An imaging system with higher spatial frequency
has better spatial resolution.
Spatial resolution in digital imaging is limited by
pixel size.
Modulation Transfer Function
can be viewed as the ratio of image to object as a function of spatial frequency.
Imaging system spatial resolution is spatial frequency at
10% MTF
Dynamic range
is the number of gray shades that an imaging system can reproduce.
Postprocessing
allows visualization of all shades of gray.
Image noise
limits contrast resolution.
What is image detail (spatial resolution) determined by?
system MTF
Contrast resolution is limited by?
Noise or SNR
Spatial resolution in screen-film radiography is determined principally by?
focal-spot size.
Contrast resolution
is preserved in digital imaging, regardless of dose.
Technique creep
should replace dose creep.
Patient dose in DR should be low because of?
high DQE (detective quantum efficiency)
DQE
is a measure of x-ray absorption efficiency.
The scatter xray beam
has lower energy than the primary xray beam.
The basic photometric unit is?
lumen
The best viewing of a digital display device is straight on and known as the?
cosine law
AMLCD (active matrix liquid crystal display)
are superior to CRT displays.
Spatial resolution
improves with the use of higher megapixel digital display devices.
Aperture ratio
is a meausre of image luminance of AMLCD's. The portion of the pixel face that is available to transmit light and is to a display device as fill factor is to a digital radio graphic detector.
Processing of digital images is largely
automatic
Postprocessing of digital images
requires operator manipulation
PACS (picture archiving & communication system)
improves image interpretation, processing, viewing, storage, and recall.
Clients
are interconnected, usually by cable in a building, by telephone or cable television lines mong buildings, and by microwave or satellite transmission to remote facilities.
Just the cost of the hospital space to accommodate a file file room may be sufficient to?
justify PACS
What are the 2 principle characteristics of a medical image?
spatial resolution & contrast resolution
What is spatial frequency?
describes the quantity of spatial resolution, measure in lp/mm.
As we increase frequency, what happens to the object size?
it becomes smaller.
What if the MFT were one, what does that mean?
perfect 100% --->everything we received was recorded<--- not possible.
What do we call how many shades of gray an imaging system has?
gray scale, dynamic range, bit depth
What does screen film have a dynamic range of?
3 decades -->1000 shades of gray
What digital system has the highest dynamic range?
mammography
Spatial frequency & spatial resolution has what % of MFT?
10%
Which of the following is responsible for bright vision?
cones
Which of the following is responsible for dim light vision?
rods
The science of what is the study of the response of the human eye?
photometry
An LCD is a material in a?
a state between liquid and a solid
What are the 4 principle components of a PACS system?
Image acquisition system, display system, network, and storage system
What does PACS stand for?
picture archiving & communication system
What does DQE measure?
amount of x-rays that are absorbed
What is a RIS?
radiology information system
Objects with high spatial frequency are harder or easier to image?
harder
If you had a perfect system, what would MTF be?
1
How many shades of gray can we image with our eye?
30 shades of gray
What is the basic photometric unit?
lumen
Preprocessing is done automatic or manually?
automatically
Should you ever repeat digital image for contrast, brightness, or overexposure?
No
What is spatial resolution in DR limited by?
pixel size
Almost all digital images in medical imaging are viewed in and interpreted on a?
digital display device
What is the ability of the yet to see black and white images?
scotopic/rods
Where do you find the rods of the eye in the greatest concentration?
periphery of the retina
Which of the following is responsible for bright light vision/color?
cones
When looking at a digital display monitor, where is the best place to view them?
straight on
Luminous flux
the fundamental quantity of photometry is expressed in lumens (lm). It is the total intensity of light from a source. (Amount of light)
Illuminance
describes the intensity of light incident on a surface. One lumen of luminous flux incident on a single square foot is a fc. (light up)
Luminance intensity
is a property of the source of light, such as a viewbox or a digital display device. Measured in lumens per steradian or candela. (# of light from source)
Luminance
is a quantity that is similar to luminance intensity. Luminance is another measure of the brightness of a source such as a digital display device expressed as units of candela per square meter or nit.
What are the 2 fundamental laws associated with photometry?
inverse square law & cosine law
preprocessing
is the ability to manipulate the images before display
postprocessing
after display
annotation
is the process of adding text to an image. Often helpful in informing the clinician about anatomy and diagnosis.
window and level
adjust grayscale. The radtech can; make all 65536 shades of gray visible.
magnification
zooming in on image. renders smallest detail visible.
image flip
used to bring images into standard viewing order.
image inversion
results in a black appearance of bone and a white appearance of soft tissue.
subtraction (DSA)
improve image contrast
pixel shift
reregister an image to correct for patient motion. movement blur
region of interest
determine average pixel value for use in quantitative imaging.
What are the 4 principal components of a PACS?
Image acquisition system, display system, network, and storage system.
What's a network?
a group, or server of clients
What's teleradiology?
is the process of remote transmission and viewing of images. or night hawk.
What's the approximate digital file size for digital mammo?
image size (MB) 10 and examination size (MB) 60
What's the approximate spatial resolution for mammo?
15 lp/mm
How does a defective pixel get fixed?
Interpolate adjacent pixel signals
What is image lag?
Ghosting. Offset correction
What happens when there's line noise?
Correct from dark reference zone. Voltage variation.