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RADT 312 Units 3, 4
| Question | Answer |
|---|---|
| ______ adds a "blanket" of total exposure to the IR | Scatter |
| T/F: Excessive scatter can also be underexposed? | True |
| What are the 3 causes of scatter radiation? | High kVp, Large Field Sizes, Large Part Thickness |
| Of the 3 causes of scatter radiation, which is minor in comparison for the production of scatter? | High kVp |
| What are the benefits of high kVp? | Adequate penetration (subject contrast), combines with low mAs reduces pt exposure, long gray scale (more information) |
| Exposure of the x-ray table or objects beyond the anatomy can create _________. | Additional noise |
| Larger body parts result in the exposure of more tissue, this results in __________. | More scatter |
| What can be used to reduce patient part thickness? | Compression paddles |
| Who will produce more scatter, asthenic or hypersthenic patients? | Hypersthenic (larger) |
| What is the primary method to prevent scatter? | Field size limitation (Collimation) |
| The primary method(s) to reduce scatter before it reaches the IR is/are ________. | Grids and air-gap technique |
| What is air-gap technique? | Purposefully increase OID so low energy x-rays from the remnant beam get absorbed in the air and do not reach the IR (increase magnification however is a negative) |
| Does air-gap technique improve contrast? | Yes (reduces the amount of scatter from reaching the IR) |
| Who invented the Grid and when? | Gustav Bucky, 1913 |
| Does the grid absorb scatter radiation before or after it reaches to IR? | Before |
| What do grids consist of? | Alternating strips of lead foil, separated by radiolucent interspace material |
| Who invented the Potter Bucky and when? | Dr. Hollis Potter, 1920 |
| What does the Potter Bucky do to grid lines and how? | Blurs the grid lines by movement of the grid during exposure |
| What does a Reciprocating Grid do? | Moves the grid plate back and fourth |
| What does an Oscillating grid do? | Move the grid in a circular pattern |
| What is the grid ratio? | High of lead strips and the distance between them (H/D) |
| What are the different grid ratios? | 5:1, 6:1, 8:1, 12:1, 16:1 |
| What is grid frequency? | Number of grid lines per inch |
| A high grid ratio absorbs _____ scatter than low | More |
| What determines the thickness of the grid plate? | Height |
| What is the grid ratio formula? | H/D |
| The critical factor in a grid's efficiency is the ______. | Grid ratio |
| What are the 3 most critical considerations for when to use a grid? | Thickness of part, size of field, kVp (70 or above) |
| For part thickness, how thick of a body part should the use of a grid occur? | Thicker than 10 cm |
| What grid ratios are used in most imaging departments? | 8:1 to 12:1 |
| What body part is an exception to using a grid despite being thicker than 5 inches or 13 cm and why? | Chest, because of high % of gas/air (low attenuation) |
| When should a grid not be used? | Small adults, pediatric patients proximal extremities |
| T/F: Grids increase patient dose | True (high kVp / technique used with grids) |
| What is Selectivity? | The ratio of primary radiation transmitted through the grid to scatter radiation transmitted through |
| For a grid, the strips are manufactured as _____ as possible. | Thin |
| What is the new mAs equation for the use of grids? | Old mAs/New mAs = From/To |
| The multiplier for No Grid is ____ | 1 |
| The multiplier for a 5:1 grid is _____ | 2 |
| The multiplier for a 6:1 grid is _____ | 3 |
| The multiplier for a 8:1 grid is _____ | 4 |
| The multiplier for a 12:1 grid is ____ | 5 |
| The multiplier for a 16:1 grid is _____ | 6 |
| What is grid cutoff? | Unwanted absorption of xays via grid |
| Grid lines may be minimized by what? | Proper distance, proper alignment, potter diaphragm |
| With what kind of grid can grid lines never be fully eliminated? | Stationary grids |
| The primary purpose of a grid is to: | Reduce scatter before it reaches the IR |
| What is most reliable in determining the effectiveness of a grid? | Grid ratio |
| The use of a grid will _________ subject contrast | Improve |
| The use of a grid will ________ patient dose. | Increase |
| A grid with a higher ratio will require ____ technique, and ______ patient dose. | more, increase |
| At what minimum kVp should grids be used? | 70 |
| T/F: Grids usually have a range of SID to be used with. | True |
| excessive grid cut-off occurs in a ___________ pattern toward both sides of the field | Symmetrical |
| What is grid radius? | The distance from which lines drawn from the canted lead strips converge to a focal point |
| A _____________ grid has no canting of the lead strips – pointing straight up | Parallel |
| A _________ grid can be placed upside down without consequence | Parallel |
| Misalignment or angling across the lead strips results in: | Asymmetrical cut-off toward one side of the field |
| Always try to center to the ________ | Grid |
| High Frequency or powered generators can _____ motion and ____ pt dose | Reduce, lower |
| What is the primary purpose of protective filters? | Eliminate unnecessary exposure |
| What are the two types of filters? | Inherent filtration (window, housing, oil), Added filtration (metal sheets) |
| Compensating Filters | Something we can place on the patient |
| What makes up inherent filtration? | Glass of the x-ray tube, Oil in the tube housing, Tube window (beryllium), Anode |
| Inherent filtration must have _____ mm lead equivalency. | 1.5 |
| Added filtration must have _____ mm aluminum. | 1 |
| Total filtration must have ____ mm aluminum. | 2.5 (1.5 inherent + 1 added) |
| The Higher the HVL, the ______ the beam penetration | Higher |
| What happens when the x-ray beam is "hardened?" | Increases average energy, Increases penetration, Lowers patient dose |
| ______ is the proper unit for directly measuring x-ray beam penetration | HVL |
| HVL is: | Amount of absorber material required to reduce intensity of beam to ½ the original output of the tube |
| Three factors determine x-ray beam penetration | kVp, Generator type, Filtration |
| Minimum HVL tables are published for each kVp level in multiples of ____ | 10 |
| With compensating filters the _______ portion of filter is placed over thinnest part of anatomy | Thickest |
| Compensating Filtration helps create: | A balanced, uniform exposure |
| Adding additional filtration would have what effect on the quantity of the photons in the x-ray beam? | Decrease the quantity of photons |
| Adding more filtration would have what effect on the average energy of the photons in the x-ray beam? | Increase the average energy |
| The main purpose of filtration is to: | Decrease patient dose |
| Added filters are usually made of what material for diagnostic x-ray machines: | Aluminum |
| Between all the different radiographic rooms within an imaging department, the automatic exposure control's (AEC) reproducibility should be within plus or minus: | 20% |
| What is defined as the distance from which lines drawn from the canted lead strips converge to the focal spot of the x-ray tube? | grid radius |
| A ___________ is used as a safety measure that prevents excessive exposure while using AEC. | backup timer |
Created by:
rdwilliams
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