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Chapter 12
Scatter Control
| Question | Answer |
|---|---|
| What are the two major factors that affect the amount of scatter radiation produced and exiting the patient? | the volume of tissue irradiated and the kVp |
| Increasing the volume of tissue irradiated results in ________ scatter production. | increased |
| Increasing kVp results in ______scatter production. | increased |
| What are two tools that radiographers can use to limit the amount of scatter radiation reaching the IR? | beam-restricting devices and radiographic grids |
| Collimation can be used interchangeably with which term? | beam restriction |
| A device that changes the shape and size of the primary beam. | beam-restricting device |
| Decreasing collimation ______ the field size. | increases |
| As the field size increases, the relative quantity of scatter radiation ________. | increases |
| The unrestricted primary beam is ________ and projects a _______ field on the patient and IR. | cone-shaped; round field |
| As collimation increases, _____ scatter radiation reaches the IR. | less |
| What are the main types of beam-restricting devices available? | aperture diaphragms, cones and cylinders, and collimators |
| Which of the beam-restricting devices is the simplest type? | aperture diaphragms |
| Which of the beam-restricting devices is the most sophisticated and most widely used in radiography? | collimators |
| Has two or three sets of lead shutters, located immediately below the tube window, to limit the size of the x-ray beam: | collimator |
| Which of the beam-restricting devices has an extended flange? | cones and cylinders |
| Another term for automatic collimator: | positive beam-limiting (PBL) device |
| Automatically limits the size and shape of the primary beam to the size and shape of the IR: | automatic collimator or PBL device |
| True or False: The U.S. federal law used to mandate the use of automatic collimators on all new radiographic equipment, but this law has since been rescinded. | True |
| True or False: It is proper practice to allow the x-ray field to extend beyond the anatomic area of interest. | False - this increases patient dose as the patient will receive unnecessary exposure |
| A device placed between the patient and the IR with their main purpose being to increase contrast by absorbing scatter radiation: | radiographic grid |
| Grids are typically used only when: | the anatomic part is greater than 10 cm and for imaging exams requiring more than 60 kVp to be used |
| Separates the lead lines to maintain a precise separation between lead strips and comprised of aluminum or plastic fiber: | interspace material |
| Expresses the number of lead lines per unit of length: | grid frequency |
| The ratio of height of the lead strips to the distance between them: | grid ratio |
| True or False: Low-ratio grids remove, or clean up, more scatter radiation than higher-ratio grids and thus further increase contrast. | False - high-ratio grids remove, or clean up, more scatter radiation than lower-ratio grids |
| As grid ratio increases, grid frequency ________. | increases |
| Refers to the linear pattern of the lead lines: | grid pattern |
| What are the two types of grid patterns? | linear and crossed or cross-hatched |
| Refers to the orientation of the lead lines to one another: | grid focus |
| What are the two types of grid focus? | parallel or non-focused and focused |
| Distance between the grid and conversion point or line: | focal distance |
| Recommended range of SIDs that can be used with a focused grid: | focal range |
| What are the two types of grids? | stationary and reciprocating |
| Which grid produces more noticeable grid lines? | stationary or non-moving grids |
| Why are reciprocating grids used? | lateral motion of the grid throughout the entire exposure blurs out the visibility of grid lines |
| Linear grids can be constructed as either _______ dimension or ______ dimension. | short or long |
| Used to determine the adjustment of mAs needed when changing from either using a grid to non-grid or when changing grid ratios: | grid conversion factor (GCF) or Bucky factor |
| As grid ratio increases, patient dose _________. | increases |
| An undesirable absorption of transmitted photons because of some misalignment of the grid: | grid cutoff |
| What are the four types of grid cutoff? | upside-down focused, off-level, off-center, and off-focus |
| Which of the grid cutoff types results in a significant loss of exposure along the edges of the image? | upside-down focused |
| Type of grid cutoff known as lateral decentering: | off-center |
| Type of grid cutoff that occurs when using an SID outside the focal range: | off-focus |
| Most common type of grid cutoff that occurs from either the tube or grid being angled: | off-level |
| An artifact that can occur when a stationary grid is used during CR imaging, forming a zebra pattern on the resulting image: | Moiré effect |
| Name the characteristics of a typical grid used: | Long-dimension linear, focused, of mid-ratio (8:1 -12:1), and a focal range that will include an SID of 40 or 72 inches |
| Pixel brightness levels throughout the displayed image should measure within ____ for proper uniformity. | 20% |
| Collimator misalignment should be less than _____ of the SID used. | 2% |
| The use of grids requires a(n) ________ in mAs to maintain exposure to the IR. | increase |
| Scatter will miss the IR completely with increased ________, which is a concept referred to as the _______________. | OID; air gap technique |
| True or False: A lead shield can be placed behind a patient to absorb more scatter produced from the exam and further increase contrast of the resulting image. | True - especially for lateral L-spine imaging |
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setelinea