Unit 4-Bone mineral densitometry Flashcards
What is osteoperosis?
-Generalized skeletal disease in which there is low bone mass, deterioration of bone tissue and an increase in bone fragility
What are the 2 types of bone? How much does it make up each?
- Cortical bone-80%
- Trabecular bone-20%
What minerals are bones primarily made of?
Calcium and phosphate
What area of bone is most affected with osteoperosis?
Trabecular bone
What are the functions of trabecular bone?
- Adds strength without excessive weight
- Red bone marrow production
- Supports compressive loading and flexibility
T/F?
With osteoperosis, the bone is no longer remodeling.
False, there is constant remodeling of bone
What is the function of osteoclasts?
Break down and reabsorb bone
What is the function of osteoblasts?
To build bone and form it
What is the first radiographic sign of healing of a fracture?
Bone reabsorption
What determines bone mass increase or decrease?
The rate of resorption compared to the rate of formation
T/F
When the osteoblast activity is higher than the osteoclast activity, there is a net loss of bone mass.
False; when osteoclast activity is higher than osteoblast activity, there is a net loss of bone mass
At what age do we reach peak bone mass?
At around age 30
At what age do women and men begin to start decreasing in bone mass?
W=50 years
M=60-65
Why do women start loosing bone mass earlier?
More pronounced at menapause because of the loss of bone preserving estrogen
Bone mass in later life is a function of what two main factors?
- The peak bone mass attained in early adult life
- The rate of age related bone loss
What does BMD exams measure?
The bone mineral content and the bone mineral density based off of the amount of attenuation occuring
What are the purposes of the values obtained from BMD imaging?
- To asses bone strength
- Assist with diagnosis of diseases assosiated with low bone density
- Monitory the effectiveness of treatment
- Predict risk of future fractures
What is the stage right before osteoperosis?
Osteopenia
Name 3 risk factors assosiated with osteoporosis?
- Increased age
- Caucasian
- Female
How does osteoperosis appear radiographically?
- Increased radiolucency in bone
- Verticalization of trabeulae (loss of horizontal trabeculae)
- Increased radiodenisty of the cortical rim
What is a common way to describe the appearance of osteoperosis?
Picture frame appearence
Where are the changes of osteoperosis most prominent in?
- The axial skeleton
- In the long ends of bones in appendicular skeleton (proximal femur, distal radius, calcaneus
T/F?
Most osteoporotic fractures are caused by falls.
True
What fracture assosiated with osteoperosis is most common?
Vertebral fractures (often compression)
What are the 3 treatment options for osteoperosis?
- Bisphosphonates
- Calcitonins
- Parathyroid hormon, Vit D, and Ca2+
What is the function of bisphosphonates?
They bind to the surfaces of the bones and slows down osteoclast action
What is the function of calcitonins?
Decrease osteoclast acitvity
What is the most versatile and commonly used technique of preforming bone densitometry exams?
Using dual energy x ray absorptiometry (DEXA/DXA)
What are 3 benefits of DXA over other methods?
- Low radiation dose
- Easy to use
- Good precision
What is the main use for DXA?
Diagnosis of osteoperosis
What are the 2 systems/manufactuerers for achiving dual energy exams for DXA?
- Hologic system
- Ge+Norland systems
How does the hologic system work?
It synchronously witches betwen 100 kVp and 140 kVp, resulting in effective photon energies of 40 and 80 kVp
How does the GE and Norland systems work?
-2 peaks are produced by x ray beam passing through cerium or samarium filters
-Cerium filter is used with a 100kV to give effecitve photon energies of 40 and 70KeV
T/F
DXA takes into account the volume of the tissue.
False
What assumption is made when using the mathematical equation to calculate bone density values?
Assumes that the body is divided into 2 compartments; soft tissue and bone
T/F?
It is necessary to eliminate soft tissue to measure the x ray attenuation of bone alone.
True
Why are there 2 different equations to figure out the bone density?
Because the u will be different for the 2 different x ray energies (one for low and high energy)
In what pattern does the detector generate information?
Bone profile is generated pixel by pixel
T/F?
A 3 dimensional area is calculated from the recieved information after the scan.
False; 2 D area is calculated
What algorithm is responsible for evaluating the bone profile?
The proprietary edge detection algorithm evaluates the bone profile and identifies where bone begins and ends after aquesition.
What occurs after the proprietary edge detection algorithm evaluates the bone profile?
- The software sums the number of pixels containing bone to calculate the BA (bone area) that was scanned
- The bone density is then calculated across bone profile
If there is a decrease in BMC, what is the result with BMD?
It decreases
If there is a decrease in BA, what does this result in BMD?
An increase in BMD
T/F?
A change in a patients BMD over time should be from a change in BMC, not area.
True
What could a change in bone area be due to?
From positioning or software errors
What is the defenition of DXA?
It is a projection technque in which 3D objects are analyzed as 2D
T/F?
Given 2 bones of identical volume, the smaller bone will have a higher areal BMD
True
What are the 2 systems of DXA?
- Pencil beam system
- Array beam system
How long does a scan take using the pencil beam system?
3-10 min
How long does a scan take using the array beam system?
Around 30 seconds
How does the pencil beam system work?
- A narrow stream of x-ray photons froom pin hole collimation are recieved by a single detector
- The x-rays and detector move in a rectillinear pattern across and along the length of the body
How does the array beam system work?
- It is a fan beam with wide slit collimation and a multicell detector
- It allows simultaneous measurements of intensities transmitted through the body
T/F
In the array beam system, the scanning motion is reduced to one direction.
True
T/F
Pencil beam sytems have software that accounts for blur and distortion.
False; Fan array beams do
What is paralax?
Divergence
When can paralax occur with DXA?
When not centering correctly with a pencil beam system
What are contraindications for imaging a specific part of the body using DEXA?
- Pregnancy
- recent oral administration of contrast (less than 5 days)
- Bone diseases in the area of imaging (spondylarthrosis)
- Previous fracture or joint replacments
What are the 2 usual areas of anatomy that are imaged in a DXA exam?
Lumbar spine and proximal femur
When the hip or spine cannot be measured, what area of anatomy is imaged?
The forearm
What area of the lumbar spine does the scan include?
L1-L4
T/F
Vertebrae with changes due to fracture or focal lesions will be exluded
True
What is the minimum required vertebra in a DXA exam?
2 minimum
What ROI of the femur is commonly used for measurements?
The femoral neck
What is the main cause of erros in the estimation of BMD?
Positioning errors and inadequate placment of ROIs
How should the patient be positioned when imaging the L spine?
Paitent lying supine with their legs flexed over a support pad to reduce lordosis
How should the patient be positioned for the hip imaging?
The patient should lie supine with the legs slightly in abduction and internally rotated to reduce forshortening
How should the patient be positioned to image the forearm?
The patient is seated, side against the table with the arm resting on tabletop with the palm of the hand facing downwards
T/F
With DEXA examinations, shielding or special protection measures for the technlogist are not ussually required.
True
What would the scattered radiation dose that the technolgist would recieve after being 1m away from the table and preforming 4 hip studies, 4 lumbar spines per hour?
4 microSv
What is bone mineral content?
It is the quantity of calcium estimated by the enrgy absorbed by it in a specific region
What is bone mineral density?
It is the mean quantity of mineral per unit area
What are the SI units for BMD?
g/cm^2
What is the SI unit for BMC?
g
What is the SI unit for area?
cm^2
When are BMD measurements from a patient most useful?
When compared statistically wtih an appropriate sex matched reference population
Why is it important that a patient goes to the same clinic for following DEXA examinations after the initial exam?
Because BMD values from scanners made by different manufcacturers cannot be directly compared
What is the T-score?
It is the number of standar deviations the patients BMD is above or below the mean for the young adult (with peak bone mass) reference population of the same sex
What T score is considered to be normal?
Above -1SD
What T score is considered to be osteopenia?
Between -1 and -2.5 SD
What T score is considered to be osteoporosis?
Below -2.5
What is the rule of thumb for risks of fracture?
For each 1 SD decrease in T score, the risk of fracture increases 1.5-2.5 times
What is the z score?
It is the number of standard deviations the patients BMD is above or below the mean ference population of the same race, sex and age
Who is the z score used for?
Is used premenopausal women, in men younger than 50 years, and in children and adolescents
What does a positive z score indicate?
That the person has a better than average bone mass when compared to individuals in the same age group
What does a Z score below-2 indicate?
That the bone mass is below the expected range
What is the Z score used for?
To determine if the measured BMD isi reasonable and if evaluation/treatment for osteoporosis is warranted
How far away should the tech be standing for pencil beam scanners?
3feet away
How far away should the tech be standing for array beam scanners?
9ft away
What are the limitations of DXA?
- Cannot predict who will experience a fracture, but can provide risk indications
- Presence of compression fractures or osteoarthrosis may interfere with accuracy of test
- Central DXA machines are more expesive even though they are better
- Baseline is always required on same machine
What area of examination is best for predicting femoral fractures?
Examination of the proximal femur
What area of anatomy is the beset site for follow up measurements, and why?
The spine, because treatment changes are ussually the largest at this site.
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