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267 Cards in this Set
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Bone densitometry |
general term that encompasses the art an science of measuring BMC and BMD of specific skeletal sites of the whole body |
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BMC |
bone mineral content |
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BMD |
bone mineral density |
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The bone measurement values are used to |
1. assess bone strength 2. assist with diagnosis of diseases associated with low bone density 3. monitor the effects of therapy for such diseases 4. predict risk of future fractures |
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Several techniques available to perform bone densitometry using |
ionization or ultrasound |
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The most versatile and widely used is |
DXA |
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DXA |
dual energy x-ray absorptiometry |
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Advantages of DXA |
1. low radiation dose 2. wide availability 3. short scan time 4. high resolution images 5. good precision 6. stable calibration |
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Differences between DXA and conventional radiography |
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DXA can be conceptualized as what type of technique |
subtraction technique |
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What is the chief benefit of using a high and low x-ray energy source with a DXA system? |
demonstrates attenuation difference between bone and soft tissue |
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WHich vertebral region(s) is (are) analyzed during a DXA scan? |
L1-L5 |
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WHich of the following is not a risk factor for osteoporosis |
Daily physical activity |
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Bone destroying cells are called |
osteoclasts |
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The most common osteoporotic fracture is found in the |
vertebrae |
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Precision relates to the ability of the system to |
reproduce the same results in repeat measurements of the same object |
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Radiation dose for DXA scans is |
similar to natural background radiation |
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The Z score is used to determine |
if the measured BMD is reasonable |
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Patient positioning should be exactly the same for all scans because the |
results will be more precise, reflecting a true biological change |
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THe measurement of bone density uses two different beam energies which allows the separation of soft tissue and bone due to |
mass attenuation coefficient differences |
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A cell that makes bone |
osteoblast |
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It does so by producing a |
matrix that then becomes mineralized |
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Bone mass is maintained by a balance between the |
activity of osteoblasts that form bone and other cells called osteoclasts that break it down |
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A cell that nibbles at and breaks down bone and is responsible for bone resorption |
osteoclast |
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Osteoclasts are large |
multinucleate cells |
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In normal bone, what two things are closely coupled processes involved in the normal remodeling of bone |
bone formation bone resorption |
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Bone is constantly going through a |
remodling process |
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Old bone is replaced with |
new bone |
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New skeleton is formed every |
7 years |
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How long does it take to break down the bone |
1 week |
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How long does it take to build it up |
3 months |
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The net rate of bone resorption exceeds the rate of bone formation which results in |
decrease in bone mass without a defect in bone mineralization |
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Osteoclast activity is increased after the age of |
35 |
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Women are __ times more likely to develop osteoporosis than men |
4 |
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Women have a decrease in |
estrogen levels |
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Men have a decrease in |
testosterone |
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Maintaining bone health |
1. calc and vit d 2. physical activity 3. not smoking 4. limit alcohol use 5. healthy weight |
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A loss of ___-____% of trabecular bone may produce the first visible changes on a radiograph |
30-50 |
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The risk of fracture is affected by |
1. age 2. body weight 3. fam history 4. cigarette smoking/excessive alcohol use |
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Bone densitometry uses what type of radiation |
ionizing |
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THe machine sends |
thin beam of low dose xrays with 2 distinct energy peaks through the bones being examined |
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One peak is absorbed mainly by |
soft tissue |
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The other peak is absorbed mainly by |
bone |
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How the exam is done (5) |
1. patient lies on padded table 2. xray generator is located below patient 3. fan beam construction 4. imaging device/detector is positioned above 5. machine moves over patient |
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THe soft tissue amount can be subtracted from the |
total |
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What remains is a patient's |
bone mineral density (BMD) |
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DXA |
dual energy xray absorptiometry |
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DXA machines feature special software that |
compute and display bone density measurements on a computer monitor |
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DXA measures the |
xray attenuation of bone itself |
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It gets rid of the |
soft tissue |
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It gets rid of the soft tissue by using |
two different xray photon energies
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It manipulates the recorded signal |
mathematically |
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Bone density results are computed by using the |
xray attenuation pattern striking the detector - not from the scan image |
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Z score |
compares the patient to an average individual of the same age/sex |
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T score |
compares the patient to an average young, healthy individual with peak bone mass -same gender |
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A score above -1 is considered |
normal |
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A score between -1 and -2.5 is classified as |
low bone mass |
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A score below -2.5 is defined as |
osteoporosis |
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The T score is used to estimate your |
risk of developing a fracture |
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If Z score is unusually high/low it may indicate a need for |
further medical tests |
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The ability of the system to measure the true value of an object |
accuracy |
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Accuracy is determined by the |
calibration of the scanner - which is set/maintained by the manufacturer |
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THe ability of the system to reproduce the same (but not necessarily accurate) results in repeat measurements of the same object |
precision |
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Each DXA lab should determine its |
precision error and calculate the least significant change (LSC)
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Bone densitometry has what type of radiation dose |
low
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Bone densitometry has a ___ availability |
wide |
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Bone densitometry has what type of scan time |
short |
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Bone densitometry produces |
high resolution images |
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Bone densitometry measures |
bone mineralization and density of precise skeletal sites - specifically bone loss |
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The bone measurement values are used to assess (4) |
1. bone strength 2. diagnose disease 3. monitor the effects of therapy 4. predict risk for future fractures |
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The density of the isolated bone is calculated on the basis of the principle that denser, more mineralized bone attenuates (absorbs) |
more xray |
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Scan images are only for the purpose of confirming (2) |
1. correct positioning of the patient 2. correct placement of the ROI |
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ROI |
regions of interest |
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How many DXA manufacturers in the US |
3 |
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Effective radiation dose for DXA is considerably higher or lower than radiation dose for Conventional radiography |
lower |
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Radiographic Absorptiometry |
taking a radiograph of bone with a known standard, placing it in the ROI, and optically comparing the densities |
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SPA |
Single photon absorptiometry |
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DPA |
dual photon absorptiometry |
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SPA and DPA are based on the |
physical principles similar to those for DXA |
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SPA is not a |
subtraction technique |
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SPA relies on what |
water bath or other medium to eliminate the effects of soft tissue |
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SPA found applications only in the |
peripheral skeleton |
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DPA uses |
photons of 2 energies |
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DPA was used to assess sites in the |
central skeleton - lumbar spine and proximal femur |
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THe radiation source for DPA/SPA |
highly collimated beam from radioisotopes |
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Isotope for SPA |
Iodine 125 |
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Isotope for DPA |
Gadolinium 153 |
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THe intensity of the attenuated beam was measured by a |
collimated scintillation counter |
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The bone mineral was |
quantified |
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First commercial DXA scanner year |
1987 |
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DXA scanners were (4) |
1. expensive 2. rare 3. short lived 4. radioisotope source replaced by xray tube |
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Improvements were |
Pencil beam or array beam collimation |
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What is the most widely accepted method for measuring bone density for DXA (2) |
hip and spine |
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The skeleton serves as (4) |
1. supports body 2. protects vital organs 3. manufactures RBC 4. stores minerals - calcium, phosphate |
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What are the two basic types of bones |
1. trabecular 2. cortical |
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Cortical |
compact |
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Cortical bone forms the |
dense, compact outer shell of all bones and the shafts of the long bones |
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Cortical bone supports |
weight, resists bending and twisting |
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Cortical bone accounts for what % of skeletal mass |
80 |
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Trabecullar |
cancellous |
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Trabecular bone is |
delicate, latticework structure within bones that adds strength without excessive weight |
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Trabecular bone supports |
compressive loading in spine, hip, calcaneus |
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Trabecular bone is also found at the |
ends of long bones- such as distal radius |
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Bone is constantly growing through what type of process |
remodling |
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Remodling process- old bone is |
replaced by new bone |
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New skeleton formed about every |
7years |
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Osteoclasts |
bone destroying cells |
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Osteoclasts do what |
break down and remove old bone |
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Osteoclasts leave |
pits |
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Osteoclasts |
resorption |
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Osteoblasts |
formation |
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Osteoblasts are what |
bone building cells |
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Osteoblasts fill pits with |
new bone |
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Comparative rates of what determine stuff about bone mass |
1. bone formation 2. bone resorption |
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Increases |
more formation than resorption |
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Decreases |
more resorption than formation |
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Remains stable |
equal formation and resoption |
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Osteoclasts and osteoblasts operate as a |
bone remodeling unit |
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Length of resorption process |
1 week |
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Length of formation process |
about 3 months |
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Bone mass increases in youth until |
peak bone mass is reached |
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Peak bone mass is reached at approximately what years of age |
20-30 |
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Decreasing in bone mass |
women- starts at approx 50 men - starts at approx 65 |
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Decrease in bone mass becomes pronounced in women at |
menopause |
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This is because of the loss of bone preserving |
estrogen |
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Low bone mass and structural deterioration of bone tissue |
osteoporosis |
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In osteoporosis, bones are at an increased risk for |
fragility fractures |
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Women |
80% |
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Men |
20% |
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Primary risk factors of osteoporosis (6) |
1. female gender 2. estrogen deficiency 3. increased age 4. low body weight 5. smoking tobacco 6. fam history |
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The exact cause of osteoporosis is |
unknown *multifactorial |
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Osteoporosis is classified as |
primary or secondary |
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Primary osteoporosis has how many types |
2 |
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Type I |
postmenopausal |
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Type II |
Senile/age related |
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Type I is caused by |
bone resorption exceeding bone formation owing to estrogen deprivation in women |
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Type II is caused by |
aging men/women which results from a decreased ability to build bone |
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Secondary Osteoporosis is caused by |
heterogenous group of skeletal disorders resulting in imbalance of bone turnover |
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Common causes of secondary osteoporosis |
hyperparathyroidism and osteomalacia |
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Fragility fractures occur with |
no apparent force being applied |
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Most common sites associated with osteoporosis (4) |
1. hip 2. spinal vertebrae 3. wrist - colles fracture 4. ribs |
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Hip fractures account for what % of osteoporotic fractures |
20% |
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Most devastating for patient |
hip |
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What is the #1 most common osteoporotic fracture |
vertebral fractures |
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Vertebral fractures cause (4) |
1. pain 2. disfigurement 3. dysfuntion 4. decrease in quality of life |
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Vertebroplasty |
injecting bone cement into the fractured vertebra under fluoroscopic guidance |
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Most osteoporotic fractures are caused by |
falls |
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Dietary calcium best sources include (3)
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1. milk 2. yogurt 3. some cheeses |
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Measurement of bone density requires the separation of the |
xray attenuating effects of soft tissues and bone |
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Mass attenuation coefficients of soft tissue and bone differ and depend on the |
energy of the xray photons |
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THe use of the 2 different photon energies (dual energy xray) optimizes the |
differentiation of soft tissue and bone |
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GE Lunar and Norland use |
rare earth filtering xray source |
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Hologic scanners use an |
energy switching system |
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The energy switching system |
synchronously switches xray potential between 100-140 kvp |
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Common physics problems of DXA (3) |
1. beam hardening in energy switching systems 2. cross over in k edge filtration systems 3. scintillating detector pileup in k edge filtration systems |
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What are attenuated differently within each patient (2) |
1. low energy xrays 2. high energy xrays |
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What is the most widely used parameter because it reduces the effect of body size |
BMD measured in g/cm2 |
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BMD = |
BMC/Area |
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BMD is based on a |
2D area - making DXA a projectional, or areal, technique |
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Pencil beam |
circular pinhole xray collimator |
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Pencil beam produces a |
narrow (or pencil beam) stream of xray photons that is recieved by a single detector |
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Pencil beam moves in what type of fashion across/along the length of the body |
serpentine - rastor/rectillinear |
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Pencil beam produces (2) |
1. good resolution 2. good reproducibility |
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Early scanners for pencil beam had relatively |
long scan times of 5-7 minutes |
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Array beam is also called |
fanbeam |
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Array beam has a wide |
slit xray collimator and a multielement detector |
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Scanning motion- |
one direction which greatly reduces scan time and permits supine lateral lumbar spine scans to be performed |
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Array beam introduces (2) |
1. geometric magnification 2. slight geometric distortion at outer edges |
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To avoid parallax careful |
centering of the body of interest |
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THe software takes into account the known degree of |
magnification and produces and estimated BMC and estimated area |
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3 statistics important in bone densitometry |
1. mean 2. standard deviation 3. % coefficient of variation |
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Mean |
average |
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SD |
variability that measures the spread of the data values around their mean |
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Smaller average |
smalled SD *smaller SD=better |
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%CV |
statistic that allows the comparison of variability between different data sets- whether or not they have the same mean |
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Smaller %CV means |
less variability and is preferred in bone densitometry |
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Goal of bone densitometry is |
accurate precise quantitative measurement by the scanner software, which requires stable equipment and careful, consistent work from the tech |
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Two important measures in bone densitometry |
1. precision 2. accuracy |
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Accury |
relates to the ability of the system to measure the true value of an object |
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Precision |
relates to the ability of the system to reproduce the same results in repeat measurements of the same object |
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Accuracy is determined primarily by |
the calibration of the scanner - set and maintained by the manufacturer |
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Precision most important performance measure in following a patients |
BMD over time - can be measures in vitro or in vivo |
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Vitro |
in an inanimate object |
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Vivo |
in a live body |
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Precision is commonly expressed as a |
% CV and a smaller value indicates better precision |
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BMD measurement from a patient is most useful when it is compared statistically with an appropriate |
sex matched reference population |
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In older adults, Z score is |
greater than T score |
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Z score indicates the # of |
SDs of the patients BMD is from the average BMD for the patients respected age and sex group |
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Z score is used to determined if the measured BMD is |
reasonable and if evaluation for secondary osteoporosis is warranted
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T score indicates the # of |
SDs the patients BMD is from the average BMD of young, normal, sex matched individuals with peak bone mass
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T score is used to assess |
fracture risk, diagnost osteoporosis and low bone mass (osteopenia) and determine if therapy is recommended |
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Discordance refers to the issue of different |
T scores occuring at anatomic sites within a patient, within populations and between modalities |
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Effective radiation dose (Sv) for DXA scans is |
low compared with conventional radiography doses |
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DXA is similar to the |
natural background radiation |
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Tech should wear an individual |
dosimetry device at the collar or on the side adjacent to the scanner |
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Most effective radiation safety practice is a |
knowledgable well educated and concientious DXA tevh |
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Patient History (4) |
1. scanning criteria 2. patient info 3. insurance info - DXA not universally covered by insurance 4. reporting info |
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WHose responsibility is to give the results to the patient |
physician |
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HIPPA for bone densitometry |
2005 |
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DXA scan results should be kept electronically indefinitely because all serial studies are |
compared with the baseline |
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DXA scan acquisition, analysis and archiving is controlled with a |
perrsonal computer |
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Computers consist of |
software and hardware |
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Software consists of programs |
written in code that instruct the computer how to perform tasks |
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Hardware compromises the physical components for |
central processing, input, output and storage |
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What procedures are performed in accordance with manufacturers recommendations |
longitudinal quality control |
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Common goal of ensuring that patients are scanned on |
properly functioning equipment with stable calibration |
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unstable calibrations can take the form of |
abrupt shifts or slow drifts in BMD |
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THese problems make BMD values |
too high/too low and prohibit a valid comparison baseline and follow up scans |
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Procedure uses either |
external/internal instruments to track the calibration of the DXA scanner over time |
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Lunar and Norland |
external calibration block to perform a calibration check |
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Hologic |
perform an automatic internal calibration check when the system is turned on |
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How many phantom scans should be performed and plotted before and after scanner preventative maintenance, repair, relocation and software or hardware upgrades |
10 |
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DXA has operating |
limits |
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Accuracy and precision may be impaired if bone mass is |
low, patient is too thick/thin, anatomy abnormal, or significant changes in soft tissue between serial scans |
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DXA calculations are based on |
soft tissue and bone |
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DXA is a ____ instrument used to monitor ___ change over time |
qualitative, BMD |
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Scans are more precise with less intervention from tech and DXA equipment reflecting a |
true biological change |
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What should be placed identically on the images?
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same scan settings and ROI |
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Results are |
comparable over time |
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What scans are most appropriate for predicting vertebral fracture risk |
spine |
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What can falsely elevate the BMD (4) |
1. degenerative changes 2. osteophytosis 3. scoliosis > 15degrees 4. compression fractures |
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What affects BMD
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artifacts |
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L5 |
scoliosis |
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L4 |
iliac crests |
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L1-L3 have what type of shape |
U shape |
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L4 has what type of shape |
H or X shape - appears to have feet |
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L5 looks like a |
sideways I or dog bone |
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Which is the widest |
L3 |
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WHich has the shortest transverse process |
L5 |
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Which is a bit taller than others |
L4 |
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Purpose of the leg positioning block |
1. reduce lordotic curve 2. open intervertebral spaces 3. reduce part image distance |
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The scan contains a portion of the |
1. iliac crest 2. half of T12 |
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Proximal femur: What scan is most important |
hip
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Difficult to perform properly and precisely because of (2) |
1. variations in anatomy 2. the small ROI |
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Patient is |
supine |
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Rotate leg |
15-25 degrees internally placing femoral neck paralled with tabletop and perp to xray beam |
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Good DXA hip scan |
lesser troch is small/barely visible |
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2 important DXA scans are present on the DXA forearm scan |
1. ultradistal region 2. 1/3 region (33%) |
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ultradistal region |
site of the common colles fracture |
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1/3 region (33%) |
measures an area that is primarily cortical bone near the midforearm |
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Nondominant forearm scanned because it is expected to have slightly |
lower BMD that the dominant arm |
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What is the most common problem in forearm scan acquisition |
motion |
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What is an established method using crosssectional CT images from commercial scanners equipped with QCT software and a bone mineral reference standard |
QCT |
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What has a unique ability to provide separate BMD measurements of trabecular and cortical bone and true volumetric density measurements in g/cm3 |
QCT |
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Lateral lumbar spine DXA scans can be performed with patient in |
decub using fan beam technology |
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VFA |
vertebral fracture assessment |
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VFA encompasses looking at the spine |
"morphometrically" in a lateral projection |
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THis means visualizing the |
shapes of vertebral bodies of the lumbar/thoracic spine |
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To determine if there has been some |
deformity with resultant compression of the vertebral bodies |
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VFA uses |
single xray absorptiometry (for image only) |
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VFA uses DXA |
(for images and BMD) lateral scans of thoracic/lumbar spines from level of about T4-L5 |
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WHole body DXA measures _____ and _____ for the total body and subregions of the body |
bone mass; body composition |
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Body composition can be measured as |
1. fat 2. fat free mass in grams or % body fat |
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WHole body DXA data are useful for studying |
1. energy stores 2. protein mass 3. relative hydration |
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Clinically, whole body scans are used routinely in |
pediatrics |
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FOR (2) |
1. body fat analysis in atheletes 2. patients with underweight disorders- anorexia nervosa |
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Diagnosis of osteoporosis is indicated by the presence of both a clinically significant |
fracture history and BMD Z-score less than of equal to -2.0 |
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A clinically significant fracture history is one of more of the following |
1. 2+ long bone fractures by age 10 2. 3+ long bone fractures at any age up to age 19 |
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DXA is the preferred method for assessing |
BMC and areal BMD |
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Hip is |
not a preferred measurement site in growing children |
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This is because |
variability in skeletal development |
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Peripheral bone density measurements include scans |
at the hand, forearm, heel, tibia |
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Peripheral measurements can predict overall |
risk of fragility fractures |
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Radiographic Absoptiometry is a modern adaptation of the |
early bone density technique |
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FRAX algorithm gives the |
10 year probability of a fracture |
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Main purpose of bone densitometry |
assist the diagnosis of osteoporosis by detecting low bone mass before fractures occur |
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What is a key factor in accurate and precise DXA acquisition and analysis |
quality assurance |
