I assume you are talking about an MRI? During an MRI, a doctor can order a die to be given to the patient during the procedure. An "enhancing" tumor is one that takes up the die. It is usually a sign that the tumor has a good blood supply to itů not good if it is a cancer since it means that the cancer cells are well feed and can grow faster. However, about one third of "nonenhancing" tumors are in fact malignant, so a biopsy is still the only sure way to tell.