bone density scan

[medstudent2005]

hey guys

real quick: what is the physics behind the bone density scan (aka DXA?). I read that it uses dual energy X ray, one high beam, one low beam, and then takes the difference between them...but, can someone explain to me the mechanics behind what the high beam and low beam tell you? i am assuming the high beam has better penetrance, and low beam doesn't...but how is this used?

thanks

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[Santiago]

hi,
The principal of DXA is a dual-energy measurement that is based on the fact that radiation of distinct energies is attenuated by tissues to different extents. In soft tissue and bone, a low-energy beam is attenuated to a greater degree than a high-energy beam. Contrast in attenuation between bone and soft tissue is greater for the lower energy beam than for the high-energy beam, such that the attenuation profile of bone may be determined
by subtracting the low- and high-energy attenuation profiles.
Hth

 

[medstudent2005]

k, i still don't get it..why not just use a high beam or low beam or whatever and compare the attenuation profiles btwn ppl? i mean, i guess i don't have the basics (never really learned about the basics of these procedures...and i forgot all my physics, so you gotta help me out here ) now, attenuation is based on the density of the material, right? greater density means the beams don't go through as well? so can't you just compare that?

thanks