CT and radiography Flashcards
CT matrix size
512x512, 2 bytes/pixel, 0.5 MB
CT spatial resolution
100 um FWHM
-depends on FOV, detector size, slice thickness
daignostic CT effective dose
15 mSv
dose for CT taken for CT/PET for anatomy and attenuation correction purposes
2 mSv
what must be done to mAs if kV is increased by 15% to maintain Kair at image receptor
halve mAs
k edge of iodine
33 keV
what are filters made from
mostly Al, some from Cu (unless mammo)
lung Z and bone Z
Z = 7.5 lung
Z= 12 bone
what is beam intensity proportional to?
kV^2
mAs
CT beam quality
HVL is 6-10 mm Al
radiography beam quality
HVL is 5 mm Al
Kair at image receptor
a few uGy
Mo kedge
20 keV
CsI kedge
36 and 33 keV
Rh kedge
23 keV
Ag k edge
25 keV
W k edge
70 keV
Pb k edge
88 keV
Ba k edge
36 keV
O2 k edge
0.5 keV
Ca k edge
4 keV
film with steeper gradient means what contrast?
better contrast
what % of xrays does film absorb vs screen film?
-film absorbs 1 %
-screen film absorbs 50%
what has BEST resolution?
photoconductor
-because charge is not dispersed by detection