1. A method of detecting a sheet object represented in computed tomography (CT) data for a region comprising: identifying a plurality of volume elements in the CT data, each volume element being associated with a density value; for each volume element, selecting a plurality of neighboring volume elements in proximity to the volume element; computing a mean density of the density values associated with the plurality of neighboring volume elements; computing a difference between the density value associated with the volume element and the mean density; comparing the computed difference to a predetermined threshold difference; and labeling the volume element as being associated with a sheet object if the computed difference exceeds the predetermined threshold difference.