New dynamic MRI methods promise to better characterize and monitor the vexing problem of brain cancer. Assessing these methods and the assumptions they rely upon is difficult as 1) no known gold standard is available for brain tumors and 2) the time window of availability for brain cancer volunteers is narrow. We present a simulator that generates realistic, heterogeneous, tumor models overlaid over normal brain tissue with user-specified permeability parameters. The simulator generates raw data for arbitrary k-space acquisition strategies. Using this simulator, new methodologies for various tumor types and sizes can be assessed before the first volunteer is ever recruited.