Intravoxel incoherent motion diffusion-weighted imaging for monitoring chemotherapeutic efficacy in gastric cancer

AIM: To assess intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) for monitoring early efficacy of chemotherapy in a human gastric cancer mouse model. METHODS: IVIM-DWI was performed with 12 b-values (0-800 s/mm(2)) in 25 human gastric cancer-bearing nude mice at baseline ( day 0), and then they were randomly divided into control and 1-, 3-, 5- and 7-d treatment groups (n = 5 per group). The control group underwent longitudinal MRI scans at days 1, 3, 5 and 7, and the treatment groups underwent subsequent folinate treatment. Together with tumor volumes (TV), the apparent diffusion coefficient (ADC) and IVIM parameters [true water molecular diffusion coefficient (D), perfusion fraction (f) and pseudo-related diffusion coefficient (D*)] were measured. The differences in those parameters from baseline to each measurement (triangle TV%, triangle ADC%, triangle D%, triangle f% and triangle D*%) were calculated. After image acquisition, tumor necrosis, microvessel density (MVD) and cellular apoptosis were evaluated by hematoxylin-eosin (HE), CD31 and terminal-deoxynucleotidyl transferase mediated nick end labeling (TUNEL) staining respectively, to confirm the imaging findings. Mann-Whitney test and Spearman's correlation coefficient analysis were performed. RESULTS: The observed relative volume increase (triangle TV%) in the treatment group were significantly smaller than those in the control group at day 5 (triangle TVtreatment% = 19.63% +/- 3.01% and triangle TVcontrol% = 83.60% +/- 14.87%, P = 0.008) and day 7 (triangle TVtreatment% = 29.07% +/- 10.01% and triangle TVcontrol% = 177.06% +/- 63.00%, P = 0.008). The difference in triangle TV% between the treatment and the control groups was not significant at days 1 and 3 after a short duration of treatment. Increases in ADC in the treatment group (triangle ADC% treatment, median, 30.10% +/- 18.32%, 36.11% +/- 21.82%, 45.22% +/- 24.36%) were significantly higher compared with the control group (triangle ADC%(control), median, 4.98% +/- 3.39%, 6.26% +/- 3.08%, 9.24% +/- 6.33%) at days 3, 5 and 7 (P = 0.008, P = 0.016, P = 0.008, respectively). Increases in D in the treatment group (triangle D%(treatment), median 17.12% +/- 8.20%, 24.16% +/- 16.87%, 38.54% +/- 19.36%) were higher than those in the control group (triangle D%(control), median -0.13% +/- 4.23%, 5.89% +/- 4.56%, 5.54% +/- 4.44%) at days 1, 3, and 5 (P = 0.032, P = 0.008, P = 0.016, respectively). Relative changes in f were significantly lower in the treatment group compared with the control group at days 1, 3, 5 and 7 follow-up (median, -34.13% +/- 16.61% vs 1.68% +/- 3.40%, P = 0.016; -50.64% +/- 6.82% vs 3.01% +/- 6.50%, P = 0.008; -49.93% +/- 6.05% vs 0.97% +/- 4.38%, P = 0.008, and -46.22% +/- 7.75% vs 8.14% +/- 6.75%, P = 0.008, respectively). D* in the treatment group decreased significantly compared to those in the control group at all time points (median, -32.10% +/- 12.22% vs 1.85% +/- 5.54%, P = 0.008; -44.14% +/- 14.83% vs 2.29% +/- 10.38%, P = 0.008; -59.06% +/- 19.10% vs 3.86% +/- 5.10%, P = 0.008 and -47.20% +/- 20.48% vs 7.13% +/- 9.88%, P = 0.016, respectively). Furthermore, histopathologic findings showed positive correlations with ADC and D and tumor necrosis (r(s) = 0.720, P < 0.001; r(s) = 0.522, P = 0.007, respectively). The cellular apoptosis of the tumor also showed positive correlations with ADC and D (r(s) = 0.626, P = 0.001; r(s) = 0.542, P = 0.005, respectively). Perfusion-related parameters (f and D*) were positively correlated to MVD (r(s) = 0.618, P = 0.001; r(s) = 0.538, P = 0.006, respectively), and negatively correlated to cellular apoptosis of the tumor (r(s) = -0.550, P = 0.004; r(s) = -0.692, P < 0.001, respectively). CONCLUSION: IVIM-DWI is potentially useful for predicting the early efficacy of chemotherapy in a human gastric cancer mouse model.