The Technique of Bone Density

Bone density/Bone Marrow Density, a medical terminology refers to the quantity of matter per square centimeter of bones. The quantity is measured through a procedure named densitometry, usually carried out in nuclear medicine or radiology departments of clinics or hospitals. Moreover, the measurement is non-invasive, painless and requires minimum exposure to radiation. Commonly, the measurements are carried out over upper region of hip and lumbar spine. The average bone density is approximately 1500 kg/m3.

The different categories of tests utilized for measurement of Bone Marrow Density (BMD) include:

a)    Dual energy X-ray absorptiometry (DEXA/DXA).
b)    Qualitative ultrasound (QUS).
c)    Quantitative Computed Tomography (QCT).
d)    Single photon absorptiometry (SPA).
e)    Single energy X-ray absorptiometry (SEXA).
f)    Digital X-ray radiogrammetry (DXR).
g)    Dual photon absorptiometry (DXR)

Amongst all these techniques, DXA is most prevalent. However, ultrasound is described as a cost-effective approach for measurement of bone density.
The technique involves various limitations including:

a)    Measurement could be affected by thickness of tissue covering the bone, size of patient as well as other unrelated factors.
b)    Bone density is considered an alternative to bone strength i.e. the resistance to fracture. Though the 2 measurements are normally related, bone density is a poor indicator of bone strength in certain circumstances.
c)    Unavailability of reference standards for a few populations (such as children).
d)    Crushed vertebrae could lead to misleadingly high bone-density and should be not be included in analysis.

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