7. Digital Imaging Characteristics Flashcards
paintings and printed photographs
Analog Images
various levels of brightness and colors
Analog Images
continuous, they are not broken into their individual pieces
Analog Images
infinite range of values
Analog Images
Analog Images examples
thermometer (mercury), photocopiers, audio tapes
recorded as multiple numeric values
Digital Images
divided into an array of small elements that can be processed in many different ways
Digital Images
discrete
Digital Images
finite range of values
Digital Images
not as exact as analog, but easier to work with
Digital Images
Film based
Analog Images
Produced when x-rays photons strike the film
Analog Images
Shows on film as a continuous spectrum of gray shades between the extremes of white and black
Analog Images
The shades “flow into” one another like a painting
Analog Images
sensor is the recording medium
Digital Images
produces a computerized images
Digital Images
uses an array of “pixel” elements with exact gray and discrete gray values for each pixel
Digital Images
more like a mosaic patterns instead of the shades “flowing together”
Digital Images
Storage: lots of physical space, required, along with time and energy required to store hard copies
Analog Images
Storage: higher likelihood of getting lost
Analog Images
Distribution: hard copy is available only at one location
Analog Images
Distribution: unless copies of image are made, healthcare professionals must travel or have image delivered
Analog Images
Viewing: hard copy is limited by its size, can only be viewed by small audiences
Analog Images
Lifespan: screen-film image quality degrades over time
Analog Images
Cost: screens and chemicals are less costly in isolation however repetitive purchase is more expensive in the long-run
Analog Images
Storage: although files are large, storage takes less time, energy and no physical space
Digital Images
Storage: less likely to get lost as file can be backed up
Digital Images
Distribution: soft copy is available on PACS, universal distributer of medical images
Digital Images
Distribution: any healthcare professional at any location can access the file
Digital Images
Distribution: easy to send image digitally
Digital Images
Viewing: soft copy can easily be viewed by large audiences
Digital Images
Lifespan: image quality does not degrade over time
Digital Images
Cost: expensive to purchase equipment at first (high resolution monitors etc.) however cost-effective in the long-run
Digital Images
When we talk about digitizing a signal from a digital radiographic unit, we are talking about assigning a numerical value to each signal point, either an ______ or a _____
electrical impulse,
light photon
refers to a device or system that captures or measures a continuously changing signal
Analog
is recorded or used in its original form
analog signal wave
is transformed into a series of pulses that corresponds to patterns of binary digits (0s, 1s)
digital signal
digital image begins as an _____
analog signal
through computer data processing, the image becomes _____ and is sampled multiples times
digitized
The critical characteristics of a digital image are:
- Spatial Resolution
- Contrast Resolution
- Noise
- Dose efficiency (of the receptor);
picture element
pixel
smallest element in a digital image
pixel
the size of the pixel is _____ related to the amount of spatial resolution or detail in the image
directly
the smaller the pixel is, the ____ the detail
greater
may change when the size of the matrix or the FOV changes
Pixel size
each ____ contains pieces or bits of information
pixel
the number of bits within a pixel is known as
pixel bit depth
each box within the ____ also corresponds to a specific location in the image and corresponds to a specific area of the patient’s tissue
matrix
the image digitized both by
position (spatial location) and intensity (gray level)
Matrix sizes
512 x 512
1024 x 1024
2500 x 2500
square arrangement of numbers in columns and rows
Matrix
in digital imaging, the numbers correspond to discrete pixel values
Matrix
the size of the _____ determines the size of the pixels
matrix
synonymous with the x-ray field
Field of View
the amount of body part or patient included in the image
Field of View
the larger the FOV, the ____ area is imaged
more
changes in the ____, will not affect the size of the matrix; however, changes in the matrix will affect pixel size
FOV
Same FOV, increase matrix, _____ pixel
decrease
a relationship may exist between the ___ of the pixel, the size of the matrix, and the FOV
size
matrix size can be changed without affecting the FOV and the FOV can be changed without affecting the matrix size, but a change in either the matrix size and/or the FOV _____ the size of the pixels
changes
refers to the amount of exposure received by the image receptor (IR), not by the patient
Exposure index
used to indicate the relative speed and sensitivity of the digital receptor to incident x-rays
Exposure index
to provide feedback to the technologist regarding the proper radiographic techniques for a specific exam that achieves an optimal image in terms of appropriate quality and corresponding low dose to the patient
Exposure index
Standard Units of Measure
- Air Kerma
- Standardized Radiation Exposure (KSTD)
- Indicated Equivalent Air Kerma (KIND)
- Target Equivalent Air Kerma Value (KTGT)
- Deviation Index
kinetic energy released per unit mass (of air) the measurement of radiation energy (joules or J) absorbed in unit of air (kg)
Air Kerma (J/kg or Gray)
standard exposure typical of that imaging receptor system
Standardized Radiation Exposure (KSTD)
exposure is made with additional filtration that hardens the beam to stimulate patient tissue
Standardized Radiation Exposure (KSTD)
used to ensure that the equipment is function properly
Standardized Radiation Exposure (KSTD)
measurement of the radiation that was incident on the IR for that particular exposure
Indicated Equivalent Air Kerma (KIND)
amount of exposure to the IR
Indicated Equivalent Air Kerma (KIND)
this value will help determine whether the IR has been overexposed or underexposed for the particular body part
Indicated Equivalent Air Kerma (KIND)
a set values, established by either the system manufacturer or the system user, the represents an optimal exposure for each specific body part and view
Target Equivalent Air Kerma Value (KTGT)
for example, there will be established perfect exposures for a PA chest, lateral chest, portable chest, pediatric chest and so on
Target Equivalent Air Kerma Value (KTGT)
the difference between the actual exposure (KIND) and the target exposure (KTGT)
Deviation Index
intended to help the technologist determine whether the image has been underexposed or overexposed
Deviation Index
can be used to adjust technical factors if the image must be repeated
Deviation Index
appearance on the display monitor of the computer and is a function of the monitor’s ability to emit light through the surface of the display
Brightness
terms to use for the measurement of brightness using a photometer
Luminance
ability of the digital system to display subtle changes in the shade of gray
Contrast Resolution
the differences between adjacent densities are enhances
Higher Contrast Resolution
more shades of gray may be demonstrated resulting in the ability to demonstrate between small differences in densities
Higher Contrast Resolution
directly related to bit depth of pixels in the image
Contrast Resolution
the ability of the imaging system to demonstrate small details of an object
Spatial Resolution
crystal size and thickness of the phosphor layer
Film-screen radiography
phosphor layer thickness and pixel size
Photostimulable Phosphors
pixel size and capture technique
Active Matrix Flat Panel Images
thinner phosphor layers and smaller pixels produces images with ____ resolution
higher
PSP pixel
200 micrometer
Gd AMFPI pixel
150 micrometer
Cs AMFPI pixel
125 to 100 micrometer
A-Se pixel
50 micrometer
the ability to respond to varying levels of exposure
Dynamic Range
more tissues densities on the digital image are seen, giving the appearance of more detail
Dynamic Range
The smaller the pixels, the _____ the spatial resolution
higher
describes the range of x-ray intensities a detector can differentiate
Dynamic Range
ability of the combine components of a system to accurately reproduce the structural details of an object within the image
Modulation Transfer Function
a way to quantify the contribution of each system component to the overall efficiency of the entire system
Modulation Transfer Function
is a ratio of the image to the object
Modulation Transfer Function
a perfect system would have an MTF of
1% or 100%
both in film-screen and digital imaging, anything that interferes with the formation of the image
Noise
superimposition of body parts
Anatomic Noise
occurs during image requisition
Radiographic Noise (Quantum/Equipment Noise)
refers to the range of exposure a digital detector can respond to
Exposure Latitude
o Range of exposure values (diagnostic image) the image detector is able to produce
Exposure Latitude
o Dependent on the image detector, the higher the dynamic range, the more values can be detected
Exposure Latitude
How efficient a system converts the X-ray input signal into a useful output image
Detective Quantum Efficiency
Measurement of the percentage of X-rays that is absorbed when they hit the detector
Detective Quantum Efficiency
System with higher quantum efficiency can produce ____-quality images at ___ doses
higher,
low
______ detector technology have increased DQE over PSP
A-Se, A-Si, TFT,CCD and CMOS
has the highest DQE since they do not have light conversions, there’s no light spread
A-Se
