Chapter 20: Digital Image Processing Flashcards
Two types of digital radiography systems
- CR
- DR
This type of digital radiographer deals with photostimulable imaging plates (PSP, IP)
CR
This type of digital radiography deals with direct conversion without scintillator and indirect conversion with scintillator
DR
When were most of the changes made for historical development?
1970s and 1990s
- digital computerization of CT, ultrasound, MRI, Mammo
Referred to as flat panel detectors (panels)
DR receptors
What type of digital radiography system does healthcare reimbursement encourage?
DR
What type of digital radiographer produces a better picture and uses less exposure to the patient, which decreases patient dose?
DR
No step of light without a scintillator, which captures a better image, requires less steps to get the image. Is directly converted into electrical signal
Direct conversion
Using light with scintillator can throw artifact. X-ray photons are converted to light photons. and a photodetector (which converts light into an electronic signal)
Indirect conversion
What is the disadvantage of indirect conversion?
It produces light in all directions which reduces spatial resolution
What is the type of material inside the CR plate?
Photostimulator phosphor (PSP)
Are the elements that capture the image and hold it in place for CR? Also holds your laten image
Photostimulator phosphor (PSP)
When you take an image is run through a processor and it takes 60 seconds for the image to show up?
CR
Not able to see the image
latent image
Visualize image you are able to see the image on the computer?
Manifest image
Is part of the post-processing where you can write on it ( AP, Supine, etc)?
Annotations
Electrical signals from receptors are converted to what?
Converted to analog format
Converts an analog signal from the image receptor or detector to a digital signal or language for the computer to manipulate for processing, display, and storage? (converting all that information to a digital picture)
Analog-to-digital conversion (ADC)
What are considered the binary numbers to be able to create the image?
0 and 1
How many bits are in 1 byte?
There’s 8 bits in 1 byte
ADC involves what two distinct steps?
- Sampling
- Quantification
Computer memory and power expressed in total bytes
-megabytes, gigabytes, terabyes, etc
Analog voltage value are measured at a chosen sampling frequency and an analog wavelength
Sampling
How the image is read
Sampling frequency
Sampling frequency is associated with what type of digital?
CR
(CR) increase sampling frequency
increase the quality of the image (spatial resolution)
means image sharpness
Spatial resolution
each sample piece now gets a number value and is assigned a binary number of 0 and 1
Quantification
made up of pixels and voxels
-field of view (FOV)
-spatial resolution dependent on matrix size
Matrix
Picture element
Pixel
volume element
- 3 dimentional
Voxel
An arrangement of cells in rows and columns
-each cell corresponds to a specific locations in the image
Matrix
-determined by the number of pixels in the rows and columns
-expressed by listing the number of pixels in each dimension (length and width)
- common sizes: 256x256, 512x512
Matrix size
One individual cell in a matrix
- also known as the picture element
Pixel
Three values associated with each pixel:
-two for location (length and width)
-one for level of brightness (of shades of gray)
The smaller the pixel
the greater the spatial resolution
what does each pixel contain
bits of information
(number of bits per pixel determines the shades of gray demonstrated)
The greater the number of pixels
the greater the image resolution
How many pixels are required to image 1lp/mm
2 pixels
When you increase your matrix and decrease your pixel what happens to your spatial resolution?
Spatial resolution increases
Number of gray shades that a pixel can produce
Bit depth
What is the formula for bit depth
2 to the n power
The higher the 2 to the n power
the more shades of gray there is
What bit depth does most radiography use?
8,10, or 12 bit depth
Determines the size of the area to be imaged / how much of the patient is imaged in the matrix?
Field of View (FOV)
Pixel size=
FOV/Matrix size
Matrix can be changed without affecting what?
The FOV and vice versa
The distance between center of one pixel to center of adjacent pixel
Pixel pitch
The smaller the pixel pitch and pixel size
The better the spatial resolution
The image file size (storage) is affeccted by:
- pixel size
- matrix
- bit depth
Your matrix, bit depth, look-up table and histogram are all what
Already bulit in
Able to transfer images to different hospitals. Communication between hospitals
Digital Imaging and Communications in Medcine (DICOM)
Has a built in picture perfect image that is comparing to that’s why is important to pick the correct body part
Histogram
Gray scale bit depth ranges from what
range from 8 to 32 bits
Is read from left to right
white to black
Histogram
Graphic representation of all of the pixel brightness values
in the image in the order of their brightness
Histogram
Generated by dividing a scanned area into pixels and determining the signal intensity for each pixel; can be calculated for specific anatomy and procedures.
Histogram
Determines image contrast and the gray scale representation of the tissue
- left and right
window width
Determines brightness of an image
- up and down
ex. think of a window shade, incresed (open) is brighter
window level
-adjustments to image contrast
-produces contrast look according to reference contrast scale for exam view
Look-up table (LUT)
What might cause a histogram error
shielding and prosthesis
Considered to be white on in image
shielding, bone, soft tissue and air
under or over exposure conditions compensated for by shifting histogram to align with reference histogram
rescalling
the lower atomic #
the more tranmission to the IR
helps increase contrast
high-pass filtering
enchancing the edges nice and sharp (lip linear)
High-pass filtering
not adjusting to lower technique increasing radiation exposure over time in an attempt to achieve better image quality
Dose creep
making the picture even smoother
low-pass filtering
makes the edges pop out. helps bring out fien details in the image
edge enhancement
changing and switching the colors of an image
inversion
long bone study stiching 2 or 3 images together to make one large picture
stiching
-Densities outside the imaged anatomy
-background information
-Usually eliminated or will skew the graph
tail or spike in histogram
You want a high signal
low noise
Ability to represent small energy values in data set
Low contrast resolution
The greater the dynamic range
the more shades of gray
How efficient it is in picking up the radiation that is hitting the IR
Detective Quantum Efficiency (DQE)
Measure of how sensitive and accurate incoming data is converted to output viewing
Detective Quantum Efficiency (DQE)
want close to 1 as possible
more efficient =less dose to patient
Detective Quantum Efficiency (DQE)
DQE of 1=
100% or no loss of information
-higher DQE means lower dose
-provides information about exposure to image receptor
-acceptable ranges for best image quality
-calculated using histogram values and pixel values of interest mid points
-varies between vendors
EI#
calculating how much exposure going on to IR and how much radiation to the pt.
Exposure index (EI)
a comparison between the actual exposure and the proper exposure received by the image detector.
Deviation Index (DI)
determines number of density values
-affects density and contrast of system
Pixel Bit depth
-acquired histogram compared to reference histogram
-produces consistent image appearance regardless of exposure
histogram rescaling
what color would bone be
high atomic number (white)
What is noise measures as
signal to noise ration
-A high SNR indicates little noise in the image. Image noise has an inverse relationship to contrast. Increased noise decreases image contrast
what happens to your density resolution when the gray scale bit depth increases
density resolution increases
-adjusting to image
-pre-processing
-built in
-corrects grays
-can enhance pathologies
Look up table
The ability of the imaging system to distinguish between small objects that attenuate the x-ray beam in a similar manner; improves the visibility of the minimum density differences or shades of gray
contrast resolution
increase bit depth
increase contrast resolution
wider window width ( low contrast and long scale)
increase contrast resolution
blur something out in the background
unsharp masking or blurring
