Purpose To assess tumor response to oxygen challenge using quantitative diffusion magnetic resonance imaging (MRI). Materials and 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/mm2) 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 ® 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). Conclusion Quantitative diffusion MRI demonstrated changes in tumor perfusion in response to oxygen challenge.
- diffusion-weighted imaging
- intravoxel incoherent motion (IVIM)
- stretched-exponential model
- tumor oxygenation