A DEXA scan is a special type of X-ray that measures bone mineral density (BMD). DEXA stands for dual energy X-ray absorptiometry.This type of scan is also often known as DXA, or dual X-ray absorptiometry.It's also sometimes referred to as a bone density scan or a bone densitometry scan. DEXA scans are often used to diagnose osteoporosis (when the bones become weak and fragile, and are more likely to break). DEXA scan is a special type of X-ray that measures bone mineral density (BMD). DEXA stands for dual energy X-ray absorptiometry.