Categorization of bone marrow abnormalities of the AS detected by low-dose whole-body MDCT and its improvement after treatment. (A) Fatty pattern (uniform low-density bone marrow with no high-density lesions detected in the bone marrow space of the metaphysis and diaphysis). (B) Focal/scattered pattern (focal pattern shows the focal high-density lesions and scattered pattern shows the multiple scattered areas of high density [>−30 HU] detected on the background of low-density medullary bone marrow of AS). More than 25% of low-density area (<−30 HU) was required for patients to be categorized as having focal/scattered pattern. (C) Diffuse pattern (uniform high-density lesion occupying >75.0% of the total bone marrow space of the metaphysis and diaphysis). (D) Resolution of a medullary abnormality of the right humerus after successful treatment of the patient in panel C.