Assessment of tumor response to oxygen challenge using quantitative diffusion MRI in an animal model

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.