Bone necrosis, also known as avascular necrosis (AVN) or osteonecrosis, is a condition in which the bone tissue dies due to a lack of blood supply. This is often caused by an injury or long-term use of certain medications, such as steroids. On an MRI scan, bone necrosis can appear as a dark area of increased signal intensity. This is because when the bone tissue dies, the area becomes more porous, allowing more water to enter the area. This increased water content results in an increased signal intensity on the MRI scan. Additionally, bone necrosis may also be accompanied by a decrease in bone density, which also shows up as an area of decreased signal intensity on an MRI scan.
In addition to the visual signal changes on an MRI scan, bone necrosis may also be diagnosed with an MRI-based analysis called T2 mapping. With this method, the signal intensity on the MRI scan is compared to the signal intensity of the adjacent bone tissue. If the signal intensity of the area of bone necrosis is significantly different from that of the surrounding bone, then it can be used to diagnose bone necrosis.
Overall, bone necrosis can appear as an area of increased signal intensity on an MRI scan. This signal change, combined with a decrease in bone density, can be used to diagnose the condition. In addition, T2 mapping can also be used to confirm the diagnosis.