pixel/voxel/hounsfield numbers

Question 1

Define pixel size

Answer 1

Question 2

complete sentance

pixel size must be matched to ……… 1

Answer 2

reconstruction filter

Question 3

Define voxel 1

Answer 3

this is a digital representation of volume elements x , y and z dimensions

Question 4

What defines the voxel depth?

Answer 4

slice width - 0.5 -10mm

Question 5

complete sentance

Spatial resolution is affected by x, y & z dimensions ………. 1

Answer 5

Spatial resolution is affected by x, y & z dimensions

Question 6

define a ct number

Answer 6

Question 7

state CT numbers for the following

water

air

bone

Answer 7

water = 0

air = -1000

bone 1000 to 3000

Question 8

How many total gray levels are there and define the range 2

Answer 8

4096 total gray levels

-1024 to +3071

Question 9

How many bits of information is used to encode the gray scale?

Answer 9

12 bit

Question 10

with windowing 4

how would you describe the following

brain

lung

assesing the bone for subtle fractures

soft tissue lesions

Answer 10

1. to asses the lung you need high contrast wide window
2. to asses the brain gray to white matter low contrast wide window
3. high contrast for bone narrow window
4. soft tissue lesions low contrast narrow window

Question 11

State a typical hu for brain tissue

Answer 11

35 - 40 hu

Question 12

which is WL and WW

40

400

Answer 12

40 = WL

400 = WW

Question 13

What would be a typical WW for

brain

what would be a typical WL and WW for

lung

Answer 13

80 - 120hu

Lung WW 2000

WL 40

Question 14

What does MPR and what would they clinically be used for

3

Answer 14

Multiplanar reformats

colonoscopy and bronscopy