Thoracentesis Once a pleural effusion is diagnosed, the cause must be determined.

Usually it can be checked by holding the cotton paper up to the light and looking just below the watermark for a number.

Cotton paper is made from cotton linters or cotton from used cloths (rags) as the primary material source, hence the name rag paper.

Usually the hip (head of the femur), lower back (lumbar spine) or heel (calcaneum) are imaged, and the bone density (amount of calcium) is determined and given a number (a T score).

The incidence of retained foreign bodies following surgery has a reported rate of 0.01 to 0.001 , of which gossypibomas make up 80 of cases.