Bone scan/DEXA Flashcards
DEXA scan dose
0.4 microsieverts
DMSA dose
0.001-0.4 mSV
what is it used for
how is it performed
what happens to patient
used to estimate BMD
firing of 2 x rays at hip or spine, low dose x ray beam with two distinct energy peaks
one ab by soft tissue the other by bone
absorption subtraction allows for BMD calculation
takes 5 minute, supine and clothed, no metal on clothes
scores from BMD
osteoporosis
osteopenia
normal
compared sex matched controls to give WHO defined T score which is based on SD from healthy adult
more than minus 2.5 is osteoporosis
-1.5 to -2.5 is osteopenis
normal is -1.0 or above
z score
comparison of BMD with age sex and ethnicity matched, used in young men, premenopausal women and children
bone scan subtance
methylene diphosphonate medronate
where taken up in bone scan
taken up by growing bone and excreted in urine
bone scan process
well hydrated
encourage void frequently once administered
empty bladder before third phase images
third phase - three hours after injection , whole body image where camera moves along length patient aking 20 min,
or spot views static images of 5 min each
bone scan process
well hydrated
encourage void frequently once administered
empty bladder before third phase images
third phase - three hours after injection , whole body image where camera moves along length patient aking 20 min,
or spot views static images of 5 min each
Injection of Tc99 Methylene Diphosphonate IV, Wait 3 hours. Gamma camera scan. AP, PA and other views PRN. 3.6mSv (equivalent to 180 CXRs and similar to an IVU).
spect study
gamma camera rotates all the way round taking images many agles
20 min
computer then reconstructs these into cross sectional images
locating 3 d images
spect ct can be gammera camera incoporating ct scanner in their design
do ct scan immediately after spect without moving patient
giving co registered spect and ct images
what do hot spots indicate on bone scan
increased bone met not specific to mets fractures pagets degenrative disease
superscan
Advanced widespread metastases that
have spread uniformly throughout the skeleton (a “superscan”) may be mistaken for
normal if only the relative counts in different bones are viewed. This can be avoided
by considering the absolute number of counts acquired or by comparing bone with
other normal areas such as kidneys, soft tissue, or distal limbs which are usually spared. A superscan often shows no renal activity because of the avid bone uptake
of the radionuclide.
bone scan dose
3.6mSv
MDP binds to in bone scan
The phosphonate compounds bind to bone by chemo-adsorption to the hydroxyapatite crystal.
Technetium 99m decays by releasing 140-kV gamma rays, which are detected by a gamma camera.
The appearance of activity on the scan usually reflects osteoblastic activity in bone.
differential for bone scan hot spot
Metastases. Infections Fractures, Trauma Pagets Arthritis
