DXA Flashcards

1
Q

what is DXA?

A

Dual X-ray absorptiometry is a diatonic modalities used to measure bone mineral density

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Whereis DXA used?

A
  1. to measure BMD
  2. diagnosis of osteoporosis
  3. fracture risk
  4. monitor disease progression
  5. monitor therapeutic intervention
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what are the advantages and limitations of DXA?

A
Advantages
1. low radiation dose
2. multiple assessment sites possible (including spine and hip)
3. strongest predictor of hip fracture  
Limitations 
1. cost - expensive 
2. size - huge
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what is scan time for DXA?

A

1/2 - 6mins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what are the principles of DXA?

A
  1. utilises dual X-ray tube
  2. emits narrow collimated beam of x-rays at 2 different energies
  3. consists of solid state detectors (scintillators)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what are two usual energies used in DXA?

A
  1. hologic - 70kVP and 140 kVP

2. GE lunar - 70-90 kVP and 40-60kVP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

deine hologic and GE lunar

A
  1. hologic - uses different parts of AC sin wave

2. GE lunar - alternate filtering with cerium (metal) filters

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is the unit of bone mineral density?

A

g/cm2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Define Z and T score?

A
  1. Z score = normalises a patients BMD by assessing the amount of bone loss compared to the expected bone loss for age-matched peers
  2. T score - quantifies difference between patients BMD and peak bone mass for young normals
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is the T score for the BMD of the following

  1. Normal
  2. Osteopenic
  3. Osteoporotic
A
  1. Normal T > -1 SD
  2. Osteopenic T > -1 SD to < -2.5 SD
  3. Osteoporotic T < -2.5 SD
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what is the relationship b/w SD and BMD fracture risk?

A

for every SD decrease in BMD fracture risk increases by x2 times

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what are the risk factors for osteoporosis?

A
  1. low body mass index
  2. current smoking habit
  3. family history of osteoporosis
  4. medical condition or. use of medication known to affect bone metabolism
  5. x-ray osteopenia
  6. history of atraumatic fracture
  7. pre-mature menopause (before the. age of 45 years) or history amenorrhea (longer than 6 months_
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what are the WHO criteria for osteoporosis?

A

WHO for

  1. postmenopausal women only
  2. T-scores should NOT be used in children, most pre-menopausal women.
  3. Z-scores of -2 or above considered normal in children and premenopausal women
  4. Risk factors should be included in fracture risk
How well did you know this?
1
Not at all
2
3
4
5
Perfectly