Representative ADC maps of PBS control (top left) and 5FC-treated tumors (bottom left) at 7 days postinitiation of 5FC administration. Note the areas of increased ADC values (bright regions) within the 5FC treatedtumor as compared to the control animal. Serial histograms of tumor pixel ADC values from the control (top right) and the 5FC- treated animal (bottom right). The number of days post - tumor cell implantation is shown to the right of each histogram. The histograms displayed in gray correspond to the same time points of the ADC diffusion maps (upper / lower left ). Administration of the adenoviral vector did not affect the average tumor diffusion values as shown in the control. Treatment with 5FC produced a nonuniform increase in tumor diffusion values, which is interpreted to be due to heterogeneous expression of the yCD transgene within the tumor mass due to the limitations of direct intratumoral injection of the vector. (Rehemtulla et al, Molecular Imaging . Vol. 1, No. 1, January 2002, pp. 43 - 55)