Digital Imaging Ch 4 Flashcards
ambient lighting
Level of light in a room or environment -
automatic rescaling
When an exposure is greater or less than what is needed to produce an image - images are produced with uniform density and contrast regardless of amount of exposure
Basically the system is trying to “fix” an image with too much or too little exposure
Histogram analysis is employed to maintain a consistent brightness (despite the under or over exposure
bit
Each 0 and 1 is called a BIT and refers to the computer’s basic unit of information.
A digital transistor can be operated in two states: off (0) or on (1).
Bit depth
number of bits
Determines the amount of precision in digitizing the analog signal and therefore the number of shades of gray that can be displayed in the image.
bit depth is expressed as 2 to the power of n, or the number of bits (2n)
brightness
Level of intensity of a digital image on a display monitor
byte
8 bits (2 bytes form a word)
contrast resolution
The ability of the imaging system to distinguish between objects that exhibit similar densities because they attenuate the x-ray beam similarly.
I.e. the ability of a digital system display changes in grayscale values
CNR
Contrast-to-noise resolution
contrast resolution compared with the amount of noise apparent in a digital image.
DQE
Measurement of the efficiency of an image receptor in converting the x-ray exposure it receives to a quality radiographic image
(i.e. measures how efficient a system converts the x-ray input signal into a useful output signal
DI
Deviation Index
Value that reflects the difference between the desired or target exposure to the IR and the actual exposure to the IR
DICOM
Digital Imaging Communication In Medicine
A standard that allows imaging modalities and PACS to communicate in the same “language”
dynamic range
ability of a detector to accurately capture the range of photon intensities that exit the patient
electronic masking
shuttering
regions of the image view can be altered
(i.e. blackens our the white collimation borders to eliminate veil glare – should NOT be used due to poor collimation practices)
fill factor
percentage of the pixel faces that is sensitive to x-rays
If the Fill factor is approximately 80%, how much of the x-ray beam would NOT contribute to the image?
pixel is smaller than the DEL
FPD
Flat Panel Detector
solid-state IRs employing a large-area active matrix array of electronic components ranging in size from 43 × 35 cm to 43 × 43 cm (17 × 14 in to 17 × 17 in).
gray scale
number of different shades of gray that can be stored and displayed by a computer system
histogram analysis
image-processing technique commonly used to identify the edges of an image and assess the raw data prior to image display.
System finds the useful signal by locating the minimum & maximum signal within an anatomic region of interest an plots it on a graph
X-axis represents the amount of exposure
Y-axis represents the incidence of pixels for each exposure level.
Imaging Plate
Used with CR system - it is housed in a cassette
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Layers of the PSP plate -
top to bottom
Protective
PSP
Reflective
Base
Backing
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Latent Image
stored as digital data and must be processed by a computer for viewing on a display monitor
LUT
Look-up Table
method of altering the image to change the DISPLAY of the digital image in various ways
FOLLOWS HISTOGRAM ANALYSIS
CR
Matrix
combination of rows and columns (array)
(comprised of usually square pixels)
512 x 512
1024 x 1024 = 1,048,576 pixels
2048 x 2048
MTF
Modulation Transfer Function
measure of the imaging system’s ability to display the contrast of anatomic objects varying in size, and the value will be between 0 (no difference in brightness levels) and 1.0 (maximum difference in brightness levels)
photostimulable luminescence
visible light when stimulate by high-intensity laser beam
PSP
Photostimulable Phosphor
IP phosphor layer made up of barium platinocynanide crystals dope w/europium
PACS
Picture Archival Computer System
computer system designed for digital imaging that can receive, store, distribute, and display digital images
pixel density
number of pixels per unit area
pixel pitch
pixel spacing or distance measured from the center of a pixel to an adjacent pixel
pixel
2D picture element
Each pixel is recorded as a single numerical value, which is represented as a single brightness level on a display monitor
sampling frequency
determines how often the analog signal is reproduced in its discrete digitized form
sampling pitch
determines how often the analog signal is reproduced in its discrete digitized form
scintillator
Used in Indirect DR cesium iodide (CsI) or gadolinium oxysulfide (Gd2O2S) to convert the exit radiation into visible light
Wikipedia:material that exhibits scintillation — the property of luminescence,[1] when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, (i.e. re-emit the absorbed energy in the form of light).[a] Sometimes, the excited state is metastable, so the relaxation back down from the excited state to lower states is delayed (necessitating anywhere from a few nanoseconds to hours depending on the material): the process then corresponds to either one of two phenomena, depending on the type of transition and hence the wavelength of the emitted optical photon: delayed fluorescence or phosphorescence, also called after-glow.
SNR
Signal-to-Noise Ratio
method of describing the strength of the radiation exposure compared with the amount of noise apparent in a digital image
spatial frequency
unit of line pairs per millimeter (lp/mm)
- can be expressed as cm or mm
- does not refer to size but line pair = black line on a light background - one pair consists of the line and interspace of the same width as the line
window level
sets the midpoint of the RANGE OF BRIGHTNESS visible in the image (i.e. the type of tissue or structure you are trying to visualize)
- Changing the window level on the display monitor allows the image brightness to be increased or decreased throughout the entire range
- may see on PACS as “center” number
window width
Specific number of gray levels or digital image numbers assigned to an image. It determines the gray scale rendition of the imaged tissue - IMAGE CONTRAST (RADIOGRAPHIC)
Because the digital image can display shades of gray ranging from black to white, the display monitor can vary the range or number of shades of gray visible on the image to show the desired anatomY
