Chest Imaging

Interface sign

radiographic feature that is helpful in the differentiation of ascites from pleural fluid within the posterior costophrenic recesses (see pleural effusion). Normally there is a sharp interface between ascites and the liver or spleen, whereas the interface between pleural fluid and liver or spleen tends to be ill defined. This is probably due to partial volume averaging as the oblique diaphragm with fluid above and solid organ below is contained within a voxel. This sign is least reliable near the dome of the diaphragm or with thinner collimation.

CF - HM