1. A method for identifying bone marrow in medical image data, the method comprising: obtaining a three-dimensional (3D) computed tomography (CT) volume data set corresponding to an imaged volume, the 3D CT volume data set acquired by a CT imaging system; identifying voxels in the 3D CT volume data set having a Hounsfield Unit (HU) value below a bone threshold, the voxels identified by one or more processors without using image continuity; marking the identified voxels as non-hone voxels and the non-identified voxels as bone voxels; determining, using the one or more processors, from the marked non-bone voxels, definite tissue voxels and non-definite tissue voxels, wherein determining includes identifying voxels surrounded by only marked non-bone voxels and connected, either directly or indirectly, to an initial voxel that is a marked non-bone voxel by other voxels that have been identified as definite tissue voxels, the identified voxels are marked as definite tissue voxels; expanding a region defined by the definite tissue voxels; masking the definite tissue voxels to remove the definite tissue voxels from the 3D CT volume data set; and identifying bone marrow from the non-definite tissue as un-masked voxels that are not the marked bone voxels.