Radt. 3000 principles of exposure
8/18/22
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Related Definitions:
*Spatial Resolution- sharpness of structural edges recorder in the image
*Receptor exposure- amount of exposure striking the IR
*Brightness- measurement of the luminants of an area in a radiographic image displayed on a monitor
*Contrast- visible difference between any 2 selected brightness levels within displayed radiographic image
*Gray Scale- refers to # of brightness levels or shades of gray
*Long Scale Contrast- slight differences between gray shades are present (low contrast); total # of gray shades is great
*Short Scale- major/considerable differences between gray shades present (high contrast); total # of gray shades is small
*Dynamic Range- range of exposures that can be captured by a detector
*Receptor Contrast- doesn’t go over
*Exposure latitude- range of exposures which produces quality images at appropriate patient dose
*Subject Contrast- magnitude of signal difference in remanent beam; as a result of different absorption characteristics of tissues & structures making up the part (difference in the part;
****Scale of contrast has to do with entire image;
****Short Scale- only when looking at bony anatomy
****Detector- IR
****ALARA- As Low As Reasonably Achievable
Selection of Technical Factors Affecting Radiographic Quality:
Digital Radiography:
*Digital Radiography- general term that includes computed & direct radiography
*Clinical Radiography (CR)- when you have to poke IR in machine to scan IR
*Digital Radiography (DR)- Wireless IR
Noise- any undesirable info that interferes with subject of interest in radiographic image
Artifact- any extraneous object or unwanted image that obscures info in radiograph
Size Distortion- aka magnification
Magnification- difference between size of object in image vs the actual size of object
Shape Distortion- difference between shape of object in image vs actual shape of object
Elongation- when object appears longer in image than it actually is
Foreshortening- when object appears shorter in image than it actually is
8/23/22
Control Panel:
*mA (milia Ambridge)- measurement of flow rate of electrons through x-ray tube
*time(s) (exposure time)- abbreviated in seconds (s); amount of time in seconds during exposure
*mAs (millie Amber seconds)- mA & time put together; total exposure
*kVp (kilovoltage peak)- energy level in which electricity is being forced across x-ray tube; peak energy level
*Focal Spot- refers to specific target area on target surface of x-ray tube
*AEC (Automatic Exposure Control)- allows radiographer to set kVp & system determines when adequate exposure has reached IR
-Density Control- each increment in density control setting represents 25% change in intensity
-Bucky Selection-
*APR (Anatomically Programmed Radiography)- preset technical factors
X-Ray Tube:
*4 things needed to produce X-Rays- 1.) source of electrons 2.) focusing cup 3.) way to speed up electrons 4.) have a way to stop electrons abruptly
*most of energy striking anode results in heat; about 1% of beam results in x-ray protons, 99% results in heat
*SID (Source to Image Distance)- distance of CR from focal spot to IR
*Primary Radiation/Beam- refers to beam from focal spot to object being imaged (patient)
*Remnant Beam- sometimes called image forming radiation; where it exits patient down to IR
*only about 5% or less of x=ray beam passes through body
*about 15% of x-ray beam results in scattered radiation
*about 80% of x-ray beam is absorbed by body
*attenuation- partial absorption of x-ray beam as it passes through body
*Inherent Filtration- built into x-ray tube; consists of 3 parts- 1.) glass envelope 2.) insulating oil 3.) exit window
*Added Filtration- added by technologist
*Filtration- purpose to absorb low energy x-ray photons before they reach patient
*Beam Restriction (Collimation)-
*Anoheel effect- difference in beam intensity along longitudinal axis of x-ray tube
*Central Ray- center of x-ray beam & direction in which it travels
*OID (Object to Image Distance)-
*Grids- absorb scatter before it reaches IR