Bone Scans Flashcards
What does a DEXA scan measure?
bone mineral density (bone mass)
What is considered the gold standard of bone scans for patients with suspected osteoporosis?
DEXA
Osteoporosis =
decreased osteoblastic activity + increased osteoclastic activity
Osteoblastic
formation of bone
Osteoclastic
resorption of bone
Is osteoporosis an increase or decrease in total bone mass or density?
decrease
What does osteoporosis increase the risk of?
fractrures
DEXA generates x-ray beams at which two different energy levels?
soft & bone tissue
Computer software reconstructs a DEXA scan to produce an image and quantifies the three components of total body composition? What are the three components on total body composition?
- bone mineral density
- total fat mass
- lean mass
What are the general recommendations for a DEXA scan?
- females 65 y/o or older
- males 70 y/o or older
- fx sustained after age 50
- female of menopausal age w/risk factors
- post-menopausal female under 65 w/risk factors
- male 50-69 w/risk factors
What is considered lean mass?
muscle, water, proteins & internal organs
What are common areas for DEXA imaging?
- hip
- heel
- lower back
What two computed scores are given to patients in their DEXA report?
t-score & z-score
T-score
a comparison of an individual’s bone density to that of an average, young, healthy adult
Z-score
compares the patient’s bone mineral density with that of an age-matched healthy adult
The ______ the density, the _________ the risk of the fracture.
lower, greater
What does a T-score greater than -2.5 indicate?
osteoporosis
What does a T-score between -2.5 to -1 indicate?
low bone density
What does a T-score greater than -1 indicate?
normal bone density
1 SD =
approx. 10% difference in bone mass
What does a standard deviation of 0 indicate?
does not deviate from the average
What does a standard deviation of +1 or +2 indicate?
bone mass is 10-20% above the average, young, healthy adult
What does a standard deviation of -2 or -3 indicate?
bone mass is 20-30% below the average, young, healthy adult
What does a Z-score greater than -2.0 indicate?
normal bone density
What patient populations would one use the z-score instead of the t-score?
- children
- teens
- women w/periods
- younger men
What is bone scintigraphy?
nuclear medicine imaging of the skeleton
What is used in bone scintigraphy to diagnose disease?
radiopharmaceuticals
What is bone scintigraphy based on?
physiological or functional changes of the skeletal tissue
What are the two types of imaging that can be obtained from bone scintigraphy?
whole body & spot imaging
What is whole body imaging helpful with?
non-focal complaints
- bony metastases
- diffuse arthralgia
What is spot imaging helpful with?
focal complaints
- isolated stress fx
- unexplained rib pain
- indeterminate tumor on x-ray
- multiple projections
Explain the science behind bone scientigraphy.
- patient inject w/radioactive tracer
- radioactive substance travels through the body & binds to sites of osteogenesis
- radiation in substance is detected by a gamma camera in areas of increased blood flow & bone formation
What are the four phases of bone scientigraphy?
- flow phase
- blood pool phase
- delayed phase
- fourth phase
What is the timeframe for the flow phase?
60-90 secs post injection
What are the results of the flow phase?
- perfusion & tissue vascularity
- blood flow to an area
What is the time frame for the blood pool phase?
approx. 10 mins post injection
What are the results of the blood pool phase?
- blood pool
- inflammation causes capillary dilation & increased blood flow
- increased soft tissue activity
What is the time frame for the delayed phase?
2-6 hours post injection
What are the results of the delayed phase?
- reflects rate of bone turnover
What is osteogenesis?
nonspecific response of bone to range of stimuli such as
- physiological growth or rebuilding
- mechanical stress or injury
- infection or tumor
Can you diagnose w/ a bone scan alone?
No - you should combine w/clinical exam & follow-up w/PCP
On a bone scan, how does normal bone appear?
transparent & grey
On a bone scan, how does abnormal bone appear?
darker black areas (radiotracer has been increasingly absorbed)
What are normal bone scan findings?
symmetric uptake
- increase uptake in articular surfaces (shoulders, hips, knees, ankles, feet, etc.)
- areas closer to camera
- epiphyseal plates in children
What are abnormal bone scan findings?
- subtle fx
- avascular necrosis
- metabolic bone disease
- occult fx
- osseous metastatic tumors
- infections
On a bone scan, how do we differentiate between shin splints versus a stress fx?
shin splints = linear activity along tibial cortex
versus
stress fx = isolated hot spot
What to keep in mind when considering an individual for bone scintigraphy?
- requires adequate kidney function
- requires adequate hydration
- requires adequate injection into blood stream NOT soft tissue
When do we typically utilize bone scintigraphy?
when patients are unable to communicate area of pain or discomfort
Is bone scintigraphy best used as a sensitivity or specificity test? Why?
sensitivity - it provides us w/an early indicator of increased bone activity.
lacks specificity because we are unable to identify WHY the increased uptake has occurred
What does a PET scan help visualize & measure?
normal vs. abnormal cellular function
Why is a PET scan used?
it can obtain imaging of metabolism at a molecular level before the disease or condition appears
What is a PET scan sometimes combined with?
CT or MRI
What is the science behind a PET scan?
- radioactive tracer via injection, inhalation, or swallowing
- traces bound to carrier molecule
- areas of body that normally absorb glucose absorb the tracer
- tracer decays & emits positron that interacts w/electrons
- releases gamma rays
- detected by gamma camera
- converted to 3D image
In a PET scan, how do areas w/increased metabolic/chemical activity appear?
areas w/a high energy demand appear as “hot spots”
