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RADT 311 Unit 1
| Question | Answer |
|---|---|
| For x-ray production, what 3 things are needed? | 1. A source if free electrons (filament wire) 2. A means to accelerate the electrons (high-voltage current) 3. A means to decelerate the electrons (anode target) |
| A minimum filament temperature needs to reach __________ to produce thermionic emmisson. | 2000° C |
| The ___________ effect refers to the equilibrium achieved when, for a given set mA, the amount of charge in the electron cloud is kept constant | Space charge |
| How is equilibrium of mA selected maintained? | For every electron that falls back into the wire, another is boiled off. |
| The electrons can accelerate to speeds up to more than________ the speed of light in just one inch of travel. | 1/2 |
| Efficiency of the x-ray tube is very low. Only approximately _______ percent of radiation emitted is x-rays | 0.5% |
| The entire anode glows “_____________” during exposure. | White hot |
| The Focusing cups around each filament have a _________ (positive or negative) electric charge. | negative |
| For most standard x-ray tubes, the small focal spot is _____ or _____ mm in size. | 0.5 or 0.6 |
| For most standard x-ray tubes, the large focal spot is _____ to _____ mm. | 1.0 to 1.2 |
| The filament is made of what? | Thorium-impregnated tungsten |
| What does the filament do? | Releases electrons while the focusing cup repels them. |
| For the 2 filaments, two wires enter the top of the filament, but only one wire exits at the bottom, why? | One is for heating the filament up to the temperature corresponding to the mA selected. The second carries the tube current by a high-voltage current to send the electrons from the cathode to the anode |
| The focal track is made of ______________. | tungsten-rhenium alloy |
| What stands for atomic number? | Z# |
| The atomic number (Z#) of tungsten is: | 74 |
| The atomic number (Z#) of rhenium is : | 75 |
| __________ of the anode is termed from fine cracks caused by the chronic effects of high heat load. | Etching |
| Excessive “_____________” not only wears on the filament, but also wears out the ball bearings in the anode. | rotoring |
| How does the braking mechanism work for the spinning anode? | The induction motor runs in reverse to create a braking effect |
| At what mA is the small focal spot selected? | Below 300mA |
| At what mA is the large focal spot selected? | Above 300mA |
| Does the small or the large focal spot have better spatial resolution? | The small focal spot has better spatial resolution (how well you can see an object in the space you are looking at on the radiograph) |
| What creates more unsharpness on the image, the large or the small focal spot? | The large focal spot creates more unsharpness on a radiograph |
| _______________________ refers to the ideal size the manufacturer is legally allowed to advertise. | Nominal focal spot |
| True or False: the effective focal spot is much smaller than the actual focal spot | True (line focus principle) |
| What does the glass envelope do? | Absorbs leakage radiation and makes all of the components of the x-ray tube to be encased within a vacuum to prevent any molecules of air or other gases impede the flow of projectile electrons |
| What is the glass envelope made of? | Pyrex glass |
| The __________ is the area through which the effective focal spot is directed out of the tube. | window |
| ______________ is the most common cause of x-ray tube failure. | Electrical arching |
| Excessive accumulated heat can cause: | Warping of the ball bearings in the anode shaft and etching or pitting of the focal track on the anode surface |
| The HU or (heat unit formula) is: | HU = kVp X mA X s |
| Thermal shock can be caused by: | Sudden heating of a cold anode or filament can crack or break the anode (remember tube warm-up: 70 kVp, 200 mA, and 1 second exposure time. Make 3 Exposures 5 seconds apart) |
| The equation used to find mAs is: | mA x time in seconds = mAs |
| mAs, mA and time are all ____________ (indirectly/directly) proportional to total exposure | directly |
| Another term for density is ___________. | receptor exposure |
| __________ is a common form of noise that is due to underexposure and has a grainy appearance. | Quantum mottle |
| What 3 things does the set mAs does directly affect: | 1. Exposure level at the IR 2. Resulting brightness of the image 3. Quantum mottle, and thereby noise level and SNR |
| The greatest enemy to sharpness of recorded detail in the image is ___________. | motion |
| What are 2 common causes of motion? | 1. Patient movement 2. Unnecessarily long exposure times |
| How can a radiographer reduce the chances of motion? | Have the patient hold still or hold their breathing and reduce exposure times. |
| What is the Direct Square Law/Exposure Maintenance formula? | mAs1/mAs2 = D1 squared/D2 squared |
| What formula is used when you are being asked to maintain a constant receptor exposure when there is a change in distance? | Direct Square Law/Exposure Maintenance Formula |
| This Law enables the radiographer to calculate the intensity of the beam at the detector when the distance between the x-ray tube and the detector changes: | Inverse Square law |
| What is the Inverse Square Law formula? | I1/I2 = D2 squared/D1 squared |
| The measurement of the electrical force or pressure behind a current of electricity, which causes it to flow is: | kVp |
| _______ controls the quantity of the xray beam | mAs |
| _______ controls the quality of the x-ray beam | kVp |
| _______ determines the penetrability of the x-ray beam | kVp |
| High kVp = _______ (high/low) contrast | low |
| Low kVp = ________ (high/low) contrast | high |
| High contrast has ___________ (more/less) shades of gray | less (appears more black and white "short scale") |
| Low contrast has ___________ (more/less) shades of gray | more "long scale" |
| _______ (more/less) kVp will be needed with the increase in the amount of bone or part thickness | more (kVp = penetration) |
| What is the 15% rule? | The 15% formula states that for every 15% change in kVp, exposure to the IR changes by a factor of 2 |
| Using the 15% rule, if you increase your kVp by 15% (.15) you need to __________ your mAs. | half |
| Using the 15% rule, if you decrease your kVp by 15% (.15) you need to __________ your mAs. | double |
| _________________ is the difference between those x-rays absorbed in the patient and those transmitted to the image receptor. | Differential Absorption |
| X-rays are produced at the ______. | anode |
| The intensity of the x-ray beam is greatest along the __________ (cathode/anode) side of the tube. | cathode |
| The direction of electron travel in the x-ray tube is: | Cathode to anode |
| The bundle of electrons formed and waiting to be transferred across the x-ray tube is termed: | space charge |
| What happens to image brightness as mAs is decreased? | brightness increases |
| __________ is the focal spot located on the anode. | Actual |
| __________ is the focal spot that is projected off the anode and is going toward the patient. | Effective |
| __________ (actual/effective fs) is larger than the ________ (actual/effective fs) due to the line focus principle. | Actual FS is larger than the Effective FS due to the line focus principle. |
| The anode spins at around _________ for normal operating motors. | 3,400 rpm |
| The anode spins at around _________ for high speed motors. | 10,000 rpm |
| High-tech ball bearings are lubricated with _________ to allow for smooth rotation. | powdered silver |
| It would take up to______ minutes for the anode to stop spinning after an exposure if it did not have a breaking mechanism. | 20 |
| All components of the x-ray tube must be encased within a _________. | vacuum |
| The glass envelope absorbs _______ radiation. | leakage |
| The glass envelope is much thinner at the __________. | window |
| The 3 types of rating charts are: | Radiographic Rating Chart, Anode Cooling Chart, and the Tube Housing Cooling Chart |
| ________ regulates the speed of electrons traveling from the cathode to the anode. | kVp |
| ________ (More/Less) kVp will be needed with the increase in the amount of bone or part thickness. | More |
| Subject contrast is dependent upon _______. | kVp |
Created by:
rdwilliams
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