Bone Scans Flashcards
what physical property do bone scans use?
(radioactive isotopes)- most commonly gamma emitting isotopes
what are the properties of an ideal radionucleotide?
- small photon energy (50-500 Kev)
- physical 1/2 life > prep time
- biological 1/2 life >exam time
- low toxicity
- stability
- a suitable chemical form for study of teh specific organ
- min. particulate emission
what radioisotope did the 1st bone scans utilize? where did it localize to?
(strontium 85 & 87m)
- localized within skeleton by exchanging w/ Ca2+ in bone matrix
- poor skeletal detail though
Where does Tc-99 localize to?
osteoblasts- on the surface of hydroxy apatite
properties of Tc-99
physical 1/2 life of 6 hrs
photon energy 140kev @90%
describe the specificity vs. sensitivity of Tc-99 bone scan.
is very sensitive but not specific (bc there are many reasons for bone turnover)
what are the 3 (and potential 4th) phases of diagnositc study for Tc-99 scan?
- blood flow phase
- blood pool phase or tissue phase
- delayed imaging phase or bone imaging
- delayed phase
* time course is 3 sec, 3 min., 3 hrs, 24 hours, respectively
What is the Gallium-67 citrate scan used most oftenly for?
used for neoplasms (lymphoma) or inflammatory disorders
what are the 3 primary mechanisms of localization for Gallium scan?
- leukocyte localization
- lactoferrin and transferrin binding & siderophores of bacteria
- bacterial uptake by phagocytes
what is the 1/2 life for gallium- 67 citrate scans?
half life is 78 hours
slower rate of excretion
when is gallium imaging performed ?
6-24 hrs post injection for infection
24-72 hrs post injection for neoplasms
Where does Indium-111 localize to?
binds to cytoplasmic component of WBC cell mb
Describe the sensitivity vs. specificity for Tc-99 vs. Indium scan.
Tc-99 is more sensitive but Indium-111 is more specific for infectious process
What is the Ceretec scan?
Tc-99 labelled WBC’s that has increased specificity for infectious processes
*is almost a hybrid of Indium-111 and Tc-99 scan
