IMAGE CHARACTERISTICS
Differentiate between long-scale and short-scale contrast.
SSC: high contrast; mostly black and white with few shades of gray in-between
LSC: Low contrast; many shades of gray and few blacks and whites
Explain how changes in the mA setting on the control panel affects the tube current
An increase in mA results in a higher production of electrons that are inside the x-ray tube which will increase the quantity of x-radiation
Explain the purpose of a radiographic grid
To reduce the scattered radiation reaching the detector, increasing radiographic contrast
List the different types of exposure technique charts
1. Variable kVp-fixed mAs
2. Fixed kVp-variable mAs
Describe how AEC device operates
Radiation is transmitted through the patient and converted into an electrical signal, terminating the exposure time
Identify the factors that affect recorded detail
Geometric: FSS, SID, OID
Motion: Patient (voluntary, involuntary), Equipment
Explain how kVp controls the quality of the x-ray beam
Regulates the speed of electrons traveling from the cathode to the anode, and determines the penetrating ability of the x-ray beam
Calculate the new mAs to be used when changing from a non-grid procedure to a grid procedure, or when changing grid ratios
mAs1/mAs2=GCF1/GCF2
Identify and describe the four major types of body habitus
Hypersthenic: (Massive)
Sthenic: (Average)
Hyposthenic: (Slender)
Asthenic: (Very Frail)
Differentiate the types of radiation detectors used in AEC systems
Photo-timers
Ionization Chambers
State the formula used to calculate geometric unsharpness
Unsharpness= FSS*OID/SOD
SOD=SID-OID
Explain how kVp controls radiographic contrast in conventional film/screen systems and digital imaging
A lower kVp will make the x-ray beam less penetrating, leading to higher contrast
Explain the air-gap technique
Method to reduce the amount of scattered x-ray radiation reaching the detector, reducing noise and improving image contrast
Identify patient factors that may affect image receptor exposure
Patient thickness, pathologic conditions, contrast media, foreign objects, or pockets of gas; tissue composition
Explain the level at which the backup timer should be set
150% to 200% of the expected exposure time
Explain the effect of change in (FSS) on unsharpness and recorded detail
As the focal spot increases, the area of unsharpness increases
Calculate changes in kVp to change and maintain radiographic density
15% rule; To maintain exposure to the IR, when increasing kVp by 15%, divide the original mAs by 2
List the different types of radiographic grids
Linear-parallel, Linear-focused, Cross-hatch, Rhombic
Differentiate between positive and negative contrast media
Negative contrast media are more radiolucent than surrounding tissues; Positive contrast media are more radiopaque
Describe the function of an APR system
system of preprogrammed exposure technique settings that is organized by position and examination and set through the control panel of the radiographic unit
To improve quality of the repeat image, the competent radiographer would...
Raise the mA and decrease the exposure time
Explain how changes in the SID affect radiographic density
As SID decreases, the radiographic density increases as a result of the square of the distance
Explain how scatter affects radiographic density and contrast
Scatter radiation will add density and decrease the radiographic image contrast
Differentiate between additive and destructive pathological conditions
Additive: has an increase in thickness, mass, density, and atomic number (greater attenuation)
Destructive (air): will have a reduced tissue mass or density (less attenuation)
Explain the purpose of the mAs readout
reports the actual mAs used for an exposure, can make exposure adjustments by switching to manual technique