17: Bone Scans - Bennett Flashcards
physical v. biological half life
amount of time it takes for 50% degradation
* needs to be greater than prep time
amount of time it takes for 50% of the isotope to remain in the organism before excretion
* needs to be greater than exam time
how does a bone scan work?
radiotracer injected into a vein emits gamma radiation as it decays
a gamma camera scans the radiation area and creates an image
strontium 85 &87
localized within the skeleton by exchanging w/ calcium in bone matrix
tec 99
rapid osteoblastic mediated chemical absorption on the surface of hydroxy appetite
physical half life 6 hrs
3 phase study =
1: dynamic of blood flow phase (3 sec)
2: blood pool or tissue phase (3min)
3: delayed imaging phase or bone imaging
(4th - delayed, ppl with poor circulation)
diagnostic tracer used for neoplasms (lymphoma) and inflammatory disorders
gallium 67 citrate
less dependent on blood flow
half life 78 hrs
slower rate of excretion
3 primary mechanism of localization for gallium 67
leukocyte localization
lactoferrin and transferrin binding and siderophores of bacteria
bacterial uptake by phagocytes
when is imaging done with gallium 67 scan for infection? neoplasms?
infection: 6-24 hrs post injection
neoplasm: 24-72 hrs post injection
oxine labeled WBC
indium 111
binds to cytoplasmic component of WBC membrane
dependent on chemotaxis of leukocytes
1/2 life 67 hrs
tec 99 labeled WBC
ceretec
increased specificity for infectious processes
bone scan results for acute osteomyelitis
all will be positive
bone scan results for inactive chronic osteomyelitis (
tc 99 phase 3 positive
ga67 and indium negative
acute cellulitis bone scan results
Ga67(diffuse) and indium positive
Tc 99 - positive in phase 1 and 2
septic arthritis bone scan results
tc 99 - phase I and II postive
ga67 and indium positive
fracture bone scan results
tc 99 positive
negative ga67 and indium
