Radiography can also be used to indirectly identify Achilles tears. Radiography uses X-rays to analyse the point of injury. This is not very effective at identifying injuries to soft tissue. X-rays are created when high energy electrons hit a metal source. X-ray images are acquired by utilising the different attenuation characteristics of dense (e.g. calcium in bone) and less dense (e.g. muscle) tissues when these rays pass through tissue and are captured on film. X-rays are generally exposed to optimise visualisation of dense objects such as bone while soft tissue remains relatively undifferentiated in the background. Radiography has little role in assessment of Achilles' tendon injury and is more useful for ruling out other injuries such as calcaneal fractures.