title: Assessment of tumor response to oxygen challenge using quantitative diffusion MRI in an animal model.
abstract: OBJECTIVE
  To assess tumor response to oxygen challenge using quantitative diffusion magnetic resonance imaging (MRI).
  
  
  METHODS
  A well-characterized Dunning R3327-AT1 rat prostate cancer line was implanted subcutaneously in the right thigh of male Copenhagen rats (n = 8). Diffusion-weighted images (DWI) with multiple b values (0, 25, 50, 100, 150, 200, 300, 500, 1000, 1500 s/mm(2) ) in three orthogonal directions were obtained using a multishot FSE-based Stejskal-Tanner DWI sequence (FSE-DWI) at 4.7T, while rats breathed medical air (21% oxygen) and with 100% oxygen challenge. Stretched-exponential and intravoxel incoherent motion (IVIM) models were used to calculate and compare quantitative diffusion parameters: diffusion heterogeneity index (α), intravoxel distribution of diffusion coefficients (DDC), tissue diffusivity (Dt), pseudo-diffusivity (Dp), and perfusion fraction (f) on a voxel-by-voxel basis.
  
  
  RESULTS
  A significant increase of α (73.9 ± 4.7% in air vs. 78.1 ± 4.5% in oxygen, P = 0.0198) and a significant decrease of f (13.4 ± 3.7% in air vs. 10.4 ± 2.7% in oxygen, P = 0.0201) were observed to accompany oxygen challenge. Correlations between f and α during both air and oxygen breathing were found; the correlation coefficients (r) were -0.90 and -0.96, respectively. Positive correlations between Dt and DDC with oxygen breathing (r = 0.95, P = 0.0003), f and DDC with air breathing were also observed (r = 0.95, P = 0.0004).
  
  
  CONCLUSIONS
  Quantitative diffusion MRI demonstrated changes in tumor perfusion in response to oxygen challenge.
authors: Department of Radiology, UT Southwestern Medical Center, Dallas, Texas, USA.
authors: Zhongwei
authors: Z
authors: Zhang
authors: Department of Radiology, UT Southwestern Medical Center, Dallas, Texas, USA.
authors: Qing
authors: Q
authors: Yuan
authors: Department of Radiology, UT Southwestern Medical Center, Dallas, Texas, USA.
authors: Heling
authors: H
authors: Zhou
authors: Department of Radiology, UT Southwestern Medical Center, Dallas, Texas, USA.
authors: Dawen
authors: D
authors: Zhao
authors: Department of Radiology, UT Southwestern Medical Center, Dallas, Texas, USA.
authors: Li
authors: L
authors: Li
authors: Department of Radiology, UT Southwestern Medical Center, Dallas, Texas, USA.
authors: Jenifer L
authors: JL
authors: Gerberich
authors: Department of Radiology, UT Southwestern Medical Center, Dallas, Texas, USA.
authors: Ralph P
authors: RP
authors: Mason
mesh_terms: D000818:Animals; D038524:Diffusion Magnetic Resonance Imaging; D004195:Disease Models, Animal; D018496:Hyperoxia / Q000503:physiopathology*; D007090:Image Interpretation, Computer-Assisted; D008297:Male; D010100:Oxygen / Q000008:administration & dosage*; D011471:Prostatic Neoplasms / Q000098:blood supply / Q000503:physiopathology*; D051381:Rats
chemical_list: D010100:Oxygen
keywords: diffusion-weighted imaging; hyperoxia; intravoxel incoherent motion (IVIM); perfusion; stretched-exponential model; tumor oxygenation