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RADT B3a Units 4-6
Beam Restriction, Grids, Film :: Bushong, 10, 11, 14, 17, Principles
| Question | Answer |
|---|---|
| Remnant x-rays are those that _____ | exit the patient. |
| Which of the following factors that affect scatter radiation can be controlled by the technologist? -Added filtration; -Field size; -Inherent filtration; -mAs; -Patient thickness | Field size |
| As kVp increases, scatter radiation will _____ | increase. (Because of more Compton interaction) |
| What is the approximate percentage of x-rays that are transmitted through the patient? | About 1% |
| At high kVp, most of the x-rays are transmitted through the body [with/without] interaction. | With interaction. |
| When kVp is increased with a compensating reduction in mAs, what happens to patient dose? | Dose to the patient is decreased due to less exposure time. |
| As field size increases, scatter radiation _____ | increases. |
| Scatter radiation reduces image quality by changing what prime factor? | Contrast. (As opposed to density, distortion, etc.) |
| The x-rays that are most useful to the technologist are: -Absorbed in the body; -Attenuated in the body; -Scattered in the body; -Transmitted in the body. | Transmitted in the body. |
| [Compton interaction/Photoelectric interaction/Transmission] causes the most scatter radiation. | Compton interaction. |
| Which of the following is not a beam-restricting device? -Cone; -PBL; -Collimator; -Filter | Added filtration |
| An aperture diaphragm should allow x-rays to expose an area [equal to/larger than/smaller than] the IR. | Just smaller than the IR; therefore, x-ray field cutoff can occur if the diaphragm is not properly positioned. |
| In a light-localizing variable aperture collimator, periodic inspection must occur to ensure that the light-field very closely predicts the x-ray beam size. [True/False] | True |
| First-stage shutters on a collimator are designed to _____ | Limit off-focus radiation. |
| Off-focus radiation is caused by _____ | Electrons from the cathode do not strike the focal spot on the anode. |
| The field-defining shutters are constructed of [Al/Pb] | Pb - Lead |
| Cones and cylinders are used to reduce _____ | scatter radiation. |
| Grids and beam-restrictors are the two general types of devices that are used to _____ | reduce scatter. |
| What does PBL stand for? | Positive Beam Limitation |
| A higher kVp results in [increased/decreased] absorption and [higher/lower] contrast. | Higher kVp decreases absorption and lowers contrast. (Less photoelectric absorption means more Compton interaction) |
| When tissue is compressed, there is improved contrast resolution because _____ | there is a reduction in scatter. (Because the amount of tissue for the beam to interact with is reduced) |
| When a smaller field size is used, what happens to image contrast? | Contrast is improved, or increased, because there is less potential for scatter. |
| What effect does a restricted beam have on optical density? | OD is reduced. |
| What is the amount of tolerance allowed between field light and x-ray beam for a variable aperture collimator? | +/- 2% of SID |
| What is the formula to determine grid ratio? | h/D; where h= height of Pb strip, and D= Distance between strips. |
| The interspace between grid (Pb) strips is occupied by _____ | radiolucent Al strips. |
| The primary purpose of a grid is _____ | the absorption of scatter radiation before it reaches the IR. |
| A higher grid ratio will [increase/decrease] the effect of scatter absorption. | Increase |
| A lower grid ratio will result in _____ latitude with regard to the effects of grid cut-off. | Greater positioning latitude. (Greater margin for error) |
| How does introducing a grid affect patient dose? | Patient dose will increase due to the requirement for more technique (preferably increase in mAs) |
| What does grid frequency refer to? | The number of grid strips per inch or cm. (The most common frequencies fall between 85-103 lines/inch) |
| What is the difference between focused and parallel grids? | Focused grids contain Pb strips that are not parallel, but are angled to a specific divergence pattern that must be matched to a determined SID. (The divergence of the x-ray beam at an SID of 40" will match the angle of a 40" focused grid. |
| What is the main advantage of a Potter-Bucky grid? | The grid rapidly oscillates or shifts, which causes the Pb lines to blur out of the image while still absorbing scatter. |
| What is the formula for the Contrast Improvement Factor (k)? | k = contrast with grid/contrast without grid Range of k should be between 1.5 and 2.5 Contrast improvement is higher with higher ratio grids. |
| The Bucky factor demonstrates the need to decrease mAs when using a Bucky grid. [True/False] | False. mAs should be increased. (~3-4 times) |
| Which of the following grid errors produces the least acceptable image? (Higher degree of cut-off) -Off-level; -Off-center; -Off-focus | Off-level grid cut-off is most severe when the CR is angle perpendicular to the direction of the Pb lines in the grid. |
| What is the primary advantage of using the Air-Gap technique as opposed to a grid to reduce scatter radiation striking the IR? | There is no possibility of grid cut-off. |
| What is the OID/SID relationship when using the Air-Gap technique? | SID should be increased by 1' for every 1" of OID increase. Typically 6" gap, 6' increase in SID. (Uses same technique as an 8:1 grid) Chief principle: Inverse Square Law |
| If the interspace dimension is constant, increasing the grid ratio will do what to the dimensions of the grid? | Will make the grid thicker. (h/D) in order to obtain a higher ratio, h would have to increase if D remained the same. |
| List the layers on a dual emulsion film, from one side of the film to the other: | Overcoat Emulsion Adhesion Base Adhesion Emulsion Overcoat |
| What is by far the greatest source of film exposure? | Light from the intensifying screens. About 1% of the emitted x-rays strike the screen and film; the other 99% of radiation is from the light emitted from those screens. |
| What is the recording medium for radiographic film? | The emulsion layer consists of Silver Halide Crystals -- Ag+Br- Ionic bond |
| The Halides present in the emulsion are Iodide and, more prevalently _____ | Bromide |
| When using single emulsion film, how should the film be loaded into the cassette? | Emulsion-side down, onto the intensifying screen. |
| Every film has an inherent OD related to the tint of the base and the properties of the processor chemistry called fog. What is the acceptable range of base + fog? | 0.1 - 0.3 OD |
| What is the range of OD that is useful for diagnostic images? | 0.25 - 2.5 (near-white to near-black) |
| What is "crossover"? | Crossover occurs in dual emulsion film when light from the intensifying screen on one side of the film permeates through the base and exposes the emulsion on the opposite side. This results in a loss of detail. |
| Small, tabular AgBr crystals relate to [high/low] resolution and [fast/slow] speed. | High resolution, slow speed. There is greater concentration of fine grain crystals per area, which decreases the speed, but increases quality (and dose, due to the extra time needed for exposure). |
| Why is direct exposure film not widely used? | Direct exposure film is exposed only from x-rays, and uses no light emitting screens. This results in much higher dose to the patient. |
| [True/False] Light emission is one of the many characteristics that should be considered when selecting film. | False, the film itself does not emit light; it is exposed by the light emitted from the screen inside the cassette. |
| [True/False] The higher the contrast of film, the greater the latitude. | False; high contrast relates to narrow latitude in technique (kVp) |
| The difference between fast film and slow film is AgHalide crystal: -Charge; -Concentration; -Shape ;-Size | Concentration. Low concentration of crystals results in a faster, grainier image. |
| Fog accumulates on a film due to _____ (multiple answers) | Light-leak exposure, background radiation, Gamma radiation leak, unshielded scatter radiation, heat/humidity. |
| Rare-earth screens require the use of a _____-tinted safelight. | Red. Rare-earth screens are paired with orthochromatic film which is sensitive to the blue/green side of the light spectrum. |
| What are the three types of static artifact on film? | Crown, Tree, Smudge |
| Fog artifact results in a change to what prime factor of image quality? | Contrast is reduced with the introduction of fog. |
| [True/False] Pressure or kink marks are artifacts on film caused by rough handling and sharp pressure on unprocessed film. | True; film is most susceptible to damage before it has been processed. |
| Static artifacts occur in what kind of storage/handling conditions? | Dry, low humidity; friction |
| Describe the proper storage technique for radiographic film. (Multiple factors) | Humidity between 40% - 60%; Temp < 68 deg F; refrigerated long-term storage; ready-to-use film must be in a light-tight, lead-lined storage bin, stored on-edge, with rotating stock so that older film is used first- before its expiration date. |
| What is a sensitivity speck? | An imperfection in within a AgHalide crystal that is the catalyst for the transformation of the exposed crystal starting from that point. |
Created by:
ShaneLewis
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