DEXA test Flashcards
(93 cards)
1
Q
what does DEXA stand for?
A
dual-energy x-ray absorptiometry
2
Q
what does BMD stand for?
A
bone mineral density
3
Q
what does ROIS stand for?
A
regions of interest
4
Q
what does BMC stand for?
A
bone mineral content
5
Q
what does SD stand for?
A
standard deviation
6
Q
what does QC stand for?
A
quality control
7
Q
systemic skeletal disease characterized by low bone mass and micro-architectural deterioration of bone
A
osteoporosis
8
Q
what scores qualify someone to have osteoporosis?
A
BMD lower than -2.5 SD (T score) for osteoporosis and BMD -1 to -2.5 for osteopenia
9
Q
osteoporosis affects ___ million in USA ___% women and ___ million people with osteopenia
A
10
80%
34
10
Q
what is type 1 osteoporosis?
(primary osteoporosis)
A
postmenopausal - due to estrogen deprivation in women (bone resorption > bone formation)
11
Q
what is type 2 osteoporosis?
(primary osteoporosis)
A
senile or age related - aging causes a decreased ability to build bone (affects both men and women)
12
Q
what is secondary osteoporosis?
A
it is caused by other conditions
examples: hyperparathyroidism, gonadal insufficiency (women and men), osteomalacia, RA, anorexia, gastrectomy, adult sprue (sensitivity to gluten), multiple myeloma, use of corticosteroids, heparin, anticonvulsants, or excessive thyroid hormone treatment
13
Q
what are the functions of the bone?
A
- supports the body
- protects vital organs
- manufactures red blood cells
- stores essential minerals like calcium and phosphate
14
Q
what is the end of the bone called?
A
epiphysis
15
Q
what is the middle of the bone called?
A
diaphysis
16
Q
what are the layers of the bone outside to inside?
A
hyaline cartilage
periosteum
compact bone
spongy bone
17
Q
where is redbone marrow located?
A
in the ends of the bone in the spongy bone
18
Q
where is yellow bone marrow located?
A
in the middle of the bone in the marrow cavity
19
Q
what are the 2 types of bone?
A
cortical (compact)
trabecular (cancellous)
20
Q
- forms the dense outer shell of all bones and the shafts of the long bones
- supports weight resists bending and twisting
- accounts for 80% of the skeletal mass
A
cortical (compact) bone
21
Q
what are osteoclasts?
A
- bone destroying cells
- break down and remove old bone leaving behind pits
- this process is called resorption
22
Q
- delicate, lattice-work structure within bones (spongy bone), adds strength without weight
- 20% of skeletal mass
- supports compressive loading in the spine, hip, and calcaneus. also found at the end of the long bones
A
trabecular (cancellous) bone
23
Q
what are osteoblasts?
A
- bone building cells
- fill the pits with new bones
- this process is called formation
24
Q
what are the steps in the remodeling cycle?
A
resorption -> formation -> completion -> cycle restarts
25
what factors affect bone remodeling?
age, pathology, hormones, vitamin D and calcium supply
26
what are the genetic risk factors for osteoporosis?
- being female
- advanced age
- white or Asian descent
- small bones or body weight <127 pounds
27
what are the endocrine risk factors for osteoporosis?
- menopause or less estrogen
- periods of time with no menstruation
- endocrine disorders
- estrogen deficiency
- nutritional: eating disorders, low calcium, and/or vitamin D intake
28
what are the lifestyle risk factors for osteoporosis?
sedentary lifestyle
- excessive physical exercise
- smoking
- excessive alcohol intake
29
what are the medication risk factors for osteoporosis?
- RA meds
- endocrine
- seizure
- GI - especially glucocorticoids
- steroids
- anticoagulants
- thyroid hormones
30
what is the Bone Mass Measurement Act (BMMA)
CMS billing and coding
medicare part B covers "medically necessary approved measurements" every 24 months
31
qualifications for Bone Mass Measurement Act (BMMA)
1. estrogen-deficient women at risk for osteoporosis
2. vertebral abnormalities
3. has received long-term glucocorticoid (steroid) therapy
4. has primary hyperparathyroidism
5. to evaluate efficacy/response to an osteoporosis medication
32
how to prevent osteoporosis with lifestyle choices?
- sufficient calcium and vitamin d
- weight bearing and muscles strengthening exercise
- not smoking
33
what puts a patient at risk for fractures?
low-bone mass (osteopenia and osteoporosis) puts the patient at a risk for fractures - especially of the spine and hips (which increases their mortality rate)
34
what instructions should be given to the patient?
- time (15 to 20 minutes)
- what to expect (noise, machine movement)
- amount of scans (usually 3, 1 minute each)
- laying on back, pigeon toed, doesn't have to hold breath
35
what patient history would be relevent to the scan?
- bone disorders
- prosthesis (scan area can't have hardware)
- peak height
- current height and weight
- biochemical markers (blood/urine labs to determine bone metabolism)
- recent contrast agents
-radio pharmaceuticals
- calcium supplements
- possible pregnancy
36
what is the proper distance to be from the scanner?
- 1 meter (3ft) away from pencil beams
- 3 meters (9ft) from fan (array) beams
37
levels of radiation in DEXA
- entrance dose (mSv):
- dose equivalent (mSv):
- entrance dose (mSv): 0.001-0.03 mSv
- dose equivalent (mSv): 1-5 micro Sv (mrem) or 0.001 to 0.005 mSv
38
types of radiation exposure, effective dose (mSv)
- daily natural background radiation:
- round trip air flight across the US:
- lateral lumbar spine radiograph:
- PA chest radiograph:
- QCT with localizer scan:
- DXA scan:
- SXA scan:
- QUS:
- daily natural background radiation: 5-8
- round trip air flight across the US: 60
- lateral lumbar spine radiograph: 700
- PA chest radiograph: 50
- QCT with localizer scan: 60
- DXA scan: 1-5
- SXA scan:
39
typical energy levels for GE Lunar and Norrland Swissray and what filter does it use?
40 keV and 70 keV (peak around 50 kVp)
rare-earth filters
40
typical energy levels for Hologic (energy switching)
100 kVp to 140 kVp (peaks at 40 kVp and 80 kVp)
41
what are the advantages of dual photon energies?
- 2 energies optimizes differentiation of soft tissue and bone
- low patient dose
42
what are the disadvantages of dual photon energies?
with energy switching systems and increased body thickness absorbs more of the low energy photons which shifts the spectrum towards the high-energy photons high-energy photons may be counted as low-energy due to attenuation in the body
43
what separates photons into low or high energy categories?
K-edge filtration
44
what is it called when the tube switches between 100 and 140 kVp (peaks 40 and 80 keV) which doesn't need a detector to separate the high and low energy photons
energy switching
45
why does the radiation detector system detect high and low energy photons?
to separate soft tissue and bone
46
mechanics of fan beam
- beam collimation:
- detector system:
- scan arm motion:
- beam collimation: wide slit x-ray collimator
- detector system: multiple detector array (multielement)
- scan arm motion: one direction (vertically) (shorter scan time compared to pencil beam)
47
geometry of fan beam
- SOD distance:
- magnification and distortion:
- object centering:
- estimated BMC and area:
- SOD distance: fixed, based on manufacturer
- magnification and distortion: outer edges of image have slight magnification and shape distortion due to beam shape
- object centering: center pt accurately to avoid magnification and distortion
- software takes into account known degree of magnification and produces estimated BMC and an estimated area
48
what are potential array beam errors?
- magnification (top)
- parallax (bottom)
49
effects of magnification with an array beam
area and BMC are influenced by magnification, while BMD is not significantly affected
50
effects of parallax with an array beam
parallax errors can cause changes in BMD by altering the beam path through the object being measured
51
scan analysis algorithm
- computation of soft tissue density:
- bone edge detection:
- computation of soft tissue density: computer subtracts soft-tissue detector signals leaving just the bone
- bone edge detection: based on machine brand, algorithms are applied to detect the bone edges so a 2D area can be calculated
52
what is bone mineral content (BMC)?
measurement of bone mineral in total area of ROI - measured in grams
53
what is bone mineral density (BMD)?
measurement of bone mineral per unit area of ROI - measured in g/cm^2
54
what is the equation for BMD and BMC?
BMD (g/cm^2) = BMC (g)/area (cm^2)
55
what is standard deviation (SD)?
measures the variability of the data by measuring the distance of each point from the mean and then takes the average of that. the smaller the average distance = smaller SD = better
56
what is coefficient of variation (%CV) and what is the equation?
- measurement of precision (smaller is better because that means there is less variability)
- comparison of variability of different datasets
- % CV = (SD/mean) x 100
57
- indicate the # of SDs the patient's BMD is from the average BMD for the patient's age and sex
- used to determine if BMD is reasonable and if an evaluation for secondary osteoporosis is warranted
- used for older adults
Z-scores
58
indicates the # of SDs the patients BMD is from the average BMD of a young, normal individual of the same sex at peak bone mass
T-scores
59
what are Z and T scores used to assess?
fracture risk, diagnose osteoporosis, low bone mass, and recommended therapy
60
WHO diagnostic therapy
- normal:
- low bone mass (osteopenia):
- osteoporosis:
- severe osteoporosis:
- normal: BMD or BMC T-score of >/= -1
- low bone mass (osteopenia): BMD or BMC T-score between -1 and -2.5
- osteoporosis: BMD or BMC T- score of /=1 fragility fractures
61
what can Z and T scores by adjusted by?
ethnicity and/or weight depending on DXA machine brand
62
what is FRAX (WHO fracture risk assessment tool)?
- tool to determine the 10 year risk factor for a hip fracture based on hip BMD (femoral)
- can't be used if the pt is on medications for osteoporosis
- helps physician create a treatment plan
63
what is vertebral fracture assessment (VFA)?
uses lateral spine image to determine shapes of the vertebra (morphometric data) and determine compression fractures
64
what is pediatric/adolescent scanning for?
- used to evaluate fracture risk or vertebral fractures
- to monitor known skeletal disease
- for short stature patients - use Z-score height
- not for diagnosing osteoporosis/osteopenia
- no T-score for pediatric patients, only Z-score
65
if the scanner speed is faster then the scan is:
less precise
66
incorrectly calibrated machine and bone edge detection =
less precise and accurate
67
parallax error is due to:
poor patient centering
68
a baseline for the variability in the machine, so that you can determine if an abnormal BMD is caused by the machine, the tech, or the patient
LSC or least significant change
69
each DXA tech needs to perform a precision assessment in vivo
1. the assessment is done:
2. for the assessment the tech will scan __ patients __ times or __ patients twice (repositioning the patient in between) to determine precision
1. after they have been trained and performed at least 100 patient scans
2. 15, 3, 30
70
acceptable values for an individual tech for a precision assessment in vivo
lumbar spine:
total hip:
femoral neck:
lumbar spine: 1.9% (LSC=5.3%)
total hip: 1.8% (LSC=5.0%)
femoral neck: 2.5% (LSC=6.9%)
71
follow-up scanning
~reproduce baseline study
- acquisition parameters:
- positioning:
- ROI placement:
~changes affecting scan validity
- patient:
- tech:
~reproduce baseline study
- acquisition parameters: mode, speed, current
- positioning: same as before, accurate, etc
- ROI placement: same ROIs as previous scan, and correct positioning
~changes affecting scan validity
- patient: new ROI, fractures, weight gain/loss
- tech: not following protocol, machine damages
72
what are the purposes of quality control?
- scanner function and calibration
- timely repairs and recalibration
- shift/drift in BMD
73
what machine uses internal calibration?
Hologic performs an automatic internal calibration check when the machine is turned on
74
what machine uses external calibration ?
GE Lunar and Norrland swissray require the tech to perform calibration using an external calibration block
75
when to do cross-calibration ?
for equipment & change in manufacturer
- always cross-calibrate to determine the average BMD relationship and LSC between the initial machine and new machine using the ISCD machine cross-calibration tool
76
anatomy related to scanning for lumbar spine
- ROI in DXA:
- bony landmarks:
- significant adjacent structures:
- ROI in DXA: L1-L4
- bony landmarks: ribs and iliac crests
- significant adjacent structures: pelvis, ribs, T-12, sacrum
77
when comparing two different scans for the same patient what should you do if there is a change in one of the scans like a fractured vertebrae?
exclude the fractured vertebrae from the comparison in both the images
78
what is the standard technique for DXA for spine and hip?
40 kVp - 80kVp
3 mAs
79
how to position a patient with scoliosis?
uncenter L5 so L1-4 are straighter but don't twist patient
80
what are the reported values for lumbar spine analysis?
- BMC
- T-score
- Percent of mean
81
anatomy related to scanning for femoral neck
- anatomy:
- ROI in DXA:
- bony landmarks:
- radiographic appearance:
- significant adjacent structures:
- anatomy: proximal femur, greater and lesser trochanter, ischium, femoral head
- ROI in DXA: femoral neck - 3-4 cm below and 2-3 cm above greater trochanter
- bony landmarks: greater and lesser trochanter, ischium, acetabulum, proximal femur
- radiographic appearance: lesser trochanter is small and round or cannot be seen, femur straight, space between ischium and femur (if no space pelvis is rotated)
- significant adjacent structures: pelvis
82
femur selection
- don't scan hip with:
- if arthritic:
- when possible do:
- don't scan hip with: replacement or fracture
- if arthritic: choose less arthritic side (if very arthritic replace hip with forearm)
- when possible do: both hips and spine
83
use _____ setting for very thin patients and the _____ setting for thick patients
fastest, slowest
84
patient positioning for femur
- rotation:
- shaft placement:
- positioning aids:
- rotation: rotate femur 15-25 deg medially so lesser trochanter is barely seen/not seen
- shaft placement: femur should be slightly abducted, so femoral shaft is straight
- positioning aids: attach feet to femur positioning device to angle leg correctly
85
what do you do if bone edges look mottled or "moth-eaten"?
try scanning slower for thicker patients and quick for thinner patients
86
what could cause inaccurate BMC or BMD values?
- short femoral neck
- inadequate space between ischium and femur
- fractures
- arthritis
- joint disease
- biochemical devices
87
scan analysis for femoral neck
- ROI placement:
- reported values:
- ROI placement: femoral neck should be in the center of the scan
- reported values: BMC, T-score, percent of mean, graphical displays
88
when do scan the forearm?
- hip and/or spine cannot be measured
- hyperparathyroidism
- very obese pt (over DEXA table weight limit)
89
forearm anatomy related to scanning
- anatomy:
- ROIs in DEXA:
- bony landmarks:
- significant adjacent structures:
- positioning:
- anatomy: radius and ulna
- ROIs in DEXA: 33% radius
- bony landmarks: styloid process of the ulna
- significant adjacent structures: carpal bones, soft tissue
- positioning: palm down
90
forearm selection
- which arm:
- length:
- which arm: choose non-dominant forearm because it usually has a lower BMD, don't scan forearm that has had surgery, hardware, fracture, or severe arthritis
- length: from ulnar styloid down (about 1/2 way down forearm) (do not need all carpal bones)
91
what is the standard technique for DXA forearm scan?
40-80 kVp and 0.15 mAs
92
what are common challenges for forearm scans?
- kyphosis & contracture
- low bone density
- arthritis and joint disease
93
scan analysis for forearm
- ROI placement:
- reported values:
- ROI placement: correctly positioned forearm
- reported values: BMC, T-score, Z-score, percent of mean
