Apparent diffusion coefficient (ADC) and magnetization transfer contrast (MTC) mapping of experimental brain tumor

Brain tumor tissue contains different pathological areas, such as tumor cell rich parts, necrotic tissues, and cyst. Furthermore, both neovascularization and edema formation progress along with the tumor progression. In this study we employed diffusion weighted (DW) and magnetization transfer contrast (MTC) imaging to chronologically investigate the biological characteristics of a rat glioma. RG-2 glioma cells were implanted stereotactically into the right hemisphere of male Wistar rats. MR images were taken 1, 2 and 3 weeks after inoculation. Apparent diffusion coefficient (ADC) and MTC values were calculated as follows; ADC = -ln (SI-DW/SI-T2)/1096, MTC = 1-SI-MTon/SI-MToff. Each mapping image was made based on the calculated average values of four pixels. The spatial signal changes and the real values were compared to the histological findings. The apparent increase of ADC was noted in the parenchyma adjacent to tumor suggesting the progression of edema. The tumor itself had similar or slightly increased ADC. Cystic and necrotic components appeared 2 weeks after implantation and they showed significantly higher ADC than those calculated in the contralateral putamen. On the other hand, MTC was slightly decreased in the parenchyma adjacent to the tumor, markedly within the tumor, and maximally in the cystic and necrotic area suggesting accumulation of macromolecules such as growth factors, cytokines, and serum albumin.