DEXA

What are the 2 peaks used in DEXA and what are they absorbed by?

1) One peak is measured by the soft tissue 2) The other peak is measured by bone

Dexa uses a ____ component model?

3

Why is the assumption that the hydration and electrolyte content of lean tissue mass is constant wrong?

Because changes in hydration of 1 kg don't affect the accuracy of measurement. * 5% change in water content of FFM will affect %BF by only about 1-2.5%

How much does a DEXA scan cost?

$250 without insurance

How much does a DEXA machine cost?

$80,000-$275,000

What are client sources of error when using DEXA?

1) Body size ( large clients exeeding length or width of scanning bed) 2) Little effect on hydration 3) No need for stopped breathing, but no chest movement 4) No body movement for clean scan

The components that DEXA measures is?

1) Bone mineral content 2) Fat 3) Lean tissue

What are instrumentation sources of error when using DEXA?

1) Calibration 2) Software analysis for sectional analysis

Why is the assumption that measurements are not affected by the anteroposterior thickness of the body wrong?

Because in theory, attenutation of a given substance is constant, but these values may systematically change with variations in thickness.

Why is the assumption that the amount of fat over bone is the same as the amount of fat over bone-free tissue wrong?

Because soft tissue compostion is calculated from pixels. For large bony areas, fewer pixels are used to estimate soft tissue compositon.

DEXA is considered the ___________ ___________ of body composition testing.

Gold standard

What does the DEXA machine specifically do?

It sends a thin, invisible beam of low dose xrays with 2 distinct energ peaks through the person being examined.

What is the common assumption associated with DEXA attenuation?

The attenuation is constant for all individuals

True or false? California requires a limited license to test using DXA.

True

What does DEXA use to determine the density of various tissues?

Very low radiation x-rays

The attentuation (weakening) of the xray energies as they pass through the various tissues (fat, bone, lean mass) differs based on what? (3 things)

1) Thickness 2) Chemical composition 3) Density

What are some of the procedures to follow when testing using DEXA?

1) No calcium supplements on testing day 2) No metal clothing ( with minimal clothing and no shoes, and no buttons or wires in bra) 3) Low radiation exposure 4) Do NOT scan if any possibility of pregancy

What are assumptions of DEXA for whole body composition?

1) The amount of fat over bone is the same as the amount of fat over bone-free tissue. 2) Measurements are not affected by the anteroposterior thickness of the body 3) The hydration and electrolyte content of lean tissue mass is constant.

What does DEXA (DXA) stand for?

Dual Energy X-ray Absorptiometry

Does radiation remain in patients after an xray exam?

NO

What was DEXA initially used for?

To determine bone mineral density for the diagnosis of osteoporosis. *It measures attenuation of Xrays with high and low photon energies.