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show | the ability of the detector to detect and respond to very low levels of visible light or radiation.
Similar to DQE
Important because it affects patient dose
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Describe DYNAMIC RANGE - detector | show 🗑
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show | DIRECT
the more sensitive the detector, the higher the DQE
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What is a CCD? | show 🗑
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show | Orth p307
detective quantum efficiency
a measurement of overall efficiency with with the detector can convert the x-ray input signal into a useful output image
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show | Increased dynamic range/wide exposure latitude
Greater contrast resolution
immediate results
improved workflow
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show | lower spatial resolution
image quality depends on processing and display monitor characteristics
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show | Signal to Noise ratio
white noise interferes w/digital image;
measure of translation of latent image to electronic image;
measures contrast resolution P p48
std method to express noise vs signal strength
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show | contrast to noise ratio;
ratio between image contrast and image noise; can be used to describe image quality
how well the latent image subject contrast translates to image contrast
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What impacts spatial resolution in detector? | show 🗑
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What is sampling ? | show 🗑
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What is sampling frequency? | show 🗑
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How does pixel pitch affect pixel size? | show 🗑
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What is fixed sampling versus fixed matrix? | show 🗑
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show | a layer of photostimulable phosphor that interacts with the x-rays to create the latent image
in CR - commonly used BaFl and Europium
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How does DEL/dexel size affect spatial resolution of the detector? | show 🗑
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What is fill factor? | show 🗑
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What is the relationship of spatial resolution to DEL size? | show 🗑
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Define LUMINESCENCE | show 🗑
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show | emission of visible light during and after stimulation
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Define FLUORESCENCE | show 🗑
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show | Random size and spread of crystals - creates light spread - lower spatial resolution
Most CR phosphors are turbid
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What is structured phosphor and how does it affect spatial resolution? | show 🗑
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show | BOTH direct and indirect
all have TFT array/AMA array composed of dexels/DELs
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show | decrease DEL size to increase SR nn increase in mAs to get enough SNR
If we make the dexels smaller, the fill factor will go down. The 20% part cannot be made smaller, so we need to increase the mAs to decrease the SNR from the smaller fill factor
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Describe DR plate elements. | show 🗑
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show | Orth p307
the material that captures the x-ray photons
in CR, it is the photostimulable phosphor
in DR, it is the NaI, CsI, and GdOS for indirect
Direct DR - amorphous Selenium
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What is conducting element? | show 🗑
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What is collecting element? | show 🗑
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Describe elements of CR plates | show 🗑
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Describe elements of early Indirect DR plates. | show 🗑
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show | Capture element - CsI and GdOS p274 Orth
Coupling element - contact layer (amorphous silicon semiconductor) painted onto the glass substrate
Collecting element - TFT
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Describe elements of Direct DR | show 🗑
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show | photomultiplier tube - a light sensitive device used to convert the light into electronic signal
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show | secondary release of light;
phosphor releases trapped energy as light when re-excited by infrared or visible light
Helium Neon laser causes this in CR reader
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show | invisible image captured on IP (CR or FPD (until activated by CR reader or processed by digital system to become visible image)
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show | a. segmentation/exposure field recognition/data recognition
b. Histogram analysis
c. Automatic rescaling/normalization (RISK of FAILURE)
d. LUT
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show | Thin-film transistor - a charge collection electrode (senses ELECTRONS) - it is a switch that is closed during exposure, allowing the charge in each DEL to be collected and stored.
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Where is the risk of failure? | show 🗑
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Describe SEGMENTATION/EXPOSURE FIELD RECOGNITION. | show 🗑
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Describe HISTOGRAM ANALYSIS/construction. | show 🗑
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Describe HISTOGRAM ERROR. | show 🗑
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Describe SEGMENTATION for CR. | show 🗑
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describe CR - image artifacts | show 🗑
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show | errors creating image during segmentation because system doesn't recognize actual exposure field. Place the part as much as possible in the CENTER aligned lengthwise.
when views are non-symmetrical -
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Describe histogram construction | show 🗑
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Describe histogram graph. | show 🗑
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Are collimated field borders important to image processing? | show 🗑
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show | PP p5
formula or set of rules for solving problem
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show | PP p5
graphical representation of different body tissues
SPATIAL RESOLUTION
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show | PP p5
Look Up Table
histogram of luminance values (image display) for pixel values CONTRAST
p165 Papp
maps the image grayscale values into some visible output intensity on the monitor
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Describe Segmentation. lecture 2hr 20min | show 🗑
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show | Selecting correct exam (choose unique histogram) tells system how to process image. If choose incorrect exam, system must post-process data resulting in loss of info, unless repeat;
choose correct technique;
Steps - select exam, histogram applied, LUT
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Describe Ideal, appropriate and inappropriate collimated fields. | show 🗑
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Describe HISTOGRAM ALGORITHM function. | show 🗑
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Describe LUT ALGORITHM function. | show 🗑
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show | system compares image data histogram with stored image histogram
reads data from left to right (low to high)(white to black)
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show | White grays are on the left side and represent collimation, scatter then bone
Possible prosthesis/Barium which can cause histogram analysis error - use correct HISTOGRAM
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On a histogram graph, what does the black side represent? | show 🗑
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Describe histogram elements. | show 🗑
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What is exposure latitude in a histogram? | show 🗑
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Describe histogram contrast. | show 🗑
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show | attenuation is loss of energy of photons
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What is VOI? | show 🗑
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show | region of interest - occurs on computer
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show | Increase kVp decreases subject contrast - flattens and widens histogram (fewer peaks/valleys - flat)
Decrease kVp increases subject contrast - more peaks/valleys, narrower histogram
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show | Shape stays fairly constant for each part exposed (anatomy specific
IE - Shape of histogram for a chest radiograph on a large adult is different than a ped knee
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show | image acquisition processing takes place in computer using processing algorithms (segmentation, histo analysis, auto-rescale, LUT) that analyze and ID components and characteristics of image
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show | all manipulation and adjustments done by the tech through various user functions after pre-processing has occurred (once visible image is displayed)
Tech must be careful not to POST PROCESS necessary data from image.
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show | Only the detector plate (CR uses IRD/CR reader)
All other steps are the same
SEGMENTATION
HISTOGRAM ANALYSIS
AUTO RESCALE
LUT
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show | p298/299 Orth/p164 Papp
to display image with appropriate brightness level regardless of the exposure
tech FAILURE possible here - select correct TECHNIQUE (ALARA)
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show | auto rescaling process
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Why does the image initially appear as a washed out gray image? | show 🗑
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show | exposure of 500% over ideal and 60% below ideal
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What does auto-rescaling do? | show 🗑
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When does auto rescaling fail? | show 🗑
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What is a LUT? | show 🗑
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show | A Priori
1. Extremity model - type 1 (common)
2. General model - type 2 (common)
3. Metal model - type 3 (fixed algorithm)
Neural - AI
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show | any error where system does not recognize data or collimation
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show | to correct values of pixels;
to give desired final image contrast
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What is mapping function of LUT? KNOW THIS | show 🗑
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How is LUT graphed? | show 🗑
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What is window width? | show 🗑
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What is window level? | show 🗑
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show | The range of techniques that will produce a quality image that has an acceptable appearance (low noise) and does not violate ALARA
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What is the biggest difference between digital and film screen? | show 🗑
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Describe WINDOW WIDTH. | show 🗑
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What is electronic collimation? | show 🗑
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What are the effects of excessive processing? | show 🗑
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show | PIXEL BIT DEPTH
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show | LOCAL spatial frequency adjustment
generating image that is pleasing to observer
Includes - contrast, edge, spatial and frequency filtering, image combining and noise reduction
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show | Local spatial frequency processing
to make changes to contrast and brightness of an image
Window width - CONTRAST
Window level - BRIGHTNESS
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What is Edge Enhancement (high pass filtering) | show 🗑
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What is smoothing (low pass filtering)? | show 🗑
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What is unsharp masking? | show 🗑
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What is DOSE CREEP? | show 🗑
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show | p288 Orth
1. kVp 15% rule
2. kVp is seen as exposure and provides adequate data to computer
3. Increasing kVp maintains contrast resolution while decreasing patient dose
4. Very low kVp = quantum mottle = repeat
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show | p298 Orth/PP p8/graph 22.6 p299
processing stretches values toward optimal exposure (values that are more appropriate for specified anatomy) brings blacks to grays
SUBTRACTS values from pixels in image to align with stored histo
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What does autorescaling do to an underexposed image? | show 🗑
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What is rescaling image brightness? | show 🗑
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show | Any unwanted image on pic
- may obscure anatomic info
- PLUS density (B)
MINUS density (W)
GHOST/2x exp's
Scratches/tears
fogging
noise
heat blur
histo error
non-parallel collimation
linear scanning artifacts
Moire
Aliasing
Light bulb
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show | blacks on image
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show | whites on image
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What is GHOST artifact? | show 🗑
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What is MOIRE pattern? | show 🗑
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Tell me about Quantum Noise. | show 🗑
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What are exposure indicator scales? | show 🗑
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Describe inversely proportional scales (S#). | show 🗑
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show | Based on 300 point system
Increase EI by 300 = 2x exp
Decrease EI by 300 + 1/2 exp
to double receptor exposure, double the mAs
to halve receptor exposure, 1/2 mAs
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