Diffusion-weighted MR imaging in the evaluation of rat brain C6 glioma and histopathologic correlation

Abstract

Objective Rat brain C6 glioma was evaluated by diffusion-weighted MRI(DWI) and its DWI manifestations were compared with histopathologic changes such as cell density and tumor necrosis to analysis the pathologic changes of DWI. Methods After 12-18 days implantation of C6 glioma cells, 16 tumor -bearing rats were examined with contrast-enhanced MRI and DWI and its manifestations of contrast-enhanced MRI and DWI were compared with pathologic changes. Results Of the 16 cases of glioma, 7 cases presented with annular enhancement on contrast-enhanced T_1-weighted image. The intensities of central part of those glioma were elevated greatly compared with the surrounding area of tumor on apparent diffusion coefficient (ADC) maps. The ADC of central part and surrounding area were [(106.5±11.9)×10~ -5 ], [(78.2±9.2)×10~ -5 ]mm~2/s respectively, there were significant differences between the two areas(t=8.26,P0.01).In the pathologic specimen, massive necrosis originating from the central part of tumors can be detected and tumor cell density in central region decreased obviously. The cell densities of central part and surrounding area were (13±8)%, (40±5)%, significant difference existed between the two areas(t=5.38,P0.05). Another 9 cases presented with homogeneous enhancement on contrast-enhanced T_1-weighted image. Among those cases, 6 cases presented heterogeneous intensities on ADC maps, the ADC of central part and surrounding area were [(94.1±12.6)×10~ -5 ],[(75.8±11.4)×10~ -5 ]mm~2/s respectively, there were significant differences between the two areas(t=5.38,P0.05). The cell densities of central part and surrounding area were (29±4)%, (41±8)%,and significant difference existed between the two areas(t=3.92,P0.05).Of the 16 cases of glioma, only 3 cases presented homogeneous intensities on ADC maps. The ADC of central part and surrounding area were [(86.7±9.0)×10~ -5 ], [(84.2±7.6)×10~ -5 ]mm~2/s respectively, there were no significant differences between the two areas(t=3.41,P0.05). The cell densities of central part and surrounding area were (38±7)%, (40±5)%,no significant differences existed between the two areas(t=1.92,P0.05).Conclusion The present results indicate that water ADC can be used as measures of cell density and necrotic fraction of tumors to differentiate necrosis from viable tissue. The differences of signal intensities on DWI and ADC may reflect microscopic changes of glioma.