Radiographic Positioning & Related Anatomy
Terms
undefined, object
copy deck
- 4 Primary Image Quality Factors
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*Density
*Contrast
*Resolution
*Distortion - Density
- is the amount of blackness on the processed film image.
- What is the primary controlling factor of film density
-
mAs.
Other factors influence density on film image include kV, part thickness, chemical development time/temperature, grid ratio & fil-screen speed. - Anode Heel Effect
- the intensity of the radiation emitted from the cathode end of the x-ray tube is greater than that at the anode end.
- Radiographic Contrast
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-the difference in density on adjacent areas of a radiographic image.
-the greated this difference, the higher the contrast; the less the density differences, the lower the contrast. - Contrast
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Different shades of gray.
Long-scale or short-scale contrast - What is the secondary controlling factor for contrast?
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kV
*general rule of thumb - states that a 15% increase in kV will increase film density, similar to doubling mAs. - Resolution
- recorded sharpness of structures on the image. AKA "detail" recorded detail, image sharpness or definition.
- Geometric Factors tath control of influence resolution.
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*Focal Spot Size
*SID
*OID (Object Image recptor Distance) - The greatest deterrent to image sharpness is?
- Motion
- Distortion
- misrepresentation of object size or shape.
- Four primary controlling factors of distorition are:
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1. SID (Source image receptor distance)
2. OID (Object image receptor distance)
3. Object image receptor alignment
4. Central ray alighment/centering - SID (Source Image receptor Distance)
- at greater SID, less magnification occurs than at a shorter SID.
- OID (Object Image receptor Distance)
- the closer the object being radiographed is to the image receptor, the less the magnification and shape distortion and the better the detail or resolution.
- Object IR (Image Receptor) Alignment
- alignment or plane of the object being radiographed in relation to the plane of the image receptor.
- Central Ray Alignment
- least possible distortion occurs at the centeral ray. Must be align properly
- Digital Images
- a numeric representation of the x-ray intensities taht are trasmitted through the patient. Viewed on computer monitor and are referred to as a soft-copy images.
- Algorithms
- systematic application of highly complex mathematical formulas
- Milliamperage (mA)
- controls the number of x-rays produced
- mAs
- controls the number of x-rays times the duration to the exposure.
- Kilovoltage (kV)
- controls the penetrating power of the x-rays with all radiographic imaging digital or film-screen systems
- Wide Latitude
- wide range of acceptance of exposure factors to produce an acceptable image.
- The factors used to evaluate digital image quality include:
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1. Brightness 2. Contrast
3.Resolution 4. Exposureindex
5.Exposure index 6. Noise - Exposure Index (Degital Imaging)
- a numeric value that is representative of the exposure the image receptor received.
- Noise
- random disturbance that obscures or reduces clarity.
- Scatter Radiation
- is a potential source of noice that can be controlled by the use of grids and correct collimation.
- Post-processing
- changing or enhancing the electronic image in order to improved its diagnostic quality.
- Post-processing options
- Windowing, smoothing, magnification, edge enhancement, subtraction, image reversal, annotation.
- 4 Types of Digital Imaging Technologies in use today?
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1. Computed Tomography (CT)
2. Digital Fluoroscopy (DF)
3. Computed Radiography (CR)
4. Direct Digital Radiography (DR) - Picture Archiving & Communication Systems (PACS)
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P-Picture - digital images
A-Archiving - "electronic" storage of images
C- Communication: routing(retrieval/sending) and displaying of the images.
S- System -specialized computer network that manages the complete system. - Alara
- the principle that radiation exposure should be kept as low as reasonably achievable.
- Attenuation
- a reduction in intensity of the x-ray beam due to absorption and scattering.
- Units of Radiation Dose
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Rad and Rem
Rad - patient dose
Rem - radiation protection - Roentgen (R)
- radiation exposure in air measured by the amount of ionization in a given unit of air
- Annual dose limit
- the dose limiting recommendation for occupationally exposed workers is 5 rem (50 mSv) of whole-body effective dose(each year)
- Cumulative dose limit
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comulative lifetime ED limit fo an occupationally exposed workers is 1 rem (10mSv) times the years of age.
ex. 50 yr tech dose 50 rem(500 mSV). - Alara Principles
- 1. Always wear a film badge or monitoring device 2. Restrint devices 3. practice used of close collimation, filtrtion of primary beam, optimum kV techniques, high speed screens and film & min. repeat exams 4. 3-part cardinal rule - time,distance, shielding
- Skin Entrance Exposure
- where radiation first strikes the body.