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RAD413 > bone densitometers DXA > Flashcards

bone densitometers DXA Flashcards

1
Q

know that there is cortical (outer part) and trabecular (spongy inner) structure of the bone

A
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2
Q

define osteopenia

A

low bone mass

  • lower density than average but not low enough to be considered osteoporotic
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3
Q

what is osteoperosis

A
  • microarchitecture of trabecular bone deteriorates and loss bone mass
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4
Q

what are the general causes of osteoporosis

A

iodiopathic (spontaneous)
or
caused by secondary cause

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5
Q

what age range has the peak bone mass

A

30-40

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6
Q

what is the difference between type 1 and 2 primary osteoporosis

A

type 1 = postmenopausal

type 2 = senile (age related_

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7
Q

give some examples of secondary causes of osteoperosis

A
  • diseases e.g autoimmune conditions
  • meds e.g high dose steroids
  • lifestyle e.g low calcium or smoking
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8
Q

what are some genetic factors that can cause osteoperosis

A

ethinicity
gender
early menopause
family history
small frame/ low BMI

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9
Q

What should be the average calcium daily intake for adults

A

700 mg

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10
Q

average vitamin D intake daily for adult is

A

10mg

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11
Q

what is Sheffield FRAX

A

fracture risk assessment

  • diagnostic tool used to evaluate the 10-year probability of bone fracture risk.
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12
Q

What is DXA, dual energy xray absoptiometery

A

DXA scans measure bone mineral density

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13
Q

what are the most routinely scanned anatomy with DXA

A

hip and lumbar spine as they are most load bearing and biggest impact if fractured

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14
Q

know that dual energy xray absorptiometre uses very low dose

A
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15
Q

what is a VFA examination using DXA

A

vertebral fracture assessment

  • resembles lateral spine xray of L5 up to T6/4
  • low dose
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16
Q

What is a VFA used for

A

assess each vertebra for any degree of vertebral fracture but not any other pathology

17
Q

why is DXA used to measure lumbar and hip

A
  • more trabecular bone prevaelnet
  • both areas whee ravoidance of fracture is best
18
Q

know that a DXA scan questionnaire bust be done prior to scan to check for osteoporosis risk factors

A
19
Q

what must be checked prior to scan

A
  • patient ID
  • pregnancy status where applicable
20
Q

how does a DXA scan work

A
  • tissue is exposed to 2 difference energy source
  • allowing contraction of 2 simultaneous attention equations
  • measures attenuation at high and low energies

two distinct energy peaks through the bones being examined. One peak is absorbed mainly by soft tissue and the other by bone. The soft tissue amount can be subtracted from the total and what remains is a patient’s bone mineral density.

21
Q

early DXA scans used pencil beam scanners, what are these

A
  • pencil beam has single detector
  • uses single radiation detector
  • attenuation is just one path through the body measured at any instant
22
Q

what was the scan time and resolution of a pencil beam scanner

A

time= 5-10 mins
resolution = 1mm

23
Q

what type of scanner do modern DEXA scans use

A

fan beam scanners

24
Q

how does a fan beam scanner work

A
  • attenuation alongmany paths through body measured simultaneously
  • allowing larger FOV to be scanned at one time
25
Q

what is the scan time and resolution of a fan beam scanner

A

scan time = 1min per site

resolution = 0.5mm

26
Q

what are the 2 values received from a DEXA scan + units

A
  • BMC bone mineral content (g/cm)
  • BMD bone mineral density (g/cm^2)
27
Q

what is used to calculate the mean peak bone mass (in general)

A

a large reference population

28
Q

what is a t score

A

standard deviation that shows difference against the mean of the peak of bone mass

29
Q

what is a z score

A

standard deviation showing difference against averge bone mass in population of their own age group

30
Q

know that the BMC AND BMD values are used to calculate the patients T/Z scores

A
31
Q

what value of t score would place someone in the category of normal, osteopenia, osteoporotic according to the WHO classification

A

T score > -1SD = normal

T score < -1 SD - 2.5 = osteopenia

T score </= -2.5 SD =osteoperotic

32
Q

what is a limitation with DEXA

A

only in pixels containing no bone can soft tissue composition (fat versus lean) be assessed

e.g degenerative changes or stent

33
Q
A

RAD413 (24 decks)

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