Microdamage accumulation in bone is now considered a contributing cause for bone fragility in older women. However, there is still no method to detect and quantify microdamage in vivo. We have found that positron emission tomography (PET) may be useful to detect and quantify bone microdamage in vivo using a high-resolution PET scanner with [18F]NaF as the tracer. We have done several experiments using the rat ulnar loading model that demonstrate that (1) high-resolution [18F]NaF PET can detect newly created microdamage in vivo; (2) the microdamage detected in this way is co-localized with damage detected by histological and autoradiographic procedures; and (3) high-resolution [18F]NaF PET can distinguish between the effects of mechanical loading that does not produce damage and fatigue loading that creates microdamage. The high-resolution [18F]NaF PET shows promise as a non-invasive means to image bone microdamage.