A system and method of evaluating the effectiveness of antiangionetic therapy is described. A patient or test animal is treated with an antiangionetic substance. Magnetic resonance imaging data is obtained prior to and subsequent to the treatment. The parameters of the imaging process are configured so that, by administering a intravascular contrast agent, the relative size of the microvascular and the total vascular volumes in a region of interest may be obtained, so as to form a vascular size index. The value of the vascular size index and other pharmacokinetic data obtained by the administration of a diffusible contrast agent are used to assess the efficacy of the treatment or the antiangionetic substance being studied.