Image Display: Chapter 4
Display devices can be either:
-A cathode-ray tube (CRT) -Some form of flat panel, such as TFT LCD
Monitors consist of:
-The display device -Circuitry to generate an image from electronic signals -An enclosure
Images cannot be displayed with a different shade of gray for each HU because:
-There are more 2,000 Hounsfield values; most monitors can only display 256 shades of gray -The human eye can differentiate only a fraction of those shades
the human eye cannot appreciate contrast differences of less than ____, whereas CT scanners can easily demonstrate difference of less than ____
10%, 1%
Many studies require each image to be viewed at _____ window settings
2 or more
A window width of 90 is most likely used to display an image of the a.Lung b.Femur c.Brain d.Abdomen
C
•The selected window width is 400 •The selected window level is 50 •Which HUs are displayed on the image as shades of gray? a.-200 to 200 b.-150 to 450 c.-150 to 250 d.350 to 450
C
first step in many display and measurement functions
Defining the size, shape, and location of the ROI
The window width determines the number of ____ represented on a specific image
HU
A cursor (+) displays a measurement of the ___ of the ____ that the cursor covers
HU, pixel
increasing the window width assigns more ____ to each ____
HU, shade of gray
circular, but may be elliptic, square, or rectangular, or may be custom drawn by the operator
ROI
values lower than the elected range will be ___
black
CT images are usually displayed on a ____ or ___ monitor
black and white, color
window level selects the ___ of ____
center CT value, window width
Digital-to-analog converters change the digital signal from the ____ back to an ____ so that the image can be displayed on the monitor
computer memory, analog format
The gray scale is used to ___ CT images
display
some instances CT images are transferred to ___
film
Wider window widths encompass ____, but subtle ____ is lost
greater anatomic diversity, density discrimination
CRT monitors are ___, ___, ___ and ___ than need LCD monitors
heavier, bulkier, hotter, and less durable
By convention, the gray scale assigns ___ values lighter shades of gray
higher HU
LCD monitors produce ____ and _____
higher luminance and high spatial resolution
In general, wide window widths (500-2,000) are best for imaging tissue types that vary greatly, when the goal is to see all of the various tissues on one image such as ____
lung
Multiformatcameras transfer the image displayed on the ____ to ____
monitor, film
The camera may be a _____, although most modern CT systems include a ____
multiformat camera, laser camera
ROI provides an averaged measurement of all of the ____ within the ____
pixels, ROI
Window width selects the ____ of ___
quantity, HU
Window level selects the ___ of ____
range, HU
The window level should be set at a point that is roughly the ____ as the _____
same value as the average attenuation number of the tissue of interest
Imaging departments typically have an established ____ for each type of exam
setting
because many factors have an effect, technologists must adjust ____ in individual situation
settings
Window level determines which HUs are displayed as ____
shades of gray
film used in CT consists of a ____
single emulsion
when an ROI is used, the ____ is also displayed
standard deviation
"Ideal" window settings are somewhat
subjective
Because wider window width settings decrease image contrast, they ____
suppress the display of noise on an image
laser cameras bypass the ____ entirely
video system
Adjusting the window width and window level will change the way an image is ____ on a monitor
viewed
HU measurements may be affected by
volume averaging or image noise
valued higher than the selected range will be ____
white
Window level is also called ____
window center
Other Image Display Options
•Distance measurements •Image annotation •Reference image •Image magnification •Multiple image display •Histogram •Multiplanar and three-dimensional reformatting
