Gross anatomy is studied using both invasive and noninvasive methods with the goal of obtaining information of the macroscopic structure and organization of organs and organ systems. Among the most common methods of study is dissection, in which the corpse of an animal or a human cadaver is surgically opened and its organs studied. Endoscopy, in which a video camera-equipped instrument is inserted through a small incision in the subject, may be used to explore the internal organs and other structures of living animals. The anatomy of the circulatory system in a living animal may be studied noninvasively via angiography, a technique in which blood vessels are visualized after being injected with an opaque dye. Other means of study include radiological techniques of imaging, such as X-ray and MRI.