Abstract： Objective To monitor the structural and metabolic transformation of growing intrahepatic hepatocellular carcinoma (HCC) by non-invasive 23Na-MRI and 1H-DWI. Methods Each animal was examined weekly for4 weeks after injection of 1 × 106 N1S1 cells into the left liver lobe. MR images were acquired with a Varian MR system. The effects of untreated growth on water apparent diffusion coefficient (ADC), total tissue Na+ and intracellular Na+ were monitored in rat HCCs using 1H-DWI,single-quantum ( SQ ) 23 Na and triple-quantum-filtered (TQF) 23 Na-MRI. Histological analysis of HCC tissues was performed. Relative extracellular space (ECS), cell numbers, and the cell to nucleus area ratio were calculated. Statistical analysis of the data was performed by ANOVA and post-hoc multiple comparison.Results The doubling time of the tumor growth was 3.9 days. During the four weeks in tumor growing, the ratio of water ADC to nearby liver was always 1.4 to 1.5. The HCC growth was associated with an increase in both total tissue and intracellular 23Na signal intensity, and the changes in Nai+ were more profound than in Nat+. The ratio of the tumor SQ, TQF 23Na signal intensity to the nearby liver at four time points(7,14,21 and28 d) was 1.05 ±0.20,1.41 ±0.32,1.50±0.45,1.62±0.50(F=2.97,P＜0.05);1.32±0.11,1.54 ± 0.18,2.38 ± 0.22,2.39 ± 0.16 ( F = 11.18, P ＜ 0.01 ), respectively. Statistical analysis of the histological slices showed that the mean of relative ECS in healthy liver was significantly lower compared to both ECS spaces in HCC viable cells and inflammation/necrosis areas. The number of viable and inflamed/necrotic cells was statistically higher compared to nearby liver tissue. However, the increase in "cellularity" was caused mostly by shrinkage of cellular cytoplasm when the ratio of cell to nucleus areas decreased from 4.0 ± 0.3 ( normal liver) to 1.6 ± 0.1 ( viable HCC cells) ( t = 20.08,P ＜ 0.05). Conclusions The water ADC and SQ23 Na-MRI reflect ECS, total tissue Na+ changes and thus reflect mostly the compartmental alterations in tumor tissue, while TQF 23Na-MRI reflects the intracellular Na+ and thus physiological,metabolic transformation in HCC cells.