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Alternatively, a technique that uses a low kV(p) and high mA setting produces images with high contrast, the bones appearing relatively white. The kV(p) selected must produce an x-ray beam sufficiently powerful to penetrate bones, so that such detail as the inner margin of the cortex and medullary trabeculae can be appreciated. Soft tissues are generally easier to evaluate using this technique, and poorly mineralized new bone formation is also easier to see. Either technique can be used depending on preference and the circumstances of the examination. Films of joints should be centered on the joint. Films of long bones should include the joints proximal and distal to the bone of interest. Care should be taken to achieve good positioning, and at least two orthogonal views must be obtained. Benign or Nonaggressive Versus Aggressive or Malignant Lesions Determining whether a skeletal lesion is aggressive or nonaggressive is a frequent diagnostic dilemma. Rather than simply a system with two or three classifications, the clinician should think of the classification of skeletal lesions as a continuous scale from nonaggressive to aggressive. Lesions may be characterized by bone destruction, new bone growth, or both. Each component should be evaluated to determine how long it has been present and how active it is. Bone Destruction Bone lysis, or destruction, is placed in one of three classifications based on the size of the holes in the bone. Large lesions (greater than 5 mm) are classed as focal or geographic. Lytic processes characterized by midsized holes (1 to 4 mm) are termed moth-eaten, and small holes (less than 1 mm) are termed permeative. In general, the smaller and more numerous the holes, the more aggressive the lesion. The observer should evaluate the margins of the holes. Well-defined, sharply demarcated borders suggest a nonaggressive lesion. Poorly defined and indistinct margins indicate an active, relatively aggressive lesion. The zone of transition at the junction between the lytic lesion and normal bone should be evaluated. A sharp, well defined transition suggests a nonaggressive process. If a sclerotic rim of bone is present at the junction of normal and abnormal bone, then that usually indicates a chronic process that the skeleton is attempting to contain. A broad zone of transition, for which it is difficult to say definitively where bone is normal or abnormal, is consistent with an aggressive process. New Bone Formation Bone production usually occurs on the periosteal surface of the cortex in response to lifting or tearing of the fibrous periosteum. Periosteal new bone should be evaluated for shape, margination, and definition. Lamellated new bone consists of multiple layers, appearing much like a cross section of an onion; it is usually chronic and the result of repeated insults. Lamellated bone may be seen at the edge of an expansile lesion where repeated growth spurts lift the periosteum from the original cortex, and then the new bone forms in layers.
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