Andrew J. Dwyer, MD

Tumors require new blood vessels in order to grow beyond a few millimeters in size. Once this "angiogenic switch" is thrown, a series of events occur that lead to the progression and spread of cancer. The vessels formed by tumors are not only larger and more numerous but also more permeable than normal vessels1 (Figure 1). Thus, when a patient with a tumor is injected with a gadolinium-chelate MR contrast agent, the tumor enhances more than the surrounding normal tissue.