Slide 2 - DXA Flashcards
DXA is the
Gold standard for measuring body composition
DXA uses
To determine…
Very low radiation x rays
to determine the density of various tissues
DXA can measure what types of composition
General
Regional
What was DXA originally used for
Measuring bone mineral density
To diagnose osteoporosis
What does DXA measure
The attenuation of x rays with HIGH and LOW Photon energies
How does DXA work
How many energy peaks
Sends thin invisible beam of LOW DOSE XRAYS
2 distinct energy peaks
What do the 2 peaks get absorbed by
One by soft tissue
Other by bone
What does attenuation of xrays mean
Weakening of xrays
What do the attenuation of xray energies pass through
Bone
Fat
Lean mass
What effects the passage of the xrays through bone, fat and lean mass
Thickness
Chemical composition
Density
What does the DXA machine featured software display
Bone density
Fat (adipose)
Lean mass
What is the radiation in DXA equivalent to
Less than a days exposure to natural radiation
Less than 1/10 dose of chest xray
Does radiation remain in patient after the dxa
NO
How much does the machine cost
What is the yearly maintenance and repairs
How much is the scan without insurance
80,000 - 275,000
4600
250
DXA is a what component model
3 component model
What components does DXA measure
Bone mineral content
Fat
Lean tissue
What assumptions does the DXA machine make
The amount of fat over bone is the same as the amount of fat over bone-free tissue
Measurements are not affected by the anteroposterior thickness of the body
The hydration and electrolyte content of LEAN TISSUE MASS is CONSTANT
What is the change in hydration that does NOT affect the accuracy of measurements
1 kg of water
How many water content will affect the %BF by in the DXA
5% change in water
Cause a 1-2.5% change in %BF
What is required to test using a DXA
California limited license
No calcium supplements on testing day
No metal on clothing
Low radiation exposure that day
DO NOT SCAN if possibility of pregnancy
What errors may occur when doing a DXA scan
Body size = too tall or wide
Body movement
What can you still do fine during a dxa scan
Breath normally
Little effect on hydration
