text: Usually we use that term when we refer to barium in the colon (a barium enema).  \n\nHere is an example of its use:\n"It is regarded as axiomatic in radiology that a temporary, circumferential, physiological narrowing of the barium column in the lumen of a hollow muscular tube is due to contraction of the walls of the tube. This supposition has not always been accepted universally. It has been argued, especially in physiology, that a barium column may appear to be narrowed in cases of incomplete filling of the lumen. Alternatively, even with complete filling, a passive "falling together" of the walls (as opposed to active contraction) may narrow the column. Whether these objections are valid or not may be determined by combining alternative modes of investigation, e.g. manometry, with radiological imaging procedures."