Unit 2 Quality Factors I: IR Exposure Flashcards
Radiographic Quality Factors
- Exposure to the Image Receptor
- Subject/Image Contrast
- Details
- Distortion
Density
The degree of blackening on an x-ray film
IR Exposure
Total signal received by the IR
S number VS EI number
Brightness
-A monitor control function that determines the overall appearance of an image.
-NOT related to exposure to IR
Window Level
post-processing function that produces changes in overall brightness/gray level
Sensitivity Number (S#) is ____________ proportional to exposure
Inversely
Exposure Index (EI) is ____________ proportional to exposure
Directly
Log Median Exposure (LgM) is ____________ proportional to exposure
Directly
Deviation Index
Indicator that compares the actual exposure received with the target exposure
Controlling factor for IR Exposure
-mAs
• mAs controls current to Tube filament
• Number of electrons boiled off filament
• Number of x-ray photons in beam (Beam Intensity)
Influencing Factors for IR Exposure
kVp, SID, OID, Grid use, Patient factors, Beam restriction, Screen speed
How does kVp affect the x-ray beam?
- Influences the number of X-ray Photons in the beam (Intensity)
- Controls the energy of the x-ray beam (Quality)
- Alters the ratio of Photoelectric to Compton interactions
-Increase in kVp = Reduction in PE = Proportional Increase in Scatter
Low kVp means
• More absorption
• Less transmission
• Less scatter
High kVp means
• Less absorption
• More transmission
• More scatter
Kilovoltage Peak (kVp): 15% Rule
A 15% increase in kVp will double the exposure to the IR.
A 15% decrease in kVp will cut the exposure in half.
When might a technologist use the 15% Rule in clinical practice?
- Pregnancy (15% increase)
- Reduce Exposure Time
What is the Exposure Maintenance Formula used for?
To maintain IR exposure when the mAs is changed
Increase in SID is a ___________ in mAs
Decrease
Directs Square Law Formula (Exposure Maintenance)
mAs 1 D1 (squared)
——— = ——————
mAs 2 D2 (squared)
mAs and exposure have a ________ equation
Linear
How does OID affect IR exposure?
-Increased OID decreases the amount of scatter/secondary radiation that reaches the IR
-Increased OID decreases the exposure to the IR
Small OID = __________ exposure to IR
Increased
Large OID = __________ exposure to IR
Decreased
Beam Restriction (Collimation)
• Decrease in overall Number of Photons interacting with the IR
• Decrease in Exposure to the IR
Screen Speed
• CR vs. DR: DR is more sensitive than CR
• Same mAs produces higher exposure on DR compared to CR
Grid Use
• Grids absorb scatter and secondary radiation before it reaches the IR
• Grids reduce overall exposure to the IR
Define Focal Spot Blooming
What effect does it have on IR exposure?
-On target, but not on the focal track
-Negligible(small/unimportant) effect on IR Exposure
Anode Heel Effect
-IR Exposure is greater at the cathode side of the tube
-More pronounced at LARGE field size (wide Collimation) and SHORT SID
Histogram
A graphic representation of the grayscale of an image. The X axis is the different shades of gray, and the Y axis represents the number of pixels of that particular color.
Define Rescaling
Computers way to correct brightness for under/over exposure (computer attempt to bring a radiographic image into the expected level of brightness)
How does Rescaling affect total IR exposure?
No affect
Does Window Level brightness change the IR exposure?
No
Insufficient Exposure causes
-Quantum Noise
-Quantum Mottle
What are Quantum Noise and Quantum Mottle
-Quantum Noise: Lack of sufficient incoming data for processing
-Quantum Mottle: Blotchy/grainy image artifact
Excessive Exposure
Excessive mAs will result in Overexposure to the patient and the IR
How should a Radiographer ensure there is no quantum noise on the image?
increase the mAs of the x-ray beam so that the number of incoming signals/x-ray photons is also increased
Increase in SID means a __________ in IR exposure
Decrease
The difference between adjacent IR exposure levels.
Image contrast
Amount of x-ray signal received by the Image receptor
Image receptor exposure
A graphic representation of the grayscale of an image. The X axis is the different shades of gray, and the Y axis represents the number of pixels of that particular color.
Histogram
The digital processing that produces changes in the range of brightness.
Window width
A monitor control function that can change the lightness and darkness of the image on a display monitor, but is not related to IR exposure.
Brightness
Image manipulation parameter that changes image brightness on the display monitor, usually through the use of a mouse
Window level
The ability of a system to differentiate on the image objects with similar densities
Low contrast resolution
Technique by which diagrams of the body on the console guide the technologist in selection of a desired kVp and mAs.
Anatomically Programmed Radiography (APR)
Alternative to using a radiographic grid in which the anatomical area of interest is placed away from the IR so that scatter and secondary radiation might be deflected away from the IR and/or absorbed in the air gap.
Air gap technique
The intensity of radiation is inversely proportional to the square of the distance from the source
Inverse Square Law (ISL)
Measures the accuracy of an image compared to the original object on a scale of 0-1. It measures the percentage of the object contrast that is recorded.
Modulation Transfer Function (MTF)
The result of differences in transmission of the beam as it passes through the patient resulting in signal differences to the digital detector
Differential attenuation
Describes the total amount of signal recieved by the IR
Exposure
A numeric representation of the quantity of exposure received by a digital image receptor. It is used by Carestream and is directly proportional to IR exposure.
Exposure Index (EI)
Controlling factor for subject contrast
kVp
