Week 6 - Window Settings Flashcards
What is displayed on the monitor?
-cross sectional images (grayscale)
-patient info, scan parameters can be displayed in colour
What factors contribute to the image being viewed differently?
WW and WL
(Bone, soft tissue, lung)
T/F
Window sheeting’s are subjective, and have a personal preference component
True
T/F
Each hounsfield unit can have many shades of gray
True
How many HUs exist?
> 2000 HU values exist (more than)
How many different shades of gray can the monitor display?
256
How many shade of gray can the human eye differentiate?
40
T/F
The human eye cannot appreciate contrast differences of <10% (less than)
True
T/F
CT can show differences in contrast <1% (less than)
True
Assigns a certain number of housfield unit to each level of grey to overcome the limitation of the human eye not being able to differentiate contrast as much as what can be displayed
Display processor
Determined by window width ( grayscale)
What shade of gray is assigned to a higher HU?
Lighter shade of gray (bone)
What shade of gray is assigned to a lower HU?
Assigned a darker shade of gray (lungs)
What is the most common image processing technique used in CT?
Windowing
Refers to a method by which the CT image grayscale can be manipulated with the CT numbers of the image
Windowing
T/F
When manipulating CT numbers of various tissues using windowing, the data is not changing but the view of it is changing
True
-range of CT numbers in the image
-determines the maximum number of shades of gray that can be displayed on the CT monitor
Window width
The Center or midpoint of the range of CT numbers
Window level
What determines how many HUs will be displayed?
Window width
*software assigns the shades of gray
-values higher than the range will appear WHITE
-values lower than the range will appear BLACK
-indicates that there is a relatively long grayscale or a large block of CT numbers that will be assigned some value of gray
-the transition between black (low CT number) and white (high CT number) will be large
Wide window width
The transition between black and white will take place over a relatively few CT numbers
Narrow window width
What are some examples of anatomy that a wide window width is used for?
*greatly differing attenuations
-350-600HU body scan
-1000-2000HU lung and bone
What are some examples of anatomy that a narrow window width would be used for?
*similar densities
-50-250HU
-80-150HU brain
-100-250HU liver
Determines the HU values to be displayed on the screen - not the quantity
Window level
Brightens darker tones
Low window level
Darkens lighter tones
High window level
Brain window setting
WW
100
WL
30
Temporal bone window setting
WW
2800
WL
600
Neck window setting
WW
250
WL
30
Mediastinum window setting
WW
350
WL
50
Lung window setting
WW
1500
WL
-600
Soft tissue abdomen window setting
WW
350
WL
50
Liver window setting
WW
150
WL
30
*high contrast
Pelvis soft tissue window setting
WW
400
WL
50
Pelvis bone window setting
WW
1800
WL
400
Spine soft tissue window setting
WW
250
WL
50
Spine bone window setting
WW
1800
WL
400
T/F
Increased WW allows for more HUs to be included in the grayscale
True
Ex. More HUs will be included in each shade of gray
T/F
WL selection should be similar to the HU of the tissue of interest
True
WW varies, but is usually:
500-2000
T/F
Increased WW shows more anatomy but decreased image contrast
True
Increased WW can suppress noise; what is this good for?
Good for metal artifacts and obese patients
T/F
Tissues with a similar density should have a narrow WW
True
WW 50-500
Ex. Brain is composed of gray (HU 25) and white matter (HU 40)
*not much difference in tissue density
T/F
As window width decreases, contrast increases
True
What windowing algorithms are available to suppress noise and improve detail?
-standard algorithm
-smoothing algorithm
-edge enhancement algorithm
Usually used before previous algorithms, especially when a balance is needed between image noise and image detail
Standard window algorithm
-reduces image noise
-shows good soft tissue anatomy
-used where soft tissue discrimination is important to visualize very low contrast resolution
Smooth window algorithm
-emphasizes edges of structures and improves detail
-creates image noise
Edge enhancement window algorithm
Edge enhancement is used in exams where fine detail is needed. What are some examples of these exams?
-inner ear bones
-bone structures
-thin slices
-fine pulmonary structures
Differing WW settings
Fixed WL setting
As WW decreases, contrast increases
Differing WL settings
Fixed WW setting
As WL decreases, the picture changes from black to white
(Higher CT numbers are displayed)
Opposite is true also
