7596109
Description
Flashcards by RadTech Fairy, updated more than 1 year ago
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Created by RadTech Fairy
about 7 years ago
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| Question | Answer |
| What are the primary factors of exposure? | mAs kVp |
| What are the secondary factors of exposure? | focal spot size OID/SOD/SID grid CR tube filtration compensating filters |
| Milliamperage (mA) | QUANTITY of photons in the x-ray beam |
| Exposure time | QUANTITY of photons being pushed through the x-ray beam measured in seconds |
| mAs | mA x time = mAs |
| mAs controls .... | the quantity of electrons boiled off of the filament and available to produce *related to the density/brightness* |
| Reciprocity Law | "the density will be the same if the mAs value is constant whether you adjust the mA or the time" mA time mAs 100 0.8 80 200 0.4 80 400 0.2 80 |
| When a radiograph is too bright or too dark, which exposure factor must be altered? | mAs |
| What are some factors to consider when adjusting your mAs? | patient's age, condition, body habitus, and presence of pathology |
| You should make a ___% change in mAs to make a visible change in the radiograph | 30% |
| Kilovoltage Peak (kVp) | QUALITY of the energy of the x-ray beam |
| kVp controls... | pushing power of the beam and the energy of the photons being pushed *related to contrast* |
| TRUE OR FALSE Before the mAs can be adjusted, the kVp must be enough to penetrate the patient. | TRUE adjusting mAs without sufficient kVp will underexpose the radiograph |
| Increasing kVp will _______ penetration and _______ absorption. It produces ____-____ contrast with low contrast, and more scatter. | increase penetration decrease absorption long-scale contrast |
| Decreasing kVp will ______ penetration and ______ absorption. It produces ______-_____ contrast with high contrast. | decrease penetration increase absorption short-scale contrast |
| You should make a __% change in kVp to make a visible difference on the radiograph | 15% |
| 15% Rule | Increase kVp 15% and decrease mAs 1/2 Decrease kVp 15% and increase mAs x2 same effect as doubling/halving mAs |
| TRUE OR FALSE If kVp is too low when you reprocess the image digitally, you may see quantum noise. | TRUE You can post process an underexposed radiograph to adjust the brightness and contrast, but you cannot fix quantum noise. |
| TRUE OR FALSE If kVp was too high during exposure, the image will be reprocessed but the brightness and contrast will not change. | FALSE: You can adjust the brightness and contrast of an overexposed image during post processing, but the patient was overexposed. |
| TRUE OR FALSE: Quantum noise is a result of overexposure. | FALSE: Quantum noise is a result from underexposure - not enough photons reached the IR, not enough mAs was used. |
| TRUE OR FALSE: An image's brightness does not depend on mAs or kVp. | TRUE. Brightness is the result of luminance on a display monitor. |
| Why does DR use higher kVp and lower mAs? | -Less patient exposure -contrast is primarily controlled during post processing so the image will turn out acceptable |
| Focal Spot Size | Size of the focal spot affects sharpness and spatial resolution recorded in the image "Actual focal spot is the area being bombarded by the filament electrons" |
| Increasing focal spot size _____ recorded detail and spatial resolution. Decreasing focal spot size _____ recorded detail and spatial resolution. | decreases increases |
| You increase the SID from 30'' to 40'' for an abdomen x-ray. What will happen to the radiograph? | - magnification decreases - spatial resolution increases - radiation intensity decreases |
| You decrease the SID from 72'' to 60'' for an AP cart CXR. What will happen to the radiograph? | - magnification increases - spatial resolution decreases - radiation intensity increases |
| TRUE OR FALSE Any time you change SID with DR, you should also adjust your kVp. | FALSE SID affects the density of a radiograph adjust the mAs when changing SID |
| How does the Air-Gap technique reduce scatter? | The photons have more space to bounce away from the IR instead of being absorbed by it *air-gap technique produces higher contrast* |
| How should you adjust your technique if you use a grid? | Grids will absorb scatter, but will also increase the contrast of the radiograph. Increase mAs when using a grid |
| TRUE OR FALSE: Tube filtration reduces patient dose. | TRUE Filtration absorbs low energy photons that don't contribute to the image |
| How would you adjust your technique if you used a compensating filter? | Increase mAs to maintain overall exposure |
| How is kVp adjusted with variable kVp-fixed mAs? | kVp increased by 2 for every 1 cm part thickness while mAs remains the same |
| How is mAs adjusted with variable mAs - fixed kVp? | mAs adjusted by factor of 2 for every 4-5 cm thickness while kVp remains the same |
| Short-Scale Contrast | Low kVp high contrast few shades of gray |
| Long-Scale Contrast | High kVp low contrast many shades of gray |
| High Subject Contrast | area of differing tissue types that produce many different densities |
| Low Subject Contrast | area of similar tissue types that produce very similar densities |
| Which factors will produce good geometric properties on a radiograph? | OID SID SOD |
| Which factor will produce sharpness of structural lines on a radiograph? | Spatial Resolution |
| Which factor will produce adequate visibility of anatomic structures? | Contrast Brightness |
| A radiograph turns out black and white. The radiographer wants to increase the contrast of the image for the repeat exposure, how will she change her technique? 75 kVp @ 10 mAs | Increase kVp by 15% divide the mAs in half 75 x .15 = 11.25 75 + 11.25 = 86.25 10/2 = 5 NEW TECHNIQUE: 86.25 kVp @ 5 mAs |
| A radiograph turns out with very high contrast. The radiographer wants to see more blacks and whites. How will she change her technique for the repeat exposure? 125 kVp @ 16 mAs | Decrease kVp by 15% double the mAs 125 x .15 = 18.75 125 - 18.75 = 106.25 16 x 2 = 32 NEW TECHNIQUE: 106.25 kVp @ 32 mAs |
| The radiographer is x-raying a 6 month old using the piggostat, but the child is still having a hard time staying still. How will the radiographer adjust the technique? 85 kVp @ 12 mAs | 85 kVp can remain the same since we just want to decrease the exposure time. 12 mAs = 100 mA x .12 sec half the exposure time, and double the mA 12 mAs = 200 mA x .06 |
| INVERSE SQUARE LAW | |
| Which formula would we use to figure out the intensity of the beam if the original x-ray beam is 2mR @ 40 SID, and we are changing it to 72 SID? | INVERSE SQUARE LAW -only to find intensity! |
| You took a CXR of a patient before surgery at 125 kVp @ 5 mAs with a 72'' SID Now you have to do a cart CXR on the same patient after surgery, and you will not get the same SID. Which law will you use to change your technique? | mAs Maintenance |
| mAs Maintenance | |
| mAs maintenance | |
| If we wanted to determine the degree of magnification of a radiograph, how would we proceed? | Use the Magnification Factor *what's after the decimal is always the percentage* |
| If we want to determine what the object size was of what we x-rayed, how would we proceed? | |
| If we add a grid when using an exam and we have to alter our mAs? | |
| As beam restriction increases (gets tighter), density ______ | density decreases |
| An image will have higher contrast if the window width is _____ | narrow |
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