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1130 #2
| Question | Answer |
|---|---|
| What technical factor does the technologist set manually when using AEC? | kVp and mA |
| The art of using AEC is the art of _______? | positioning |
| When more than 1 cell is activated, the cell recieving the most radiation will contribute the ________ electrical signal and therefore have the ________ influence on the overall exposure. | greatest, greatest |
| If 3 cells are sctivated during a BE so that the barium was over 1 cell and normal tissue was over the other 2 cells, the resultant image would be? | readable |
| If all 1 cell is activated during a BE so that the barium is over the cell, what would be the result? | underexposed |
| A supine abdomen x-ray is ordered on a 350 lb pt, should the technologist adjust the density control to +2? | no, it won't do any good |
| When should the technologist use the density control? | when densitiy is improper (over a prostesis) |
| ___________ _________ collimation skills result is an increase repeat rate when using AEC? | Poor collimation |
| A proper ___________ __________ can reduce the number of repeated images and produce excellent images? | Detector selections |
| When using AEC, the technologist should do what when it comes to collimation? | not over collimate |
| When preforming a CXR your collimation does not cover am activated chamber, what will be the result? | TOo dark |
| The back-up timer should always be set at ______% of the anticipated manual exposure time? | 150 or 2-3 times |
| Will AEC always provide for a precisely repeatable exposure? | yes |
| A technologist inadvertently selected all 3 cells while using an 8X10 film in the table bucky. Since the portion of the detector will be located outside of the collimated area, one can expect the film to have ______ density? | decreased |
| If a pt with a large consolidated pneumonia of the right and middle lobes. In the order to obain an image that evaluated the entire thorax, the _____ detector should be activated? | all 3 |
| If the patient has a left pneumectomy, the _______ detectors should be activated | Rt |
| The cathode is on the _____ side? | neg |
| The filament and focusing cup are on the ________? | cathode (x-ray ciruit) |
| What material is the filament made out of? | tungsten |
| By increasing what factor will increase the number of electrons boiled off by the filament? | mA |
| What size are the small focal spots? | 1.0-3.0 mm |
| Name the advantages of a small focal spot? | Better detail |
| What are the disadvantages of a small forcal spot? | Have to use lower mA, limit size of primary beam field at a short SID |
| What is the function of the filament? | produces thermionic cloud by providing resistence to the flow of electrons |
| What amperage is neccessary for thermionic emission? | 3-5 |
| What is the purpose of the focusing cup? | Narrow the thermionic cloud, repels staying electrons. As the electrons build up in the filament, the neg charges begin to oppose additional electrons |
| What is the function of the anode? | Primary thermal conductor, serves as a target for high voltage electrons, conduct high voltage from cathode back to x-ray generator |
| What is the purpose of the rotating anode? | Turns during exposure, the faster it turns the more heat is dissapated |
| What material is the anode made out of? | tungsten |
| What are the advantages to tungsten? | high melting point, high atomic #, heat conducting ability |
| What problems are associated with the anode? | will vaporize enough target focal track material to pit the target |
| Small target angle limits the size of the primary beam when used with? | short SID |
| Describe the target area? | point at which x-ray photons are created |
| How does the target area related to SID? | Starts form target to measure |
| The total # of x-ray photons produced at the target is contingent upon what factor? | kinetic energy |
| What is the common diagnostic radiographic target angle? | 12 degrees |
| Diagnostic tube gave focal spots of ____mm to ___mm? | 2-6 |
| Due to the anode heel effect, how much total variance in the number of photons can occur? | 45% |
| Describe why the anode heel effect is a problem? | cause 20% more photons at the cathode end |
| What positioning change should be used to overcome the anode heel effect? | Thicker part on cathode end |
| What is the stator function? | induction-motor electromagnetics comprise the stator that turns the anode |
| Where is the stator located? | outside the vacuum of the glass envelope |
| What is the rotor's function? | hollow copper cylinder is attached to the anode disk by a molybdenum shaft. Silver plated ball barings around the shaft that attach to the glass envelope. |
| What problem indicates a grinding noise in the x-ray tube? | bad ball bearings |
| What is the glass envelope's function? | houses entire cathode and anode assembly. Keeps the vacuum |
| What is the window? | the primary x-ray beam exits the glass envelope |
| What is the protective housing's function? | Controls scatter and leakage, isolates high voltage, provides a means to cool the tube |
| Leakage radioation must not exceed ____ mR/hour at _____ meter? | 100 at 1 |
| Within the tube, space charge refers to? | limits the electrons from the filament |
| What is off focus radioation? | composed of photons that were not produced at the focal spot |
| Off-focus radiation can contribute to as much as _____% of the primary beam? | 25-30% |
| How are tube rating charts used? | plot mA, kVp, and time. Any combination under the curve is good |
| What is heat unit? | 0.78 joules |
| What is the heat unit formula? | kVp x mA X time X recitification constant. Single 1.00, 3 1.35, high 1.40 |
| Know how to use cooling charts | find total heat units applied on the vertical scale, read from the HU over to the cooling curve and then down to corresponding time. Calculate necessary for teh anode to cool to any desired level and subtract the initial exposure. |
| Know Bremsstrahlung Radiation? | braking or slowing |
| What happens in Bremsstraglung radiation, the incident electron? | Interacts w/ the force field of the nucleus |
| In Characteristic radiation, the incident electron is? | interacts with the inner shell |
| What shell do electrons drop into to produce characteristic photons in the diagnostic range? | k shell |
| What kVp is required for Characteristic Radiation? | 80-100 Kvp |
| What interactions make up the majority of the primary beam? | Brems |
| What is the average primary beam photon energy? | keV energy of only 30-40% of kVp |
| What are the factors that affect both amplitude and position of the em\mision spectrum? | kVp |
| Name the factor that affects amplitude on the emission spectrum? | mA, time or mAs |
| Incoming line current hertz? | 60 |
| Type of current in the US Volts? | 200-240 |
| Type of current in the US | constant fluxuation (in volts) |
| X-ray equipment operates on what incoming line voltage? | low voltage |
| Describe a 3 phase generator? | when full-wave rectification is applied to 3 phase current, it produces a voltage ripple of 6 hz or 360 pulse per sec. ripple of 13-25%. Tube never falls below 75-87% of peak kilovoltage |
| What is line compensation and why is it used? | |
| Filament circuit operates between ___and _____ amperes? | 3-5 and 6-12 volts |
| The filament circuit decreases _______ to increase _________ for thermionic emission? | |
| Electronis timers? | |
| How many amperes and volts must the imcoming line power be modified to? | 3-5 ampes and 6-12 volts |
| Single phase generators? | full wave rectification 120 pps 100% ripple 70.7% rms (peak voltage) voltage drops to 0 twice per cycle |
| 3 phase, 6 pulse? | 360 pps, 13-25% ripple 87% rms peak voltage voltage never falls below 75-87% |
| 3 phase, 12 pulse? | 720 pps 4-10% ripple 90-96% rms (peak voltage) kVp never drops below 90-96% |
| What is the formula for generator power rating? | P=v x amp |
| What are hight frequency generators? | convert incoming live voltage from 60 to 6000 hz |
| Describe a battery-operated mobile unit? | supplies AC current, mobile with recharging capabilities |
| Ionization chambers? | Lg, patient radiation is absorbed and less converted to electrical signal. Takes longer exposure to get predetermines level. Length of time is directly related to density. |
| How many ionizaion chambers are used? | 3 |
| What is the minimum reation time for most ionization chambers? | 0.001 sec |
| What is the function of the back-up timer? | protects patient fromexcessive radiation |
| What should the back-up timer be set at ______% for an anticipated manual exposure mAs? | 150 % or 2-3 times |
| What cannot be controlled by the radiographer when using AEC? | time |
| In an AEC circuit, the ionization chamber? | radiaion detection that produces small electrical current when struck by radiation |
| The _____ of the AEC circuit is primarily resposible for controlling the length of the exposure? | |
| AEC devices automatically terminate an exposure after a predeterined amount of? | radiation |
| If a patient is properly positioned for a left shoulder radiograph, which of the following detector choices should be used? | center cell |
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