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

Abstract

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 MRI scans after a specified 5-fluorouracil/calcium 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 (ΔTV%, ΔADC%, ΔD%, Δf% and ΔD(*)%) 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 (ΔTV%) in the treatment group were significantly smaller than those in the control group at day 5 (ΔTVtreatment% = 19.63% ± 3.01% and ΔTVcontrol% = 83.60% ± 14.87%, P = 0.008) and day 7 (ΔTVtreatment% = 29.07% ± 10.01% and ΔTVcontrol% = 177.06% ± 63.00%, P = 0.008). The difference in ΔTV% 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 (ΔADC%treatment, median, 30.10% ± 18.32%, 36.11% ± 21.82%, 45.22% ± 24.36%) were significantly higher compared with the control group (ΔADC%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 (ΔD%treatment, median 17.12% ± 8.20%, 24.16% ± 16.87%, 38.54% ± 19.36%) were higher than those in the control group (ΔD%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.

Keywords: Gastric cancer; Intravoxel incoherent motion diffusion-weighted imaging; Microvessel density; Nude mouse model; Terminal-deoxynucleoitidyl transferase mediated nick end labeling.

Figure 1

Anti-tumor effects of 5-fluorouracil therapy in mouse gastric cancer xenografts. A: Actual tumor volume changes in the control group; B: Actual tumor volume changes in the treatment groups; C: The comparison of the change in tumor volumes relative to baseline (day 0) between the control and treatment groups. The control group showed increases in tumor volume, while the treatment group showed as significant tumor growth delay from day 5. Center line = median; upper and lower margins of the box = 25^th to the 75^th percentile, respectively; whiskers = data from the minimum to the maximum. Error bars denote standard errors. ^aP < 0.05 vs control group, n = 5 in each group.

Figure 2

Comparison of the mean percentage changes from baseline in the intravoxel incoherent motion diffusion-weighted imaging derived values between the control (dark) and the 1-, 3-, 5- and 7-d treatment groups (grey). A: ADC value; B: D value; C: f value; D: D* value. Standard deviations are represented by vertical bars. Relative changes were determined by comparing the values at baseline and those in follow-up. ^aP < 0.05 vs control. n = 5 in each group. ADC: Apparent diffusion coefficient.

Figure 3

Box-and-Whisker plots show the results of histopathological analysis in the control and the 1-, 3-, 5- and 7-d treatment groups, respectively (n = 5 per group). A: Necrosis fraction of tumor; B: Microvessel density of tumor; C: Cellular apoptosis of tumor. Center line = median; upper and lower margins of box = 25^th to the 75^th percentile, respectively; whiskers = data from the minimum to the maximum; ○ = outlier.

Figure 4

Representative scatter diagrams showing the relationships between intravoxel incoherent motion diffusion-weighted imaging derived parameters and the histological features (n = 25). A and B: ADC and D were positively correlated with tumor necrosis fraction; C and D: f and D^* were positively correlated with microvascular density of tumor; E and F: ADC, D were positively correlated with tumor cellular apoptosis; G and H: f and D^* were negatively correlated with tumor cellular apoptosis. P values are shown in Table 2. ADC: Apparent diffusion coefficient.

Figure 5

Calculated maps of intravoxel incoherent motion diffusion-weighted imaging parameters and the histopathological images. A: The lower ADC (0.521 × 10^-3 mm²/s) and D values (0.475 × 10^-3 mm²/s) and the higher f (40.92%) and D* (0.131 mm²/s) values, which correspond to low necrosis (10%) and cellular apoptosis (7%) and high MVD (36) in the control group; B: Increased ADC (0.875 × 10^-3 mm²/s) and D (0.851 × 10^-3 mm²/s) values and reduced f (17.20%) and D^* (0.098 mm²/s) values, which correspond to the increased necrosis (18%) and cellular apoptosis (23%) and decreased MVD (17) in the 3-d treatment group. Note high signal intensity within tumor suggesting necrosis. asterisk means necrosis area; The triangle symbol means skin of the mouse. ADC: Apparent diffusion coefficient; MVD: Microvessel density.