Unit 2 (Computed Radiography)
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Name some terms for CR (5):
- Photostimulable luminescence (PSL)
- Storage phosphor radiography (SPR)
- Digital luminescence radiograpy (DLR)
- Photostimulable storage phosphor (PSP)
- Digital storage phosphor (DSP)
When and where do we acknowledge as the origin of the use of luminescent phosphors?
- the 1600s, in Italy (the Bolognese stone)
- the 1800s, by Becquerel (measuring radioactivity)
- 1983, commercialized (Fuji, Kodak, Konica, Gavaert)
What are the 4 steps of imaging processing?
- image acquisition
- image plate scanning and erasure
- image processing
- image display
"Implementation issues" can come up in CR when dealing with the following:
- radiation exposure
- technique selection
What happens during Image Acquisition?
- (latent image on IP is released when inserted in an IRD)
- laser scanning
- conversion of the PSL
- Digitization of the signal by the ADC
What are the two aspects of Image Processing?
Name three elements of Pre-processing:
- Pattern recognition
- exposure field recognition
Name three elements of Post-processing:
- Contrast enhancement
- Edge enhancement
- Energy subtraction imaging
Immediately after the image is processed, where is it displayed (before it is sent to PACS)?
a CRT or LCD workstation monitor, where the radtech can determine if the image is of diagnostic quality
Name 5 required characteristics of phosphors:
- high absorption efficiency
- sensitive to helium-neon
- light emission must be detectable by a PMT
- luminescence must be shorter than 1 micro-sec
- must be able to store a latent image for several hours without compromising the signal from the IP
Approximately how long will a latent image last on an IP plate before it begins loosing enough energy to compromise the image?
- over 8 hours
- (loses around 25%)
Name some phosphors that meet the required characteristics for CR:
- BaFX: Eu
- (X) can be chlorine (Cl), bromine (Br), or iodine (I)
- BaFBr/I: Eu
- CsBr: Eu (cesium bromide and Euporium)
When euporium atoms are ionized by radiation, the electrons move from ___________ to __________.
- the valence band
- the conduction band
Electrons in the conduction band are free to flow to __________.
___________ refers to the time it takes for a latent image to disappear.
Which layer of the imaging plate is mixed with an organic binder (a polymer such as polyester)?
Which layer of the imaging plate allows x-ray and light to pass through easily and is durable enough to prevent damage to the PSP IP?
Which layer of the imaging plate reduces any problems with the IP when transported into the IRD and decreases static electricity problems that may degrade image quality?
Which layer of the imaging plate prevents reflected light from degrading image quality?
light shield layer
Name two main types of IPs:
- Standard resolution
- High resolution
Describe the differences between standard resolution IPs and high resolution IPs:
- Standard: thicker phosphors, faster speed, absorbs more radiation
- High: thinner phosphors, slower speed (good w/ extremeties), absorbs less radiation
- sharper image quality (thinner phosphors reduces lateral spread of the laser light)
What are CR cassettes constructed from?
aluminum honeycomb panel
How should the front and the back of a CR cassette be composed?
- front must be radiolucent
- back must be lead to prevent backscatter radiation
What are two main types of CR readers?
- cassette-based systems
- cassette-less systems
What are two CR reader scanning technologies?
- point-scan CR reader
- line-scan CR reader
Describe a point-scan CR reader:
- one light source reflected off light channeling guide
Describe a line-scan CR reader:
- several light sources with shaping lens
- lens array to direct light to CCD
- CCD photodetectors
As the IP moves into the reader, it is called a _________. The laser scanning the IP is called a _________.
Name some advantages of Dual-Sided reading:
- the acquisition of images is quicker
- the signal-to-noise ratio is improved
- the image quality is improved
- some incorporate larger phosphor layers which increases absorption (improving efficiency)
Name some things provided by the CR workstation:
- input patient identification
- selection of patient data to target exposure
- image preview
- image processing
- quality assurance procedures
- image printing
- sending images to PACS with the assistance of DICOM
What does a typical CR workstation consist of?
- image processing computer
- display monitor (CRT or LCD)
- barcode reader
- magnetic card reader
Name three Image Processing Techniques:
- Image contrast
- brightness control
- spatial frequency filtering
What is used to identify, correct, and scale the raw image data obtained when the IP is scanned in the CR reader (and before the image is displayed for viewing and subject to post-processing)?
What is another name for Pre-processing Operations?
What are some alternate names for Exposure Field Recognition by different manufacturers?
- Exposure Data Recognition (Fuji)
- Segmentation (Kodak)
Name two functions that are carried out by Exposure Field Recognition:
- collimated edges are detected and expected anatomical structures are identified by specific algorithms
- "shift and subtraction" can occur
maps the degree of penetration of the anatomical regions to the degree of luminescence of the display device; large and small peptration values are mapped to the maximum luminescence and minimum luminescence, respectively:
What appears on the displayed image and serves to provide the technologist with a visual cue as to whether correct or incorrect exposure technique was used?
Exposure Indicator (aka Exposure Index)
Name some different terms for Exposure Index by different manufacturers:
- Fugi: Sensitivity number (S-number)
- Agfa: log of Median (lgm)
- Kodak: exposure index (EI)
- Konica: S-value
What are acceptable ranges for Exposure Indicators for Various Manufacturers?
- S-number: 150-300
- LgM: 2.05-2.35
- EI: 1850-2150
Give alternate names for Contrast Enhancement for various manufacturers:
- Fuji: Gradation Processing
- Kodak and Agfa: Tone Scaling/ Latitude Reduction
- *newest algorithm: MUSICA (Agfa)
Algorithms that are intended to adjust or control the sharpness or detail of an image by adjusting the frequency components of the image:
Edge Enhancement/ Spacial Frequency Processing
Improves the visualization of areas with different densities in the same image:
dynamic range control (DRC)
Allows visualization and typification of structures that may be obscured by overlying or underlying anatomy:
frequency enhancement which adjusts both large and small structures independently within the same image simultaneously:
multi-objective frequency processing (MFP)
software that separates noise and image signals enabling selective supression of noise levels to enhance diagnostic interpretation:
flexible noise control (FNC)
removes grid patterns from the image to supress moire patterns within an image:
grid pattern removal (GPR)
when seperate images are stiched (joined together) to form a single image:
Which manufacturers make Exposure Controls that have indirect/direct relationships to exposure?
- S-number: indirect
- LgM: direct
- Exposure Index: direct
Name the two groups that have been working on standardization of exposure indicators:
- IEC (International Electrotechnical Commision)
Name several factors that affect exposure indicators:
- patient positioning
- beam centering
- processing algorithms
A bit depth of 8 with have how many shades of gray per pixel?
Who developed the Continuour Quality Improvement (CQI)?
the Joint Commission
What are the two areas designed to ensure quality is met?
- Quality Control (QC)
- Quality Assurance (QA)
What specific areas does CQI deal with?
- quality assessment
- continuing education
- usefulness of quality control procedures
- assessment of the outcomes
- deals with administrative aspects of quality patient care
What is a component of QA that refers specifically to the monitoring of important variables the affect image quality and radiation dose?
Quality Control (QC)
What is the first major step in a QC program and it ensures that the equipment meets the specifications set by the manufacturer?
Acceptance testing (AT)
The FCR 1 shot Plus System is a "flat plate" tool for QC testing that tests for:
- relative "S" number
- laser jitter
Hard-copy film testing is an analog tool for AAPM and includes:
- Cu and AI filters
- calibrated ion chambers
- wire mesh
- anti-scatter grid
- low contrast phantoms
what is the QC Test 1 for? describe.
- for dark noise
- erase a single screen and read it without exposing it
what is the QC Test 2 for? describe.
- for uniformity
- expose imaging plate using appropriate exposure factors
what is the QC Test 3 for? describe.
- for distortion (spatial)
- place a regular wire mesh screen-film contact test tool over the CR IP and expose the IP to appropriate exposure technique
what is the QC Test 4 for? describe.
- for erasure thoroughness
- place a step-wedge at the center of a 14x17 CR IP and expose using appropriate exposure technique and process in IRD, then re-expose the same IP without step wedge using the appropriate technique. (ghost image)
Which offers wider dynamic range, digital or analog?
What controls speed class in digital?
the x-ray tech, by the technique set
At what % below optimal signal level may quantom mottle be objectional to the viewer?
greather than 50%
At what % above the optimal signal level is the ALARA principle violated?
greater than 100%
Before Exposure Indicators, what was used to evaluate the accuracy of the receptor exposure?
Analysis of histogram is depended on what two things?
- accurate reader calibration
- appropriate exposure field recognition
name three important factors that contribute to high image clarity and visualization of desired anatomical structures:
- correct technical factors
- correct positioning of part
- correct alignment of part, beam, and receptor
what does >200% overexpsure of the pate cause?
with a 400 speed film system to CR, the receptor exposure need to be increased by about how much?
Due to the sensitivity of the PSP, the background exposure will do what to contrast?
As the grid ratio increases, does the ESE increase or decrease?
what occurs when the alignment of the divergence of the x-ray beam does not align with the lead strips of the grid?
If you increase the kVp, does the ESE increase or decrease?
what is the most common histogram analysis error?
exposure field recognition failure
in cr, what can occur when there is image loss due to image over-exposure of 4x to 5x?
how is sampling frequency expressed?
pixels per mm (pixel density)
the higher the kvp, the signal difference _________, the data range ________, and the dose ________.
- signal difference: decreases
- data range: narrows
- dose: decreases
As the frequency of a grid _________, the lead content ________.
with fuji systems, pre-processing operations are called:
exposure data recognition
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