Bone scan Flashcards
What are the three phases of a bone scan and when do they happen?
1) Vasculature - Immediate
2) Soft Tissue - 5-10 min
3) Bone - 2-3 hours
What is the activity of 99mTc MDP that is given to smal animals?
Small dogs and cats = 5mCi
Meduim dogs = 10-15mCi
Large dogs = 20-25mCi
Giant dogs = 30mCi
What are the two types of radiopharm used in bone scans?
99mTc-HDP (oxidronate)
99mTc - MDP (methylene diphosphonate)
What is the difference of the blood supply in large animals vs small to the long bones?
The bone vessels do NOT cross the physis to supply the epiphysis in dogs and cats but they do in large animals.
Articular cartilage is what type of cartilage?
Hyaline cart
What is the main unit of bone and what is in the center?
A osteon is the main unit and the haversian canal is in the middle which allows blood flow through it and supplies surrounding osteocytes
What is another name for the bone matrix?
Osteoid
What is the main inorganic component of osteoid?
Hydoxyapatitie crystal
What is uptake of 99mTc MDP directly related to?
Osteoblastic activity
Blood supply
Which is more rapidly cleared from the body…99mTc HDP or 99mTc MDP?
99mTc HDP - Therefore the bone phase is 1-2 hours rather than 2-3 hours
What is the bone phase for HDP vs MDP?
HDP - 1-2 hours
MDP - 2-3 hours
What happens if air is injected into a bottle of MDP? What will you see on a scan?
It will produce oxidative degradation which will produce 99mTc04 resulting in thyroid, salivary, gastric, liver or spleen
Perfusion of callcelous bone is how much higher than compact bone?
5-13x higher and therefore why you have it light up on bone scans
One of the most common artifacts in a bone scan is what?
perivascular injection…this will cause a hot spot where the injection site was and cause the lymph node to light up.
This is why they suggest to inject in another leg besides the one that is lame
What type of collimator is used in bone scans?
Low-energy
What type of scan is used for the vascular phase?
Dynamic - everything else is static
Non-skeletal uptake of 99mTc-MDP happens with what?
Dystrophic or metastatic mineralization
Rhabdomyolysis
Thyroid if Tc is bad
Hepatic and spleen is Tc is oxidized
What would there be a decrease in skeletal uptake or decrease in the target to background ratio?
- Decreased cardiac output
- Soft tissue mass overlying area of interest
- Generalized edema
- Renal failure
- Old age
Bone scans tend to over or underestimate the extent of a primary bone tumor?
Over estimate (bloom)
What neoplastic disease can have a normal bone scan?
Multiple myeloma
What is the most affect skeletal region from mets?
Axial
Septic arthritis and osteomyelitis are differentiated from other diseases due to what?
The marked increase in the vascular and soft tissue phases
Can bone scans tell if an infection site is active or not?
NO.
Uptake in the area of the medial coronoid has two differentials…
Medial coronoid disease
Proximal radial physis
When should you do a bone scan after trauma to look for fractures?
3-7 days to allow the bone activity to spike
What arteries supply the femoral heads?
70% from the medial femoral arteries (external iliac)
30% from the lateral circumflex artery (femoral)
How long might it take to get a negative on bone scan from a previous fracture?
2 years
Contaminated stall with 99mTc should not be cleaned until how many half lives have past? How many hours is that?
10 half lives or 60 hours
What is the dose of 99mTcMDP that is needed for a horse
0.2-0.3mCi/kg
At auburn ~ 250mCi per horse
What inorganic compound does 99mTc MDP attach to?
hydroxyapatite crystal
What does the m mean in 99mTc?
meta stable — it already gave off a beta particle and is now waiting to give off a gamma ray
What is the half-value layer for 99mTc?
5cm … so there is 50% attenuation at 5cm of soft tissue
What ortho lesions do not cause increase in uptake?
OCD or osseous like cyst
Acepromazine can be used in horse bone scans if what happens?
If you have cold legs because Acepromazine is a peripheral vessel dilator
Why does rhabdomyolysis cause increase in ST uptake which 99mTcMDP?
They bind with calcium salts in the muscle
DDx for photopenic area of bone?
Infarct
Avascular necrosis
Tumor necrosis
What does lidocaine solution cause in a bone scan?
Increase in uptake at the injection site
How long does increased uptake secondary to a lidocaine block last?
Up to 17 days
