Test 1 - Hemming
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Maginification radiography requires a large ___ value?
Magnification radiography is used to image what type of structure/part?
Formula for figuring the "magnification factor"?
SID / SOD
A major disadvantage for magnif. rad. is?
Increased patient dose
Goal of AEC?
To provide consistant optical density and img quality
Another name for "AEC"?
How does an AEC system work?
- -Measures rad. exposure reaching the IR
- -Once apreset optical density is reached
- -The system shuts off the xray timer and rad. stops
AECs eliminate the radiographer's need to select ___?
AEC's allow the radiographer to select ___ ?
What is AEC dependency?
When u stop using manual techniques
2 types of AEC systems? Which is more commonly used?
Phototimers and Ionization Chambers...IC's more common
How do photocell systems work?
- -Radiation is abosrbed and converted to light
- -Created light is converted to an electrical current
- -Once preset current reached xray exposure stops
How do ionization chambers systems work?
- -Radiation ionizes the air in the chamber, creating an electrical charge
- -The charge runs along a wire to a timer circuit
- -Once a large enough charge trips the timer, xray exposure stops
How does an operational amplifier work?
- -Receives and average signal from each chamber
- -Exposure stops once deisred intesnity reached
- -When more than one chamber is selected, the signal is averaged
Detectors are the AEC devices that meaure?
The amount of radiation transmitted
4 other names for "Detectors"?
Explain the configuration of an AEC on a wall bucky
- -3 chambers
- -Center (Center of IR)
- -L and R (Higher and lateral than center)
-Poor positioning skills result in?
Increased repeat rate
Manula techniques always provide a ____ exposure?
Inadequate collimation results in?
- -Lighter, underexposed image
Collimation within an activated chamber will result in?
An over exposed image
Minimum response time for a xray timer?
What is the backup time limit?
150% of expected time
If your backup time is too short, your img will be?
Federal requires automatic termination at ___ mAs when above __ Kvp
600 / 50
What are the 4 exposure factors?
What are the 3 types of filtration? What is required?
Added, Inherent, Total / 2.5mm
What is the purpose of filtration?
Reduce low energy xrays
When do you use large or small focal spots?
- L- Thick parts / Shorter exposure time
- S- Fine detail / Mag. Radiography
What type of generator provides the lowest PT dose?
High freq generators
What 3 factors determine the basic characteristics of Rad Exp of IR and PT?
- -Patient (habitus)
- -Img Quality (Contract/Density)
- -Exposure Technique (SID, mAs, Kvp)
Most technique charts are based on which type of body habitus?
Image quality is measured by 2 means...
- -Recorded Detail - Sharpness of image
- -Visible Detail - Ability to see the detail
What is spatial resolution?
Difference between elongation and foreshortening?
- EL - Part appears larger (IR/TUBE alignment)
- FS - Part appears smaller (Poor part alignment)
Technique systems work best when....
- -Large number of variables remain constant
- -A method of consistency is used to produce a quality image
What is used to measure a PT part thickness?
4 types of technique charts
- Fixed kvp
- Var. kvp
- Automatically programmed devices
Advantages and disadvantages to fixed kvp systems?
- -Lower pt dose, lower exposure time, lower tube wear
- -Part measurement is less critical
- -Uniform Contrast
- -Lower contract compare to variable systems
- -Small technique changes not possible on small parts
What is optimal Kvp?
A kvp level that sufficiently penetrates PTs and produces an acceptable image
3 criteria of the KVP scales...
- -All image contrast acceptable by radiologist
- -Small part recommendations provide good penetration
- -Large part recommendations provide acceptable levels of scatter and fog
What are the 7 steps for establishing a technique chart?
- 1.) Produce Phantom images
- 2.) Select optimum phantom images
- 3.) Make Technique chart
- 4.) Test Tech. chart on phantom
- 5.) Do clinical trials
- 6.) Clinical fine tuning
- 7.) Ongoing fine tuning
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