A metal element that is used in magnetic resonance imaging (MRI) and other imaging methods. It is a contrast agent, which helps show abnormal tissue in the body during imaging with a special machine. Gadolinium texaphyrin is a substance that is being studied in the treatment of cancer. It may make tumor cells more sensitive to radiation therapy, improve tumor images using magnetic resonance imaging (MRI), and kill cancer cells. It is a type of metalloporphyrin complex. Also called motexafin gadolinium.