CT Scans

Question 1

what is a Voxel?

Answer 1

pixel in 2D from CT scan

Question 2

increased attenuation means?

Answer 2

whiter more xrays absorbed

Question 3

decreased attenuation means?

Answer 3

darker, fewer xrays absorbed

Question 4

how many housfield units is water?

Answer 4

0

Question 5

how many housfield units is air?

Answer 5

-1000

Question 6

how many housfield units is bone?

Answer 6

+1000

Question 7

contrast adds how many hounsfield units?

Answer 7

+130

Question 8

what is windowing?

Answer 8

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

Question 9

danger of preset windows?

Answer 9

may mask pathology

Question 10

2 main groups of contrasts:

Answer 10

intravascular

gastrointestinal/rectal

Question 11

when do you not sure intravascular agents for?

Answer 11

skeletal
lung
renal calculi

Question 12

how does a positive contrast agent look on xray?

Answer 12

hyperdense because higher atomic number

Question 13

what does it mean when kidney is more dense than muscle?

Answer 13

used contrast

Question 14

what does it mean when kidney is the same density ofmuscle?

Answer 14

no contrast, normal

Question 15

3 phases of intravascular contrast?

Answer 15

arterial phase: early
venous phase: later
late phase: in kidney excreted in the urine

Question 16

Reformats do what?

Answer 16

give you clear display of a system, like with curved formating to see just the renal system

Question 17

why does an acute haematoma show up hypredense on CT?

Answer 17

more iron, higher atomic number

Question 18

gall stones see in CT?

Answer 18

not really. better for kidney calculi

Question 19

cysts look like what on CT?

Answer 19

look like water

Question 20

puss looks like what on CT?

Answer 20

like water

Question 21

renal caculi look like what on CT?

Answer 21

hyperdense

Question 22

pure fat density on CT?

Answer 22

less than water

Question 23

liver usually more or less dense than blood?

Answer 23

more dense

Question 24

contrast in brain tumour shows up how?

Answer 24

leaks out because no intact BBB

Question 25

cytotoxic oedema of brain affect white or grey matter?

Answer 25

both

Question 26

vasogenic oedema of brain affect white or grey matter?

Answer 26

white

Question 27

CT angiography does what?

Answer 27

using a CT scan to image the vessels only

Question 28

what is CT-IVS

Answer 28

CT - intravenous cholengiography

used for gall stones/biliary

Question 29

what can cause artifacts in CT?

Answer 29

patient movement

metal objects