The two major forms of bone densitometry are distinguished by the type of equipment used and the area of the body that is imaged:

• DEXA (or DXA) bone densitometry. This procedure is performed using equipment known as a central device. It is the more frequently performed type of densitometry and focuses on the lower spine and hips, where fractures associated with osteoporosis most often occur. Central devices are composed of a table (on which the patient lies down) with an arm-like device suspended overhead. They most often are found in hospitals and physicians’ offices. In addition, a lateral vertebral assessment procedure may be performed using the DXA equipment to screen for vertebral fractures. These fractures are common in older people.
  
  
• pDEXA bone densitometry. This procedure involves a portable machine known as a peripheral device. It is used to measure bone loss in the fingers, heels or wrists. Peripheral devices weigh about 60 pounds (27.2 kilograms) and include a space where a patient’s foot or arm is inserted. These devices most often found in locations such as pharmacies or mobile health vehicles. Peripheral devices are not as sensitive as central devices and are not used to monitor a patient’s progress during treatment because they do not detect changes in bone during therapy. The central devices are more sensitive in measuring bone density than peripheral devices.
  
  

Less commonly, bone density is assessed with:

• Ultrasound. Imaging with sound waves does not use radiation and may be used to screen small areas such as the heel, but it is less accurate and less comprehensive than a DEXA scan.
  
  
• CAT scan (computed axial tomography). A variation known as quantitative computed tomography (QCT) involves more radiation and higher cost than DEXA scans but may be recommended in some cases, such as if a patient has a spinal deformity.
  
  
• Dual photon absorptiometry (DPA). This radionuclide (nuclear medicine) test can predict risk of fractures but has disadvantages including limited ability to monitor changes in bone density over time.
  
  

Recent research suggests that dental x-rays might help reveal osteoporosis. MRI (magnetic resonance imaging) is also being investigated as a diagnostic tool for the disorder.

Some researchers have proposed the use of DEXA testing for estimating body composition. However, studies indicate that DEXA procedures are not reliable methods of measuring body fat.