Test 1 - Hemming
Card Set Information
Test 1 - Hemming
Test 1 - Hemming
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
-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?
-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
Automatically programmed devices
Advantages and disadvantages to fixed kvp systems?
-Lower pt dose, lower exposure time, lower tube wear
-Part measurement is less critical
-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