Single photon absorptiometry

Single Photon Absorptiometry (SPA) is a medical imaging technique used to measure bone mineral density (BMD). It is a type of Absorptiometry that uses a single energy photon source.

History[edit | edit source]

The technique was first developed in the 1960s as a method to measure bone mineral content. It was later refined and became widely used in the 1980s and 1990s for the diagnosis and monitoring of Osteoporosis.

Technique[edit | edit source]

In Single Photon Absorptiometry, a radioactive source, typically Iodine-125 or Americium-241, emits gamma rays which are then passed through the patient's body. The amount of radiation absorbed by the bone is measured by a detector on the other side. The amount of radiation absorbed is directly proportional to the amount of mineral in the bone.

SPA is most commonly used to measure BMD in the forearm, although it can also be used for the heel and other peripheral sites. It is less commonly used for central sites, such as the spine or hip, as these require more advanced techniques such as Dual-energy X-ray absorptiometry (DXA).

Advantages and Disadvantages[edit | edit source]

The main advantage of SPA is its simplicity and low cost. It is also relatively safe, as it uses a low level of radiation. However, it is less accurate than other techniques such as DXA, and it can only measure BMD at peripheral sites.

Clinical Use[edit | edit source]

SPA is primarily used in the diagnosis and monitoring of osteoporosis. It can also be used to assess fracture risk, monitor the effects of treatment, and in research studies.