DXA Flashcards
strengths of SXA, pDXA
low radiation dose
low cost
portable
limitations of SXA, pDXA
use on appendicular sites only
cannot measure trabcular and cortical bone seperately
scan time SXA, pDXA
3-5 minutes
strengths of DXA
low raditaion dose
multiple assessment sites possible
strongest predictor of hip fracture
limitations of DXA
cost
size
scan time of DXA
1/2 - 6 mins
strengths of QCT
gives volumetric densities
discriminates trabular from cortical bone
limitations of QCT
radiation dose
capital and running cost
N/A to the proximal femur
rigorous QC and slow
scan time of DXA
10 minutes
strengths of QUS
no radiation exposure small and postable fast easy to use low cost
limitation of QUS
limited to calcaneus, radius and tibia
sacn time of QUS
1-5 minutes
principles of DXA
utilise xray tube
emits a narrowly collimated beam of xray at 2 different energies
differeniated between soft tissue and bone
why lift legs slightly when scanning lumbar spine
flattens spine
prevent vertebrate tilt
how is osteoarthrtis idenitfied in images
white patches
what do you do to the hip to improve image
twist hip to enlongate femoral neck
ensure there is sufficietn soft tissue surronding the hip
how much can the femoral neck chnage by due to meds
2-4%
how much can the size of the hip be altered due to positioning
9%
z score calculatoion
patient BMD - age matched mean/age matched SD
t score calculation
patient BMD - young normal mean/ young adult SD
use of risk factors
help clincians idenfity those who may be at risk
- histroy of atraumic fracture
- xray osteopenia
- medical conditions or use of meds known to affect bone metabolism
- premature menopause
- family history of osetoprosis
- low BMI
- current smoking habit
normal t score
T>-1SD
osteopenic t score
T>-1SD to
osteoporotic t score
T
