Chemotherapy response evaluation in a mouse model of gastric cancer using intravoxel incoherent motion diffusionweighted MRI and histopathology

AIM To determine the role of intravoxel incoherent motion(IVIM) diffusion-weighted(DW) magnetic resonance imaging(MRI) using a bi-exponential model in chemotherapy response evaluation in a gastric cancer mouse model.METHODS Mice bearing MKN-45 human gastric adenocarcinoma xenografts were divided into four treated groups(TG1, 2, 3 and 4, n = 5 in each group) which received Fluorouracil and Calcium Folinate and a control group(CG, n = 7). DW-MRI scans with 14 b-values(0-1500 s/mm2) were performed before and after treatment on days 3, 7, 14 and 21. Fast diffusion component(presumably pseudo-perfusion) parameters including the fast diffusion coefficient(D*) and fraction volume(f p), slow diffusion coefficient(D) and the conventional apparent diffusion coefficients(ADC) were calculated by fitting the IVIM model to the measured DW signals. The median changes from the baseline to each posttreatment time point for each measurement(ΔADC, ΔD* and Δf p) were calculated. The differences in the median changes between the two groups were compared using the mixed linear regression model by the restricted maximum likelihood method shown as z values. Histopathological analyses including Ki-67, CD31, TUNEL and H&E were conducted in conjunction with the MRI scans. The median percentage changes were compared with the histopathological analyses between the pre-and post-treatment for each measurement.RESULTS Compared with the control group, D* in the treated group decreased significantly(ΔD*treated% =-30%,-34% and-20%, with z =-5.40,-4.18 and-1.95. P = 0.0001, 0.0001 and 0.0244) and f p increased significantly(Δfptreated% = 93%, 113% and 181%, with z = 4.63, 5.52, and 2.12, P = 0.001, 0.0001 and 0.0336) on day 3, 7 and 14, respectively. Increases in ADC in the treated group were higher than those in the control group on days 3 and 14(z = 2.44 and 2.40, P = 0.0147 and P = 0.0164). CONCLUSION Fast diffusion measurements derived from the biexponential IVIM model may be more sensitive imaging biomarkers than ADC to assess chemotherapy response in gastric adenocarcinoma.

Evaluation of the malignant potential of gliomas using diffusion-weighted and gadolinium-enhanced magnetic resonance imaging

Objective:This study aimed to determine whether the apparent diffusion coefficients(ADCs)determined by diffusion-weighted imaging(DWI)of magnetic resonance imaging(MRI)could facilitate the malignancy grading of various gliomas.Methods:Sixty patients with a primary cerebral glioma underwent diffusion-weighted and gadolinium-enhanced(Gd)T1-weighted MRI using a 1.5-T MRI scanner.Scoring was performed based on signal intensities on DWI and Gd images.The mean and minimum ADC values were calculated,and Ki-67 staining was performed for each histological sample to evaluate their tumor proliferative potential.Then,the DWI,Gd,and combined scores were analyzed and compared with the Ki-67 staining index and malignant grade.The relationships among the mean and minimum ADC values,Ki-67staining index,and malignant grade were also evaluated.Results:The minimum ADC was inversely correlated with the Ki-67staining index,with a low minimum ADC suggestive of tumor malignancy.The qualitative evaluation of the D score of water molecule diffusion on DWI accurately reflected the pathological grades of gliomas,with an effectiveness that was at least as good as the quantitative analysis using the minimum ADC.The diagnostic value of Gd images in determining glioma malignancy grades was inferior to that of DWI.Conclusion:Both DWI and gadolinium-enhanced images of MRI should be considered essential for the diagnosis of tumor malignancy.