation, Heterologous; D014867:Water / Q000032:analysis
chemical_list: D014867:Water; D002794:Choline