CT Scans Flashcards
what is a Voxel?
pixel in 2D from CT scan
increased attenuation means?
whiter more xrays absorbed
decreased attenuation means?
darker, fewer xrays absorbed
how many housfield units is water?
0
how many housfield units is air?
-1000
how many housfield units is bone?
+1000
contrast adds how many hounsfield units?
+130
what is windowing?
when you take a small slice of an area of interest of the CT to displayless gray scales as we can only perceive 30 shades of grey
danger of preset windows?
may mask pathology
2 main groups of contrasts:
intravascular
gastrointestinal/rectal
when do you not sure intravascular agents for?
skeletal
lung
renal calculi
how does a positive contrast agent look on xray?
hyperdense because higher atomic number
what does it mean when kidney is more dense than muscle?
used contrast
what does it mean when kidney is the same density ofmuscle?
no contrast, normal
3 phases of intravascular contrast?
arterial phase: early
venous phase: later
late phase: in kidney excreted in the urine
Reformats do what?
give you clear display of a system, like with curved formating to see just the renal system
why does an acute haematoma show up hypredense on CT?
more iron, higher atomic number
gall stones see in CT?
not really. better for kidney calculi
cysts look like what on CT?
look like water
puss looks like what on CT?
like water
renal caculi look like what on CT?
hyperdense
pure fat density on CT?
less than water
liver usually more or less dense than blood?
more dense
contrast in brain tumour shows up how?
leaks out because no intact BBB
